Author name code: poedts
ADS astronomy entries on 2022-09-14
author:"Poedts, Stefaan"
------------------------------------------------------------------------
Title: COCONUT, a Novel Fast-converging MHD Model for Solar Corona
Simulations: I. Benchmarking and Optimization of Polytropic Solutions
Authors: Perri, Barbara; Leitner, Peter; Brchnelova, Michaela;
Baratashvili, Tinatin; Kuźma, Błażej; Zhang, Fan; Lani, Andrea;
Poedts, Stefaan
Bibcode: 2022ApJ...936...19P
Altcode: 2022arXiv220503341P
We present a novel global 3D coronal MHD model called COCONUT,
polytropic in its first stage and based on a time-implicit backward
Euler scheme. Our model boosts run-time performance in comparison
with contemporary MHD-solvers based on explicit schemes, which is
particularly important when later employed in an operational setting
for space-weather forecasting. It is data-driven in the sense that
we use synoptic maps as inner boundary inputs for our potential-field
initialization as well as an inner boundary condition in the further MHD
time evolution. The coronal model is developed as part of the EUropean
Heliospheric FORecasting Information Asset (EUHFORIA) and will replace
the currently employed, more simplistic, empirical Wang-Sheeley-Arge
(WSA) model. At 21.5 R ⊙ where the solar wind is already
supersonic, it is coupled to EUHFORIA's heliospheric model. We validate
and benchmark our coronal simulation results with the explicit-scheme
Wind-Predict model and find good agreement for idealized limit cases
as well as real magnetograms, while obtaining a computational time
reduction of up to a factor 3 for simple idealized cases, and up to 35
for realistic configurations, and we demonstrate that the time gained
increases with the spatial resolution of the input synoptic map. We
also use observations to constrain the model and show that it recovers
relevant features such as the position and shape of the streamers
(by comparison with eclipse white-light images), the coronal holes
(by comparison with EUV images), and the current sheet (by comparison
with WSA model at 0.1 au).
Title: Implementation and validation of the FRi3D flux rope model
in EUHFORIA
Authors: Maharana, Anwesha; Isavnin, Alexey; Scolini, Camilla; Wijsen,
Nicolas; Rodriguez, Luciano; Mierla, Marilena; Magdalenić, Jasmina;
Poedts, Stefaan
Bibcode: 2022AdSpR..70.1641M
Altcode: 2022arXiv220706707M
The "Flux Rope in 3D" (FRi3D, Isavnin, 2016), a coronal mass ejection
(CME) model with global three-dimensional (3D) geometry, has been
implemented in the space weather forecasting tool EUHFORIA (Pomoell
and Poedts, 2018). By incorporating this advanced flux rope model in
EUHFORIA, we aim to improve the modelling of CME flank encounters and,
most importantly, the magnetic field predictions at Earth. After using
synthetic events to showcase FRi3D's capabilities of modelling CME
flanks, we optimize the model to run robust simulations of real events
and test its predictive capabilities. We perform observation-based
modelling of the halo CME event that erupted on 12 July 2012. The
geometrical input parameters are constrained using the forward
modelling tool included in FRi3D with additional flux rope geometry
flexibilities as compared to the pre-existing models. The magnetic
field input parameters are derived using the differential evolution
algorithm to fit FRi3D parameters to the in situ data at 1 AU. An
observation-based approach to constrain the density of CMEs is adopted,
in order to achieve a better estimation of mass corresponding to
the FRi3D geometry. The CME is evolved in EUHFORIA's heliospheric
domain and a comparison of FRi3D's predictive performance with the
previously implemented spheromak CME in EUHFORIA is presented. For
this event, FRi3D improves the modelling of the total magnetic
field magnitude and Bz at Earth by ∼ 30 % and ∼ 70 %
, respectively. Moreover, we compute the expected geoeffectiveness of
the storm at Earth using an empirical Dst model and find that the FRi3D
model improves the predictions of minimum Dst by ∼ 20 % as compared
to the spheromak CME model. Finally, we discuss the limitations of
the current implementation of FRi3D in EUHFORIA and propose possible
improvements.
Title: Over-expansion of coronal mass ejections modelled using 3D
MHD EUHFORIA simulations
Authors: Verbeke, Christine; Schmieder, Brigitte; Démoulin, Pascal;
Dasso, Sergio; Grison, Benjamin; Samara, Evangelia; Scolini, Camilla;
Poedts, Stefaan
Bibcode: 2022AdSpR..70.1663V
Altcode: 2022arXiv220703168V
Coronal mass ejections (CMEs) are large scale eruptions observed close
to the Sun. They are travelling through the heliosphere and possibly
interacting with the Earth environment creating interruptions or even
damaging new technology instruments. Most of the time their physical
conditions (velocity, density, pressure) are only measured in situ
at one point in space, with no possibility to have information on
the variation of these parameters during their journey from Sun to
Earth. Our aim is to understand the evolution of internal physical
parameters of a set of three particular fast halo CMEs. These
CMEs were launched between 15 and 18 July 2002. Surprisingly, the
related interplanetary CMEs (ICMEs), observed near Earth, have a low,
and in one case even very low, plasma density. We use the EUropean
Heliosphere FORecasting Information Asset (EUHFORIA) model to simulate
the propagation of the CMEs in the background solar wind by placing
virtual spacecraft along the Sun--Earth line. We set up the initial
conditions at 0.1 au, first with a cone model and then with a linear
force free spheromak model. A relatively good agreement between
simulation results and observations concerning the speed, density and
arrival times of the ICMEs is obtained by adapting the initial CME
parameters. In particular, this is achieved by increasing the initial
magnetic pressure so that a fast expansion is induced in the inner
heliosphere. This implied the develop First, we show that a magnetic
configuration with an out of force balance close to the Sun mitigates
the EUHFORIA assumptions related to an initial uniform velocity. Second,
the over-expansion of the ejected magnetic configuration in the inner
heliosphere is one plausible origin for the low density observed
in some ICMEs at 1 au. The in situ observed very low density has a
possible coronal origin of fast expansion for two of the three ICMEs.
Title: Analysis of Voyager 1 and Voyager 2 in situ CME observations
Authors: Hosteaux, Skralan; Rodiguez, Luciano; Poedts, Stefaan
Bibcode: 2022AdSpR..70.1684H
Altcode: 2022arXiv220700471H
This paper studies ICMEs detected by both Voyager spacecraft
during propagation from 1 to 10 AU, with observations from 1977
to 1980. ICMEs are detected by using several signatures in the in
situ data, the primary one being the low measured to expected proton
temperature ratio. We found 21 events common to both spacecraft and
study their internal structure in terms of plasma and magnetic field
properties. We find that ICMEs are expanding as they propagate outwards,
with decreasing density and magnetic field intensities, in agreement
with previous studies. We first carry out a statistical study and
then a detailed analysis of each case. Furthermore, we analyse one
case in which a shock can be clearly detected by both spacecraft. The
methods described here can be interesting for other studies combining
data sets from heliospheric missions. Furthermore, they highlight the
importance of exploiting useful data from past missions.
Title: To E or not to E: Numerical Nuances of Global Coronal Models
Authors: Brchnelova, Michaela; Kuźma, Błażej; Perri, Barbara;
Lani, Andrea; Poedts, Stefaan
Bibcode: 2022arXiv220904481B
Altcode:
In the recent years, global coronal models have experienced an ongoing
increase in popularity as tools for forecasting solar weather. Within
the domain of up to 21.5Rsun, magnetohydrodynamics (MHD) is used to
resolve the coronal structure using magnetograms as inputs at the
solar surface. Ideally, these computations would be repeated with
every update of the solar magnetogram so that they could be used in
the ESA Modelling and Data Analysis Working Group (MADAWG) magnetic
connectivity tool (http://connect-tool.irap.omp.eu/). Thus, it is
crucial that these results are both accurate and efficient. While
much work has been published showing the results of these models in
comparison with observations, not many of it discusses the intricate
numerical adjustments required to achieve these results. These range
from details of boundary condition formulations to adjustments as large
as enforcing parallelism between the magnetic field and velocity. By
omitting the electric field in ideal-MHD, the description of the physics
can be insufficient and may lead to excessive diffusion and incorrect
profiles. We formulate inner boundary conditions which, along with
other techniques, reduce artificial electric field generation. Moreover,
we investigate how different outer boundary condition formulations and
grid design affect the results and convergence, with special focus on
the density and the radial component of the B-field. The significant
improvement in accuracy of real magnetic map-driven simulations is
illustrated for an example of the 2008 eclipse.
Title: Relaxation of electron beams/strahls in solar outflows:
observations vs. modeling
Authors: Lazar, Marian; Fichtner, Horst; Poedts, Stefaan; López,
Rodrigo A.; Micera, Alfredo; Shaaban, Shaaban M.
Bibcode: 2022cosp...44.1668L
Altcode:
Electron beams or strahls represent an interesting component of the
more or less energetic solar outflows, with multiple implications in
various applications in heliosphere. The electron strahl carries the
major heat flux being regulated not only by the solar wind expansion and
magnetic focusing, but also the selfgenerated wave instabilities. On the
other hand, the more energetic electron beams are believed to be at the
origin of radio emissions in coronal sources (type-III bursts), but also
in interplanetary shocks driven by the CMEs (type-II bursts). We aim
to discuss a number of advances made in recent years in understanding
these radiative plasma processes, confronting the in-situ observations
with theoretical and numerical modeling of the electron plasma beams.
Title: Kinetic firehose instabilities under the interplay of electrons
and protons in the solar wind
Authors: López, Rodrigo A.; Lapenta, Giovanni; Zhukov, Andrei;
Lazar, Marian; Poedts, Stefaan; Micera, Alfredo; Shaaban, Shaaban M.;
Boella, Elisabetta
Bibcode: 2022cosp...44.1658L
Altcode:
The solar wind is a hot and dilute plasma, where collisions are
rare but kinetic instabilities triggered by non-thermal features of
particle distributions can play an essential role in limiting the
deviations from isotropy. For instance, firehose instabilities may
inhibit the growth of the temperature in the direction parallel to the
background magnetic field, counterbalancing the effect of the solar wind
expansion. Depending on the main parameters of the plasma particles,
electrons and protons, different branches of firehose instabilities
can be triggered, and despite the significant difference between their
nature (e.g., periodic and aperiodic), and between electron and proton
scales, firehose branches can interplay and compete to alter the plasma
dynamics. We use a fully kinetic 2D semi-implicit particle-in-cell
simulation, iPic3D, to study the evolution and interplay of firehose
instabilities triggered by electrons and protons when both species are
anisotropic. The aperiodic (oblique) electron firehose instability
remains largely unaffected by the proton anisotropy and saturates
rapidly at low-level fluctuations. On the other hand, the presence of
anisotropic electrons has a considerable impact on the proton firehose
modes, especially on the aperiodic (oblique) branch, shifting the
onset of the instability and boosting the saturation levels of the
fluctuations. One can conclude that anisotropic electrons contribute
to a more effective regulation of proton anisotropy.
Title: On the effect of propagation direction on observed intensity
of radio emission
Authors: Jebaraj, Immanuel; Krupar, Vratislav; Kouloumvakos,
Athanasios; Magdalenic, Jasmina; Poedts, Stefaan
Bibcode: 2022cosp...44.1548J
Altcode:
During solar energetic events such as flares and coronal mass ejections
(CMEs), fast electron beams are accelerated, and they can generate
different types of radio emission. Theories of the plasma emission
mechanism can describe the generation of radio emission but cannot
fully explain the observed characteristics of the radio emission. While
different propagation effects such as scattering and refraction may
change the observed time profiles by elongating the travel time of
the signal, many studies suggest (Thejappa et al. 2007; Bonnin et
al. 2008; Krupar et al. 2020) that the highest intensity of the radio
burst is still mostly observed within the original cone. Namely, the
intensity of the radio emission is considered to be the strongest in the
direction of its propagation. Our study aims to test this not yet fully
understood relationship between intensity and directivity of the radio
emission. We employ the radio triangulation method and direction-finding
observations from at least two different viewing points, i.e. Wind and
Stereo spacecraft, in order to estimate the propagation path of the
radio bursts. The information on the propagation of the radio bursts
and the intensity of the radio emission is then combined, in order to
estimate how the intensity of radio emission changes with the distance
from the observing spacecraft.
Title: Modelling the influence of a stream interaction region on a
gradual solar energetic particle event
Authors: Wijsen, Nicolas; Aran, Angels; Dresing, Nina; Richardson, Ian
G.; Vainio, Rami; Pacheco, Daniel; Sanchez-Cano, Beatriz; Lario, David;
Kwon, Ryun Young; Palmerio, Erika; Afanasiev, Alexandr; Kollhoff,
Alexander; Poedts, Stefaan; Esteban Niemela, Antonio; Riihonen, Esa
Bibcode: 2022cosp...44.1161W
Altcode:
On 9 October 2021, a gradual solar energetic particle (SEP) event was
detected by multiple spacecraft located within a heliolongitudinal range
of less than 50 degrees, including Solar Orbiter (SolO), BepiColombo
(Bepi), and near-Earth spacecraft such as the Advanced Composition
Explorer (ACE). Even though Bepi and SolO shared a nominal magnetic
connection to the presumed parent coronal mass ejection (CME), the
particle enhancements observed at both spacecraft showed different
features. In particular, for energies below 5 MeV, the energetic ions
detected by Bepi resembled more closely the intensity-time profiles
observed by ACE, while both spacecraft were approximately radially
aligned at the time of the solar eruption. During the SEP event, both
spacecraft observed the passage of a high-speed stream (HSS) a few hours
prior to the arrival of the CME. In this work, we study to what extent
the HSS is responsible for the observed particle intensity-time profiles
at Earth and Bepi, by modelling the event using the magnetohydrodynamic
model EUHFORIA (EUropean Heliospheric FORecasting Information Asset)
together with the energetic particle transport model PARADISE (PArticle
Radiation Asset Directed at Interplanetary Space Exploration). In
particular, EUHFORIA is used to model the HSS and the CME, whereas
PARADISE is used to model the energetic particle transport through the
EUHFORIA solar wind. The simulation results illustrate the potential
impact that intervening large-scale structures may have in shaping SEP
events. This research has received funding from the European Union's
Horizon 2020 research and innovation programme under grant agreement
No 870405 (EUHFORIA 2.0).
Title: The ESA Virtual Space Weather Modelling Centre
Authors: Poedts, Stefaan; Heynderickx, Daniel
Bibcode: 2022cosp...44.3342P
Altcode:
The ESA Virtual Space Weather Modelling Centre (VSWMC) project
was defined as a long term project including different successive
parts. Parts 1 and 2 were completed in the first 4-5 years and designed
and developed a system that enables models and other components to be
installed locally or geographically distributed and to be coupled and
run remotely from the central system. A first, limited version went
operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE
Portal. It is similar to CCMC but interactive (no runs on demand)
and the models are geographically distributed and coupled over the
internet. The goal of the ESA project "Virtual Space Weather Modelling
Centre - Part 3" (2019-2021) was to further develop the Virtual Space
Weather Modelling Centre, building on the Part 2 prototype system
and focusing on the interaction with the ESA SSA SWE system. The
objectives and scope of this new project include maintaining the
current operational system, the efficient integration of 11 new models
and many new model couplings, including daily automated end-to-end
(Sun to Earth) simulations, the further development and wider use
of the coupling toolkit and front-end GUI, making the operational
system more robust and user-friendly. The VSWMC-Part 3 project
finished recently. The 11 new models that have been integrated are
Wind-Predict (a global coronal model from CEA, France), the Coupled
Thermosphere/Ionosphere Plasmasphere (CTIP) model, Multi-VP (another
global coronal model form IRAP/CNRS, France), the BIRA Plasma sphere
Model of electron density and temperatures inside and outside the
plasmasphere coupled with the ionosphere (BPIM, Belgium), the SNRB
(also named SNB3GEO) model for electron fluxes at geostationary orbit
(covering the GOES 15 energy channels >800keV and >2MeV) and the
SNGI geomagnetic indices Kp and Dst models (University of Sheffield,
UK), the SPARX Solar Energetic Particles transport model (University of
Central Lancashire, UK), Spenvis DICTAT tool for s/c internal charging
analysis (BISA, Belgium), the Gorgon magnetosphere model (ICL, UK),
and the Drag Temperature Model (DTM) and operations-focused whole
atmosphere model MCM being developed in the H2020 project SWAMI. Many
new couplings have also been implemented and a dynamic coupling facility
has been installed. Moreover, Daily runs are implemented of two model
chains covering the whole Sun-to-Earth domain. The results of these
daily runs are made available to all VSWMC users. We will provide an
overview of the state-of-the-art, including the new available model
couplings and daily model chain runs, and demonstrate the system.
Title: Simulating the gradual SEP event of 15 March 2013 with PARADISE
Authors: Esteban Niemela, Antonio; Rodriguez, Luciano; Poedts, Stefaan;
Aran, Angels; Magdalenic, Jasmina; Wijsen, Nicolas
Bibcode: 2022cosp...44.1152E
Altcode:
In this work, we model the gradual solar energetic particle (SEP) event
that was observed by near-Earth spacecraft on March 15, 2013. This is
done by using the model PARADISE (PArticle Radiation Asset Directed
at Interplanetary Space Exploration), which simulates the transport
of SEPs through non-nominal solar wind configurations generated by the
magnetohydrodynamic (MHD) model EUHFORIA (EUropean Heliospheric FOrecast
Information Asset). On March 15, a GOES M 1.1 X-ray flare was observed
originating from the NOAA active region 11692 and with peak intensity
registered at 06:58 UT. An Earth-directed asymmetric halo CME erupted
from the Sun at 07:12UT, as seen by the coronagraphs aboard SOHO and
STEREO. On March 16, the particle counts at L1 started increasing. A
first sudden increase was registered, for energies up to 80 MeV, at
around 20:00 UT and almost 6 hours after, the bulk of the particles
arrived and the flux remained enhanced until the ICME ended on March
17, at around 06:00 UT. Several CMEs occurred in the days prior to the
solar eruption of March 15. These proceeding CMEs disturbed the solar
wind, which may have affected the interplanetary transport of the SEPs,
potentially explaining the delayed onset of the SEP event at Earth. To
investigate this effect with the PARADISE model, also the preceding
CMEs were included in the EUHFORIA simulation by using the CME Cone
model. The main CME event was simulated using the Spheromak model,
which approximates the CME's magnetic cloud by a linear force-free
spheroidal magnetic field. This work presents the results of the
simulations and an in-depth analysis of the event characteristics.
Title: The ESA Virtual Space Weather Modelling Centre-Part 3
Authors: Poedts, Stefaan; Heynderickx, Daniel
Bibcode: 2022cosp...44.1372P
Altcode:
The ESA Virtual Space Weather Modelling Centre (VSWMC) project
was defined as a long term project including different successive
parts. Parts 1 and 2 were completed in the first 4-5 years and designed
and developed a system that enables models and other components to be
installed locally or geographically distributed and to be coupled and
run remotely from the central system. A first, limited version went
operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE
Portal. It is similar to CCMC but interactive (no runs on demand)
and the models are geographically distributed and coupled over the
internet. The goal of the ESA project "Virtual Space Weather Modelling
Centre - Part 3" (2019-2021) was to further develop the Virtual Space
Weather Modelling Centre, building on the Part 2 prototype system
and focusing on the interaction with the ESA SSA SWE system. The
objectives and scope of this new project include maintaining the
current operational system, the efficient integration of 11 new models
and many new model couplings, including daily automated end-to-end
(Sun to Earth) simulations, the further development and wider use
of the coupling toolkit and front-end GUI, making the operational
system more robust and user-friendly. The VSWMC-Part 3 project
finished recently. The 11 new models that have been integrated are
Wind-Predict (a global coronal model from CEA, France), the Coupled
Thermosphere/Ionosphere Plasmasphere (CTIP) model, Multi-VP (another
global coronal model form IRAP/CNRS, France), the BIRA Plasma sphere
Model of electron density and temperatures inside and outside the
plasmasphere coupled with the ionosphere (BPIM, Belgium), the SNRB
(also named SNB3GEO) model for electron fluxes at geostationary orbit
(covering the GOES 15 energy channels >800keV and >2MeV) and the
SNGI geomagnetic indices Kp and Dst models (University of Sheffield,
UK), the SPARX Solar Energetic Particles transport model (University of
Central Lancashire, UK), Spenvis DICTAT tool for s/c internal charging
analysis (BISA, Belgium), the Gorgon magnetosphere model (ICL, UK),
and the Drag Temperature Model (DTM) and operations-focused whole
atmosphere model MCM being developed in the H2020 project SWAMI. Many
new couplings have also been implemented and a dynamic coupling facility
has been installed. Moreover, Daily runs are implemented of two model
chains covering the whole Sun-to-Earth domain. The results of these
daily runs are made available to all VSWMC users. We will provide an
overview of the state-of-the-art, including the new available model
couplings and daily model chain runs, and demonstrate the system.
Title: EUHFORIA modeling of slow CMEs with well-defined magnetic
signatures
Authors: Prete, Giuseppe; Carbone, Vincenzo; Wijsen, Nicolas; Poedts,
Stefaan; Schmieder, Brigitte; Esteban Niemela, Antonio; Lepreti, Fabio
Bibcode: 2022cosp...44.2467P
Altcode:
Coronal mass ejections (CMEs) are one of the main drivers of strong
space weather disturbances. The interaction between CMEs and the
Earth's magnetic field can cause a wide range of phenomena and the
magnetic configuration and orientation are key factors in determining
the geo-effectiveness of this type of events. Modeling these events
accurately is an ongoing challenge, and data-driven simulations
are a valuable operational and research tool, widely used by the
community. Using the 3D data-driven magneto-hydrodynamical (MHD)
heliospheric solar wind and CME evolution model EUHFORIA (European
Heliospheric FORecasting Information Asset), our aim is to model two
CME events previously investigated by Al-Haddad et al. (2018). These
particular events are characterized by propagation slow velocities
and well-organized magnetic field characteristics. We also explore
how these structures affect Earth, even in the absence of an ICME.
Title: Simulation of SEP Events with the ICARUS+PARADISE Model
Authors: Husidic, Edin; Poedts, Stefaan; Vainio, Rami; Wijsen, Nicolas;
Baratashvili, Tinatin
Bibcode: 2022cosp...44.1296H
Altcode:
The study of space weather has an increasingly important place in our
technology-driven world. Among the various space weather events, coronal
mass ejections (CMEs) and associated gradual solar energetic particle
(SEP) events are of particular interest as they can pose a significant
threat to astronauts and technology. During their propagation,
fast CMEs generate shock waves that can efficiently accelerate SEPs
to energies of deka-MeV energies and beyond. There is thus a great
deal of interest in the community in numerical simulations that can
realistically model and predict the acceleration and transport of
SEPs. We simulate SEP events in the inner heliosphere with the novel
coupled model ICARUS+PARADISE. Using the MPI-AMRVAC-based ICARUS
code, we generate realistic background solar wind configurations
at heliocentric distances of 0.1 AU to 2 AU including superposed
transients. To study the propagation of SEPs, we use the PARADISE
(PArticle Radiation Asset Directed at Interplanetary Space Exploration)
code. PARADISE takes solar wind configurations obtained from ICARUS
as input to calculate energetic particle distributions by solving the
focused transport equation in a stochastic manner. We present results
of first simulations. We exploit ICARUS's ability of grid stretching
and Adaptive Mesh Refinement (AMR), allowing us to increase the spatial
resolution at interplanetary shock waves. By using different levels
of AMR, we investigate how the simulation results are affected by
different resolutions. We compare our results to previous results of
the EUHFORIA+PARADISE model. This research has received funding from
the European Union's Horizon 2020 research and innovation programme
under grant agreements No 870405 (EUHFORIA 2.0) and 955620 (SWATNet),
and the ESA project "Heliospheric modelling techniques" (Contract
No. 4000133080/20/ NL/CRS).
Title: Calibrating the WSA velocity formula in EUHFORIA based on
PSP measurements
Authors: Samara, Evangelia; Rodriguez, Luciano; Magdalenic, Jasmina;
Pinto, Rui; Arge, Charles; Poedts, Stefaan
Bibcode: 2022cosp...44.1417S
Altcode:
Coronal models, usually extending from 1.01 to $\sim$30 Rsun, are an
integral part of many space weather forecasting tools. They reconstruct
the magnetic field in the solar corona and provide the necessary plasma
conditions for initiating heliospheric wind models such as EUHFORIA
and Enlil. A big gap in the literature is identified when it comes
to the validation of coronal models because of lack of observations,
especially in situ. However, the launch of the Parker Solar Probe (PSP)
has provided, for the first time, in situ observations very close to
the Sun, closer than the Helios mission in the late '70s - mid '80s,
that can help with the evaluation of such models. In this work, we aim
to calibrate the Wang-Sheeley-Arge (WSA) semi-empirical formula used
in EUHFORIA for the reconstruction of plasma and magnetic parameters
at 0.1 AU. We exploit PSP in situ measurements between 0.1 - 0.4 AU
obtained from the first 8 perihelia. We show how a parametric study
of the WSA formula influences the velocity and density distributions
very close to the Sun, how the modeled distributions are compared to
PSP observations and present the relevant forecasting results at Earth.
Title: Generation of fine structures in interplanetary type III
radio bursts
Authors: Jebaraj, Immanuel; Krupar, Vratislav; Magdalenic, Jasmina;
Krasnoselskikh, Vladimir; Poedts, Stefaan
Bibcode: 2022cosp...44.1525J
Altcode:
Solar type III radio bursts are the radio signatures of fast
electron beams propagating through open and quasi-open magnetic field
lines. Although they have been well explored in the past 60 years,
several open questions remain to the present day which concerns
their generation and propagation. The generally accepted emission
mechanism of the coronal type III bursts is the plasma emission, and
a substantial amount of work has been done to support this idea from
both, observational and theoretical side. Some of the previous studies
addressed the fine structures of type III radio bursts observed mostly
in the metric to decametric range. The presently available advanced
ground-based radio imaging spectroscopic techniques (using e.g., LOFAR,
MWA, etc.,) and space-based observations (Wind, STEREO A & B, Parker
solar probe, Solar Orbiter) provide a unique opportunity to identify,
and study fine structures observed not only in the low corona but also
in the interplanetary space. In this study, we focus on the radio fine
structures observed in the range of hecto-kilometric wavelengths that
were, in comparison to the one in the metric-decametric range, studied
only occasionally. We present for the first time three different types
of fine structures observed in interplanetary type III radio bursts. The
presented fine structures show spectral characteristics similar to
the striae-like fine structures observed within the type IIIb radio
bursts at decametric wavelengths. We employ the probabilistic model
(PM) for beam-plasma interaction to investigate the role of density
inhomogeneities on the generation of the striae elements. PM not
only accounts for different levels of density inhomogeneities, but
also for the intensity of the generated Langmuir waves and associated
electromagnetic radiation. Our analyses suggests that there is a good
correlation between the width of the striae elements and the scale of
density inhomogeneities found in interplanetary space.
Title: Real-time modelling and forecasting of solar wind disturbances
from their cradle
Authors: Pinto, Rui; Bourdarie, Sebastien; Daglis, Ioannis A.; Genot,
Vincent; Lavraud, Benoit; Rouillard, Alexis; Brunet, Antoine; Samara,
Evangelia; Poedts, Stefaan; Kieokaew, Rungployphan
Bibcode: 2022cosp...44.3219P
Altcode:
We present the solar wind forecast pipeline developed in the scope of
the H2020 SafeSpace project, highlighting the part of the pipeline
that forecasts the properties of the nascent solar wind (MULTI-VP)
and drives models of the solar wind propagation across the heliosphere
(HELIO1D and EUHFORIA). The overarching goal of this project is to
use several tools in a modular fashion to address the physics of Sun -
interplanetary space - Earth's magnetosphere, allowing for comparison
to spacecraft measurements and to the formulation of space weather
warnings. The solar wind model constitutes the first element in chain
of models, and is driven by coronal field reconstruction methods using
different magnetogram sources (WSO, GONG, ADAPT). Various validation
and calibration schemes are introduced at model interfaces in order to
select optimal subsets of the ensemble and to correct for model biases,
and to potentiate interactions with other space weather actors and
services. Ensemble forecasts are produced at a daily cadence and with
a lead time of a few days. We will describe the current capabilities
of the solar wind forecasting system as well as the future steps in
terms of quality control and performance optimisation. This work has
received funding from the European Union"s Horizon 2020 research and
innovation programme under grant agreement No 870437.
Title: Employing PSP observations to calibrate near-Sun solar wind
modelling by EUHFORIA
Authors: Pavai Valliappan, Senthamizh; Rodriguez, Luciano; Magdalenic,
Jasmina; Samara, Evangelia; Poedts, Stefaan
Bibcode: 2022cosp...44.1340P
Altcode:
The recent flyby space missions, like Parker Solar Probe (PSP),
allow us to map and study the solar wind characteristics at many
different radial and angular distances, and particularly in the low
solar corona. Up to now, in situ observations of solar wind plasma
parameters at radial distances close to the Sun were insufficiently
mapped. Hence, our understanding of the origin and the propagation
of the fast solar wind, and its accurate modelling, can be improved
with PSP observations. Additionally, we can test the performance of
solar wind modelling by EUHFORIA (European heliospheric forecasting
information asset, Pomoell & Poedts, 2018) at different distances
from the Sun. In this study, we inspect the solar wind characteristics
during the first eight closest approaches to the Sun by PSP. The
solar wind plasma characteristics observed by PSP are compared with
the modelling results using the default set-up of EUHFORIA. We also
calibrate the inner boundary (0.1 AU) conditions in EUHFORIA, but
without changing the Wang-Sheeley-Arge formula which describes the solar
wind characteristics at the inner boundary. The aim is to improve the
modelling of solar wind at distances close to the Sun. We also use a
magnetic connectivity tool (developed by ESA's MADAWG group) to better
associate the fast solar wind with its source region on the Sun.
Title: Improving the Predictions of the Outer Van Allen Belt Dynamics
Authors: Daglis, Ioannis A.; Bourdarie, Sebastien; Santolik, Ondrej;
Darrouzet, Fabien; Lavraud, Benoit; Sandberg, Ingmar; Cueto Rodriguez,
Juan; Poedts, Stefaan
Bibcode: 2022cosp...44.3338D
Altcode:
The European SafeSpace project has been implementing a synergistical
approach to improve the forecasting of the outer Van Allen belt
dynamics from the current lead times of a few hours to 2-4 days. We
have combined the solar wind acceleration model MULTI-VP with the
heliospheric propagation models Helio1D and EUHFORIA to compute the
evolution of the solar wind from the surface of the Sun to the Earth
orbit. The forecasted solar wind conditions are then fed into the
ONERA Geoffectiveness Neural Network Tool, to forecast the level of
geomagnetic activity with the Kp index as the chosen proxy. The Kp
index is used as the input parameter for the IASB plasmasphere model
and for the Salammbô radiation belts code. The plasma density is used
to estimate VLF wave amplitude and then VLF diffusion coefficients,
while the predicted solar wind parameters are used to estimate the ULF
diffusion coefficients. Plasmaspheric density and VLF/ULF diffusion
coefficients are used by the Salammbô radiation belts code to deliver
a detailed flux map of energetic electrons. Finally, particle radiation
indicators will also be provided as a prototype space weather service
of use to spacecraft operators and space industry. The performance of
the prototype service will be evaluated in collaboration with space
industry stakeholders. The work leading to this paper has received
funding from the European Union's Horizon 2020 research and innovation
programme under grant agreement No 870437 for the SafeSpace (Radiation
Belt Environmental Indicators for the Safety of Space Assets) project.
Title: Modelling the SEP Event of April 11 2013
Authors: Esteban Niemela, Antonio; Rodriguez, Luciano; Poedts, Stefaan;
Aran, Angels; Magdalenic, Jasmina; Wijsen, Nicolas; Sarkar, Ranadeep
Bibcode: 2022cosp...44.1183E
Altcode:
We present a study of the Solar Energetic Particle (SEP) event of
April 11, 2013. The Solar Dynamics Observatory (SDO) spacecraft
registered, in many EUV channels, a high energetic flare associated
with a halo Coronal Mass Ejection (CME) and type II radio bursts. The
CME was moderately fast but intense enough to generate an SEP event was
registered by multiple spacecraft. The long-duration GOES M6.5 flare
(peaked at 07:16 UT) originated from NOAA active region 11719 situated
at the moment of eruption at N09E12. It was associated with a CME with
a projected line of the sight speed of about 800 km/s, observed by
multiple spacecraft positioned in a broad range of heliolongitudes. The
CME-driven shock generated by the event could have accelerated
particles in the heliosphere. Energetic protons, with more than 1 MeV,
and electrons, with energies over a few keVs, were clearly observed at
Earth and STEREO-B, while STEREO-A only registered a small and delayed
energetic particle enhancement. This low enhancement might be the
result of cross-field diffusion, as STEREO-A did not have a nominal
magnetic connection to the parent solar eruption site. In this work,
we present simulations of the background solar wind and CME evolution
with EUHFORIA (EUropean Heliospheric FOrecasting Information Asset),
and we focused on capturing magnetic characteristics of the CME. For
the associated energetic particle event we used the newly developed
solar energetic particle transport model, PARADISE (PArticle Radiation
Asset Directed at Interplanetary Space Exploration). In particular,
we investigate which pitch-angle scattering and cross-field diffusion
conditions reproduce best the energetic particle profiles seen by the
different spacecraft.
Title: On the comparison of flux rope CME models in EUHFORIA
Authors: Maharana, Anwesha; Poedts, Stefaan; Linan, Luis
Bibcode: 2022cosp...44.2439M
Altcode:
Coronal mass ejections, the giant plasma blobs erupting from the Sun,
that propagate in the interplanetary medium are observed to have a flux
rope structure. Flux rope CME models such as the spheromak model with
spherical geometry and the FRi3D model with a global CME geometry are
already functional in studying CME evolution and propagation in the
heliosphere with EUropean Heliosphere FORecasting Information Asset
(EUHFORIA). Although FRi3D is an upgrade over the spheromak model,
including a much more realistic flux-rope geometry, it requires much
more CPU time and it has some implementation drawbacks related to
the CME legs disconnection at the EUHFORIA inner boundary. In this
study, we employ a novel flux rope CME model, the Soloviev CME model in
observations-based CME modelling. The Soloviev CME model is based on the
analytical solution of the Grad-Shafranov equation derived by Soloviev
(Soloviev, Reviews of Plasma Physics, 1975). It has a toroidal geometry
which is similar to the actual CME geometry although not as close as
the FRi3D geometry. However, the practical implementation advantage of
Soloviev CME over FRi3D is that it is not connected to the Sun while
being injected at the inner boundary and it thus is pushed fully across
the boundary, not interfering with eventual following CMEs. We apply
the Soloviev flux-rope model to an observed CME event and compare it
to the geoeffectiveness predictions by spheromak and FRi3D. With this
novel analytical CME model, we explore its potential in improvement of
the computation time of high resolution EUHFORIA runs and the strength
of magnetic field components at Earth.
Title: Influence of large-scale interplanetary structures on the
propagation of solar energetic particles: The multi-spacecraft event
on 2021 October 9
Authors: Lario, David; Aran, Angels; Dresing, Nina; Richardson, Ian
G.; Vainio, Rami; Pacheco, Daniel; Wijsen, Nicolas; Sanchez-Cano,
Beatriz; Kwon, Ryun Young; Palmerio, Erika; Afanasiev, Alexandr;
Kollhoff, Alexander; Poedts, Stefaan; Riihonen, Esa
Bibcode: 2022cosp...44.1191L
Altcode:
An intense solar energetic particle (SEP) event associated with a fast
($\sim$980 km/s) coronal mass ejection (CME) and an M1.6/2B solar flare
was observed on 2021 October 9 by multiple spacecraft at heliocentric
radial distances R$\le$1 au and within a heliolongitudinal range of
less than $\sim$50 degrees. We analyze solar wind plasma, magnetic
field and energetic particle data collected by Solar Orbiter (SolO)
at 0.68 au, STEREO-A at 0.96 au, and near-Earth spacecraft such as
ACE, SOHO, and Wind. The presence of a stream interaction region
(SIR) in the inner heliosphere sequentially observed at STEREO-A,
SolO, and near-Earth regulated the observed intensity-time profiles
and the anisotropic character of the SEP event at each one of these
spacecraft. BepiColombo (Bepi) at R=0.33 au and almost radially
aligned with Earth at the time of the solar eruption that generated
the SEP event provides valuable energetic particle and magnetic field
observations to determine the effects that the SIR had on the SEP
transport and hence shaping the properties of the SEP event. STEREO-A
and SolO detected strong anisotropies at the onset of the SEP event,
which may result from the fact that both spacecraft were in the tail
of the solar wind stream responsible for the SIR. By contrast, the
intensity-time profiles observed near-Earth displayed a delayed onset
at proton energies $>$13 MeV and an accumulation of $<$5 MeV
protons between the SIR and the shock driven by the CME. Moreover,
despite the fact that Bepi and SolO were nominally connected to the
same region of the Sun, the particle intensity-time profiles at Bepi
had a close similarity to those observed near Earth, with the bulk of
low-energy ions confined between the SIR and the CME-driven shock. This
event exemplifies how large-scale interplanetary structures may regulate
the observed properties of SEP events.
Title: Modelling the 2020 November 29 solar energetic particle event
using the EUHFORIA and the iPATH model
Authors: Ding, Zheyi; Li, Gang; Wijsen, Nicolas; Poedts, Stefaan
Bibcode: 2022cosp...44.3299D
Altcode:
On November 29 2020, a M4.4 flare erupted from active region 12790,
accompanied by a fast coronal mass ejection (CME). This is the first
widespread solar energetic particle (SEP) event of solar cycle 25,
observed by Parker Solar Probe, Solar Orbiter, Solar Terrestrial
Relations Observatory(STEREO)-A, Solar and Heliospheric Observatory
(SOHO) and Tianwen-1. The longitudinal spread of the corresponding
SEPs extends to at least 238 degrees. We model this event using a
data-driven model of the solar wind and the 3-D spheromak-type CME with
the EUropean Heliospheric FORecasting Information Asset (EUHFORIA). The
3-D CME-driven shock is identified for a 2-hour interval, and the
shock parameters, including shock speed, compression ratio and shock
obliquity, are obtained. We find that the propagation of CME-driven
shock and the temporal variation of the shock parameters depends on the
background solar wind. With the shock data from the EUHFORIA simulation
as input, we further model the particle acceleration and transport using
the improved Particle Acceleration and Transport in the Heliosphere
(iPATH) model. The modeled time intensity profiles and spectra at
multiple spacecraft are compared with the observations. We suggest that
the dynamic evolution of the shock parameters significantly affects
the shock acceleration in SEP events. We also note that the geometry
of the magnetic field lines near the Sun may play an important role
in this event.
Title: Impact of the solar activity cycle on the propagation of ICMEs
Authors: Perri, Barbara; Poedts, Stefaan; Schmieder, Brigitte
Bibcode: 2022cosp...44.2444P
Altcode:
The propagation of ICMEs in the heliosphere is influenced by a
great number of physical phenomena, related both to the internal
structure of the ICME but also to its interaction with the ambient
solar wind and heliospheric current sheet. The understanding of such
phenomena is crucial to be able to improve numerical modelling and
provide better space weather forecasts for the time of arrival of
perturbations at Earth. As individual structures of the solar wind such
as helmet streamers of high-speed streams have begun to be discussed,
the influence of the long-term variability of solar activity on
transient events is still not clear. Indeed, the solar magnetic field
is modulated by the 11-year dynamo cycle generated inside the Sun,
and then affecting the entire heliosphere structure by means of the
Parker spiral and its shaping of the solar corona. We know that there
are more transient events at maximum of activity and that they are
usually more intense, but the exact influence of solar activity on
their propagation remains to be discussed. It is becoming even more
important to assess these differences as solar cycle 25 is rising,
and thus many models calibrated on the minimum of activity between
cycles 24 and 25 may become less accurate. We perform a theoretical
study to try to answer these questions. We begin by trying to define
what is an average CME at 0.1 AU, using both observations and numerical
simulations. We choose a spheromak to model the CME, as it allows us
to explore also the magnetic interactions along its propagation. We
then use the heliospheric propagator EUHFORIA to inject the same CME
in two different background wind environments: the first corresponds
a very quiet minimum of activity in December 2008, the other one to a
maximum of activity during a solar eclipse as seen form Earth in March
2015. We then study how the flows and magnetic structures impact the
propagation of the ICME towards Earth. We also discuss the influence
of the injection point with regards to specific structures such as
the position of the current sheet.
Title: Validation of the Linear-Force-Free Spheromak ICME model
in Icarus
Authors: Baratashvili, Tinatin; Verbeke, . Christine; Poedts, Stefaan
Bibcode: 2022cosp...44.1371B
Altcode:
Coronal Mass Ejections (CMEs) are the main drivers of interplanetary
shocks and space weather disturbances. Strong CMEs directed towards
Earth can have a severe impact on our planet and their timely prediction
can enable us to mitigate (part of) the damage they cause. One of the
key parameters that determine the geo-effectiveness of a CME is its
internal magnetic configuration. The novel heliospheric wind and CME
propagation model Icarus, which is implemented within the framework of
MPI-AMRVAC (Xia et al., 2018) introduces new capabilities for better and
faster space weather forecasts. Advanced numerical techniques, such as
solution adaptive mesh refinement (AMR) and radial grid stretching are
implemented. These techniques enable us to avoid cell deformation and
to only refine the mesh in the required/desired areas. The different
refinement and coarsening conditions and thresholds are controlled by
the user. These techniques result in optimised computer memory usage
and a significant execution speed-up, which is crucial for forecasting
purposes. In this study we validate a new magnetized CME model in
Icarus by simulating interplanetary coronal mass ejections (ICMEs). We
consider some well-observed ICME events and model them with appropriate
parameters in Icarus using a Linear Force-Free Spheromak model. We
compare the internal CME magnetic field configuration upon their CMEs
at multiple satellites. Using observations of different satellites we
can track the propagation of the CMEs in the heliospheric domain and
assess the accuracy of the model at different locations. Different AMR
criteria are used to achieve higher spatial resolutions at propagating
shock fronts and in the interiors of the ICMEs. This way the complex
structure of the magnetic field and the deformation and (plasma and
magnetic flux) erosion can be simulated with higher accuracy. Higher
resolution is especially important for the Linear Force-Free spheromak
model, because the internal magnetic field configuration affects the
CME evolution and its interaction with the also magnetized heliospheric
wind significantly. Finally, the obtained synthetic time-series of
plasma quantities at different satellite locations are compared to the
available observational data. This research has received funding from
the European Union's Horizon 2020 research and innovation programme
under grant agreement No 870405 (EUHFORIA 2.0).
Title: Influence of Large-scale Interplanetary Structures on the
Propagation of Solar Energetic Particles: The Multispacecraft Event
on 2021 October 9
Authors: Lario, D.; Wijsen, N.; Kwon, R. Y.; Sánchez-Cano, B.;
Richardson, I. G.; Pacheco, D.; Palmerio, E.; Stevens, M. L.; Szabo,
A.; Heyner, D.; Dresing, N.; Gómez-Herrero, R.; Carcaboso, F.; Aran,
A.; Afanasiev, A.; Vainio, R.; Riihonen, E.; Poedts, S.; Brüden,
M.; Xu, Z. G.; Kollhoff, A.
Bibcode: 2022ApJ...934...55L
Altcode:
An intense solar energetic particle (SEP) event was observed on 2021
October 9 by multiple spacecraft distributed near the ecliptic plane
at heliocentric radial distances R ≲ 1 au and within a narrow range
of heliolongitudes. A stream interaction region (SIR), sequentially
observed by Parker Solar Probe (PSP) at R = 0.76 au and 48° east
from Earth (ϕ = E48°), STEREO-A (at R = 0.96 au, ϕ = E39°),
Solar Orbiter (SolO; at R = 0.68 au, ϕ = E15°), BepiColombo (at
R = 0.33 au, ϕ = W02°), and near-Earth spacecraft, regulated the
observed intensity-time profiles and the anisotropic character of the
SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at
the onset of the SEP event, which resulted from the fact that PSP and
STEREO-A were in the declining-speed region of the solar wind stream
responsible for the SIR and from the passage of a steady magnetic
field structure by SolO during the onset of the event. By contrast,
the intensity-time profiles observed near Earth displayed a delayed
onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV
protons between the SIR and the shock driven by the parent coronal
mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were
nominally connected to the same region of the Sun, the intensity-time
profiles at BepiColombo resemble those observed near Earth, with
the bulk of low-energy ions also confined between the SIR and the
CME-driven shock. This event exemplifies the impact that intervening
large-scale interplanetary structures, such as corotating SIRs, have
in shaping the properties of SEP events.
Title: Implementation of the Soloviev equilibrium as a new CME model
in EUHFORIA
Authors: Linan, Luis; Keppens, Rony; Maharana, Anwesha; Poedts,
Stefaan; Schmieder, Brigitte
Bibcode: 2022cosp...44.2431L
Altcode:
The EUropean Heliosphere FORecasting Information Asset (EUHFORIA) is
designed to model the evolution of solar eruptions in the heliosphere
and to accurately forecast their geo-effectiveness. In EUHFORIA,
Coronal Mass Ejections (CMEs) are superposed on a steady background
solar wind and injected at $r=0.1\;AU$ into a 3D time-dependent ideal
magnetohydrodynamics heliospheric domain. Our study focuses on the
implementation of a new CME model to improve and extend the CME models
that are currently implemented, for instance by providing a more
realistic geometry or a faster execution time. The novel CME model
is based on an analytical solution of the Grad-Shafranov equation,
called the Soloviev solution, which describes a plasma equilibrium in
a toroidal geometry (Soloviev, Reviews of Plasma Physics, 1975). One of
the main advantages is that magnetic field and other physical quantities
like pressure and density can be determined in terms of an analytic
magnetic flux formula. This flux being a polynomial function of the
local coordinates, we can directly control the interior properties
(in terms of shape and topology) within the cross-section of the toroid
with the spherical inner boundary at $r=0.1\;AU$. Hence, in practice,
the numerical computation of this model is less time consuming than the
FRi3D CME model that requires the numerical solution of differential
equations in each time step (Isavnin, Astrophys. J., 2016). Furthermore,
our implementation offers a wide range of free parameters, including the
shape of the model (aspect ratio, shape of the poloidal cross-section)
to the distribution and strength of the magnetic field lines in the
torus. This suffices to approach the geometry and characteristics
of observed CMEs. Some parameters are limited well-defined ranges,
to ensure basic physical aspects like positivity of thermodynamic
quantities. After the Soloviev CME is injected into the heliospheric
domain of EUHFORIA as a time-dependent boundary condition, it is
self-consistently evolved by the magnetohydrodynamics equations to
Earth. Finally, we present a test case CME modelled with Soloviev
and compare the plasma and magnetic field predictions with the
observations. This research has received funding from the European
Union's Horizon 2020 research and innovation programme under grant
agreement No 870405 (EUHFORIA 2.0)
Title: Interaction of coronal mass ejections and the solar wind. A
force analysis
Authors: Talpeanu, D. -C.; Poedts, S.; D'Huys, E.; Mierla, M.;
Richardson, I. G.
Bibcode: 2022A&A...663A..32T
Altcode: 2022arXiv220309393T
Aims: Our goal is to thoroughly analyse the dynamics of single
and multiple solar eruptions, as well as a stealth ejecta. The data
were obtained through self-consistent numerical simulations performed
in a previous study. We also assess the effect of a different background
solar wind on the propagation of these ejecta to Earth.
Methods:
We calculated all the components of the forces contributing to the
evolution of the numerically modelled consecutive coronal mass ejections
(CMEs) obtained with the 2.5D magnetohydrodynamics (MHD) module of the
code MPI-AMRVAC. We analysed the thermal and magnetic pressure gradients
and the magnetic tension dictating the formation of several flux ropes
in different locations in the aftermath of the eruptions. These three
components were tracked in the equatorial plane during the propagation
of the CMEs to Earth. Their interaction with other CMEs and with the
background solar wind was also studied.
Results: We explain the
formation of the stealth ejecta and the plasma blobs (or plasmoids)
occurring in the aftermath of solar eruptions. We also address the
faster eruption of a CME in one case with a different background
wind, even when the same triggering boundary motions were applied,
and attribute this to the slightly different magnetic configuration and
the large neighbouring arcade. The thermal pressure gradient revealed a
shock in front of these slow eruptions, formed during their propagation
to 1 AU. The double-peaked magnetic pressure gradient indicates that
the triggering method affects the structure of the CMEs and that a
part of the adjacent streamer is ejected along with the CME.
Title: Modeling the propagation of solar disturbances to Earth for
the EU H2020 SafeSpace project
Authors: Kieokaew, Rungployphan; Bourdarie, Sebastien; Grison,
Benjamin; Daglis, Ioannis; Pinto, Rui; Genot, Vincent; Lavraud, Benoit;
Rouillard, Alexis; Brunet, Antoine; Samara, Evangelia; Soucek, Jan;
Poedts, Stefaan
Bibcode: 2022cosp...44.3444K
Altcode:
The EU H2020 SafeSpace project aims to develop a prototype pipeline
that connects several tools in a modular fashion to address the physics
of the Sun - Interplanetary space - Earth's magnetosphere with the
ultimate goal to forecast radiation belts dynamics. We present a part
of the pipeline called Helio1D that is dedicated to forecasting the
solar wind properties at the Lagrangian L1 point. Helio1D models solar
wind propagation using input data obtained from the MULTI-VP model,
which models solar wind emergence near Sun based on magnetograms and
coronal field reconstruction. In particular, we aim to forecast the
properties of the regular solar wind and Corotating Interaction Regions
(CIRs) and their high-speed streams, which are most geo-effective (for
radiation belts in particular). We take an ensemble forecasting approach
to provide optimum forecast up to 2 - 4 days of lead time. Using the
near-Sun long-term prediction data from Multi-VP during the solar
cycles 23 and 24, we benchmarked the Helio1D pipeline with the solar
wind monitoring at L1. The performance of the pipeline was measured
using the Dynamic Time Warping technique, which is efficient in mapping
macroscopic features of CIRs from the model to the observations. This
technique also allows us to calibrate the pipeline to improve the
model's performance. Finally, the Helio1D pipeline is connected to
neural network models that predict geomagnetic indices such as the Kp
index for magnetospheric space weather forecasting. We will present
the Helio1D pipeline status and its benchmarking and calibration to
provide optimum forecasting in real-time. This project has received
funding from the European Union's Horizon 2020 research and innovation
programme under grant agreement No 870437.
Title: Modelling the geoeffectiveness of the CME-CME interaction
event of early September 2014
Authors: Maharana, Anwesha; Scolini, Camilla; Poedts, Stefaan;
Schmieder, Brigitte
Bibcode: 2022cosp...44.1391M
Altcode:
Coronal mass ejections (CMEs) undergo interaction with other CMEs and
the structures in the solar wind like high-speed streams, co-rotating
interaction regions and stream interaction regions, while propagating
through the heliosphere. In this study, we present the evolution of
two successive CMEs that erupted from the Sun on September 8, 2014,
and September 10, 2014, respectively, from AR12158. The first CME was
a side hit on Earth and provided preconditioning in the heliosphere
for the second CME's propagation. The second CME was predicted to be
geoeffective based on the remote observations of the CME chirality and
tilt. However, a mismatch in the tilt of the second CME was observed
close to Earth (Cho et al., 2017), pointing to CME rotation during its
propagation. The magnetic ejecta, unexpectedly, resulted in positive
Bz but a geoeffective sheath was developed during the evolution
and the interaction in the heliosphere that resulted in a minimum
Dst ~ -100nT at Earth. Hence, the geoeffectiveness of the various
sub-structures involved in this event was mis-predicted. In-situ
observations taken at sparse localized points in the heliosphere pose
a challenge in capturing the complete picture of the CME and solar
wind dynamics. Therefore, we perform 3D MHD simulations that provide
a global picture, making it convenient to probe into the interesting
phenomena of this event. We use the EUropean Heliosphere FORecasting
Information Asset (EUHFORIA) to model the background solar wind in 3D,
launch the flux rope CMEs in it and let the CMEs evolve till Earth. In
this work, we aim to reproduce the observed plasma and magnetic field
properties, especially the negative Bz of the sheath and the positive
Bz of the ejecta at Earth. We investigate the possible factors and
processes responsible for the development of geoeffectiveness, such as
CME rotation, the interplay of the two CMEs, and the interaction with
the surrounding solar wind. This research has received funding from
the European Union's Horizon 2020 research and innovation programme
under grant agreement No 870405 (EUHFORIA 2.0)
Title: Towards realistic COOLFluiD global coronal model for
EUHFORIA2.0 space weather forecast: comparison with observations
and multi-fluid perspectives.
Authors: Kuźma, Błażej; Poedts, Stefaan; Baratashvili, Tinatin;
Perri, Barbara; Brchnelova, Michaela; Zhang, Fan; Leitner, Peter;
Lani, Andrea
Bibcode: 2022cosp...44.1105K
Altcode:
We developed a novel global coronal model based on the COOLFluiD
code. The steady-state model is predetermined by magnetograms set as
boundary conditions, while inside the numerical domain the corona is
described by the set of MHD equations which is solved implicitly on an
unstructured grid. Our code has passed a set of benchmark tests and
proved its accuracy for simple dipole/quadrupole solutions as well
as for a wide range of magnetograms, both during solar minimum and
solar maximum. With various numerical optimizations and an adaptive
CFL step we decreased the computation time while maintaining the high
robustness and reliability. Finally, we coupled the obtained results
with a heliospheric wind model to show its forecast abilities. This
leads to an accurate MHD solution obtained within only a few hours of
computation, which is crucial for space weather forecast systems. Here
we present some numerically obtained results for 2008, 2015, 2017
and 2019 magnetograms (CR 2072, CR 2161, CR 2194, CR 2219). These
magnetograms were chosen to represent a variety of stages of solar
activity, from minimum to maximum, with each of them corresponding to
a particular solar eclipse. With several maps and several levels of
accuracy of reconstruction we address the problem of map reconstruction
and its impact on the results which is especially important for
computationally challenging maximum-activity maps. We use a validation
scheme to investigate the predicted distribution of magnetic structures
within the obtained coronal magnetic field topology. The detailed
comparison with observations reveals an unprecedented combination of
accuracy, computation speed and robustness accomplished at this stage,
with possible improvement in a foreseeable perspective. We conclude
with the development prospects, with the ultimate goal of the present
step of our efforts being the extension of the existing MHD model into
a multifluid solar atmosphere model, including the chromosphere.
Title: Impact of magnetic photospheric observations on the modelling
of coronal and heliospheric magnetic structures
Authors: Perri, Barbara; Poedts, Stefaan; Baratashvili, Tinatin; Kuzma,
Blazej; Brchnelova, Michaela; Zhang, Fan; Leitner, Peter; Lani, Andrea
Bibcode: 2022cosp...44.1078P
Altcode:
Space weather requires a fast and accurate modelling of magnetic
and flow structures in the heliosphere to anticipate their impact on
Earth spatial environment. In particular, it is well known that the
position of the current sheet is a crucial information to determine
the interaction with the Earth magnetosphere and anticipate ICMEs
propagation. Because modelling the entire heliosphere is so challenging,
the current approach is to combine coronal and heliospheric models,
as is done in the EUHFORIA 2.0 project. This however leads to the
open question of the transmission of uncertainties between the models,
which is not clearly answered yet. In particular, at the beginning of
the chain of modelling lies a crucial choice that is not always obvious:
the choice of the input solar observations to provide the magnetic field
boundary conditions at the solar surface. To this day, there is a great
variety of sources with different treatments, especially at the poles
to fill the currently missing observations. The impact of the synoptic
map source has started to be discussed for PFSS models, but a clear
overview of the consequences for MHD models and their description of the
corona and the heliosphere is still missing. We present here the newly
developed MHD coronal model for the EUHFORIA 2.0 project, based on the
COOLFluiD framework. This model has the advantage of using an implicit
solver for speed and an unstructured mesh for accuracy, especially
around the polar region. After briefly presenting its benchmarking
and validation procedure for its polytropic version, we will use it to
explore how various synoptic maps can affect the simulation results. We
select the date of 2nd of July 2019 because of the low solar activity
and the associated solar eclipse seen on Earth. We use data from all
currently available sources (GONG, GONG-ADAPT, WSO, MWO, SOLIS, HMI)
and perform the same simulation with the same pre-processing and the
same physical parameters, to assess only the impact of the choice of
the input synoptic map. We focus on the implications for the magnetic
field configuration by comparison with white-light eclipse pictures,
for the coronal hole locations by comparison with SDO/AIA and for
the position of the HCS at 0.1 AU by comparison with standard WSA
models. We demonstrate that even at minimum of activity the input
synoptic map has a great influence on the output of coronal models,
and that the modelling of the poles is crucial for the shape of the
HCS. We finally discuss the future developments of the model such as
the inclusion of heating terms to model CIRs.
Title: Pressure balance of coronal mass ejections during their
Sun-Earth journey modelled by 3D MHD EUHFORIA simulations
Authors: Schmieder, Brigitte; Dasso, Sergio; Grison, Benjamin;
Demoulin, Pascal; Verbeke, Christine; Scolini, Camilla; Samara,
Evangelia; Poedts, Stefaan
Bibcode: 2022cosp...44.2474S
Altcode:
The aim of this work is to understand the signatures of three coronal
mass ejections (CMEs) at the Lagrange point L1 launched from the Sun
between 15 and 18 July 2002. We use the EUropean Heliosphere FORecasting
Information Asset (EUHFORIA) model to simulate their propagation and
interaction in the background solar wind. The approach is to place
virtual spacecraft along the Sun-Earth line. We set up the initial
conditions at 0.1 au, modelling each CME using the linear force free
spheromak model. We perform an analysis on the pressures acting
within the first and the last CMEs of the series (CME1 and CME3)
and investigate the role of pressure (un)balance in their expansion,
while the second CME (CME2) was too compressed to be able to expand
its ejecta during propagation. We find that the magnetic pressure
within CME1 and CME3 was prominent at 0.1 au and rapidly decreased
between 0.1 au and Earth, so that the gas pressure was progressively
dominating in their extended ejecta.
Title: Categorization model of moving small-scale intensity
enhancements in solar active regions
Authors: Shergelashvili, B. M.; Philishvili, E.; Buitendag, S.;
Poedts, S.; Khodachenko, M.
Bibcode: 2022A&A...662A..30S
Altcode: 2022arXiv220306285S
Context. The small-scale moving intensity enhancements remotely observed
in the extreme ultraviolet images of the solar active regions, which we
refer to as active region moving campfires (ARMCs), are related to local
plasma temperature and/or density enhancements. Their dynamics is driven
by the physical processes in the entire coronal plasma. Our previous
study of ARMCs indicates that they have characteristic velocities at
around the background sound speed. In the present paper, we further
investigate the dynamical and statistical properties of ARMCs.
Aims: The main goal of our work is to carry out a simultaneous analysis
of EUV images from two observational missions, SDO/AIA and Hi-C 2.1. The
aims of the performed cross-validating analysis of both SDO/AIA and
Hi-C 2.1 data were to reveal how the observed moving features are
distributed over the studied active region, AR12712, and to perform
a statistical hypothesis test of the existence of different groups
of ARMCs with distinct physical characteristics.
Methods:
We use the statistical model of intensity centroid convergence and
tracking that was developed in our previous paper. Furthermore, a
Gaussian mixture model fit of the observed complex of moving ARMCs
is elaborated to reveal the existence of distinct ARMC groups and to
study the physical characteristics of these different groups.
Results: In data from the 171 Å, 193 Å and 211 Å channels of
SDO/AIA, we identified several groups of ARMCs with respect to both
blob intensity and velocity profiles. The existence of such groups
is confirmed by the cross-validation of the 172 Å data sets from
Hi-C 2.1.
Conclusions: The ARMCs studied in this paper have
characteristic velocities in the range of the typical sound speeds in
coronal loops. Hence, these moving objects differ from the well-known
rapid Alfvénic velocity jets from magnetic reconnection sites. This
is also proven by the fact that ARMCs propagate along the active region
magnetic structure (strands). The nature of the discovered statistical
grouping of the ARMC events is not known. Further theoretical studies
and modeling is required to reveal this nature.
Title: Influence of coronal hole morphology on the solar wind speed
at Earth
Authors: Samara, Evangelia; Magdalenić, Jasmina; Rodriguez, Luciano;
Heinemann, Stephan G.; Georgoulis, Manolis K.; Hofmeister, Stefan J.;
Poedts, Stefaan
Bibcode: 2022A&A...662A..68S
Altcode: 2022arXiv220400368S
Context. It has long been known that the high-speed stream (HSS) peak
velocity at Earth directly depends on the area of the coronal hole
(CH) on the Sun. Different degrees of association between the two
parameters have been shown by many authors. In this study, we revisit
this association in greater detail for a sample of 45 nonpolar CHs
during the minimum phase of solar cycle 24. The aim is to understand how
CHs of different properties influence the HSS peak speeds observed at
Earth and draw from this to improve solar wind modeling.
Aims:
The CHs were extracted based on the Collection of Analysis Tools for
Coronal Holes which employs an intensity threshold technique applied to
extreme-ultraviolet filtergrams. We first examined all the correlations
between the geometric characteristics of the CHs and the HSS peak
speed at Earth for the entire sample. The CHs were then categorized
in two different groups based on morphological criteria, such as the
aspect ratio and the orientation angle. We also defined the geometric
complexity of the CHs, a parameter which is often neglected when the
formation of the fast solar wind at Earth is studied. The quantification
of complexity was done in two ways. First, we considered the ratio
of the maximum inscribed rectangle over the convex hull area of the
CH. The maximum inscribed rectangle provides an estimate of the area
from which the maximum speed of the stream originates. The convex hull
area is an estimate of how irregular the CH boundary is. The second
way of quantifying the CH complexity was carried out by calculating
the CH's fractal dimension which characterizes the raggedness of the
CH boundary and internal structure.
Methods: When treating
the entire sample, the best correlations were achieved between the
HSS peak speed observed in situ, and the CH longitudinal extent. When
the data set was split into different subsets, based on the CH aspect
ratio and orientation angle, the correlations between the HSS maximum
velocity and the CH geometric characteristics significantly improved
in comparison to the ones estimated for the whole sample. By further
dividing CHs into subsets based on their fractal dimension, we found
that the Pearson's correlation coefficient in the HSS peak speed -
CH area plot decreases when going from the least complex toward
the most complex structures. Similar results were obtained when we
considered categories of CHs based on the ratio of the maximum inscribed
rectangle over the convex hull area of the CH. To verify the robustness
of these results, we applied the bootstrapping technique. The method
confirmed our findings for the entire CH sample. It also confirmed the
improved correlations, compared to the ones found for the whole sample,
between the HSS peak speed and the CH geometric characteristics when we
divided the CHs into groups based on their aspect ratio and orientation
angle. Bootstrapping results for the CH complexity categorizations are,
nonetheless, more ambiguous.
Results: Our results show that the
morphological parameters of CHs such as the aspect ratio, orientation
angle, and complexity play a major role in determining the HSS peak
speed at 1 AU. Therefore, they need to be taken into consideration
for empirical models that aim to forecast the fast solar wind at Earth
based on the observed CH solar sources.
Title: ICARUS, a new inner heliospheric model with a flexible grid
Authors: Verbeke, C.; Baratashvili, T.; Poedts, S.
Bibcode: 2022A&A...662A..50V
Altcode:
Context. Simulating the propagation and predicting the arrival time
of coronal mass ejections (CMEs) in the inner heliosphere with a
full three-dimensional (3D) magnetohydrodynamic (MHD) propagation
model requires a significant amount of computational time. For CME
forecasting purposes, multiple runs may be required for different
reasons such as ensemble modeling (uncertainty on input parameters) and
error propagation. Moreover, higher resolution runs may be necessary,
which also requires more CPU time, for example for the prediction of
solar energetic particle acceleration and transport or in the framework
of more in-depth studies about CME erosion and/or deformation during
its evolution.
Aims: In this paper we present ICARUS, a new inner
heliospheric model for the simulation of a steady background solar wind
and the propagation and evolution of superposed CMEs. This novel model
has been implemented within the MPI-AMRVAC framework which enables the
use of stretched grids and solution adaptive mesh refinement (AMR). The
usefulness and efficiency (speed-up) of these advanced features are
explored. In particular, we model a typical solar wind with ICARUS
and then launch a simple cone CME and follow its evolution. We focus
on the effect of radial grid stretching and two specific methods or
criteria to trigger solution AMR on this typical simulation run.
Methods: For the solar background wind simulation run, we limited
the mesh refinement to the area(s) of interest, in this case a
co-rotating interaction region (CIR). For the CME evolution run, on
the other hand, we apply AMR where the CME is located by the use of a
tracing function. As such, the grid is coarsened again after the CME
has passed.
Results: The implemented AMR is flexible and only
refines the mesh in a particular sector of the computational domain,
for example around the Earth or a single CIR, and/or for a particular
feature such as CIR or CME shocks. Radial grid stretching alone yields
speed-ups of up to 4 and more, depending on the resolution. Combined
with solution adaptive mesh refinement, the speed-ups can be much larger
depending on the complexity of the simulation (e.g., number of CIRs in
the background wind, number of CMEs) and on the chosen AMR criteria,
thresholds and the number of refinement levels.
Conclusions:
The ICARUS model implemented in the MPI-AMRVAC framework is a new
inner heliospheric 3D MHD model that uses grid stretching as well as
AMR techniques. The flexibility in the grid and its resolution allows
an optimization of the computational time required for CME propagation
simulations for both scientific and forecasting purposes.
Title: Observation from Earth of an atypical cloud system in the
upper Martian atmosphere
Authors: Lilensten, J.; Dauvergne, J. L.; Pellier, C.; Delcroix, M.;
Beaudoin, E.; Vincendon, M.; Kraaikamp, E.; Bertrand, G.; Foster,
C.; Go, C.; Kardasis, E.; Pace, A.; Peach, D.; Wesley, A.; Samara,
E.; Poedts, S.; Colas, F.
Bibcode: 2022A&A...661A.127L
Altcode:
Context. The atmosphere of Mars is characterised by a complex seasonal
cycle of cloud formation related to the condensation of CO2
and H2O, and to the lifting of surface dust. Several decades
of spacecraft observations have provided an impressive amount of
data to constrain cloud properties. However, observations of a given
cloud obtained from Mars orbit are typically limited in time sampling
and spatial coverage. As a complement to this existing dataset,
Earth-based telescopic observations have the potential to provide a
global and dynamic view of some large-scale Mars clouds.
Aims:
On 17 November 2020, Mars and Earth were close to opposition. We took
advantage of this configuration to attempt observing large-scale
high-altitude atmospheric phenomena from Earth with a high time
sampling, over several hours.
Methods: Ten amateur astronomers
were coordinated along with professional astronomers to observe
Mars.
Results: We observed the occurrence of a large-scale
high-altitude cloud system, extending over thousands of kilometres
from the equator to 50°S. Over 3 h, it emerged from the night side at
92−16+30 km and dissipated on the dayside. It
occurred at a solar longitude of 316° (southern summer) concomitantly
to a regional dust storm and west of the magnetic anomaly. Despite
its high altitude, it was composed of relatively large particles
(effective radius in the 1-2 µm range). While dust appears an unlikely
candidate, possible composition by CO2 or H2O are
both conceivable, although the whole properties of the cloud makes it
atypical compared to previously reported clouds. We discuss the possible
connections with the dust storm, along with the hypothetical role of
nucleation from cosmic particle precipitation.
Conclusions:
We continuously followed a high-altitude huge cloud system on Mars
from Earth, emerging from the Martian night, from its appearance at the
terminator until its complete dissipation. It is either a large-grained
water ice cloud system or an extended mid-summer dawn CO2
cloud system. Movies associated to Fig. 9 are only available at https://www.aanda.org
Title: Mixing the Solar Wind Proton and Electron Scales. Theory and
2D-PIC Simulations of Firehose Instability
Authors: López, R. A.; Micera, A.; Lazar, M.; Poedts, S.; Lapenta,
G.; Zhukov, A. N.; Boella, E.; Shaaban, S. M.
Bibcode: 2022ApJ...930..158L
Altcode: 2022arXiv220502338L
Firehose-like instabilities (FIs) are cited in multiple astrophysical
applications. Of particular interest are the kinetic manifestations
in weakly collisional or even collisionless plasmas, where these
instabilities are expected to contribute to the evolution of macroscopic
parameters. Relatively recent studies have initiated a realistic
description of FIs, as induced by the interplay of both species,
electrons and protons, dominant in the solar wind plasma. This work
complements the current knowledge with new insights from linear theory
and the first disclosures from 2D-PIC simulations, identifying the
fastest growing modes near the instability thresholds and their long-run
consequences on the anisotropic distributions. Thus, unlike previous
setups, these conditions are favorable to those aperiodic branches
that propagate obliquely to the uniform magnetic field, with (maximum)
growth rates higher than periodic, quasi-parallel modes. Theoretical
predictions are, in general, confirmed by the simulations. The aperiodic
electron FI (a-EFI) remains unaffected by the proton anisotropy,
and saturates rapidly at low-level fluctuations. Regarding the FI at
proton scales, we see a stronger competition between the periodic
and aperiodic branches. For the parameters chosen in our analysis,
the aperiodic proton FI (a-PFI) is excited before than the periodic
proton FI (p-PFI), with the latter reaching a significantly higher
fluctuation power. However, both branches are significantly enhanced
by the presence of anisotropic electrons. The interplay between EFIs
and PFIs also produces a more pronounced proton isotropization.
Title: Effects of mesh topology on MHD solution features in coronal
simulations
Authors: Brchnelova, M.; Zhang, F.; Leitner, P.; Perri, B.; Lani,
A.; Poedts, S.
Bibcode: 2022JPlPh..88b9005B
Altcode: 2022arXiv220213696B
Magnetohydrodynamic (MHD) simulations of the solar corona have
become more popular with the increased availability of computational
power. Modern computational plasma codes, relying upon computational
fluid dynamics (CFD) methods, allow the coronal features to be resolved
using solar surface magnetograms as inputs. These computations are
carried out in a full three-dimensional domain and, thus, selection
of the correct mesh configuration is essential to save computational
resources and enable/speed up convergence. In addition, it has been
observed that for MHD simulations close to the hydrostatic equilibrium,
spurious numerical artefacts might appear in the solution following
the mesh structure, which makes the selection of the grid also a
concern for accuracy. The purpose of this paper is to discuss and
trade off two main mesh topologies when applied to global solar corona
simulations using the unstructured ideal MHD solver from the COOLFluiD
platform. The first topology is based on the geodesic polyhedron and
the second on $UV$ mapping. Focus is placed on aspects such as mesh
adaptability, resolution distribution, resulting spurious numerical
fluxes and convergence performance. For this purpose, first a rotating
dipole case is investigated, followed by two simulations using real
magnetograms from the solar minima (1995) and solar maxima (1999). It
is concluded that the most appropriate mesh topology for the simulation
depends on several factors, such as the accuracy requirements, the
presence of features near the polar regions and/or strong features
in the flow field in general. If convergence is of concern and the
simulation contains strong dynamics, then grids which are based on the
geodesic polyhedron are recommended compared with more conventionally
used $UV$-mapped meshes.
Title: How the area of solar coronal holes affects the properties
of high-speed solar wind streams near Earth: An analytical model
Authors: Hofmeister, Stefan J.; Asvestari, Eleanna; Guo, Jingnan;
Heidrich-Meisner, Verena; Heinemann, Stephan G.; Magdalenic, Jasmina;
Poedts, Stefaan; Samara, Evangelia; Temmer, Manuela; Vennerstrom,
Susanne; Veronig, Astrid; Vršnak, Bojan; Wimmer-Schweingruber, Robert
Bibcode: 2022A&A...659A.190H
Altcode: 2022arXiv220315689H
Since the 1970s it has been empirically known that the area of
solar coronal holes affects the properties of high-speed solar wind
streams (HSSs) at Earth. We derive a simple analytical model for the
propagation of HSSs from the Sun to Earth and thereby show how the
area of coronal holes and the size of their boundary regions affect
the HSS velocity, temperature, and density near Earth. We assume that
velocity, temperature, and density profiles form across the HSS cross
section close to the Sun and that these spatial profiles translate
into corresponding temporal profiles in a given radial direction due
to the solar rotation. These temporal distributions drive the stream
interface to the preceding slow solar wind plasma and disperse with
distance from the Sun. The HSS properties at 1 AU are then given by
all HSS plasma parcels launched from the Sun that did not run into
the stream interface at Earth distance. We show that the velocity
plateau region of HSSs as seen at 1 AU, if apparent, originates from
the center region of the HSS close to the Sun, whereas the velocity
tail at 1 AU originates from the trailing boundary region. Small
HSSs can be described to entirely consist of boundary region plasma,
which intrinsically results in smaller peak velocities. The peak
velocity of HSSs at Earth further depends on the longitudinal width
of the HSS close to the Sun. The shorter the longitudinal width of
an HSS close to the Sun, the more of its "fastest" HSS plasma parcels
from the HSS core and trailing boundary region have impinged upon the
stream interface with the preceding slow solar wind, and the smaller
is the peak velocity of the HSS at Earth. As the longitudinal width
is statistically correlated to the area of coronal holes, this also
explains the well-known empirical relationship between coronal hole
areas and HSS peak velocities. Further, the temperature and density
of HSS plasma parcels at Earth depend on their radial expansion from
the Sun to Earth. The radial expansion is determined by the velocity
gradient across the HSS boundary region close to the Sun and gives
the velocity-temperature and density-temperature relationships at
Earth their specific shape. When considering a large number of HSSs,
the assumed correlation between the HSS velocities and temperatures
close to the Sun degrades only slightly up to 1 AU, but the correlation
between the velocities and densities is strongly disrupted up to 1
AU due to the radial expansion. Finally, we show how the number of
particles of the piled-up slow solar wind in the stream interaction
region depends on the velocities and densities of the HSS and preceding
slow solar wind plasma.
Title: Toward a Realistic Evaluation of Transport Coefficients in
Non-equilibrium Space Plasmas
Authors: Husidic, Edin; Scherer, Klaus; Lazar, Marian; Fichtner,
Horst; Poedts, Stefaan
Bibcode: 2022ApJ...927..159H
Altcode: 2022arXiv220105157H
Recent studies have outlined the interest for the evaluation of
transport coefficients in space plasmas, where the observed velocity
distributions of plasma particles are conditioned not only by the binary
collisions, e.g., at low energies, but also by the energization of
particles from their interaction with wave turbulence and fluctuations,
generating the suprathermal kappa-distributed populations. This
paper provides a first estimate of the main transport coefficients
based on regularized kappa distributions, which, unlike standard
kappa distributions (SKDs), enable macroscopic parameterization
without mathematical divergences or physical inconsistencies. All
transport coefficients derived here, i.e., the diffusion and mobility
coefficients, electric conductivity, thermoelectric coefficient,
and thermal conductivity, are finite and well defined for all values
of κ > 0. Moreover, for low values of κ (i.e., below the SKD
poles), the transport coefficients can be orders of magnitudes higher
than the corresponding Maxwellian limits, meaning that significant
underestimations can be made if suprathermal electrons are ignored.
Title: Observation-based modelling of the energetic storm particle
event of 14 July 2012
Authors: Wijsen, N.; Aran, A.; Scolini, C.; Lario, D.; Afanasiev,
A.; Vainio, R.; Sanahuja, B.; Pomoell, J.; Poedts, S.
Bibcode: 2022A&A...659A.187W
Altcode: 2022arXiv220106454W
Aims: We model the energetic storm particle (ESP) event of
14 July 2012 using the energetic particle acceleration and transport
model named `PArticle Radiation Asset Directed at Interplanetary Space
Exploration' (PARADISE), together with the solar wind and coronal
mass ejection (CME) model named `EUropean Heliospheric FORcasting
Information Asset' (EUHFORIA). The simulation results illustrate both
the capabilities and limitations of the utilised models. We show that
the models capture some essential structural features of the ESP event;
however, for some aspects the simulations and observations diverge. We
describe and, to some extent, assess the sources of errors in the
modelling chain of EUHFORIA and PARADISE and discuss how they may be
mitigated in the future.
Methods: The PARADISE model computes
energetic particle distributions in the heliosphere by solving the
focused transport equation in a stochastic manner. This is done
using a background solar wind configuration generated by the ideal
magnetohydrodynamic module of EUHFORIA. The CME generating the ESP
event is simulated by using the spheromak model of EUHFORIA, which
approximates the CME's flux rope as a linear force-free spheroidal
magnetic field. In addition, a tool was developed to trace CME-driven
shock waves in the EUHFORIA simulation domain. This tool is used in
PARADISE to (i) inject 50 keV protons continuously at the CME-driven
shock and (ii) include a foreshock and a sheath region, in which the
energetic particle parallel mean free path, λ∥, decreases
towards the shock wave. The value of λ∥ at the shock
wave is estimated from in situ observations of the ESP event.
Results: For energies below ∼1 MeV, the simulation results agree
well with both the upstream and downstream components of the ESP event
observed by the Advanced Composition Explorer. This suggests that these
low-energy protons are mainly the result of interplanetary particle
acceleration. In the downstream region, the sharp drop in the energetic
particle intensities is reproduced at the entry into the following
magnetic cloud, illustrating the importance of a magnetised CME model.
Title: Dynamic Time Warping as a Means of Assessing Solar Wind
Time Series
Authors: Samara, E.; Laperre, B.; Kieokaew, R.; Temmer, M.; Verbeke,
C.; Rodriguez, L.; Magdalenić, J.; Poedts, S.
Bibcode: 2022ApJ...927..187S
Altcode: 2021arXiv210907873S
Over the last decades, international attempts have been made to
develop realistic space weather prediction tools aiming to forecast
the conditions on the Sun and in the interplanetary environment. These
efforts have led to the development of appropriate metrics to assess the
performance of those tools. Metrics are necessary to validate models, to
compare different models, and to monitor the improvements to a certain
model over time. In this work, we introduce dynamic time warping (DTW)
as an alternative way of evaluating the performance of models and,
in particular, of quantifying the differences between observed and
modeled solar wind time series. We present the advantages and drawbacks
of this method, as well as its application to Wind observations and
EUHFORIA predictions at Earth. We show that DTW can warp sequences
in time, aiming to align them with the minimum cost by using dynamic
programming. It can be applied for the evaluation of modeled solar wind
time series in two ways. The first calculates the sequence similarity
factor, a number that provides a quantification of how good the forecast
is compared to an ideal and a nonideal prediction scenario. The second
way quantifies the time and amplitude differences between the points
that are best matched between the two sequences. As a result, DTW
can serve as a hybrid metric between continuous measurements (e.g.,
the correlation coefficient) and point-by-point comparisons. It is
a promising technique for the assessment of solar wind profiles,
providing at once the most complete evaluation portrait of a model.
Title: Study of the propagation, in situ signatures, and
geoeffectiveness of shear-induced coronal mass ejections in different
solar winds
Authors: Talpeanu, D. -C.; Poedts, S.; D'Huys, E.; Mierla, M.
Bibcode: 2022A&A...658A..56T
Altcode: 2021arXiv211114909T
Aims: Our goal is to propagate multiple eruptions -obtained
through numerical simulations performed in a previous study- to 1
AU and to analyse the effects of different background solar winds
on their dynamics and structure at Earth. We also aim to improve the
understanding of why some consecutive eruptions do not result in the
expected geoeffectiveness, and how a secondary coronal mass ejection
(CME) can affect the configuration of the preceding one.
Methods: Using the 2.5D magnetohydrodynamics package of the code
MPI-AMRVAC, we numerically modelled consecutive CMEs inserted in two
different solar winds by imposing shearing motions onto the inner
boundary, which in our case represents the low corona. In one of
the simulations, the secondary CME was a stealth ejecta resulting
from the reconfiguration of the coronal field. The initial magnetic
configuration depicts a triple arcade structure shifted southward,
and embedded into a bimodal solar wind. We triggered eruptions by
imposing shearing motions along the southernmost polarity inversion
line, and the computational mesh tracks them via a refinement method
that applies to current-carrying structures, and is continuously
adapted throughout the simulations. We also compared the signatures
of some of our eruptions with those of a multiple CME event that
occurred in September 2009 using data from spacecraft around Mercury
and Earth. Furthermore, we computed and analysed the Dst index for all
the simulations performed.
Results: The observed event fits well
at 1 AU with two of our simulations, one with a stealth CME and the
other without. This highlights the difficulty of attempting to use in
situ observations to distinguish whether or not the second eruption was
stealthy, because of the processes the flux ropes undergo during their
propagation in the interplanetary space. We simulate the CMEs propagated
in two different solar winds, one slow and another faster one. In the
first case, plasma blobs arise in the trail of eruptions. The faster
solar wind simulations create no plasma blobs in the aftermath of
the eruptions, and therefore we interpret them as possible indicators
of the initial magnetic configuration, which changes along with the
background wind. Interestingly, the Dst computation results in a
reduced geoeffectiveness in the case of consecutive CMEs when the
flux ropes arrive with a leading positive Bz. When the
Bz component is reversed, the geoeffectiveness increases,
meaning that the magnetic reconnections with the trailing blobs and
eruptions strongly affect the impact of the arriving interplanetary
CME. Movies associated to Fig. 6 are available at https://www.aanda.org
Title: Comparing the Heliospheric Cataloging, Analysis, and Techniques
Service (HELCATS) Manual and Automatic Catalogues of Coronal Mass
Ejections Using Solar Terrestrial Relations Observatory/Heliospheric
Imager (STEREO/HI) Data
Authors: Rodriguez, L.; Barnes, D.; Hosteaux, S.; Davies, J. A.;
Willems, S.; Pant, V.; Harrison, R. A.; Berghmans, D.; Bothmer, V.;
Eastwood, J. P.; Gallagher, P. T.; Kilpua, E. K. J.; Magdalenic, J.;
Mierla, M.; Möstl, C.; Rouillard, A. P.; Odstrčil, D.; Poedts, S.
Bibcode: 2022SoPh..297...23R
Altcode:
We present the results of a comparative study between automatic
and manually compiled coronal mass ejection (CME) catalogues based
on observations from the Heliospheric Imagers (HIs) onboard NASA's
Solar Terrestrial Relations Observatory (STEREO) spacecraft. Using
the Computer Aided CME Tracking software(CACTus), CMEs are identified
in HI data using an automatic feature-detection algorithm, while
the Heliospheric Imagers Catalogue(HICAT) includes CMEs that are
detected by visual inspection of HI images. Both catalogues were
compiled as part of the EU FP7 Heliospheric Cataloguing, Analysis and
Techniques Service (HELCATS) project (www.helcats-fp7.eu). We compare
observational parameters of the CMEs from CACTus to those listed in
HICAT, such as CME frequency, position angle (PA), and PA-width. We
also compare CACTus-derived speeds to speeds derived from applying
geometric modelling to the majority of the HICAT CMEs, the results
of which are listed in the HELCATS Heliospheric Imagers Geometric
Catalogue(HIGeoCAT). We find that both CACTus and HICAT catalogues
contain a similar number of events when we exclude events narrower than
20∘, which are not included in the HICAT catalogue but are
found to be identified by CACTus. PA-distributions are strongly peaked
around 90∘ and 270∘, with a slightly larger
CME frequency northwards of the equatorial plane (particularly for the
STEREO-A versions of both catalogues). The CME PA-widths in both HICAT
and CACTus catalogues peak at approximately 60∘. Manually
derived speeds from HIGeoCAT and automatically derived speeds by
CACTus correlate well for values lower than 1000 km s−1,
in particular when CMEs are propagating close to the plane of the sky.
Title: Propagation of the Alfvén Wave and Induced Perturbations in
the Vicinity of a 3D Proper Magnetic Null Point
Authors: Sabri, S.; Ebadi, H.; Poedts, S.
Bibcode: 2022ApJ...924..126S
Altcode:
The aim of the present work is to study the propagation of the Alfvén
wave around a 3D proper magnetic null point and its accompanying
perturbations. In this line, the shock-capturing Godunov-type PLUTO
code is used to solve the magnetohydrodynamic (MHD) equations. It
is found that the Alfvén wave propagates toward the null point at
the fan plane and the wave-wave interaction could be the main reason
for the Alfvén wave energy dissipation, ehile, at two other planes
including the spine axis, the Alfvén wave spreads toward the spine
axis and accumulates along it. Furthermore, the fast magnetoacoustic
wave moves toward the null point at the fan plane and also at two other
planes including the spine axis. The fast magnetoacoustic wave also
refracts around the null point without any significant accumulation
along the spine axis. Finally, the slow mode moves toward the null
point at the fan plane. It is illustrated that, at the x,z plane,
in addition to the refraction of the slow wave around the null point,
there is an accumulation of the slow mode along the spine axis, while,
at the other plane including the spine axis, the slow magnetoacoustic
wave refracts around the null point. Moreover, it is found that the 3D
structure results in the high amplitude of MHD wave energy in comparison
with the 2.5D structure. Finally, it is found that the Alfvén wave
gives its energy to the induced fast and slow magnetoacoustic waves
and they have more time to heat the plasma.
Title: Temperature anisotropy instabilities stimulated by the solar
wind suprathermal populations
Authors: Lazar, Marian; López, R. A.; Shaaban, Shaaban Mohammed;
Poedts, Stefaan; Yoon, Peter Haesung; Fichtner, Horst
Bibcode: 2022FrASS...8..249L
Altcode:
This review paper compiles recent results describing the effects of
suprathermal populations present in space plasmas (up to a few keVs)
on temperature anisotropy instabilities. Of particular interest are
the electromagnetic cyclotron and firehose excitations, which play a
major role in limiting temperature anisotropy, resulting, for instance,
from the adiabatic expansion of the solar wind. Relying on a rigorous
modeling and interpretation of the observed velocity distributions,
both theoretical models and numerical simulations indicate a systematic
stimulation of these excitations in the presence of suprathermal
populations of electrons or protons. Moreover, the enhanced fluctuations
react back on particles, and determine a faster and deeper relaxation
of their anisotropy. The present comparative analysis suggests
that previous studies, considering only quasi-thermal, low-energy
populations may have significantly underestimated these excitations
and their implications in various applications in space plasmas.
Title: Self-similarity for astrophysical MHD transients revisited
Authors: Rogava, Andria; Poedts, Stefaan; Dadiani, Ekaterine
Bibcode: 2022AdSpR..69..474R
Altcode:
The problem of the existence of self-similar solutions for astrophysical
magnetohydrodynamic (MHD) transient flows is considered. Our approach
is based on the pioneering works by B.C. Low for coronal transients and
their further generalizations. The axiomatic basis of the approach is
adjusted and verified. It is shown that the introduction of a new type
of "triple-compound" variable may lead to the appearance of new classes
of analytic self-similar solutions, possibly relevant for a number of
interesting astrophysical situations. The possibility of the development
of a self-similar model for a strongly magnetized plasma with pressure
anisotropy is indicated. It is argued that proper changes of the model's
geometric and kinematic features may lead to the discovery of other,
more complex and less idealized classes of self-similar solutions.
Title: Designing Radiation Belt Environmental Indicators for the
safety of space assets: a transition of powerful tools from research
to operations (R2O)
Authors: Daglis, Ioannis; Bourdarie, Sebastien; Poedts, Stefaan;
Santolik, Ondrej; Darrouzet, Fabien; Cueto Rodriguez, Juan; Lavraud,
Benoit; Sandberg, Ingmar
Bibcode: 2021AGUFMSH45E2410D
Altcode:
The SafeSpace project aims at advancing space weather nowcasting
and forecasting capabilities and, consequently, at contributing to
the safety of space assets through the transition of powerful tools
from research to operations (R2O). This will be achieved through the
synergy of five well-established space weather models (CNRS/CDPP solar
disturbance propagation tool, KULeuven EUHFORIA CME evolution model,
ONERA Neural Network tool, IASB plasmasphere model and ONERA Salammbo
radiation belts code), which cover the whole Sun interplanetary space
Earths magnetosphere chain. The combined use of these models will enable
the delivery of a sophisticated model of the Van Allen electron belt
and of a prototype space weather service of tailored particle radiation
indicators. Moreover, it will enable forecast capabilities with a target
lead time of 2 to 4 days, which is a tremendous advance from current
forecasts that are limited to lead times of a few hours. SafeSpace
will improve radiation belt modelling through the incorporation into
the Salammbo model of magnetospheric processes and parameters of
critical importance to radiation belt dynamics. Furthermore, solar and
interplanetary conditions will be used as initial conditions to drive
the advanced radiation belt model and to provide the link to the solar
origin and the interplanetary drivers of space weather. This approach
will culminate in a prototype early warning system for detrimental space
weather events, which will include indicators of particle radiation of
use to space industry and spacecraft operators. Indicator values will
be generated by the advanced radiation belt model and the performance
of the prototype service will be evaluated in collaboration with space
industry stakeholders. The work leading to this paper has received
funding from the European Unions Horizon 2020 research and innovation
programme under grant agreement No 870437 for the SafeSpace (Radiation
Belt Environmental Indicators for the Safety of Space Assets) project.
Title: Evolution of shock waves and associated type II radio emission
in the low corona and interplanetary space
Authors: Jebaraj, Immanuel; Kouloumvakos, Athanasios; Magdalenic,
Jasmina; Rouillard, Alexis; Warmuth, Alexander; Mann, Gottfried;
Krupar, Vratislav; Poedts, Stefaan; Vainio, Rami
Bibcode: 2021AGUFMSM35D2002J
Altcode:
Type II radio bursts are generally observed in association with
flare-generated or CME-driven (coronal mass ejection) shock waves. They
are signatures of fast electron beams which are accelerated at the
shock front. The exact shock and coronal conditions necessary for
the production of the type II radio emission are still debated. The
preferred location of the type II radio sources on the surface of
the shock wave, can either be at regions close to the CME/shock
leading edge or at the CME/shock flanks, or both, and has been a
long-standing discussion. We address this question in a twofold study:
In Kouloumvakos et al. (2021), we study a coronal shock wave associated
with a multi-lane metric type II on 05 November 2014 and in Jebaraj et
al. (2021), we study a shock wave associated with a flare/CME event and
a complex radio event on September 27, 2012. In these studies, we employ
a novel approach, combining shock wave modelling with radio techniques
such as radio triangulation. Using, data from radio observatories and
modern modeling techniques, we study the evolution of the shock waves
in the low corona and in interplanetary space. First we reconstruct the
shock wave in 3D space using multi-viewpoint observations of the solar
corona and then we estimate the evolution of shock wave parameters in
3D using an MHD model of the background corona produced by the MAS
(Magnetohydrodynamics Around a Sphere) model. Our results are based
on a two-step analysis. We first analyze the global evolution of the
wave parameters and then localize the areas which could be the source
regions of radio emission. We study the temporal evolution of the
upstream plasma characteristics and the shock wave parameters. We have
visualized the complex relationship between the different shock wave
parameters in a novel way by producing synthetic radio spectra. The
conclusions of the two studies have been published in separate papers
and suggest that the shock wave geometry and its relationship with the
shock strength seem to play the most vital role in the generation of
type II radio emission.
Title: The ESA Virtual Space Weather Modelling Centre-Part 3
Authors: Poedts, Stefaan
Bibcode: 2021AGUFMSH53B..04P
Altcode:
The ESA Virtual Space Weather Modelling Centre (VSWMC) project
was defined as a long term project including different successive
parts. Parts 1 and 2 were completed in the first 4-5 years and designed
and developed a system that enables models and other components to be
installed locally or geographically distributed and to be coupled and
run remotely from the central system. A first, limited version went
operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE
Portal. It is similar to CCMC but interactive (no runs on demand)
and the models are geographically distributed and coupled over the
internet. The goal of the ESA project "Virtual Space Weather Modelling
Centre - Part 3" (2019-2021) is to further develop the Virtual Space
Weather Modelling Centre, building on the Part 2 prototype system
and focusing on the interaction with the ESA SSA SWE system. The
objectives and scope of this new project include maintaining the
current operational system, the efficient integration of 11 new models
and many new model couplings, including daily automated end-to-end
(Sun to Earth) simulations, the further development and wider use
of the coupling toolkit and front-end GUI, making the operational
system more robust and user-friendly. The new models that are being
integrated are Wind-Predict (a global coronal model from CEA, France),
the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model, Multi-VP
(another global coronal model form IRAP/CNRS, France), the BIRA Plasma
sphere Model of electron density and temperatures inside and outside
the plasmasphere coupled with the ionosphere (BPIM, Belgium), the SNRB
(also named SNB3GEO) model for electron fluxes at geostationary orbit
(covering the GOES 15 energy channels >800keV and >2MeV) and the
SNGI geomagnetic indices Kp and Dst models (University of Sheffield,
UK), the SPARX Solar Energetic Particles transport model (University of
Central Lancashire, UK), Spenvis DICTAT tool for s/c internal charging
analysis (BISA, Belgium), the Gorgon magnetosphere model (ICL, UK), and
the Drag Temperature Model (DTM) and operations-focused whole atmosphere
model MCM being developed in the H2020 project SWAMI. We will provide
an overview of the state-of-the-art, including the new available model
couplings and daily model chain runs, and demonstrate the system.
Title: Magnetized CMEs and solution adaptive mesh refinement in
EUHFORIA
Authors: Baratashvili, Tinatin; Verbeke, Christine; Poedts, Stefaan
Bibcode: 2021AGUFMSH33A..06B
Altcode:
Coronal Mass Ejections (CMEs) are the main drivers of interplanetary
shocks and space weather disturbances. One of the key parameters
that determine the geo-effectiveness of the CME is its internal
magnetic configuration. Strong CMEs directed towards Earth can have
a severe impact on our planet and their prediction can mitigate
possible damages. The novel heliospheric model ICARUS, which is
implemented within the framework of MPI-AMRVAC (Xia et al., 2018)
introduces new capabilities to model the heliospheric wind and real
CME events. Advanced techniques, such as adaptive mesh refinement and
grid stretching are implemented. By imposing these techniques, we avoid
cell deformation in the domain and only the necessary/desired areas
are refined to higher spatial resolutions (and coarsened again when the
high resolution is no longer necessary, e.g. behind a travelling shock
wave). The refinement and coarsening conditions are controlled by the
user. These techniques result in optimised computer memory usage and
a significant speed-up, which is crucial for forecasting purposes. In
order to model the magnetic field and its interaction with the solar
wind, the linear force-free spheromak (LFFS) model from EUHFORIA is
imported and applied in the new heliospheric model. In order to assess
the ICARUS model capabilities to predict the solar wind conditions
in the heliosphere, especially at L1, we consider several real CME
events. Further, we perform a comparison of the results of the original
EUHFORIA model and the novel heliospheric model, while we also monitor
the time that simulations require to model the heliospheric wind and CME
events. The solution mesh refinement is applied to the CMEs in order to
model its arrival time and interior magnetic field better. To analyze
the results, the radial, longitudinal and latitudinal components of the
magnetic field are compared to the original EUHFORIA simulations and
the observed data. As a result, the new heliospheric model provides
accurate results and gives various options to apply to the domain in
simulations, while the simulations are much more efficient and save
significant amounts of computational resources and time. This research
has received funding from the European Unions Horizon 2020 research
and innovation program under grant agreement No 870405 (EUHFORIA 2.0).
Title: The Dynamic Time Warping Technique as an Alternative Way to
Evaluate Space Weather Predictions
Authors: Samara, Evangelia; Chane, Emmanuel; Laperre, Brecht; Kieokaew,
Rungployphan; Temmer, Manuela; Verbeke, Christine; Rodriguez, Luciano;
Magdalenic, Jasmina; Poedts, Stefaan
Bibcode: 2021AGUFMSH55C1860S
Altcode:
In this work, the Dynamic Time Warping (DTW) technique is presented
as an alternative method to quantify differences between observed
and modeled time series in solar wind forecasting. The method was
initially developed for speech recognition purposes and over the years
it met great interest by other scientific fields. In the frame of this
study, we show for the first time how we can apply DTW to assess the
performance of modeled time series produced by space weather forecasting
tools. Dynamic Time Warping can quantify how similar two time series
are by providing a temporal alignment between them, in an optimal
way, under certain restrictions. We further discuss the benefits and
limitations of this method compared to other widely used metrics and
we show examples on how the technique is applied to predicted solar
wind time series modeled by EUHFORIA.
Title: Evolution of Interplanetary Coronal Mass Ejection Complexity:
a Numerical Study Through a Swarm of Simulated Spacecraft
Authors: Scolini, Camilla; Winslow, Reka; Lugaz, Noe; Poedts, Stefaan
Bibcode: 2021AGUFMSH15A2023S
Altcode:
Coronal mass ejections (CMEs) are the main source of adverse space
weather in the inner heliosphere. These large-scale transients,
characterized by intense and highly-twisted magnetic field bundles,
often drive fast-forward interplanetary shocks and turbulent sheaths,
and contain prolonged periods of southward pointing magnetic field. The
interaction of CMEs with other interplanetary structures and other
CMEs can drastically alter their global and local properties during
propagation, and increase their complexity. In-situ measurements
carried out by spacecraft in radial alignment are critical to
advance our knowledge on the evolutionary behavior of CMEs and their
magnetic structures during propagation. Yet, the scarcity of radially
aligned CME crossings restricts investigations on the evolution of CME
magnetic structures to a few case studies, preventing a comprehensive
understanding of CME complexity changes during propagation. In this
study, we perform numerical simulations of CMEs interacting with
different solar wind streams using the linear force-free spheromak
CME model incorporated into the EUropean Heliospheric FORecasting
Information Asset (EUHFORIA) model. The novelty of our approach lies
in the investigation of the evolution of CME complexity using a swarm
of radially aligned, simulated spacecraft. Our scope is to determine
under which conditions, and to what extent, CMEs exhibit variations of
their magnetic structure and complexity during propagation, as measured
by spacecraft that are radially aligned. Results indicate that the
interaction with large-scale solar wind structures, and particularly
with stream interaction regions, doubles the probability to detect
an increase of the CME magnetic complexity between two spacecraft in
radial alignment, compared to cases without such interactions. This work
represents the first attempt to quantify the probability of detecting
complexity changes in CME magnetic structures by spacecraft in radial
alignment using numerical simulations, and it provides support to the
interpretation of multi-point CME observations involving past, current,
and future missions.
Title: Revisiting the Two-fluid Modeling of Acoustic Wave and Shock
Propagation in the Gravitationally Stratified Partially Ionized Plasma
Authors: Zhang, Fan; Poedts, Stefaan; Lani, Andrea
Bibcode: 2021AGUFMSH45B2369Z
Altcode:
The chromosphere is a dynamic thin layer of the lower solar
atmosphere. Understanding this thin layer is, however, essential
for understanding the energetics of the solar atmosphere because all
the nonthermal energy heating the corona and driving the solar wind
propagates through the chromosphere before it arrives in the higher
regions of the atmosphere. In this dynamic layer, waves are ubiquitous
and may carry enough energy to heat the solar atmosphere. However,
high-frequency waves are relatively difficult to observe, and, in fact,
also difficult to numerically model because of CPU requirements. In
particular, modeling the partially ionized chromospheric plasma,
ideally, needs to take into account non-equilibrium ionization,
non-LTE radiative transfer, and multi-fluid effects, which are all
computationally expensive. We apply simplified models including
the hydrogen ion-neutral collision, optical thin radiative losses,
and ionization/recombination, to numerically investigate acoustic
wave and shock propagation in the partially ionized plasma, which
partly reproduces the chromospheric quantities. We assume an initial
hydrostatic and ionization equilibrium. However, as the chromosphere
is highly dynamic and there are still different opinions about its
structure, we change the plasma quantities to study their influence
on the wave propagation and dissipation, which are essential for
understanding the energy transport. In addition, as our previous
numerical simulations [Zhang et al. (2021) ApJ, 911, 119] showed that
the energy carried by acoustic waves might be sufficient to compensate
the chromospheric radiative energy losses, here we include radiative
loss functions to investigate their influence on the dynamic wave
propagation process. Parametric studies will also be provided to
explain the limits of the models quantitatively.
Title: How to Benchmark a Coronal Model for Space Weather Forecasting:
Validating EUHFORIA 2.0 Coronal Model Using Simulations and
Observations
Authors: Perri, Barbara; Leitner, Peter; Brchnelova, Michaela;
Baratashvili, Tinatin; Zhang, Fan; Kuzma, Bazej; Ben Ameur, Firas;
Lani, Andrea; Poedts, Stefaan
Bibcode: 2021AGUFMSH15E2061P
Altcode:
Space weather has become a major stake for many countries, with the
issue of anticipating the most precisely as possible the arrival
of eruptive events and their impact on Earth. As eruptive events
propagate through the interplanetary medium, they interact with
the large-scale magnetic field generated inside the Sun by dynamo
effect and the continuous solar wind. Thus, the prediction of their
arrival time depends strongly on the capacity to model this complex
background medium. The EUHFORIA 2.0 project aims at going beyond the
empirical description of WSA models, and developing a coronal model
that will be both physically precise, robust and fast, to provide
reliable input to chains of models such as the VSWMC to compute the
chain of propagation from Sun to Earth. To develop our coronal model,
we used the code COOLFluiD. To validate it, we developed a benchmark
protocol: we compared it to the coronal model Wind-Predict, first
on simple configurations such as dipole and quadrupole, and then on
realistic configurations by using magnetograms at minimum and maximum
of activity as simulation input. We then confronted our model to
observations using eclipse and coronograph pictures. Finally, we have
used various numerical techniques to optimize the code for forecast,
such as unstructured meshes, implicit schemes and AMR. We will present
the methodology used for the benchmark, discuss the results and explain
the next steps to make the model even more realistic regarding the
coronal heating.
Title: Plasma Flow Generation due to the Nonlinear Alfvén Wave
Propagation around a 3D Magnetic Null Point
Authors: Sabri, S.; Ebadi, H.; Poedts, S.
Bibcode: 2021ApJ...922..123S
Altcode:
The behavior of current density accumulation around the sharp gradient
of magnetic field structure or a 3D magnetic null point and with the
presence of finite plasma pressure is investigated. It has to be stated
that in this setup, the fan plane locates at the xy plane and the spine
axis aligns along the z-axis. Current density generation in presence
of the plasma pressure that acts as a barrier for developing current
density is less well understood. The shock-capturing Godunov-type PLUTO
code is used to solve the magnetohydrodynamic set of equations in the
context of wave-plasma energy transfer. It is shown that propagation
of Alfvén waves in the vicinity of a 3D magnetic null point leads to
current density excitations along the spine axis and also around the
magnetic null point. Besides, it is pointed out the x component of
current density has oscillatory behavior while the y and z components
do not show this property. It is plausible that it happens because
the fan plane encompasses separating unique topological regions,
while the spine axis does not have this characteristic and is just a
line without separate topological regions. Besides, current density
generation results in plasma flow. It is found that the y component of
the current density defines the x component of the plasma flow behavior,
and the x component of the current density prescribes the behavior of
the y component of the plasma flow.
Title: Employing advanced FRi3D CME model coupled with EUHFORIA in
predictions of CME geo-effectiveness
Authors: Maharana, Anwesha; Poedts, Stefaan; Scolini, Camilla;
Isavnin, Alexey; Wijsen, Nicolas; Rodriguez, Luciano; Mierla, Marilena;
Magdalenic, Jasmina
Bibcode: 2021AGUFMSH33A..01M
Altcode:
The Flux Rope in 3D (FRi3D, Isavnin 2016), a CME model with global
three-dimensional geometry, has been implemented in the space
weather forecasting tool EUHFORIA (Pomoell and Poedts, 2018). The
aim of implementing this advanced flux rope model with EUHFORIA is to
improve the modelling of CME flank encounters, especially the magnetic
field predictions at Earth. As the CMEs in FRi3D model are connected
to the Sun upon their injection into EUHFORIA, we test different
CME leg disconnection methods to avoid numerical discrepancies
(e.g. negative pressure) and obtain a stable and more accurate CME
evolution in EUHFORIA. The model was first validated with synthetic
events. Afterwards it was optimised to run robust simulations of
two real events (previously studied by Scolini et al. 2019 using
the spheromak CME model) constrained using an observations-based
approach. The geometrical parameters were obtained using the forward
modelling tool included in FRi3D with additional flux rope geometry
flexibilities as compared to the Graduated Cylindrical Shell (GCS,
Thernisien 2011) model. Further, the magnetic field parameters were
derived using the differential evolution algorithm to fit FRi3D
parameters to the in-situ observations at 1 AU. Herein, a comparison
of the magnetic field parameters with those obtained using other
observational techniques (Gopalswamy et al., 2017) is presented. The
observation-based approach is adopted to constrain the density of
FRi3D CMEs (based on Temmer et al., 2020), which provides a better
estimation for this geometry, in comparison to the standard density
used in EUHFORIA. Finally, the CMEs are modelled in EUHFORIA with the
best set of CME parameters obtained from the methods described above
and FRi3Ds predictive performance is compared with the previously
implemented spheromak CME in EUHFORIA. Geo-effectiveness of studied
storms is computed at Earth by coupling EUHFORIA with the magnetospheric
model OpenGGCM, i.e. replacing observational solar wind data at L1 by
synthetic data obtained from EUHFORIA.
Title: Observation-based modelling of the energetic storm particle
event of 14 July 2012
Authors: Wijsen, Nicolas; Aran, Angels; Scolini, Camilla; Lario,
David; Afanasiev, Alexandr; Vainio, Rami; Pomoell, Jens; Sanahuja,
Blas; Poedts, Stefaan
Bibcode: 2021AGUFMSH52B..06W
Altcode:
In this work, we perform a comprehensive analysis of the Energetic Storm
Particle (ESP) event that was observed in the near-Earth environment
on 14 July 2012. This ESP was part of a large solar energetic particle
(SEP) event associated with the coronal mass ejection (CME) that erupted
from the Sun on 12 July 2012. During the prompt component of the SEP
event, energetic protons with energies up to ~100 MeV were detected near
Earth. In addition, an increase in energetic particle intensities was
also measured by the Solar Terrestrial Relations Observatory-Behind
(STEREO-B), which was located 115 degrees east from Earth. Scolini
et al. (2019) recently modelled the Sun-to-Earth propagation of
this CME by using the spheromak model integrated in the data-driven
magnetohydrodynamic model EUHFORIA (EUropean Heliospheric Forecasting
Information Asset). In this work, we extend this modelling effort by
using PARADISE (Particle Radiation Asset Directed at Interplanetary
Space Exploration) to also study the SEP component of this event. The
PARADISE model computes energetic particle distributions in the
inner heliosphere by solving the five-dimensional focused transport
equation in a solar wind generated by EUHFORIA. We study which particle
scattering conditions at the CME front can reproduce the observed ESP
event. In addition, we discuss the viability of the spheromak model
in studying gradual SEP events. Reference: Scolini et al. A&A 626,
A122 (2019)
Title: Evidence for local particle acceleration in the first recurrent
galactic cosmic ray depression observed by Solar Orbiter. The ion
event on 19 June 2020
Authors: Aran, A.; Pacheco, D.; Laurenza, M.; Wijsen, N.; Lario, D.;
Benella, S.; Richardson, I. G.; Samara, E.; Freiherr von Forstner,
J. L.; Sanahuja, B.; Rodriguez, L.; Balmaceda, L.; Espinosa Lara,
F.; Gómez-Herrero, R.; Steinvall, K.; Vecchio, A.; Krupar, V.;
Poedts, S.; Allen, R. C.; Andrews, G. B.; Angelini, V.; Berger, L.;
Berghmans, D.; Boden, S.; Böttcher, S. I.; Carcaboso, F.; Cernuda, I.;
De Marco, R.; Eldrum, S.; Evans, V.; Fedorov, A.; Hayes, J.; Ho, G. C.;
Horbury, T. S.; Janitzek, N. P.; Khotyaintsev, Yu. V.; Kollhoff, A.;
Kühl, P.; Kulkarni, S. R.; Lees, W. J.; Louarn, P.; Magdalenic, J.;
Maksimovic, M.; Malandraki, O.; Martínez, A.; Mason, G. M.; Martín,
C.; O'Brien, H.; Owen, C.; Parra, P.; Prieto Mateo, M.; Ravanbakhsh,
A.; Rodriguez-Pacheco, J.; Rodriguez Polo, O.; Sánchez Prieto, S.;
Schlemm, C. E.; Seifert, H.; Terasa, J. C.; Tyagi, K.; Verbeeck, C.;
Wimmer-Schweingruber, R. F.; Xu, Z. G.; Yedla, M. K.; Zhukov, A. N.
Bibcode: 2021A&A...656L..10A
Altcode:
Context. In mid-June 2020, the Solar Orbiter (SolO) mission reached its
first perihelion at 0.51 au and started its cruise phase, with most of
the in situ instruments operating continuously.
Aims: We present
the in situ particle measurements of the first proton event observed
after the first perihelion obtained by the Energetic Particle Detector
(EPD) suite on board SolO. The potential solar and interplanetary
(IP) sources of these particles are investigated.
Methods: Ion
observations from ∼20 keV to ∼1 MeV are combined with available
solar wind data from the Radio and Plasma Waves (RPW) instrument and
magnetic field data from the magnetometer on board SolO to evaluate
the energetic particle transport conditions and infer the possible
acceleration mechanisms through which particles gain energy. We compare
> 17-20 MeV ion count rate measurements for two solar rotations,
along with the solar wind plasma data available from the Solar Wind
Analyser (SWA) and RPW instruments, in order to infer the origin of
the observed galactic cosmic ray (GCR) depressions.
Results:
The lack of an observed electron event and of velocity dispersion at
various low-energy ion channels and the observed IP structure indicate
a local IP source for the low-energy particles. From the analysis
of the anisotropy of particle intensities, we conclude that the
low-energy ions were most likely accelerated via a local second-order
Fermi process. The observed GCR decrease on 19 June, together with the
51.8-1034.0 keV nuc−1 ion enhancement, was due to a solar
wind stream interaction region (SIR). The observation of a similar
GCR decrease in the next solar rotation favours this interpretation
and constitutes the first observation of a recurrent GCR decrease
by SolO. The analysis of the recurrence times of this SIR suggests
that it is the same SIR responsible for the 4He events
previously measured in April and May. Finally, we point out that
an IP structure more complex than a common SIR cannot be discarded,
mainly due to the lack of solar wind temperature measurements and the
lack of a higher cadence of solar wind velocity observations. Movies associated to Figs. B.1 and B.2 are available at https://www.aanda.org
Title: Transport coefficients enhanced by suprathermal particles in
nonequilibrium heliospheric plasmas
Authors: Husidic, E.; Lazar, M.; Fichtner, H.; Scherer, K.; Poedts, S.
Bibcode: 2021A&A...654A..99H
Altcode: 2021arXiv210811614H
Context. In heliospheric plasmas, such as the solar wind and planetary
magnetospheres, the transport of energy and particles is governed
by various fluxes (e.g., heat flux, particle flux, current flow)
triggered by different forces, electromagnetic fields, and gradients
in density or temperature. In the outer corona and at relatively
low heliocentric distances in the solar wind (i.e., < 1 AU),
particle-particle collisions play an important role in the transport
of energy, momentum, and matter, described within classical transport
theory by the transport coefficients, which relate the fluxes to their
sources.
Aims: The aim of the present paper is to improve the
evaluation of the main transport coefficients in such nonequilibrium
plasmas, on the basis of an implicit realistic characterization of
their particle velocity distributions, in accord with the in situ
observations. Of particular interest is the presence of suprathermal
populations and their influence on these transport coefficients.
Methods: Using the Boltzmann transport equation and macroscopic laws
for the energy and particle fluxes, we derived transport coefficients,
namely, electric conductivity, thermoelectric coefficient, thermal
conductivity, diffusion, and mobility coefficients. These are
conditioned by the electrons, which are empirically well described
by the Kappa distribution, with a nearly Maxwellian (quasi-thermal)
core and power-law tails enhanced by the suprathermal population. Here
we have adopted the original Kappa approach that has the ability to
outline and quantify the contribution of suprathermal populations.
Results: Without exception, the transport coefficients are found to
be systematically and markedly enhanced in the presence of suprathermal
electrons (i.e., for finite values of the κ parameter), due to the
additional kinetic energy with which these populations contribute to
the dynamics of space plasma systems. The present results also show
how important an adequate Kappa modeling of suprathermal populations
is, which is in contrast to other modified interpretations that
underestimate the effects of these populations.
Title: Generation of interplanetary type II radio emission
Authors: Jebaraj, I. C.; Kouloumvakos, A.; Magdalenic, J.; Rouillard,
A. P.; Mann, G.; Krupar, V.; Poedts, S.
Bibcode: 2021A&A...654A..64J
Altcode:
Context. Coronal mass ejections (CMEs) are eruptive phenomena that can
accelerate energetic particles and drive shock waves. The CME-driven
shocks propagate from the low corona to interplanetary space. The radio
emission that results from fast electrons energised by shock waves are
called type II bursts. This radio emission can provide information on
the physical properties of the shock and its evolution as it travels
through the corona and interplanetary space.
Aims: We present
a comprehensive analysis of the shock wave associated with two type
II radio bursts observed on 27 September 2012. The aim of the study
is to isolate and understand the shock wave properties necessary
for accelerating electrons, leading to the production of the radio
emission.
Methods: First, we modelled the 3D expansion of the
shock wave by exploiting multi-viewpoint reconstruction techniques based
on extreme ultraviolet imaging. The physical properties of the shock
front were then deduced by comparing the triangulated 3D expansion with
properties of the background corona provided by a 3D magnetohydrodynamic
model. The radio triangulation technique provided the location of
radio source on the surface of the modelled wave in order to compare
radio sources with the shock properties.
Results: This study
is focused on the temporal evolution of the shock wave parameters and
their role in the generation of radio emission. Results show a close
relationship between the shock wave strength and its geometry. We
deduce from this analysis that there may be several mechanisms at play
that generally contribute to the generation of radio emission.
Conclusions: The comparison between the reconstructed sources of radio
emission and the ambient shock wave characteristics reveals the complex
relationship between shock parameters and show how they can influence
the morphology of the observed type II radio emission.
Title: Editorial: Data-driven MHD -Novel Applications to the Solar
Atmosphere
Authors: Srivastava, A. K.; Erdélyi, R.; Poedts, S.; Chen, P. F.;
Yan, Y.
Bibcode: 2021FrASS...8..140S
Altcode:
No abstract at ADS
Title: A new type of cloud discovered from Earth in the upper
Martian atmosphere
Authors: Lilensten, Jean; Dauvergne, Jean-Luc; Pellier, Christophe;
Delcroix, Marc; Beaudoin, Emmanuel; Vincendon, Mathieu; Kraaikamp,
Emil; Bertrand, Guillaume; Foster, Clyde; Go, Christopher; Kardasis,
Μanos; Pace, Alexei; Peach, Damian; Wesley, Anthony; Samara,
Evangelia; Poedts, Stefaan; Colas, Francois
Bibcode: 2021EPSC...15....7L
Altcode:
During the 2020 Mars opposition, we observe from Earth the occurrence of
a non-typical large-scale high-altitude clouds system, extending over
thousands of km from the equator to 50°S. Over 3 hours, they emerge
from the night side at an altitude of 90 (-15/+30) km and progressively
dissipate in the dayside. They occur at a solar longitude of 316°,
west of the magnetic anomaly and concomitantly to a regional dust
storm. Despite their high altitude, they are composed of relatively
large particles, suggesting a probable CO2 ice composition, although
H2O cannot be totally excluded. Such ice clouds were not reported
previously. We discuss the formation of this new type of clouds and
suggest a possible nucleation from cosmic particle precipitation.
Title: 3D numerical simulations of propagating two-fluid, torsional
Alfvén waves and heating of a partially ionized solar chromosphere
Authors: Kuźma, B.; Murawski, K.; Poedts, S.
Bibcode: 2021MNRAS.506..989K
Altcode:
We present a new insight into the propagation, attenuation, and
dissipation of two-fluid, torsional Alfvén waves in the context
of heating of the lower solar atmosphere. By means of numerical
simulations of the partially ionized plasma, we solve the set of
two-fluid equations for ion plus electron and neutral fluids in 3D
Cartesian geometry. We implement initially a current-free magnetic
field configuration, corresponding to a magnetic flux-tube that is
rooted in the solar photosphere and expands into the chromosphere and
corona. We put the lower boundary of our simulation region in the low
chromosphere, where ions and neutrals begin to decouple, and implement
there a monochromatic driver that directly generates Alfvén waves
with a wave period of 30 s. As the ion-neutral drift increases with
height, the two-fluid effects become more significant and the energy
carried by both Alfvén and magneto-acoustic waves can be thermalized
in the process of ion-neutral collisions there. In fact, we observe
a significant increase in plasma temperature along the magnetic
flux-tube. In conclusion, the two-fluid torsional Alfvén waves can
potentially play a role in the heating of the solar chromosphere.
Title: Eigenspectra of solar active region long-period oscillations
Authors: Dumbadze, G.; Shergelashvili, B. M.; Poedts, S.; Zaqarashvili,
T. V.; Khodachenko, M.; De Causmaecker, P.
Bibcode: 2021A&A...653A..39D
Altcode: 2021arXiv210904189D
Context. We studied the low-frequency ≲0.5 h−1
(long-period ≳2 h) oscillations of active regions (ARs). The
investigation is based on an analysis of a time series built from Solar
Dynamics Observatory/Helioseismic and Magnetic Imager photospheric
magnetograms and comprises case studies of several types of AR
structures.
Aims: The main goals are to investigate whether ARs
can be engaged in long-period oscillations as unified oscillatory
entities and, if so, to determine the spectral pattern of such
oscillations.
Methods: Time series of characteristic parameters
of the ARs, such as, the total area, total unsigned radial magnetic
flux, and tilt angle, were measured and recorded using the image moment
method. The power spectra were built out of Gaussian-apodised and
zero-padded datasets.
Results: There are long-period oscillations
ranging from 2 to 20 h, similarly to the characteristic lifetimes of
super-granulation, determined from the datasets of the AR total area
and radial magnetic flux, respectively. However, no periodicity in
tilt angle data was found.
Conclusions: Whatever nature these
oscillations have, they must be energetically supported by convective
motions beneath the solar surface. The possible interpretations can be
related to different types of magnetohydrodynamic oscillations of the
multi-scale structure of the AR magnetic field, which is probably linked
with the characteristic turnover timescales of the super-granulation
cells. The presence of oscillations in the radial magnetic flux data
may be connected to periodic flux emergence or cancellation processes.
Title: Evolution of Interplanetary Coronal Mass Ejection Complexity:
A Numerical Study through a Swarm of Simulated Spacecraft
Authors: Scolini, Camilla; Winslow, Reka M.; Lugaz, Noé; Poedts,
Stefaan
Bibcode: 2021ApJ...916L..15S
Altcode: 2021arXiv210610554S
In-situ measurements carried out by spacecraft in radial alignment
are critical to advance our knowledge on the evolutionary behavior
of coronal mass ejections (CMEs) and their magnetic structures during
propagation through interplanetary space. Yet, the scarcity of radially
aligned CME crossings restricts investigations on the evolution of CME
magnetic structures to a few case studies, preventing a comprehensive
understanding of CME complexity changes during propagation. In this
Letter, we perform numerical simulations of CMEs interacting with
different solar wind streams using the linear force-free spheromak
CME model incorporated into the EUropean Heliospheric FORecasting
Information Asset model. The novelty of our approach lies in the
investigation of the evolution of CME complexity using a swarm of
radially aligned, simulated spacecraft. Our scope is to determine under
which conditions, and to what extent, CMEs exhibit variations of their
magnetic structure and complexity during propagation, as measured
by spacecraft that are radially aligned. Results indicate that the
interaction with large-scale solar wind structures, and particularly
with stream interaction regions, doubles the probability to detect
an increase of the CME magnetic complexity between two spacecraft in
radial alignment, compared to cases without such interactions. This work
represents the first attempt to quantify the probability of detecting
complexity changes in CME magnetic structures by spacecraft in radial
alignment using numerical simulations, and it provides support to the
interpretation of multi-point CME observations involving past, current
(such as Parker Solar Probe and Solar Orbiter), and future missions.
Title: Solar chromosphere heating and generation of plasma outflows
by impulsively generated two-fluid Alfvén waves
Authors: Pelekhata, M.; Murawski, K.; Poedts, S.
Bibcode: 2021A&A...652A.114P
Altcode: 2021arXiv210712032P
Context. We address the heating of the solar chromosphere and the
related generation of plasma inflows and outflows.
Aims: We
attempt to detect variations in ion temperature and vertical plasma
flows, which are driven by impulsively excited two-fluid Alfvén
waves. We aim to investigate the possible contribution of these waves
to solar chromosphere heating and plasma outflows.
Methods:
We performed numerical simulations of the generation and evolution
of Alfvén waves with the use of the JOANNA code, which solves
the two-fluid equations for ions+electrons and neutrals, coupled
by collision terms.
Results: We confirm that the damping of
impulsively generated small-amplitude Alfvén waves slightly affects the
temperature of the chromosphere and generates slow plasma flows. In
contrast, the Alfvén waves generated by large-amplitude pulses
increase the chromospheric plasma temperature more significantly and
result in faster plasma outflows. The maximum heating occurs when the
pulse is launched from the central photosphere, and the magnitude of
the related plasma flows grows with the amplitude of the pulse.
Conclusions: Large-amplitude two-fluid Alfvén waves can contribute
significantly to the heating of the solar chromosphere and to the
generation of plasma outflows.
Title: Modelling a multi-spacecraft coronal mass ejection encounter
with EUHFORIA
Authors: Asvestari, E.; Pomoell, J.; Kilpua, E.; Good, S.;
Chatzistergos, T.; Temmer, M.; Palmerio, E.; Poedts, S.; Magdalenic, J.
Bibcode: 2021A&A...652A..27A
Altcode: 2021arXiv210511831A
Context. Coronal mass ejections (CMEs) are a manifestation of the
Sun's eruptive nature. They can have a great impact on Earth, but also
on human activity in space and on the ground. Therefore, modelling
their evolution as they propagate through interplanetary space is
essential.
Aims: EUropean Heliospheric FORecasting Information
Asset (EUHFORIA) is a data-driven, physics-based model, tracing
the evolution of CMEs through background solar wind conditions. It
employs a spheromak flux rope, which provides it with the advantage of
reconstructing the internal magnetic field configuration of CMEs. This
is something that is not included in the simpler cone CME model used
so far for space weather forecasting. This work aims at assessing the
spheromak CME model included in EUHFORIA.
Methods: We employed
the spheromak CME model to reconstruct a well observed CME and compare
model output to in situ observations. We focus on an eruption from 6
January 2013 that was encountered by two radially aligned spacecraft,
Venus Express and STEREO-A. We first analysed the observed properties of
the source of this CME eruption and we extracted the CME properties as
it lifted off from the Sun. Using this information, we set up EUHFORIA
runs to model the event.
Results: The model predicts arrival
times from half to a full day ahead of the in situ observed ones,
but within errors established from similar studies. In the modelling
domain, the CME appears to be propagating primarily southward, which
is in accordance with white-light images of the CME eruption close
to the Sun.
Conclusions: In order to get the observed magnetic
field topology, we aimed at selecting a spheromak rotation angle for
which the axis of symmetry of the spheromak is perpendicular to the
direction of the polarity inversion line (PIL). The modelled magnetic
field profiles, their amplitude, arrival times, and sheath region length
are all affected by the choice of radius of the modelled spheromak.
Title: Spatial variation in the periods of ion and neutral waves in
a solar magnetic arcade
Authors: Kuźma, B.; Murawski, K.; Musielak, Z. E.; Poedts, S.;
Wójcik, D.
Bibcode: 2021A&A...652A..88K
Altcode: 2021arXiv210509882K
Context. We present new insight into the propagation of ion
magnetoacoustic and neutral acoustic waves in a magnetic arcade in the
lower solar atmosphere.
Aims: By means of numerical simulations,
we (a) study two-fluid waves propagating in a magnetic arcade embedded
in the partially ionised, lower solar atmosphere and (b) investigate the
effect of the background magnetic field configuration on the observed
wave-periods.
Methods: We considered a 2D approximation of the
gravitationally stratified and partially ionised lower solar atmosphere
consisting of ion plus electron and neutral fluids that are coupled
by ion-neutral collisions. In this model, the convection below the
photosphere causes the excitation of ion magnetoacoustic-gravity and
neutral acoustic-gravity waves.
Results: We find that in the
solar photosphere, where ions and neutrals are strongly coupled by
collisions, ion magnetoacoustic-gravity and neutral acoustic-gravity
waves have periods ranging from 250 s to 350 s. In the chromosphere,
where the collisional coupling is weak, the wave characteristics
strongly depend on the magnetic field configuration. Above the
footpoints of the considered arcade, the plasma is dominated by a
vertical magnetic field along which ion magnetoacoustic-gravity waves
propagate. These waves exhibit a broad range of periods, and the most
prominent periods are 180 s, 220 s, and 300 s. Above the main loop of
the solar arcade, where mostly horizontal magnetic field lines guide
ion magnetoacoustic-gravity waves, the main spectral power reduces to
the period of about 180 s, and no longer wave-periods exist.
Conclusions: In photospheric regions, ongoing solar granulation excites
a broad spectrum of wave-periods that undergoes complex interactions:
mode-coupling, refractions through the inhomogeneous atmosphere, real
physical absorption, and conversion of wave power. We found that, in
addition, the magnetic arcade configuration with a partially ionised
plasma drastically changes the image of wave-periods observed in the
upper layers of the chromosphere and corona. Our results agree with
recent observational data.
Title: Chromospheric heating and generation of plasma outflows by
impulsively generated two-fluid magnetoacoustic waves
Authors: Niedziela, R.; Murawski, K.; Poedts, S.
Bibcode: 2021A&A...652A.124N
Altcode: 2021arXiv210712050N
Context. The origin of the heating of the solar atmosphere is still
an unsolved problem. As the photosphere and chromosphere radiate more
energy than the solar corona, it is challenging but important to reveal
all the mechanisms that contribute to plasma heating there. Ion-neutral
collisions could play an important role.
Aims: We aim to
investigate the impulsively generated two-fluid magnetoacoustic waves
in the partially ionized solar chromosphere and to study the associated
heating and plasma outflows, which higher up may result in nascent
solar wind.
Methods: To describe the plasma dynamics, we applied
a two-fluid model in which ions+electrons and neutrals are treated
as separate fluids. We solved the two-fluid equations numerically
using the JOANNA code.
Results: We show that magnetoacoustic
waves triggered in the photosphere by localised velocity pulses can
steepen into shocks which heat the chromosphere through ion-neutral
collisions. Pulses of greater amplitude heat plasma more effectively
and generate larger plasma outflows. Rising the altitude at which the
pulse is launched results in opposite effects, mainly in local cooling
of the chromosphere and slower plasma outflows.
Conclusions:
Even a solitary pulse results in a train of waves. These waves can
transform into shock waves and release thermal energy, heating the
chromosphere significantly. A pulse can drive vertical flows which
higher up can result in the origin of the solar wind.
Title: A Case for Electron-Astrophysics
Authors: Verscharen, Daniel; Wicks, Robert T.; Alexandrova, Olga;
Bruno, Roberto; Burgess, David; Chen, Christopher H. K.; D'Amicis,
Raffaella; De Keyser, Johan; de Wit, Thierry Dudok; Franci, Luca;
He, Jiansen; Henri, Pierre; Kasahara, Satoshi; Khotyaintsev, Yuri;
Klein, Kristopher G.; Lavraud, Benoit; Maruca, Bennett A.; Maksimovic,
Milan; Plaschke, Ferdinand; Poedts, Stefaan; Reynolds, Christopher S.;
Roberts, Owen; Sahraoui, Fouad; Saito, Shinji; Salem, Chadi S.; Saur,
Joachim; Servidio, Sergio; Stawarz, Julia E.; Štverák, Štěpán;
Told, Daniel
Bibcode: 2021ExA...tmp...67V
Altcode:
The smallest characteristic scales, at which electron dynamics
determines the plasma behaviour, are the next frontier in space
and astrophysical plasma research. The analysis of astrophysical
processes at these scales lies at the heart of the research theme of
electron-astrophysics. Electron scales are the ultimate bottleneck
for dissipation of plasma turbulence, which is a fundamental process
not understood in the electron-kinetic regime. In addition, plasma
electrons often play an important role for the spatial transfer
of thermal energy due to the high heat flux associated with their
velocity distribution. The regulation of this electron heat flux is
likewise not understood. By focussing on these and other fundamental
electron processes, the research theme of electron-astrophysics links
outstanding science questions of great importance to the fields of
space physics, astrophysics, and laboratory plasma physics. In this
White Paper, submitted to ESA in response to the Voyage 2050 call,
we review a selection of these outstanding questions, discuss their
importance, and present a roadmap for answering them through novel
space-mission concepts.
Title: 3D numerical simulations of propagating two-fluid, torsional
Alfvén waves and heating of a partially-ionized solar chromosphere
Authors: Kuźma, B.; Murawski, K.; Poedts, S.
Bibcode: 2021arXiv210610537K
Altcode:
We present a new insight into the propagation, attenuation and
dissipation of two-fluid, torsional Alfvén waves in the context of
heating of the lower solar atmosphere. By means of numerical simulations
of the partially-ionized plasma, we solve the set of two-fluid equations
for ion plus electron and neutral fluids in three-dimensional (3D)
Cartesian geometry. We implement initially a current-free magnetic
field configuration, corresponding to a magnetic flux-tube that is
rooted in the solar photosphere and expands into the chromosphere and
corona. We put the lower boundary of our simulation region in the low
chromosphere, where ions and neutrals begin to decouple, and implement
there a monochromatic driver that directly generates Alfvén waves
with a wave period of 30 s. As the ion-neutral drift increases with
height, the two-fluid effects become more significant and the energy
carried by both Alfvén and magneto-acoustic waves can be thermalized
in the process of ion-neutral collisions there. In fact, we observe
a significant increase in plasma temperature along the magnetic
flux-tube. In conclusion, the two-fluid torsional Alfvén waves can
potentially play a role in the heating of the solar chromosphere.
Title: Exploring the radial evolution of interplanetary coronal mass
ejections using EUHFORIA
Authors: Scolini, C.; Dasso, S.; Rodriguez, L.; Zhukov, A. N.;
Poedts, S.
Bibcode: 2021A&A...649A..69S
Altcode: 2021arXiv210207569S
Context. Coronal mass ejections (CMEs) are large-scale eruptions
coming from the Sun and transiting into interplanetary space. While
it is widely known that they are major drivers of space weather,
further knowledge of CME properties in the inner heliosphere is
limited by the scarcity of observations at heliocentric distances
other than 1 au. In addition, most CMEs are observed in situ by a
single spacecraft and in-depth studies require numerical models to
complement the few available observations.
Aims: We aim to
assess the ability of the linear force-free spheromak CME model of
the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) to
describe the radial evolution of interplanetary CMEs in order to yield
new contexts for observational studies.
Methods: We modelled one
well-studied CME with EUHFORIA, investigating its radial evolution by
placing virtual spacecraft along the Sun-Earth line in the simulation
domain. To directly compare observational and modelling results, we
characterised the interplanetary CME signatures between 0.2 and 1.9 au
from modelled time series, exploiting techniques that are traditionally
employed to analyse real in situ data.
Results: Our results show
that the modelled radial evolution of the mean solar wind and CME values
is consistent with the observational and theoretical expectations. The
CME expands as a consequence of the decaying pressure in the surrounding
solar wind: the expansion is rapid within 0.4 au and moderate at larger
distances. The early rapid expansion was not sufficient to explain
the overestimated CME radial size in our simulation, suggesting this
is an intrinsic limitation of the spheromak geometry applied in this
case. The magnetic field profile indicates a relaxation on the part
of the CME structure during propagation, while CME ageing is most
probably not a substantial source of magnetic asymmetry beyond 0.4
au. Finally, we report a CME wake that is significantly shorter than
what has been suggested by observations.
Conclusions: Overall,
EUHFORIA provides a consistent description of the radial evolution of
solar wind and CMEs, at least close to their centres. Nevertheless,
improvements are required to better reproduce the CME radial extension.
Title: Predicting geo-effectiveness of CMEs with EUHFORIA coupled
to OpenGGCM
Authors: Maharana, Anwesha; Scolini, Camilla; Raeder, Joachim;
Poedts, Stefaan
Bibcode: 2021EGUGA..23.9854M
Altcode:
The EUropean Heliospheric FORecasting Information Asset (EUHFORIA,
Pomoell and Poedts, 2018) is a physics-based heliospheric and CME
propagation model designed for space weather forecasting. Although
EUHFORIA can predict the solar wind plasma and magnetic field
parameters at Earth, it is not designed to evaluate indices like
Disturbance-storm-time (Dst) or Auroral Electrojet (AE) that
quantify the impact of the magnetized plasma encounters on Earth"s
magnetosphere. To overcome this limitation, we coupled EUHFORIA with
Open Geospace General Circulation Model (OpenGGCM, Raeder et al, 1996)
which is a magnetohydrodynamic model of Earth"s magnetosphere. In
this coupling, OpenGGCM takes the solar wind and interplanetary
magnetic field obtained from EUHFORIA simulation as input to produce
the magnetospheric and ionospheric parameters of Earth. We perform
test runs to validate the coupling with real CME events modelled using
flux rope models like Spheromak and FRi3D. We compare these simulation
results with the indices obtained from OpenGGCM simulations driven by
the measured solar wind data from spacecrafts like WIND. We further
discuss how the choice of CME model and observationally constrained
parameters influences the input parameters, and hence the geomagnetic
disturbance indices estimated by OpenGGCM. We highlight limitations
of the coupling and suggest improvements for future work.
Title: Acoustic/shock wave heating in the gravitationally stratified
partially ionized plasmas: the two-fluid effects
Authors: Zhang, Fan; Poedts, Stefaan; Lani, Andrea; Kuźma, Błażej;
Murawski, Kris
Bibcode: 2021EGUGA..2310359Z
Altcode:
The chromospheric heating problem is a long-standing intriguing
topic of solar physics, and the acoustic wave/shock wave heating in
the chromospheric plasma has been investigated in the last several
decades. It has been confirmed that acoustic waves, and the shock
waves induced by the steepening acoustic waves in the gravitationally
stratified chromospheric plasma, are able to transport energy to the
chromosphere, but the energy supplied in this way is not necessarily
sufficient for heating the chromosphere. Here, we further investigate
the acoustic/shock wave heating process while taking into account
the two-fluid effects. As the plasma in the chromosphere is weakly or
partially ionized, neutrals play an important role in wave propagation
in this region. Therefore, a two-fluid computational model treating
neutrals and charged particles (electrons and ions) as two separate
fluids is used for modelling the acoustic/shock wave propagation
in idealised partially ionized plasmas, while taking into account
the ion-neutral collisions, ionization and recombination. We have
thus investigated the collisional and reactive interactions between
separated ions and neutrals, as well as the resulting effects in
the acoustic/shock wave propagation and damping. In the numerical
simulations, both the initial hydrostatic equilibrium and chemical
equilibrium are taken into account to provide different density profiles
for comparison.We have found that the shock heating in the partially
ionized plasmas strongly depends on the ionization fraction. In
particular, the relatively smaller ionization fraction resulting from
the initial chemical equilibrium significantly enhances the shock wave
heating, which dominates the overall heating effect according to an
approximated quantitative comparison. Moreover, the decoupling between
ions and neutrals is also enhanced while considering ionization and
recombination, resulting in stronger collisional heating.
Title: Modeling the Sun - Earth propagation of solar disturbances
for the H2020 SafeSpace project
Authors: Lavraud, Benoit; Pinto, Rui; Kieokaew, Rungployphan; Samara,
Evangelia; Poedts, Stefaan; Génot, Vincent; Rouillard, Alexis;
Brunet, Antoine; Bourdarie, Sebastien; Grison, Benjamin; Soucek, Jan;
Daglis, Yannis
Bibcode: 2021EGUGA..2310796L
Altcode:
We present the solar wind forecast pipeline that is being implemented
as part of the H2020 SafeSpace project. The Goal of this project is to
use several tools in a modular fashion to address the physics of Sun -
interplanetary space - Earth"s magnetosphere. This presentation focuses
on the part of the pipeline that is dedicated to the forecasting - from
solar measurements - of the solar wind properties at the Lagrangian
L1 point. The modeling pipeline puts together different mature
research models: determination of the background coronal magnetic
field, computation of solar wind acceleration profiles (1 to 90 solar
radii), propagation across the heliosphere (for regular solar wind,
CIRs and CMEs), and comparison to spacecraft measurements. Different
magnetogram sources (WSO, SOLIS, GONG, ADAPT) can be combined, as well
as coronal field reconstruction methods (PFSS, NLFFF), wind (MULTI-VP)
and heliospheric propagation models (CDPP 1D MHD, EUHFORIA). We aim
at providing a web-based service that continuously supplies a full
set of bulk physical parameters of the solar wind at 1 AU several
days in advance, at a time cadence compatible with space weather
applications. This work has received funding from the European Union"s
Horizon 2020 research and innovation programme under grant agreement
No 870437.
Title: Conditions needed for generation of type II radio emission
in the interplanetary space
Authors: Jebaraj, Immanuel Christopher; Kouloumvakos, Athanasios;
Magdalenic, Jasmina; Rouillard, Alexis; Krupar, Vratislav; Poedts,
Stefaan
Bibcode: 2021EGUGA..2310997J
Altcode:
Eruptive events such as Coronal mass ejections (CMEs) and flares
cangenerate shock waves. Tracking shock waves and predicting
their arrival at Earth is a subject of numerous space weather
studies. Ground-based radio observations allow us to locate shock
waves in the low corona while space-based radio observations provide us
opportunity to track shock waves in the inner heliosphere. We present
a case study of CME/flare event, associated shock wave and its radio
signature, i.e. type II radio burst.In order to analyze the shock wave
parameters, we employed a robust paradigm. We reconstructed the shock
wave in 3D using multi-viewpoint observations and modelled the evolution
of its parameters using a 3D MHD background coronal model produced by
the MAS (Magnetohydrodynamics Around a Sphere).To map regions on the
shock wave surface, possibly associated with the electron acceleration,
we combined 3D shock modelling results with the 3D source positions of
the type II burst obtained using the radio triangulation technique. We
localize the region of interest on the shock surface and examine the
shock wave parameters to understand the relationship between the shock
wave and the radio event. We analyzed the evolution of the upstream
plasma characteristics and shock wave parameters during the full
duration of the type II radio emission. First results indicate that
shock wave geometry and its relationship with shock strength play an
important role in the acceleration of electrons responsible for the
generation of type II radio bursts.
Title: ICMEs and low plasma density in the solar wind observed at L1
Authors: Schmieder, Brigitte; Verbeke, Christine; Chané, Emmanuel;
Démoulin, Pascal; Poedts, Stefaan; Grison, Benjamin
Bibcode: 2021EGUGA..23.1799S
Altcode:
Different regimes of the solar wind have been observed at L1 during and
after the passage of ICMEs, particularly anomalies with very low plasma
density. From the observations at L1 (ACE) we identified different
possible cases. A first case was explained by the evacuation of the
plasma due over expansion of the ICME (May 2002). The second case on
July 2002 is intriguing.In July 2002, three halo fast speed ICMEs,
with their origin in the central part of the Sun, have surprisingly
a poor impact on the magnetosphere (Dst > -28 nT). Analyzing the
characteristics of the first ICME at L1, we conclude that the spacecraft
crosses the ICME with a large impact (Bx component in GSE coordinates is
dominant). The plasma density is low, just behind this first ICME. Next,
we explore the generic conditions of low density formation in the
EUHFORIA simulations.The very low density plasma after the sheath
could be explained by the spacecraft crossing, on the side of the
flux rope, while behind the front shock. We investigate two possible
interpretations. The shock was able to compress and accelerate so much
the plasma that a lower density is left behind. This can also be due
to an effect of the sheath magnetic field which extends the flux rope
effect on the sides of it, so a decrease of plasma density could occur
like behind a moving object (here the sheath field). The following ICME,
with also a low density, could be an intrinsic case with the formation
in the corona of a cavity. Finally, we present some runs of EUHFORIA
which fit approximately these data and argue in favor of the possible
interpretations detailed above.
Title: The Solar Energetic Particle Event of March 15 2013 -
Characterization of the interplanetary medium conditions
Authors: Niemela, Antonio; Wijsen, Nicolas; Rodriguez, Luciano;
Magdalenic, Jasmina; Poedts, Stefaan
Bibcode: 2021EGUGA..2310332N
Altcode:
On March 15, 2013, an Earth directed halo CME, associated with an SEP
event, was observed. This study aims to characterize the interplanetary
medium conditions in which the event propagated, in order to make the
first steps towards the validation of the modeling of SEPs employing
two recently coupled models, EUHFORIA (EUropean Heliosferic FORcasting
Information Asset) and PARADISE (PArticle Radiation Asset Directed at
Interplanetary Space Exploration).The Sun in the days prior and after
the event was very active, with several strong flares and coronal
mass ejections during this period. The main event was associated with
the long duration GOES M1.1 X-ray flare originating from the active
region (AR) 11692, located at N11E12. Imagers aboard SOHO and STEREO
spacecrafts observed the CME launch at 7:12 UT and the projected
line of the sight speed was estimated to be about 1060 km/s. A rise
in the >10 MeV GOES proton count was observed the following day,
with flux exceeding the 1000 pfu threshold, and stayed above it for
several days. Another strong CME was launched, within the following
hours, towards the west but with a good magnetic connection to Earth's
position, which could have accelerated even further the particle
population seeded by the main event.We model the solar wind and
its transients CMEs with EUHFORIA, in order to obtain the realistic
conditions of the ambient plasma through which the associated particles
are propagating. Different spatial and temporal resolutions of the
model will be explored to run the newly developed model for energetic
protons PARADISE in an optimal environment and make a step towards
better SEP predictions.
Title: Two-fluid Modeling of Acoustic Wave Propagation in
Gravitationally Stratified Isothermal Media
Authors: Zhang, Fan; Poedts, Stefaan; Lani, Andrea; Kuźma, Błażej;
Murawski, Kris
Bibcode: 2021ApJ...911..119Z
Altcode: 2020arXiv201113469Z
To study acoustic wave propagation and the corresponding energy
deposition in partially ionized plasmas, we use a two-fluid
computational model that treats neutrals and charged particles
(electrons and ions) as two separate fluids. This two-fluid model
takes into account the ion-neutral collisions, ionization, and
recombination, allowing us to investigate both the collisional and
reactive interactions between uncoupled ions and neutrals in the
plasmas. In the present numerical simulations, the initial density
is specified to reach hydrostatic equilibrium, and as a comparison,
chemical equilibrium is also taken into account to provide a
density profile that differs from typical hydrostatic equilibrium
profiles. External velocity drivers are then imposed to generate
monochromatic acoustic waves. As is well known, the upward propagating
acoustic waves steepen in gravitationally stratified plasmas due to
the exponentially decreasing density, and they heat the plasmas in the
nonlinear regimes where kinetic energy is dissipated by shock waves and
collisional interactions. In particular, the lower ionization fraction
resulting from the present initial chemical equilibrium significantly
enhances the heating efficiency. Moreover, the ionization process
absorbs a significant amount of energy, and the decoupling between
ions and neutrals is also enhanced while considering ionization and
recombination. Therefore, simulations without considering ionization
and recombination may overestimate the overall heating effects but also
underestimate the energy dissipation. The results also suggest that
a more accurate ionization and recombination model could be essential
for improving the modeling of partially ionized plasmas.
Title: Improving CME evolution and arrival predictions with AMR and
grid stretching in EUHFORIA
Authors: Baratashvili, Tinatin; Verbeke, Christine; Wijsen, Nicolas;
Chané, Emmanuel; Poedts, Stefaan
Bibcode: 2021EGUGA..23.9193B
Altcode:
Coronal Mass Ejections (CMEs) are the main drivers of interplanetary
shocks and space weather disturbances. Strong CMEs directed towards
Earth can cause severe damage to our planet. Predicting the arrival time
and impact of such CMEs can enable to mitigate the damage on various
technological systems on Earth. We model the inner heliospheric solar
wind and the CME propagation and evolution within a new heliospheric
model based on the MPI-AMRVAC code. It is crucial for such a numerical
tool to be highly optimized and efficient, in order to produce timely
forecasts. Our model solves the ideal MHD equations to obtain a steady
state solar wind configuration in a reference frame corotating with
the Sun. In addition, CMEs can be modelled by injecting a cone CME
from the inner boundary (0.1 AU).Advanced techniques, such as grid
stretching and Adaptive Mesh Refinement (AMR) are employed in the
simulation. Such methods allow for high(er) spatial resolution in the
numerical domain, but only where necessary or wanted. As a result, we
can obtain a detailed, highly resolved image at the (propagating) shock
areas, without refining the whole domain.These techniques guarantee more
efficient simulations, resulting in optimised computer memory usage and
a significant speed-up. The obtained speed-up, compared to the original
approach with a high-resolution grid everywhere, varies between a factor
of 45 - 100 depending on the domain configuration. Such efficiency gain
is momentous for the mitigation of the possible damage and allows for
multiple simulations with different input parameters configurations to
account for the uncertainties in the measurements to determine them. The
goal of the project is to reproduce the observed results, therefore,
the observable variables, such as speed, density, etc., are compared to
the same type of results produced by the existing (non-stretched, single
grid) EUropean Heliospheric FORecasting Information Asset (EUHFORIA)
model and observational data for a particular event on 12th of July,
2012. The shock features are analyzed and the results produced with
the new heliospheric model are in agreement with the existing model and
observations, but with a significantly better performance. This research
has received funding from the European Union"s Horizon 2020 research
and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).
Title: Spatial variation of periods of ion and neutral waves in a
solar magnetic arcade.
Authors: Kuźma, Błażej; Murawski, Kris; Musielak, Zdzisław;
Poedts, Stefaan; Wójcik, Dariusz
Bibcode: 2021EGUGA..23.6726K
Altcode:
We present a new insight into the propagation of ion magnetoacoustic
and neutral acoustic waves in a magnetic arcade in the lower solar
atmosphere. By means of numerical simulations, we aim to: (a) study
two-fluid waves propagating in a magnetic arcade embedded in the
partially-ionized, lower solar atmosphere; and (b) investigate the
impact of the background magneticfield configuration on the observed
wave-periods. We consider a 2D approximation of the gravitationally
stratified and partially-ionized lower solar atmosphere consisting
of ion + electron and neutral fluids that are coupled by ion-neutral
collisions. In this model, the convection below the photosphere
is responsible for the excitation of ion magnetoacoustic-gravity
and neutral acoustic-gravity waves. We find that in the solar
photosphere, where ions and neutrals are strongly coupled by collisions,
magnetoacoustic-gravity and acoustic-gravity waves have periods ranging
from250s to350s. In the chromosphere, where the collisional coupling
is weak, the wave characteristics strongly depend on the magnetic
field configuration. Above the foot-points of the considered arcade,
the plasma is dominated by vertical magnetic field along which ion
slow magnetoacoustic-gravity waves are guided. These waves exhibit a
broad range of periods with the most prominent periods of 180 s, 220
s, and 300 s. Above the main loop of the solar arcade, where mostly
horizontal magnetic field lines guide ion magnetoacoustic waves,
the main spectral power reduces to the period of about 180 s and
longer wave-periods do not exist. The obtained results demonstrate
unprecedented, never reported before level of agreement with the
recently reported observational data of Wisniewska et al. (2016)
and Kayshap et al. (2018). We demonstrate that the two-fluid approach
is indeed crucial for a description of wave-related processes in the
lower solar atmosphere, with energy transport and dissipation being
of the highest interest among them.
Title: Constraining the CME parameters of the spheromak flux rope
implemented in EUHFORIA
Authors: Asvestari, Eleanna; Pomoell, Jens; Kilpua, Emilia; Good,
Simon; Chatzistergos, Theodosios; Temmer, Manuela; Palmerio, Erika;
Poedts, Stefaan; Magdalenic, Jasmina
Bibcode: 2021EGUGA..23.3291A
Altcode:
Coronal mass ejections (CMEs) are primary drivers of space weather
phenomena. Modelling the evolution of the internal magnetic field
configuration of CMEs as they propagate through the interplanetary
space is an essential part of space weather forecasting. EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) is a data-driven,
physics-based model, able to trace the evolution of CMEs and CME-driven
shocks through realistic background solar wind conditions. It employs
a spheromak-type magnetic flux rope that is initially force-free,
providing it with the advantage of modelling CME as magnetised
structures. For this work we assessed the spheromak CME model
employed in EUHFORIA with a test CME case study. The selected CME
eruption occurred on the 6th of January 2013 and was encountered
by two spacecraft, Venus Express and STEREO--A, which were radially
aligned at the time of the CME passage. Our focus was to constrain
the input parameters, with particular interest in: (1) translating
the angular widths of the graduated cylindrical shell (GCS) fitting
to the spheromak radius, and (2) matching the observed magnetic field
topology at the source region. We ran EUHFORIA with three different
spheromak radii. The model predicts arrival times from half to a full
day ahead of the one observed in situ. We conclude that the choice
of spheromak radius affected the modelled magnetic field profiles,
their amplitude, arrival times, and sheath region length.
Title: On the prediction of magnetic field vectors of ICME using
data constrained simulation with EUHFORIA
Authors: Sarkar, Ranadeep; Pomoell, Jens; Asvestari, Eleanna; Kilpua,
Emilia; Mierla, Marilena; Rodriguez, Luciano; Poedts, Stefaan
Bibcode: 2021EGUGA..2310325S
Altcode:
Coronal mass ejections (CMEs), the most violent eruptive phenomena
occurring in the heliosphere, erupt in the form of gigantic clouds
of magnetized plasma from the Sun and can reach Earth within several
hours to days. If the magnetic field inside an Earth-directed CME or its
associated sheath region has a southward directed component (Bz), then
it interacts stronger with the Earth"s magnetosphere, leading to severe
geomagnetic storms. Therefore, it is crucial to predict the magnitude
and orientation of Bz inside an Earth impacting interplanetary CME
(ICME) in order to forecast the intensity of the resulting geomagnetic
storms. However, due to lack of realistic inputs and the complexity of
the Sun-Earth system in a time-dependent heliospheric context, it is
very difficult to perform a reliable forecast of Bz at 1 AU. In this
work, we use recently developed observational techniques to constrain
the kinematic and magnetic properties of CME flux ropes. Using
those observational properties as realistic inputs, we construct an
analytical force free flux rope model to mimic the magnetic structure
of a CME and simulate its evolution from Sun to Earth using the
"European heliospheric forecasting information asset" (EUHFORIA). In
order to validate our tool, we simulate an Earth-directed CME event
on 2013 April 11 and compare the simulation results with the in-situ
observations at 1 AU. Further, we assess the performance of EUHFORIA
in forecasting of Bz, using different flux rope models like spheromak
and torus. The results obtained from this study help to improve our
understanding to build the steppingstones towards the forecasting
of Bz in near real time.This research has received funding from the
European Union"s Horizon 2020 research and innovation programme under
grant agreement No 870405 (EUHFORIA 2.0).
Title: A self-consistent simulation of proton acceleration and
transport near a high-speed solar wind stream
Authors: Wijsen, Nicolas; Samara, Evangelia; Aran, Àngels; Lario,
David; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2021EGUGA..23.8189W
Altcode:
Solar wind stream interaction regions (SIRs) are often characterised
by energetic ion enhancements. The mechanisms accelerating these
particles as well as the locations where the acceleration occurs,
remains debated. Here, we report the findings of a simulation of a
SIR-event observed by Parker Solar Probe at 0.56 au and the Solar
Terrestrial Relations Observatory-Ahead at 0.96 au in September 2019
when both spacecraft were approximately radially aligned with the
Sun. The simulation reproduces the solar wind configuration and the
energetic particle enhancements observed by both spacecraft. Our results
show that the energetic particles are produced at the compression waves
associated with the SIR and that the suprathermal tail of the solar
wind is a good candidate to provide the seed population for particle
acceleration. The simulation confirms that the acceleration process does
not require shock waves and can already commence within Earth's orbit,
with an energy dependence on the precise location where particles are
accelerated. The three-dimensional configuration of the solar wind
streams strongly modulates the energetic particle distributions,
illustrating the necessity of advanced models to understand these
particle events.This research has received funding from the European
Union"s Horizon 2020 research and innovation programme under grant
agreement No 870405 (EUHFORIA 2.0).
Title: Predicting geo-effectiveness of CMEs using a novel 3D CME
model FRi3D integrated into EUHFORIA
Authors: Poedts, Stefaan; Maharana, Anwesha; Scolini, Camilla;
Isavnin, Alexey
Bibcode: 2021EGUGA..2311605P
Altcode:
Previous studies of Coronal Mass Ejections (CMEs) have shown the
importance of understanding their geometrical structure and internal
magnetic field configuration for improving forecasting at Earth. The
precise prediction of the CME shock and the magnetic cloud arrival time,
their magnetic field strength and the orientation upon impact at Earth
is still challenging and relies on solar wind and CME evolution models
and precise input parameters. In order to understand the propagation
of CMEs in the interplanetary medium, we need to understand their
interaction with the complex features in the magnetized background
solar wind which deforms, deflects and erodes the CMEs and determines
their geo-effectiveness. Hence, it is important to model the internal
magnetic flux-rope structure in the CMEs as they interact with
CIRs/SIRs, other CMEs and solar transients in the heliosphere. The
spheromak model (Verbeke et al. 2019) in the heliospheric wind and
CME evolution simulation EUHFORIA (Pomoell and Poedts, 2018), fits
well with the data near the CME nose close to its axis but fails to
predict the magnetic field in CME legs when these impact Earth (Scolini
et al. 2019). Therefore, we implemented the FRi3D stretched flux-rope
CME model (Isavnin, 2016) in EUHFORIA to model a more realistic CME
geometry. Fri3D captures the three-dimensional magnetic field structure
with parameters like skewing, pancaking and flattening that quantify
deformations experienced by an interplanetary CME. We perform test
runs of real CME events and validate the ability of FRi3D coupled with
EUHFORIA in predicting the CME geo-effectiveness. We have modeled two
real events with FRi3D. First, a CME event on 12 July 2012 which was a
head-on encounter at Earth. Second, the flank CME encounter of 14 June
2012 which did not leave any magnetic field signature at Earth when
modeled with Spheromak. We compare our results with the results from
non-magnetized cone simulations and magnetized simulations employing
the spheromak flux-rope model. We further discuss how constraining
observational parameters using the stretched flux rope CME geometry
in FRi3D affects the prediction of the magnetic field strength in
our simulations, highlighting improvements and discussing future
perspective.This research has received funding from the European
Union"s Horizon 2020 research and innovation programme under grant
agreement No 870405 (EUHFORIA 2.0)
Title: Implementing the MULTI-VP coronal model in EUHFORIA: Test
case results and comparisons with the WSA coronal model
Authors: Samara, E.; Pinto, R. F.; Magdalenić, J.; Wijsen, N.;
Jerčić, V.; Scolini, C.; Jebaraj, I. C.; Rodriguez, L.; Poedts, S.
Bibcode: 2021A&A...648A..35S
Altcode: 2021arXiv210206617S
Context. In this study, we focus on improving EUHFORIA (European
Heliospheric Forecasting Information Asset), a recently developed 3D
magnetohydrodynamics space weather prediction tool. The EUHFORIA
model consists of two parts covering two spatial domains: the
solar corona and the inner heliosphere. For the first part, the
semiempirical Wang-Sheeley-Arge (WSA) model is used by default;
this model employs the potential field source surface and Schatten
current sheet models to provide the necessary solar wind plasma and
magnetic conditions above the solar surface, at 0.1 AU, which serve
as boundary conditions for the inner heliospheric part. Herein, we
present the first results of the implementation of an alternative
coronal model in EUHFORIA, the so-called MULTI-VP model.
Aims: After we replace the default EUHFORIA coronal setup with the
MULTI-VP model, we compare their outputs both at 0.1 AU and 1 AU,
for test cases involving high speed wind streams (HSSs). We select
two distinct cases in which the standard EUHFORIA setup failed to
reproduce the HSS plasma and magnetic signatures at Earth to test
the performance of MULTI-VP coupled with EUHFORIA-heliosphere.
Methods: To understand the quality of modeling with MULTI-VP in
comparison with the default coronal model in EUHFORIA, we considered
one HSS case during a period of low solar activity and another one
during a period of high solar activity. Moreover, the modeling of
the two HSSs was performed by employing magnetograms from different
providers: one from the Global Oscillation Network Group (GONG)
and the second from the Wilcox Space Observatory (WSO). This way, we
were able to distinguish differences arising not only because of the
different models but also because of different magnetograms.
Results: The results indicate that when employing a GONG magnetogram,
the combination MULTI-VP+EUHFORIA-heliosphere reproduces the majority
of HSS plasma and magnetic signatures measured at L1. On the contrary,
the standard WSA+EUHFORIA-heliosphere combination does not capture
the arrival of the HSS cases at L1. When employing WSO magnetograms,
MULTI-VP+EUHFORIA-heliosphere reproduces the HSS that occurred during
the period of high solar activity. However, it is unclear if it
models the HSS during the period of low solar activity. For the same
magnetogram and periods of time, WSA+EUHFORIA-heliosphere is not able to
capture the HSSs of interest.
Conclusions: The results show that
the accuracy of the simulation output at Earth depends on the choice
of both the coronal model and input magnetogram. Nevertheless, a more
extensive statistical analysis is necessary to determine how precisely
these choices affect the quality of the solar wind predictions.
Title: Over-expansion of a coronal mass ejection generates
sub-Alfvénic plasma conditions in the solar wind at Earth
Authors: Chané, E.; Schmieder, B.; Dasso, S.; Verbeke, C.; Grison,
B.; Démoulin, P.; Poedts, S.
Bibcode: 2021A&A...647A.149C
Altcode:
Context. From May 24-25, 2002, four spacecraft located in the solar
wind at about 1 astronomical unit (au) measured plasma densities
one to two orders of magnitude lower than usual. The density was
so low that the flow became sub-Alfvénic for four hours, and the
Alfvén Mach number was as low as 0.4. Consequently, the Earth lost
its bow shock, and two long Alfvén wings were generated.
Aims: This is one of the lowest density events ever recorded in the
solar wind at 1 au, and the least documented one. Our goal is to
understand what caused the very low density.
Methods: Large
Angle and Spectrometric Coronagraph (LASCO) and in situ data were
used to identify whether something unusual occurred that could have
generated such low densities
Results: The very low density was
recorded inside a large interplanetary coronal mass ejection (ICME),
which displayed a long, linearly declining velocity profile, typical
of expanding ICMEs. We deduce a normalised radial expansion rate of
1.6. Such a strong expansion, occurring over a long period of time,
implies a radial size expansion growing with the distance from the Sun
to the power 1.6. This can explain a two-orders-of-magnitude drop in
plasma density. Data from LASCO and the Advanced Composition Explorer
show that this over-expanding ICME was travelling in the wake of a
previous ICME.
Conclusions: The very low densities measured
in the solar wind in May 2002 were caused by the over-expansion of
a large ICME. This over-expansion was made possible because the ICME
was travelling in a low-density and high-velocity environment present
in the wake of another ICME coming from a nearby region on the Sun and
ejected only three hours previously. Such conditions are very unusual,
which explains why such very low densities are almost never observed.
Title: Quo vadis, European Space Weather community?
Authors: Lilensten, Jean; Dumbović, Mateja; Spogli, Luca; Belehaki,
Anna; Van der Linden, Ronald; Poedts, Stefaan; Barata, Teresa; Bisi,
Mario M.; Cessateur, Gaël; De Donder, Erwin; Guerrero, Antonio;
Kilpua, Emilia; Korsos, Marianna B.; Pinto, Rui F.; Temmer, Manuela;
Tsagouri, Ioanna; Urbář, Jaroslav; Zuccarello, Francesca
Bibcode: 2021JSWSC..11...26L
Altcode:
This paper was written by a group of European researchers believing
that now is the right time to frame the Space Weather and Space
Climate discipline in Europe for future years. It is devoted to
openly discussing the organisation and sustainability of the European
Space Weather community and its assets in the (near) future. More
specifically, we suggest that the European Space Weather community
lacks a uniting organisation to help the community to sustain and
develop the successful efforts made thus far. Our aim is not to draw
a complete and exhaustive panorama of Space Weather throughout the
world, nor even throughout Europe. It is not a new white paper on the
science and applications: there exist many (e.g. Tsurutani et al.,
2020 Nonlinear Processes Geophys 27(1): 75-119); nor another roadmap:
several important have been published recently (e.g. Schrijver et al.,
2015. Adv Space Res 55(12): 2745-2807; Opgenoorth et al., 2019. J Space
Weather Space Clim 9: A37). Our aim is to question our practices and
organisation in front of several changes that have occurred in the
recent years and to set the ground to provide coordinated answers
to these questions being posed in Europe, and to make these answers
discussed throughout the world. This group was assembled first through
a series of sessions devoted to the sustainability of Space Weather
research during the European Space Weather Week (ESWW) series of
meetings, specifically: ESWW 14 (2017), ESWW 15 (2018), and ESWW 16
(2019). It then grew from discussions and personal contacts. The authors
do not pretend to identify the full range of opinions in Europe,
although they do come from 13 different European countries with a
large span of ages (around half are below the age of 40 years old at
the time of writing) with a good gender balance ending with a diverse
mix of young and motivated scientists and senior people who have played
a role in shaping the Space Weather community in Europe. The questions
and the propositions to organise Space Weather in Europe in the future
result from their discussions through these meetings and through remote
meetings during the pandemic. We wish to share them with all those who
consider themselves as members of the European Space Weather community
and/or are interested in its future and to propose actions. We do this,
bearing in mind that Europe plays a key international role in Space
Weather which extends beyond the ESA and EU/EC geographic area.
Title: A Self-consistent Simulation of Proton Acceleration and
Transport Near a High-speed Solar Wind Stream
Authors: Wijsen, Nicolas; Samara, Evangelia; Aran, Àngels; Lario,
David; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2021ApJ...908L..26W
Altcode: 2021arXiv210210950W
Solar wind stream interaction regions (SIRs) are often characterized
by energetic ion enhancements. The mechanisms accelerating these
particles, as well as the locations where the acceleration occurs,
remain debated. Here, we report the findings of a simulation of a
SIR event observed by Parker Solar Probe at ∼0.56 au and the Solar
Terrestrial Relations Observatory-Ahead at ∼0.95 au in 2019 September
when both spacecraft were approximately radially aligned with the
Sun. The simulation reproduces the solar wind configuration and the
energetic particle enhancements observed by both spacecraft. Our results
show that the energetic particles are produced at the compression waves
associated with the SIR and that the suprathermal tail of the solar
wind is a good candidate to provide the seed population for particle
acceleration. The simulation confirms that the acceleration process does
not require shock waves and can already commence within Earth's orbit,
with an energy dependence on the precise location where particles are
accelerated. The three-dimensional configuration of the solar wind
streams strongly modulates the energetic particle distributions,
illustrating the necessity of advanced models to understand these
particle events.
Title: CME-CME interactions as sources of CME helio-effectiveness:
the early September 2017 events
Authors: Scolini, Camilla; Rodriguez, Luciano; Poedts, Stefaan; Kilpua,
Emilia; Guo, Jingnan; Pomoell, Jens; Dissauer, Karin; Veronig, Astrid;
Dumbovic, Mateja; Chané, Emmanuel; Palmerio, Erika
Bibcode: 2021cosp...43E1030S
Altcode:
Coronal Mass Ejections (CMEs) are the primary source of strong
space weather disturbances at Earth and other locations in the
heliosphere. Understanding the physical processes involved in their
formation at the Sun, propagation in the heliosphere, and impact
on planetary bodies is therefore critical to improve current space
weather predictions throughout the heliosphere. It is known that
the capability of individual CMEs to drive strong space weather
disturbances at Earth (known as "geo-effectiveness") and other
locations in the heliosphere (here referred to as "helio-effectiveness")
primarily depends on their dynamic pressure, internal magnetic field
strength, and magnetic field orientation at the impact location. At
the same time, observational and modelling studies also established
that CME-CME interactions can significantly alter the properties of
individual CMEs, in such a way that their geo-effectiveness is often
dramatically amplified. However, the actual quantification of this
amplification has been rarely investigated, mostly via observational
studies of individual events, or via explorative studies performed using
idealized simulations of CME events, for which no truthful comparison
with observations is possible. Additionally, the amplification effect
of CME-CME interactions has been traditionally quantified only for the
near-Earth region of space, without considering its full space-time
evolution as the CMEs propagate to the Earth and beyond. In this work,
we present a comprehensive study on the role of CME-CME interactions
as sources of CME helio-effectiveness by performing simulations of
complex CME events with the EUHFORIA heliospheric model. As a case
study, we consider the sequence of CMEs observed during the unusually
active week of 4-10 September 2017. As their source region rotated on
the solar disk, CMEs were launched over a wide range of longitudes,
interacting with each other and paving the way for the propagation of
the following ones. CME signatures were observed at Mars and Earth,
where an intense geomagnetic storm triggered by CME-CME interactions
was recorded. Using input parameters derived from remote-sensing
multi-spacecraft observations of the CMEs and their source region,
we perform global simulations of magnetised CMEs with EUHFORIA. We
investigate how their interactions affected the propagation and
internal properties of individual CME structures, and their in-situ
signatures at Earth and Mars. Taking advantage of 3D simulation
outputs, we quantify the amplification of the helio-effectiveness of
the individual CMEs involved, as a function of the interaction phase
and of the location within the CME structure. Additionally, we also
explore the possibility of the existence of a "helio-effectiveness
amplification zone", i.e. a characteristic heliocentric distance at
which CME-CME interactions have the highest probability to develop into
highly helio-effective events. Results from this study benchmark our
current prediction capabilities in the case of complex CME events,
and provide insights on their large-scale evolution and potential
impact throughout the heliosphere.
Title: Advanced Numerical Tools for Studying Waves and Instabilities
in Kappa Distributed Plasmas
Authors: López, Rodrigo A.; Moya, Pablo S.; Shaaban, Shaaban M.;
Lazar, Marian; Yoon, Peter H.; Poedts, Stefaan
Bibcode: 2021ASSL..464..163L
Altcode:
In this chapter we focus on the recent progress made on numerical
analysis and tools facilitating the investigation of dispersion
and stability of anisotropic Kappa distributed plasmas. Plasma
waves and fluctuations are directly dependent on the non-thermal
features of the particle velocity distributions, and understanding
their properties is a primary goal, especially for collision-poor
plasmas where physical processes are conditioned by the wave-particle
interactions. Numerical dispersion solvers are developed to resolve
complex (integral) dispersion relations and decode the full spectra
of stable or unstable modes, but, traditionally, limited to idealized
(bi-)Maxwellian representation of plasma populations. Here we discuss
the advanced dispersion solvers recently developed for magnetized
plasmas with anisotropic Kappa populations (e.g., bi-Kappa, combined
or not with drifts), and compare their capabilities. The implication
of these numerical solvers was extended to quasi-linear (QL) studies
of kinetic instabilities, providing a complete description of their
saturation as well as the relaxation of anisotropic populations. We
will also emphasize the progress made in numerical simulations using
different techniques, e.g., Vlasov or Particle-In-Cell (PIC) codes, to
capture suprathermal effects in the initial Kappa distributions. Some
illustrative cases of kinetic instabilities are considered to describe
capabilities of these new codes, and compare the simulations with the
results provided by the linear and QL numerical solvers.
Title: SafeSpace: Designing Radiation Belt Environmental Indicators
for the safety of space assets
Authors: Daglis, Ioannis A.; Bourdarie, Sebastien; Santolik, Ondrej;
Darrouzet, Fabien; Poedts, Stefaan; Lavraud, Benoit; Sandberg, Ingmar;
Cueto Rodriguez, Juan
Bibcode: 2021cosp...43E2353D
Altcode:
The SafeSpace project aims at advancing space weather nowcasting
and forecasting capabilities and, consequently, at contributing
to the safety of space assets through the transition of powerful
tools from research to operations (R2O). This will be achieved
through the synergy of five well-established space weather models
(CNRS/CDPP solar disturbance propagation tool, KULeuven EUHFORIA CME
evolution model, ONERA Neural Network tool, IASB plasmasphere model
and ONERA Salammbô radiation belts code), which cover the whole Sun -
interplanetary space - Earth's magnetosphere chain. The combined use
of these models will enable the delivery of a sophisticated model of
the Van Allen electron belt and of a prototype space weather service
of tailored particle radiation indicators. Moreover, it will enable
forecast capabilities with a target lead time of 2 to 4 days, which is
a tremendous advance from current forecasts that are limited to lead
times of a few hours. SafeSpace will improve radiation belt modelling
through the incorporation into the Salammbô model of magnetospheric
processes and parameters of critical importance to radiation belt
dynamics. Furthermore, solar and interplanetary conditions will be
used as initial conditions to drive the advanced radiation belt model
and to provide the link to the solar origin and the interplanetary
drivers of space weather. This approach will culminate in a prototype
early warning system for detrimental space weather events, which will
include indicators of particle radiation of use to space industry and
spacecraft operators. Indicator values will be generated by the advanced
radiation belt model and the performance of the prototype service will
be evaluated in collaboration with space industry stakeholders. The
work leading to this paper has received funding from the European
Union's Horizon 2020 research and innovation programme under grant
agreement No 870437 for the SafeSpace (Radiation Belt Environmental
Indicators for the Safety of Space Assets) project.
Title: Modelling the acceleration and transport of energetic particles
near an interplanetary CME
Authors: Wijsen, Nicolas; Poedts, Stefaan; Aran, Angels; Pomoell,
Jens; Vainio, Rami; Lario, David; Afanasiev, Alexandr
Bibcode: 2021cosp...43E.903W
Altcode:
When a fast coronal mass ejection (CME) propagates through
interplanetary space, it may drive a shock wave which can act as a
powerful ion accelerator. In that case, increased levels of turbulence
may efficiently trap particles at the shock front where they can
gain energy through diffusive shock acceleration. In addition, the
strong magnetic enhancement at the shock can act as an efficient
magnetic mirror, potentially trapping the ions for a prolonged
amount of time between the Sun and the CME shock. This, among other
processes, can strongly affect the in-situ observed properties of
the associated gradual solar energetic particle event. In this work,
we use PARADISE (PArticle Radiation Asset Directed at Interplanetary
Space Exploration) to model the transport and acceleration of ions
near a CME propagating through interplanetary space. In PARADISE,
energetic particle distributions are calculated by solving the focused
transport equation in a prescribed background solar wind. We use
the three-dimensional magnetohydrodynamic model EUHFORIA (EUropean
Heliospheric FORecasting Information Asset) to generate a solar wind in
which CMEs of different speeds are injected. In this study, we focus on
the acceleration and transport of low- energy protons (< 1 MeV),
as these particles may still undergo substantial diffusive shock
acceleration in interplanetary space. We investigate how different
parallel and cross-field diffusion conditions at the CME shock front
affect the obtained particle intensity profiles measured by virtual
observers located at various positions in the heliosphere.
Title: Predicting geo-effectiveness of CMEs using a novel 3D CME
model FRi3D integrated into EUHFORIA
Authors: Maharana, Anwesha; Scolini, Camilla; Isavnin, Alexey;
Poedts, Stefaan
Bibcode: 2021cosp...43E1755M
Altcode:
Previous studies of Coronal Mass Ejections (CMEs) have shown
the importance of understanding their geometrical structure and
internal magnetic field configuration for improving forecasting at
Earth. The precise prediction of the CME shock, the magnetic cloud
arrival time, their magnetic field strength and the orientation upon
impact at Earth is still challenging and relies on solar wind and CME
evolution models. In order to understand the propagation of CMEs in
the interplanetary medium, we need to understand their interaction
with the complex features in the magnetized background solar wind
which deforms, deflects and erodes the CMEs and determines their
geo-effectiveness. Hence, it is important to model the internal magnetic
flux-rope structure in the CMEs as they interact with CIRs/SIRs, other
CMEs and solar transients in the heliosphere. The spheromak model
(Verbeke et al. 2019) in the heliospheric wind and CME evolution
simulation EUHFORIA (Pomoell and Poedts, 2018), fits well with the
data well near the CME nose close to its axis but fails to predict
the magnetic field in CME legs when these impact Earth (Scolini et
al. 2019). Therefore, we implemented the FRi3D stretched flux-rope
CME model (Isavnin, 2016) in EUHFORIA in an attempt to model a more
realistic CME geometry. Fri3D captures the three-dimensional magnetic
field structure with parameters like skewing, pancaking and flattening
that quantify deformations experienced by an interplanetary CME. We
perform test runs of real CME events and validate the ability of FRi3D
coupled with EUHFORIA in predicting the CME geo-effectiveness. We
compare our results with the results from non-magnetized cone
simulations and magnetized simulations employing the spheromak flux-rope
model. We further discuss how obtaining observational parameters using
the stretched flux rope CME geometry in FRi3D affects the prediction
of the magnetic field strength in our simulations, highlighting
improvements and discussing future perspective.
Title: Numerical modelling of consecutive solar eruptions inserted
in different solar wind speeds and comparison of in-situ signatures
at 1AU and their geoeffectiveness
Authors: Talpeanu, Dana-Camelia; Poedts, Stefaan; Mierla, Marilena;
D'Huys, Elke; Chané, Emmanuel; Roussev, Ilia
Bibcode: 2021cosp...43E1003T
Altcode:
Coronal Mass Ejections (CMEs) are some of the most energetic solar
events that expel plasma and magnetic field into the interplanetary
medium. Stealth CMEs represent a special type of solar eruptions that,
in most cases, can be clearly seen in coronagraph observations, but
lack distinct source signatures. In order to determine the triggering
mechanism for these stealth CMEs, we are using the MPI-AMRVAC code
developed at KU Leuven. We simulate consecutive CMEs ejected from the
southernmost part of an initial configuration constituted by three
magnetic arcades embedded in a globally bipolar magnetic field. The
first eruption is driven through shearing motions at the solar
surface. The following eruption is a stealth blob-like CME, resulting
from the reconnection of the coronal magnetic field. Both CMEs are
expelled into a bimodal solar wind. We analyse the parameters that
contribute to the occurrence of the second CME. We obtain 3 different
eruption scenarios and dynamics by varying the shearing speed with only
1%. The difference between the 3 cases consists in the characteristics
of the second CME, which can be a failed eruption, a stealth CME, or
a CME with a traceable source. We track the two erupting cases until
1AU and compare their simulated signatures with the in-situ data of
a similar multiple CME event that occurred between 21-22 Sept. 2009,
obtaining a good correlation. Furthermore, we impose the same shearing
speeds along the polarity inversion line of the southern arcade,
but immersed into a faster solar wind, to analyze the effect of the
overall magnetic structure and of the wind onto the resulting eruptions,
propagation and geoeffectiveness. The latter is studied via the Dst
index, computed using an empirical model from the simulated parameters
of the ICMEs.
Title: Modelling the acceleration and transport of energetic particles
in a corotating interaction region
Authors: Aran, Angels; Poedts, Stefaan; Pomoell, Jens; Lario, David
Bibcode: 2021cosp...43E1070A
Altcode:
Spacecraft equipped with particle detectors will occasionally measure
enhanced levels of energetic ions in the vicinity of corotating
interaction regions (CIRs). These ions can have energies up to
${\sim}$20 MeV/nuc and are believed to result from interplanetary
acceleration processes for which the supra-thermal tail of the solar
wind may constitute the seed population. Conceivable acceleration
mechanisms of these ions include compressional or diffusive
shock acceleration, which can happen in the forward and reverse
compression/shock waves bounding the CIR. Once accelerated, these ions
may stream away from the CIR, and can therefore sometimes be detected
in, for example, the fast solar wind stream trailing the CIR. In this
work we present the results of a modelling effort aimed at increasing
our understanding of the transport and acceleration of supra-thermal
ions in the vicinity of CIRs. This is accomplished by using the
three-dimensional particle transport model PARADISE, which solves
the focused transport equation by propagating pseudo-particles in a
solar wind generated by the three-dimensional magnetohydrodynamic model
EUHFORIA. The latter model is used to generate a solar wind containing
a CIR, in which we subsequently inject ions of ${\sim}$10 keV/n at a
continuous rate. We study the particle acceleration efficiency of both
the reverse and forward CIR compression/shock waves, by considering
different particle scattering conditions. In addition, we investigate
how the magnetic topology near and within the CIR affects the transport
of the accelerated ions into the inner heliosphere, up to heliocentric
radial distances visited by Parker Solar Probe.
Title: Coupling the MULTI-VP model with EUHFORIA
Authors: Samara, Evangelia; Rodriguez, Luciano; Poedts, Stefaan;
Magdalenic, Jasmina; Pinto, Rui; Scolini, Camilla; Jercic, Veronika
Bibcode: 2021cosp...43E1002S
Altcode:
The EUropean Heliospheric FORecasting Information Asset (EUHFORIA)
is a new 3D magnetohydrodynamic (MHD) space weather prediction tool
(Pomoell and Poedts, 2018). EUHFORIA models solar wind and coronal
mass ejections (CMEs) all the way from the Sun to 2 AU. It consists
of two different domains; the coronal part, which extends from the
solar surface to 0.1 AU and the heliospheric part, which covers the
spatial domain from 0.1 AU onwards. For the reconstruction of the
global solar corona, the empirical Wang-Sheeley-Arge (WSA, Arge, 2003)
model is currently used, in combination with the potential field source
surface (PFSS) model and the Schatten current sheet (SCS) model, in
order to reconstruct the magnetic field up to 0.1 AU and produce the
plasma boundary conditions required by the 3D MHD heliospheric part
to initiate. In the framework of the ongoing validation of the solar
wind modeling with EUHFORIA, we implemented and tested a different
coronal model, the so-called MULTI-VP model (Pinto and Rouillard,
2017). Therefore, results and comparisons of EUHFORIA's modeled output
at Earth with real insitu data (e.g., solar wind bulk speed, density,
temperature, magnetic field) by employing both the WSA and MULTI-VP
coronal models, will be presented. Moreover, evaluation of the models'
success to reproduce the aforementioned solar wind conditions at Earth,
will be made.
Title: Initiation of CMEs and their geo-effectiveness
Authors: Schmieder, Brigitte; Poedts, Stefaan; Grison, Benjamin;
Demoulin, Pascal; Kim, Rok-Soon; Verbeke, Christine
Bibcode: 2021cosp...43E1013S
Altcode:
Physical conditions of solar eruptions triggering coronal mass ejections
(CMEs) have been determined by recent multi-wavelength observations
as well by numerical simulations (e.g. OHM). CMEs and flares are the
seeds of the Space Weather. Our analyze consists on a few case studies
of CMEs which have all the good proxies for inducing geo-effectivity
e.g. fast halo CME, central solar disk source. We follow the CMEs
surfing in the solar wind as interplanetary coronal mass ejections
(ICME) or magnetic clouds. We use numerical simulations (EUHFORIA) to
investigate the geo-effectiveness of these ICMEs We study the degree
of deviation of these halo CMEs from the Sun-Earth axis as well as
their deformation and erosion due to their interaction with the ambient
solar wind resulting in magnetic reconnections according to the input
of parameters and their chance to hit other planets. The inhomogeneous
nature of the solar wind and encounters are also important parameters
influencing the impact of CMEs on planetary magnetospheres
Title: Fine structures of interplanetary radio bursts
Authors: Jebaraj, Immanuel; Poedts, Stefaan; Krupar, Vratislav;
Magdalenic, Jasmina
Bibcode: 2021cosp...43E1067J
Altcode:
Although solar radio bursts are studied for well over 60 years, and
there are still a number of open questions on their generation and
emission processes. It is generally accepted that majority of solar
radio bursts observed in the corona is due to the coherent plasma
emission mechanism, and a substantial amount of work has been done
to support this idea. The study of fine structures of solar radio
bursts can therefore help us to understand plasma processes in
the corona and interplanetary space. While most of the works done
in this respect are using older observational facilities, new and
advanced ground-based radio imaging spectroscopic techniques (using
e.g. LOFAR, MWA, etc.,) and space-based observations (Wind/WAVES,
STEREO/WAVES A & B, PSP, and SolO in the future) provide a unique
opportunity to identify, and study fine structures observed in the
low corona and interplanetary space. Although, extensive studies of
fine structures have been performed for the metric radio bursts, not
much work was devoted to study the fine structures of interplanetary
radio emission. Radio signatures of solar dynamic phenomena observed in
interplanetary space are mostly confined to two different types, type
II bursts (due to propagating MHD shock waves), and type III bursts
(suprathermal electron beams propagating along open and quasi-open
magnetic field lines). In this study, three types of fine structures
of interplanetary radio bursts are presented. The striae-like fine
structures within type IIIb bursts, continuum-like emission patches,
and drifting narrowband structures within type II radio bursts. Since
space-based radio observations are limited to dynamic spectra, we use
the novel radio triangulation technique employing direction finding
measurements from spacecraft observations (Wind/WAVES, STEREO/WAVES A
& B) to estimate 3D positions of the radio emission sources. Results
of the study show that locating the radio sources of fine structures can
help us understand their generation mechanism and the plasma conditions
necessary for generating them. We discuss the possible relationship
between the fine structures, the broadband emission they are part of,
and the associated solar eruptive events.
Title: Modeling Coronal Mass Ejections with EUHFORIA
Authors: Verbeke, Christine; Schmieder, Brigitte; Rodriguez, Luciano;
Poedts, Stefaan; Magdalenic, Jasmina; Pomoell, Jens; Temmer, Manuela;
Asvestari, Eleanna; Scolini, Camilla; Heinemann, Stephan; Hinterreiter,
Jürgen; Samara, Evangelia
Bibcode: 2021cosp...43E2358V
Altcode:
Fully understanding the origin and evolution of Coronal Mass Ejections
(CMEs) from the Sun to the Earth remains a major topic in current
solar-terrestrial physics and is of key importance to improve our space
weather prediction capabilities. CMEs can drive strong space weather
disturbances at Earth, and their dynamical pressure, magnetic field
configuration and interaction with the solar wind can significantly
alter their arrival time and impact at Earth. One of the key parameters
that determine the geo-effectiveness of the CME is its internal magnetic
configuration. With the EUHFORIA inner-heliosphere magnetohydrodynamics
model, we can model a magnetised CME using a Linear Force Free Spheromak
(LFFS) model, in order to model the internal magnetic structure of
the CME throughout the inner heliosphere. In this talk, we present
an overview of the model assessment efforts that have been made
with EUHFORIA over the past years. We discuss the validation of the
solar wind, as well as the development of the LFFS model. We focus
on determining the sensitivity of the LFFS model input parameters,
as well as some case studies to show our improved modeling of the
CME magnetic field structures at Earth. Finally, we discuss current
limitations and future improvements of the EUHFORIA model.
Title: Advanced Interpretation of Waves and Instabilities in Space
Plasmas
Authors: Shaaban, Shaaban M.; Lazar, Marian; López, Rodrigo A.;
Yoon, Peter H.; Poedts, Stefaan
Bibcode: 2021ASSL..464..185S
Altcode:
This chapter focuses on the small-scale plasma waves and fluctuations
directly conditioned by the velocity distributions of plasma
particles. The dynamics of collision-poor plasmas from space is
governed by wave-particle interactions, which trigger important
kinetic phenomena, such as wave instabilities or emissions induced
by the free energy of particles, as well as the energization of
particles by waves. In-situ measurements in the solar wind reveal
multiple non-thermal features of particle distributions, combining
beaming populations with anisotropic temperatures, and the ubiquitous
suprathermal populations well reproduced by the Kappa power-laws. These
sources of free energy can excite various waves and fluctuations
with different dispersive characteristics (frequencies, wave-numbers,
growth rates). In turn, the enhanced fluctuations can interact with
plasma particles shaping their distributions and constraining their
anisotropies. We review recent linear and quasi-linear (QL) theories
that have adopted realistic Kappa approaches and interpretations,
and managed to describe a series of plasma waves and instabilities of
interest in heliospheric plasmas. In order to unveil how these wave
spectra change in the presence of suprathermal populations, it is
also performed a direct comparative analysis with previous results,
largely relying on idealized Maxwellian models of distributions. A
number of contradictory results from the literature are also explained,
being based on modified and less relevant Kappa approaches.
Title: Thermal conduction effects on formation of chromospheric
solar tadpole-like jets
Authors: Navarro, Anamaría; Lora-Clavijo, F. D.; Murawski, K.;
Poedts, Stefaan
Bibcode: 2021MNRAS.500.3329N
Altcode: 2020MNRAS.tmp.3231N; 2020MNRAS.500.3329N; 2020arXiv201102006N
We measure the effects of non-isotropic thermal conduction on
generation of solar chromospheric jets through numerical simulations
carried out with the use of one fluid magnetohydrodynamics (MHD) code
MAGNUS. Following the work of Srivastava et al. (2018), we consider
the atmospheric state with a realistic temperature model and generate
the ejection of plasma through a gas pressure driver operating in the
top chromosphere. We consider the magnetic field mimicking a flux tube
and perform parametric studies by varying the magnetic field strength
and the amplitude of the driver. We find that in the case of thermal
conduction the triggered jets exhibit a considerably larger energy and
mass fluxes and their shapes are more collimated and penetrate more
the solar corona than for the ideal MHD equations. Low magnetic fields
allow these jets to be more energetic, and larger magnetic fields
decrease the enhancement of mass and energy due to the inclusion of
the thermal conductivity.
Title: Diagnosing CME/Shock wave association using the radio
triangulation technique
Authors: Jebaraj, Immanuel; Poedts, Stefaan; Krupar, Vratislav; Kilpua,
Emilia; Magdalenic, Jasmina; Podladchikova, Tatiana; Pomoell, Jens;
Dissauer, Karin; Veronig, Astrid; Scolini, Camilla
Bibcode: 2021cosp...43E1000J
Altcode:
Eruptive events such as Coronal mass ejections (CMEs) and flares can
accelerate particles and generate shock waves. Tracking of shock waves
and predicting their arrival at the Earth is an important scientific
goal. Space based radio observations provide us the unique opportunity
to track shock waves in the inner heliosphere. We present study of
the CME/flare event on September 27/28, 2012. The GOES C3.7 flare
that originated from NOAA AR 1577 was associated with a full-halo CME
(first seen in the SOHO/LASCO C2 field of view at 23:47 UT) and white
light shock wave observed by all three spacecraft STEREO A, STEREO B,
and SOHO. The associated radio event shows a group of type III bursts
and two somewhat unusual type II bursts with significantly different
starting frequencies. To understand the origin of the two shock waves we
performed multi-wavelength and radio triangulation study. For the radio
triangulation we used direction-finding measurements from STEREO/WAVES
and WIND/WAVES instruments. We reconstructed the shock wave propagation
and compared results with the CME propagation using the data-driven
EUHFORIA cone model (EUropean Heliospheric FORecasting Information
Asset). Results of the study indicate that the interaction of the
shock wave and the nearby streamer, situated close to the southern
polar coronal hole, is the most probable source of the observed low
frequency type II burst. Furthermore, we also demonstrate the importance
of radio triangulation studies in understanding the projection effects
when interpreting radio observations.
Title: Case study on the identification and classification of
small-scale flow patterns in flaring active region
Authors: Philishvili, E.; Shergelashvili, B. M.; Buitendag, S.; Raes,
J.; Poedts, S.; Khodachenko, M. L.
Bibcode: 2021A&A...645A..52P
Altcode: 2020arXiv201107634P
Context. We propose a novel methodology to identity flows in the solar
atmosphere and classify their velocities as either supersonic, subsonic,
or sonic.
Aims: The proposed methodology consists of three
parts. First, an algorithm is applied to the Solar Dynamics Observatory
(SDO) image data to locate and track flows, resulting in the trajectory
of each flow over time. Thereafter, the differential emission measure
inversion method is applied to six Atmospheric Imaging Assembly (AIA)
channels along the trajectory of each flow in order to estimate its
background temperature and sound speed. Finally, we classify each flow
as supersonic, subsonic, or sonic by performing simultaneous hypothesis
tests on whether the velocity bounds of the flow are larger, smaller,
or equal to the background sound speed.
Methods: The proposed
methodology was applied to the SDO image data from the 171 Å spectral
line for the date 6 March 2012 from 12:22:00 to 12:35:00 and again for
the date 9 March 2012 from 03:00:00 to 03:24:00. Eighteen plasma flows
were detected, 11 of which were classified as supersonic, 3 as subsonic,
and 3 as sonic at a 70% level of significance. Out of all these cases,
2 flows cannot be strictly ascribed to one of the respective categories
as they change from the subsonic state to supersonic and vice versa. We
labeled them as a subclass of transonic flows.
Results: The
proposed methodology provides an automatic and scalable solution to
identify small-scale flows and to classify their velocities as either
supersonic, subsonic, or sonic. It can be used to characterize the
physical properties of the solar atmosphere.
Conclusions:
We identified and classified small-scale flow patterns in flaring
loops. The results show that the flows can be classified into four
classes: sub-, super-, trans-sonic, and sonic. The flows occur in the
complex structure of the active region magnetic loops. The detected
flows from AIA images can be analyzed in combination with the other
high-resolution observational data, such as Hi-C 2.1 data, and be used
for the development of theories describing the physical conditions
responsible for the formation of flow patterns.
Title: CME-CME Interactions as Sources of CME Helio-Effectiveness:
the Early September 2017 Events
Authors: Scolini, C.; Chané, E.; Temmer, M.; Pomoell, J.; Kilpua,
K. E. J.; Dissauer, K.; Veronig, A.; Palmerio, E.; Dumbovic, M.; Guo,
J.; Rodriguez, L.; Poedts, S.
Bibcode: 2020AGUFMSH0440017S
Altcode:
Coronal Mass Ejections (CMEs) are the main source of intense space
weather disturbances in the heliosphere. It is known that the
capability of individual CMEs to drive strong space weather events
at Earth (called "geo-effectiveness") and other locations (here
referred to as "helio-effectiveness") primarily depends on their
speed, density, and magnetic field strength and orientation at the
impact location. Moreover, previous studies established that CME--CME
interactions can significantly alter the properties of individual
CMEs, in such a way that their geo-effectiveness is often dramatically
amplified. However, the actual quantification of this amplification has
been rarely investigated, and previous studies have mostly focused on
the near-Earth region only, i.e. without considering its full space-time
evolution as the CMEs propagate to 1 AU and beyond. Here, we
present a study on the role of CME--CME interactions as sources of CME
helio-effectiveness by performing simulations of complex CME events
with the EUHFORIA heliospheric model. As a case study, we consider
a sequence of CMEs observed in early September 2017. As their source
region rotated on the solar disk, CMEs were launched over a wide range
of longitudes, interacting with each other and paving the way for the
propagation of the following ones. At Earth, their interaction resulted
in an intense geomagnetic storm. Using initial parameters derived
from remote-sensing observations, we perform global simulations of
magnetised CMEs with EUHFORIA, investigating how their interactions
affected the propagation and internal properties of individual CME
structures. Taking advantage of 3D simulation outputs, we quantify
the amplification of the helio-effectiveness of the individual CMEs
involved, as a function of the interaction phase and of the location
within the CME structure. Additionally, we explore the possibility of
the existence of a "helio-effectiveness amplification zone", i.e. a
characteristic heliocentric distance at which CME--CME interactions have
the highest probability to develop into helio-effective events. Results
from this study benchmark our current prediction capabilities in
the case of complex CME events, and provide new insights on their
large-scale evolution and potential impact throughout the heliosphere.
Title: The Low-Energy Ion Event on 19 June 2020 Measured by Solar
Orbiter
Authors: Aran, A.; Pacheco, D.; Wijsen, N.; Samara, E.; Gomez-Herrero,
R.; Laurenza, M.; Benella, S.; Sanahuja, B.; Poedts, S.; Freiherr
von Forstner, J. L.; Berger, L.; Mason, G. M.; Allen, R. C.;
O'Brien, H.; Evans, V.; Angelini, V.; Horbury, T. S.; Ho, G. C.;
Wimmer-Schweingruber, R. F.; Rodriguez-Pacheco, J.
Bibcode: 2020AGUFMSH039..06A
Altcode:
Shortly after reaching the first perihelion, the Energetic Particle
Detector (EPD) onboard Solar Orbiter measured a small particle
event. The observed ion intensity enhancement extended from few
keV(/nuc) to <1 MeV(/nuc) and had different durations depending on
the particles' energy. The increase above pre-event intensity levels
was detected at the beginning of June 19 for ions in the energetic
particle range (~50 keV to ~MeV) and lasted up to the noon of June
20. In contrast, the particle event lasted from the 18th to the ~21st
of June in the energy range from ~10 keV to < 40 keV, corresponding
to the highest energies of the suprathermal particle population in the
solar wind. This low-energy increase coincides with a decrease in the
count rates of ions with energies > 17 MeV/nuc. On the other hand,
no electron increases were detected. In this work, we present and
analyse the particle data gathered by the EPD instruments during this
event and discuss its possible sources. To interpret the particle
data, we also use interplanetary magnetic field data from the MAG
instrument. As seen from 1 AU, there is no clear evidence of solar
activity from the visible disk associated with this ion event; it might,
however, have a possible association with solar activity erupting from
behind the limb and/or with a source of interplanetary origin. We
further discuss on the latter scenario by using three-dimensional
simulations for both the solar wind and the particles' transport
and acceleration. For the former, we employ the magnetohydrodynamic
model EUHFORIA (EUropean Heliospheric FORecasting Information Asset)
while for the particles' transport and acceleration we use the PARADISE
(PArticleRadiation Asset Directed at Interplanetary Space Exploration)
model.
Title: Implementing the MULTI-VP Coronal Model in EUHFORIA: Results
and Comparisons with the WSA Coronal Model
Authors: Samara, E.; Pinto, R.; Magdalenic, J.; Jercic, V.; Scolini,
C.; Wijsen, N.; Jebaraj, I. C.; Rodriguez, L.; Poedts, S.
Bibcode: 2020AGUFMSH046..06S
Altcode:
The EUropean Heliospheric FORecasting Information Asset (EUHFORIA)
is a new 3D magnetohydrodynamic (MHD) space weather prediction tool
(Pomoell and Poedts, 2018). EUHFORIA models solar wind and coronal mass
ejections (CMEs) all the way from the Sun to 2 AU. It consists of two
different spatial domains; the coronal part, which extends from the
solar surface to 0.1 AU and the heliospheric part, which covers the
spatial domain from 0.1 AU onwards. For the first part, the empirical
Wang-Sheeley-Ar ge (WSA; Arge et al., 2004) m odel is currently used,
in combination with the potential field source surface (PFSS) model
(Altschuler and Newkirk, 1969) and the Schatten current sheet (SCS)
model (Schatten et al., 1969) , in order to rec onstruct the magnetic
field up to 0.1 AU and produce the plasma boundary conditions required
by the 3D MHD heliospheric part to initiate. In the current work, we
replace the default coronal set-up of EUHFORIA with the physics-based
MULTI-VP model (Pinto and Rouillard, 2017) and we compare the different
output, both at 0.1 AU and 1 AU, for high-speed stream cases during
solar minimum and maximum activity. Further comparisons for the events
of interest are made by employing different magnetograms.
Title: Collisional and Reactive Multi-fluid Modeling of Acoustic Wave
Propagation and Heating in Gravitationally Stratified Chromospheric
plasma
Authors: Zhang, F.; Poedts, S.; Lani, A.; Kuźma, B.; Murawski, K.
Bibcode: 2020AGUFMSH0010018Z
Altcode:
To study acoustic wave propagation and the corresponding energy
deposition in the partially ionized solar chromosphere, we use a
multi-fluid computational model which treats neutrals and charged
particles (electrons and ions) as two separate fluids. This two-fluid
model takes into account the ion-neutral collisions, ionization
and recombination, allowing us to investigate both the collisional
and reactive interactions between uncoupled ions and neutrals in
the chromospheric plasma. In the present numerical simulations, the
initial density is first specified to reach hydrostatic equilibrium, and
chemical equilibrium is also taken into account to provide a consistent
density profile that differs from the hydrostatic equilibrium density
profiles. While the equilibrium is reached, external photospheric
velocity drivers are imposed to introduce monochromatic acoustic
waves. As is well known, the acoustic waves steepen in the lower solar
atmospheric plasma due to the exponentially decreasing density, and
at the same time they heat the plasma via the nonlinear collisional
interaction leading to more dissipation. In particular, the present
numerical results suggest that the initial chemical equilibrium is an
important factor which eventually changes the heating rate. Moreover,
introducing the ionization and recombination slows down the heating
rate, since ionization process itself absorbs a significant amount
of energy. In addition, the heating rate relates to the frequency
of the acoustic waves, of which the steepening wave fronts introduce
significant decoupling between ions and neutrals. More specifically,
low frequency waves tend to heat the higher layers of the atmosphere
at higher heating rates, because their kinetic energy is essentially
not reduced in the lower regions and thus more energy may be deposited
in higher altitudes where the density is much lower.
Title: Spontaneous Magnetic Fluctuations of Kappa Electron
Distributions
Authors: Hermosilla, D.; Moya, P. S.; López, R. A.; Lazar, M.;
Poedts, S.
Bibcode: 2020AGUFMSH0370019H
Altcode:
In situ measurement of particle distributions in space plasmas
usually exhibit a variety of non-equilibrium features in the form of
temperature anisotropy, suprathermal tails, and field-aligned beams,
among others. The departure from thermal equilibrium provides a source
for spontaneous emissions of electromagnetic fluctuations, such as
whistler-cyclotron fluctuations at the electron scales. Analysis of
these fluctuations provides relevant information about the plasma state
and its macroscopic properties. By comparing 1.5D PIC simulations of
a finite temperature magnetized electron-proton plasma loaded with
Maxwellian and generalized kappa velocity distributions, we found new
insights of the wave-particle interaction behavior, suggesting a strong
dependence between the shape of the velocity distribution function and
the spontaneous magnetic fluctuations wave spectrum. This feature may
be used as a proxy to identify the nature of electron populations in
space plasmas at locations where direct measurements of particle fluxes
are not available. Acknowledgement: these results were obtained
in the framework of the projects SCHL 201/35-1 (DFG-German Research
Foundation), GOA/2015-014 (KU Leuven), G0A2316N (FWO- Vlaanderen),
C~90347 (ESA Prodex 9), and Fondecyt No. 1191351 (ANID, Chile). P.S.M is
grateful for the support of KU Leuven BOF Network Fellowship NF/19/001.
Title: Real time physics-based solar wind forecasts for SafeSpace
Authors: Pinto, R.; Kieokaew, R.; Lavraud, B.; Genot, V. N.; Bouchemit,
M.; Rouillard, A. P.; Samara, E.; Poedts, S.; Brunet, A.; Bourdarie,
S. A.; Daglis, I. A.
Bibcode: 2020AGUFMSH0030010P
Altcode:
We present the solar wind forecast module implemented on the Sun -
interplanetary space - Earth's magnetosphere chain of the H2020
SafeSpace project. The wind modelling pipeline, developed at the
IRAP, performs real-time robust simulations (forward modelling)
of the solar wind from the surface of the Sun up to the L1 point,
from which magnetospheric indices are determined using a neural
network. The pipeline effectively combines in a synergistic way
different mature research models: determination of the background
coronal magnetic field, computation of many individual solar wind
acceleration profiles (1 to 90 solar radii), propagation across the
heliosphere and formation of CIRs (up to 1 AU or more), estimation of
synthetic diagnostics (white-light and EUV imaging, in-situ time-series)
and comparison to observations and spacecraft measurements. Different
magnotograms sources (WSO, SOLIS, GONG, ADAPT) can be combined, as well
as coronal field reconstruction methods (PFSS, NLFFF), wind models
(MULTI-VP), and heliospheric propagation models (CDPP/AMDA 1D MHD,
EUHFORIA), magnetospheric indices neural network (ONERA). We tested and
validated the wind forecasts against different in-situ observatories
using a dynamic time-warping metric. We provide a web-based service
that continuously supplies a full set of bulk physical parameters
(wind speed, density, temperature, magnetic field, phase speeds) of
the solar wind up to 6-7 days in advance, at a time cadence compatible
with other space weather applications.
Title: Modelling energetic particles in the vicinity of high-speed
solar wind streams with PARADISE
Authors: Wijsen, N.; Samara, E.; Aran, A.; Lario, D.; Pomoell, J.;
Poedts, S.
Bibcode: 2020AGUFMSH054..05W
Altcode:
Corotating interaction regions (CIRs) are an important source of
energetic particles in the heliosphere. These particles are believed to
be mainly accelerated in the high amplitude compression waves bounding
CIRs. To allow efficient particle acceleration, these waves need to
steepen sufficiently which typically only happens at distances past
the orbit of Earth. However, the detection of isotropic and low energy
particle populations at small radial distances near high-speed streams
(HSS) might suggest the presence of local acceleration mechanisms (e.g.,
Allen et al. 2020). In this work we use the particle transport
model PARADISE (PArticle Radiation Asset Directed at Interplanetary
Space Exploration) to study the transport and acceleration of
supra-thermal ions in the vicinity of HSSs. PARADISE models the
evolution of energetic particle populations propagating in a solar wind
generated by the data-driven three-dimensional magnetohydrodynamic model
EUHFORIA (EUropean Heliospheric FORecasting Information Asset). The
latter model is used to generate solar wind configurations that
contain HSSs, in which we subsequently inject supra-thermal ions at
a continuous rate. We discuss which properties HSSs need to have in
order to produce and sustain energetic particle populations through
e.g., diffusive shock or compressional acceleration mechanisms. We
investigate how the properties of such energetic particle populations
change from large heliocentric radial distances where the CIR shock
waves are formed (>1 AU) to the smaller radial distances visited
by Parker Solar Probe and Solar Orbiter.
Title: The ESA Virtual Space Weather Modelling Centre - Part 3
Authors: Poedts, S.
Bibcode: 2020AGUFMSH0030023P
Altcode:
The ESA Virtual Space Weather Modelling Centre (VSWMC )project
was defined as a long term project including different successive
parts. Parts 1 and 2 were completed in the first 4-5 years and designed
and developed a system that enables models and other components to be
installed locally or geographically distributed and to be coupled and
run remotely from the central system. A first, limited version went
operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE
Portal. Part 3 is the next development step before all objectives
of the VSWMC are achieved. The goal of the ESA project "Virtual
Space Weather Modelling Centre - Part 3" (2019-2021) is to further
develop the Virtual Space Weather Modelling Centre, building on the
Part 2 prototype system and focusing on the interaction with the ESA
SSA SWE system. The objective and scope of this new project include,
apart from maintaining the current operational system, the efficient
integration of new models and new model couplings, including daily
automated end-to-end (Sun to Earth) simulations, the further development
and wider use of the coupling toolkit and front-end GUI, making the
operational system more robust and user-friendly. The VSWMC-Part 3
project started on 1 October 2019. The new models that are being
integrated are Wind-predict (a global coronal model from CEA, France),
the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model, Multi-VP
(another global coronal model form IRAP/CNRS, France), the BIRA Plasma
sphere Model of electron density and temperatures inside and outside
the plasmasphere coupled with the ionosphere (BPIM, Belgium), the SNRB
(also named SNB3GEO) model for electron fluxes at geostationary orbit
(covering the GOES 15 energy channels >800keV and >2MeV) and the
SNGI geomagnetic indices Kp and Dst models (University of Sheffield,
UK), the SPARX Solar Energetic Particles transport model (University of
Central Lancashire, UK), Spenvis DICTAT tool for s/c internal charging
analysis (BISA, Belgium), the Gorgon magnetosphere model (ICL, UK), and
the Drag Temperature Model (DTM) and operations-focused whole atmosphere
model MCM being developed in the H2020 project SWAMI. We will
provide an overview of the state-of-the-art and demonstrate the system.
Title: Fire-hose instability of inhomogeneous plasma flows with
heat fluxes
Authors: Uchava, E. S.; Tevzadze, A. G.; Shergelashvili, B. M.;
Dzhalilov, N. S.; Poedts, S.
Bibcode: 2020PhPl...27k2901U
Altcode: 2020arXiv200504313U
We study the effects of heat flows and velocity shear on the parallel
firehose instability in weakly collisional plasma flow. For this
purpose, we apply an anisotropic 16-moment MHD fluid closure model
that takes into account the pressure and temperature anisotropy,
as well as the effect of anisotropic heat flux. The linear stability
analysis of the firehose modes is carried out in the incompressible
limit, where the MHD flow is parallel to the background magnetic field,
while the velocity is sheared in the direction transverse to the flow
direction. It seems that an increase in the velocity shear parameter
leads to higher growth rates of the firehose instability. The increase
in the instability growth rate is most profound for perturbations
with oblique wave-numbers k ⊥ / k ∥
< 1 . Combined action of the velocity shear and heat fluxes
introduces an asymmetry of the instability growth in the shear plane:
perturbations with wave-vectors with a component in the direction of
the velocity shear grow significantly stronger as compared to those
with components in the opposite direction. We discuss the implications
of the presented study on the observable features of the solar wind
and possible measurements of local parameters of the solar wind based
on the stability constraints set by the firehose instability.
Title: Plasmoids and Resulting Blobs due to the Interaction of
Magnetoacoustic Waves with a 2.5D Magnetic Null Point
Authors: Sabri, S.; Ebadi, H.; Poedts, S.
Bibcode: 2020ApJ...902...11S
Altcode:
We performed a numerical study for interpreting observations of
plasma blobs occurring in the solar corona. Considering all of the
previous studies and the presence of magnetic null points together
with propagating magnetohydrodynamic waves in the solar corona,
we guessed that the interaction of fast magnetoacoustic waves with
null points could give rise to blobs under coronal conditions. The
outcome of these interactions contributes to coronal jets and flares
that directly affects us on Earth. The propagation of magnetoacoustic
waves in the vicinity of a magnetic null point contributes to the
high current density accumulation at the small scale around the
magnetic null point, which has significant magnetic gradients. When
nonlinearity becomes dominant, the variation of current density could
result in instabilities and thus anomalous resistivity. Moreover,
it is demonstrated that plasmoids with eruption events take place in
the solar corona without considering the transition region. In our
numerical simulation results, it is interesting that plasma blobs
manifest themselves in many parameters, including current density,
temperature, plasma density, flows, and magnetic fields, simultaneously
and consistent with the generation of plasmoids. In this work, it is
found that plasmoid instability is the reason for the plasma blobs
and tiny blobs are produced by the tearing instability occurring in
thin current sheets.
Title: Domain of Influence analysis: implications for Data
Assimilation in space weather forecasting
Authors: Millas, Dimitrios; Innocenti, Maria Elena; Laperre, Brecht;
Raeder, Joachim; Poedts, Stefaan; Lapenta, Giovanni
Bibcode: 2020FrASS...7...73M
Altcode: 2020arXiv200904211M
Solar activity, ranging from the background solar wind to energetic
coronal mass ejections (CMEs), is the main driver of the conditions in
the interplanetary space and in the terrestrial space environment, known
as space weather. A better understanding of the Sun-Earth connection
carries enormous potential to mitigate negative space weather effects
with economic and social benefits. Effective space weather forecasting
relies on data and models. In this paper, we discuss some of the
most used space weather models, and propose suitable locations
for data gathering with space weather purposes. We report on the
application of Representer analysis (RA) and Domain of Influence (DOI)
analysis to three models simulating different stages of the Sun-Earth
connection: the OpenGGCM and Tsyganenko models, focusing on solar wind
- magnetosphere interaction, and the PLUTO model, used to simulate CME
propagation in interplanetary space. Our analysis is promising for space
weather purposes for several reasons. First, we obtain quantitative
information about the most useful locations of observation points, such
as solar wind monitors. For example, we find that the absolute values
of the DOI are extremely low in the magnetospheric plasma sheet. Since
knowledge of that particular sub-system is crucial for space weather,
enhanced monitoring of the region would be most beneficial. Second,
we are able to better characterize the models. Although the current
analysis focuses on spatial rather than temporal correlations, we find
that time-independent models are less useful for Data Assimilation
activities than time-dependent models. Third, we take the first steps
towards the ambitious goal of identifying the most relevant heliospheric
parameters for modelling CME propagation in the heliosphere, their
arrival time, and their geoeffectiveness at Earth.
Title: Characteristics of solar wind suprathermal halo electrons
Authors: Lazar, M.; Pierrard, V.; Poedts, S.; Fichtner, H.
Bibcode: 2020A&A...642A.130L
Altcode:
A suprathermal halo population of electrons is ubiquitous in space
plasmas, as evidence of their departure from thermal equilibrium
even in the absence of anisotropies. The origin, properties, and
implications of this population, however, are poorly known. We provide a
comprehensive description of solar wind halo electrons in the ecliptic,
contrasting their evolutions with heliospheric distance in the slow
and fast wind streams. At relatively low distances less than 1 AU,
the halo parameters show an anticorrelation with the solar wind speed,
but this contrast decreases with increasing distance and may switch
to a positive correlation beyond 1 AU. A less monotonic evolution is
characteristic of the high-speed winds, in which halo electrons and
their properties (e.g., number densities, temperature, plasma beta)
exhibit a progressive enhancement already distinguishable at about 0.5
AU. At this point, magnetic focusing of electron strahls becomes weaker
and may be counterbalanced by the interactions of electrons with wave
fluctuations. This evolution of halo electrons between 0.5 AU and 3.0
AU in the fast winds complements previous results well, indicating a
substantial reduction of the strahl and suggesting that significant
fractions of strahl electrons and energy may be redistributed to the
halo population. On the other hand, properties of halo electrons at
low distances in the outer corona suggest a subcoronal origin and a
direct implication in the overheating of coronal plasma via velocity
filtration.
Title: Alternative High-plasma Beta Regimes of Electron Heat-flux
Instabilities in the Solar Wind
Authors: López, R. A.; Lazar, M.; Shaaban, S. M.; Poedts, S.; Moya,
P. S.
Bibcode: 2020ApJ...900L..25L
Altcode: 2020arXiv200604263L
Heat transport in the solar wind is dominated by suprathermal electron
populations, i.e., a tenuous halo and a field-aligned beam/strahl, with
high energies and antisunward drifts along the magnetic field. Their
evolution may offer plausible explanations for the rapid decrease
of the heat flux with the solar wind expansion, and self-generated
instabilities, or so-called "heat flux instabilities" (HFIs), are
typically invoked to explain this evolution. This Letter provides a
unified description of the full spectrum of HFIs, as prescribed by
the linear kinetic theory for high beta conditions (βe ≫
0.1) and different relative drifts (U) of the suprathermals. HFIs of
different natures are examined, i.e., electromagnetic, electrostatic
or hybrid, propagating parallel or obliquely to the magnetic field,
etc., as well as their regimes of interplay (co-existence) or
dominance. These alternative regimes of HFIs complement each other
and may be characteristic of different relative drifts of suprathermal
electrons and various conditions in the solar wind, e.g., in the slow
or fast winds, streaming interaction regions, and interplanetary
shocks. Moreover, these results strongly suggest that heat flux
regulation may not involve just one but several HFIs, concomitantly
or successively in time. Conditions for a single, well-defined
instability with major effects on the suprathermal electrons and,
implicitly, the heat flux, seem to be very limited. Whistler HFIs
are more likely to occur but only for minor drifts (as also reported
by recent observations), which may explain a modest implication in
their regulation, shown already in quasilinear studies and numerical
simulations.
Title: EUropean Heliospheric FORecasting Information Asset 2.0
Authors: Poedts, Stefaan; Lani, Andrea; Scolini, Camilla; Verbeke,
Christine; Wijsen, Nicolas; Lapenta, Giovanni; Laperre, Brecht; Millas,
Dimitrios; Innocenti, Maria Elena; Chané, Emmanuel; Baratashvili,
Tinatin; Samara, Evangelia; Van der Linden, Ronald; Rodriguez,
Luciano; Vanlommel, Petra; Vainio, Rami; Afanasiev, Alexandr; Kilpua,
Emilia; Pomoell, Jens; Sarkar, Ranadeep; Aran, Angels; Sanahuja, Blai;
Paredes, Josep M.; Clarke, Ellen; Thomson, Alan; Rouilard, Alexis;
Pinto, Rui F.; Marchaudon, Aurélie; Blelly, Pierre-Louis; Gorce,
Blandine; Plotnikov, Illya; Kouloumvakos, Athanasis; Heber, Bernd;
Herbst, Konstantin; Kochanov, Andrey; Raeder, Joachim; Depauw, Jan
Bibcode: 2020JSWSC..10...57P
Altcode:
Aims: This paper presents a H2020 project aimed at developing
an advanced space weather forecasting tool, combining the
MagnetoHydroDynamic (MHD) solar wind and coronal mass ejection (CME)
evolution modelling with solar energetic particle (SEP) transport
and acceleration model(s). The EUHFORIA 2.0 project will address
the geoeffectiveness of impacts and mitigation to avoid (part of
the) damage, including that of extreme events, related to solar
eruptions, solar wind streams, and SEPs, with particular emphasis on
its application to forecast geomagnetically induced currents (GICs)
and radiation on geospace. Methods: We will apply innovative methods and
state-of-the-art numerical techniques to extend the recent heliospheric
solar wind and CME propagation model EUHFORIA with two integrated key
facilities that are crucial for improving its predictive power and
reliability, namely (1) data-driven flux-rope CME models, and (2)
physics-based, self-consistent SEP models for the acceleration and
transport of particles along and across the magnetic field lines. This
involves the novel coupling of advanced space weather models. In
addition, after validating the upgraded EUHFORIA/SEP model, it will
be coupled to existing models for GICs and atmospheric radiation
transport models. This will result in a reliable prediction tool for
radiation hazards from SEP events, affecting astronauts, passengers
and crew in high-flying aircraft, and the impact of space weather
events on power grid infrastructure, telecommunication, and navigation
satellites. Finally, this innovative tool will be integrated into both
the Virtual Space Weather Modeling Centre (VSWMC, ESA) and the space
weather forecasting procedures at the ESA SSCC in Ukkel (Belgium), so
that it will be available to the space weather community and effectively
used for improved predictions and forecasts of the evolution of CME
magnetic structures and their impact on Earth. Results: The results of
the first six months of the EU H2020 project are presented here. These
concern alternative coronal models, the application of adaptive mesh
refinement techniques in the heliospheric part of EUHFORIA, alternative
flux-rope CME models, evaluation of data-assimilation based on Karman
filtering for the solar wind modelling, and a feasibility study of
the integration of SEP models.
Title: Electromagnetic Ion-Ion Instabilities in Space Plasmas:
Effects of Suprathermal Populations
Authors: Shaaban, S. M.; Lazar, M.; López, R. A.; Poedts, S.
Bibcode: 2020ApJ...899...20S
Altcode: 2020arXiv200606103S
In collision-poor plasmas from space, three distinct ion-ion
instabilities can be driven by the proton beams streaming along
the background magnetic field: left-hand resonant, nonresonant, and
right-hand resonant instabilities. These instabilities are in general
investigated considering only idealized proton beams with Maxwellian
velocity distributions, and ignoring the implications of suprathermal
populations, usually reproduced by the Kappa power laws. Moreover,
the existing theories minimize the kinetic effects of electrons,
assuming them isotropic and Maxwellian distributed. In an attempt to
overcome these limitations, in the present paper we present the results
of an extended investigation of ion-ion instabilities, which show that
their dispersion and stability properties (e.g., growth rates, wave
frequencies, and the unstable wavenumbers) are highly sensitive to the
influence of suprathermal populations and anisotropic electrons. These
results offer valuable explanations for the origin of the enhanced
low-frequency fluctuations, frequently observed in space plasmas and
associated with proton beams.
Title: A new class of discontinuous solar wind solutions
Authors: Shergelashvili, Bidzina M.; Melnik, Velentin N.; Dididze,
Grigol; Fichtner, Horst; Brenn, Günter; Poedts, Stefaan; Foysi,
Holger; Khodachenko, Maxim L.; Zaqarashvili, Teimuraz V.
Bibcode: 2020MNRAS.496.1023S
Altcode: 2020MNRAS.tmp.1543S; 2020arXiv200506426S
A new class of one-dimensional solar wind models is developed within
the general polytropic, single-fluid hydrodynamic framework. The
particular case of quasi-adiabatic radial expansion with a localized
heating source is considered. We consider analytical solutions with
continuous Mach number over the entire radial domain while allowing
for jumps in the flow velocity, density, and temperature, provided
that there exists an external source of energy in the vicinity of the
critical point that supports such jumps in physical quantities. This is
substantially distinct from both the standard Parker solar wind model
and the original nozzle solutions, where such discontinuous solutions
are not permissible. We obtain novel sample analytic solutions of the
governing equations corresponding to both slow and fast winds.
Title: Numerical simulations of the lower solar atmosphere heating
by two-fluid nonlinear Alfvén waves
Authors: Kuźma, B.; Wójcik, D.; Murawski, K.; Yuan, D.; Poedts, S.
Bibcode: 2020A&A...639A..45K
Altcode:
Context. We present new insight into the long-standing problem of
plasma heating in the lower solar atmosphere in terms of collisional
dissipation caused by two-fluid Alfvén waves.
Aims: Using
numerical simulations, we study Alfvén wave propagation and dissipation
in a magnetic flux tube and their heating effect.
Methods:
We set up 2.5-dimensional numerical simulations with a semi-empirical
model of a stratified solar atmosphere and a force-free magnetic field
mimicking a magnetic flux tube. We consider a partially ionized plasma
consisting of ion + electron and neutral fluids, which are coupled by
ion-neutral collisions.
Results: We find that Alfvén waves,
which are directly generated by a monochromatic driver at the bottom
of the photosphere, experience strong damping. Low-amplitude waves do
not thermalize sufficient wave energy to heat the solar atmospheric
plasma. However, Alfvén waves with amplitudes greater than 0.1 km
s-1 drive through ponderomotive force magneto-acoustic waves
in higher atmospheric layers. These waves are damped by ion-neutral
collisions, and the thermal energy released in this process leads
to heating of the upper photosphere and the chromosphere.
Conclusions: We infer that, as a result of ion-neutral collisions,
the energy carried initially by Alfvén waves is thermalized in the
upper photosphere and the chromosphere, and the corresponding heating
rate is large enough to compensate radiative and thermal-conduction
energy losses therein.
Title: Using radio triangulation to understand the origin of two
subsequent type II radio bursts
Authors: Jebaraj, I. C.; Magdalenić, J.; Podladchikova, T.; Scolini,
C.; Pomoell, J.; Veronig, A. M.; Dissauer, K.; Krupar, V.; Kilpua,
E. K. J.; Poedts, S.
Bibcode: 2020A&A...639A..56J
Altcode: 2020arXiv200604586J
Context. Eruptive events such as coronal mass ejections (CMEs)
and flares accelerate particles and generate shock waves which can
arrive at Earth and can disturb the magnetosphere. Understanding the
association between CMEs and CME-driven shocks is therefore highly
important for space weather studies.
Aims: We present a study
of the CME/flare event associated with two type II bursts observed
on September 27, 2012. The aim of the study is to understand the
relationship between the observed CME and the two distinct shock
wave signatures.
Methods: The multiwavelength study of the
eruptive event (CME/flare) was complemented with radio triangulation
of the associated radio emission and modelling of the CME and the
shock wave employing MHD simulations.
Results: We found that,
although temporal association between the type II bursts and the CME is
good, the low-frequency type II (LF-type II) burst occurs significantly
higher in the corona than the CME and its relationship to the CME is not
straightforward. The analysis of the EIT wave (coronal bright front)
shows the fastest wave component to be in the southeast quadrant of
the Sun. This is also the quadrant in which the source positions
of the LF-type II were found to be located, probably resulting
from the interaction between the shock wave and a streamer.
Conclusions: The relationship between the CME/flare event and the
shock wave signatures is discussed using the temporal association,
as well as the spatial information of the radio emission. Further,
we discuss the importance and possible effects of the frequently
non-radial propagation of the shock wave.
Title: On the Dependency between the Peak Velocity of High-speed
Solar Wind Streams near Earth and the Area of Their Solar Source
Coronal Holes
Authors: Hofmeister, Stefan J.; Veronig, Astrid M.; Poedts, Stefaan;
Samara, Evangelia; Magdalenic, Jasmina
Bibcode: 2020ApJ...897L..17H
Altcode: 2020arXiv200702625H
The relationship between the peak velocities of high-speed solar
wind streams near Earth and the areas of their solar source regions,
I.e., coronal holes, has been known since the 1970s, but it is still
physically not well understood. We perform 3D magnetohydrodynamic (MHD)
simulations using the European Heliospheric Forecasting Information
Asset (EUHFORIA) code to show that this empirical relationship
forms during the propagation phase of high-speed streams from the
Sun to Earth. For this purpose, we neglect the acceleration phase of
high-speed streams, and project the areas of coronal holes to a sphere
at 0.1 au. We then vary only the areas and latitudes of the coronal
holes. The velocity, temperature, and density in the cross section of
the corresponding high-speed streams at 0.1 au are set to constant,
homogeneous values. Finally, we propagate the associated high-speed
streams through the inner heliosphere using the EUHFORIA code. The
simulated high-speed stream peak velocities at Earth reveal a linear
dependence on the area of their source coronal holes. The slopes of
the relationship decrease with increasing latitudes of the coronal
holes, and the peak velocities saturate at a value of about 730 km
s-1, similar to the observations. These findings imply
that the empirical relationship between the coronal hole areas and
high-speed stream peak velocities does not describe the acceleration
phase of high-speed streams, but is a result of the high-speed stream
propagation from the Sun to Earth.
Title: Electromagnetic instabilities of low-beta alpha/proton beams
in space plasmas
Authors: Rehman, M. A.; Shaaban, S. M.; Yoon, P. H.; Lazar, M.;
Poedts, S.
Bibcode: 2020Ap&SS.365..107R
Altcode: 2020arXiv200605337R
Relative drifts between different species or particle populations
are characteristic to solar plasma outflows, e.g., in the fast
streams of the solar winds, coronal mass ejections and interplanetary
shocks. This paper characterizes the dispersion and stability of the
low-beta alpha/proton drifts in the absence of any intrinsic thermal
anisotropies, which are usually invoked in order to stimulate various
instabilities. The dispersion relations derived here describe the
full spectrum of instabilities and their variations with the angle
of propagation and plasma parameters. The results unveil a potential
competition between instabilities of the electromagnetic proton
cyclotron and alpha cyclotron modes. For conditions specific to a
low-beta solar wind, e.g., at low heliocentric distances in the outer
corona, the instability operates on the alpha cyclotron branch. The
growth rates of the alpha cyclotron mode are systematically stimulated
by the (parallel) plasma beta and/or the alpha-proton temperature
ratio. One can therefore expect that this instability develops even in
the absence of temperature anisotropies, with potential to contribute to
a self-consistent regulation of the observed drift of alpha particles.
Title: Solar Flare Prediction Using Magnetic Field Diagnostics above
the Photosphere
Authors: Korsós, M. B.; Georgoulis, M. K.; Gyenge, N.; Bisoi, S. K.;
Yu, S.; Poedts, S.; Nelson, C. J.; Liu, J.; Yan, Y.; Erdélyi, R.
Bibcode: 2020ApJ...896..119K
Altcode: 2020arXiv200512180K
In this article, we present the application of the weighted horizontal
gradient of magnetic field (WGM) flare prediction method
to three-dimensional (3D) extrapolated magnetic configurations of
13 flaring solar active regions (ARs). The main aim is to identify
an optimal height range, if any, in the interface region between the
photosphere and lower corona, where the flare onset time prediction
capability of WGM is best exploited. The optimal height
is where flare prediction, by means of the WGM method, is
achieved earlier than at the photospheric level. 3D magnetic structures,
based on potential and nonlinear force-free field extrapolations, are
constructed to study a vertical range from the photosphere up to the
low corona with a 45 km step size. The WGM method is applied
as a function of height to all 13 flaring AR cases that are subject to
certain selection criteria. We found that applying the WGM
method between 1000 and 1800 km above the solar surface would improve
the prediction of the flare onset time by around 2-8 hr. Certain caveats
and an outlook for future work along these lines are also discussed.
Title: Multi-spacecraft Observations of interacting CME flux ropes
Authors: Kilpua, Emilia; Good, Simon; Palmerio, Erika; Asvestari,
Eleanna; Pomoell, Jens; Lumme, Erkka; Ala-Lahti, Matti; Kalliokoski,
Milla; Morosan, Diana; Price, Daniel; Magdalenic, Jasmina; Poedts,
Stefaan; Futaana, Yoshimi
Bibcode: 2020EGUGA..22.6043K
Altcode:
Interactions between coronal mass ejections (CMEs) in interplanetary
space are a highly important aspect for understanding their physical
dynamics and evolution as well as their space weather consequences. Here
we present an analysis of three CMEs that erupted from the Sun on June
12-14, 2012 using almost radially aligned spacecraft at Venus and Earth,
complemented by heliospheric imaging and modelling with EUHFORIA. These
multi-spacecraft observations were critical for interpreting the event
correctly, in particular regarding the last two CMEs in the series
(June 13 and June 14). At the orbit of Venus these CMEs were mostly
separate with the June 14 CME just about to reach the previous CME. A
significant interaction occurred before the CMEs reached the Earth. The
shock of the June 14 CME had propagated through the June 13 CME and
the two CMEs had coalesced into a single large flux rope structure
before they reached the Earth. This merged flux rope had one of the
largest magnetic field magnitudes observed in the near-Earth solar
wind during Solar Cycle 24. We discuss also the general importance of
multi-spacecraft observations and modelling using them in analyzing
solar eruptions.
Title: Numerical simulations of shear-induced consecutive coronal
mass ejections
Authors: Talpeanu, D. -C.; Chané, E.; Poedts, S.; D'Huys, E.; Mierla,
M.; Roussev, I.; Hosteaux, S.
Bibcode: 2020A&A...637A..77T
Altcode: 2020arXiv200407654T
Context. It is widely accepted that photospheric shearing motions play
an important role in triggering the initiation of coronal mass ejections
(CMEs). Even so, there are events for which the source signatures
are difficult to locate, while the CMEs can be clearly observed
in coronagraph data. These events are therefore called `stealth'
CMEs. They are of particular interest to space weather forecasters,
since eruptions are usually discarded from arrival predictions if
they appear to be backsided, which means not presenting any clear
low-coronal signatures on the visible solar disc. Such assumptions
are not valid for stealth CMEs since they can originate from the front
side of the Sun and be Earth-directed, but they remain undetected and
can therefore trigger unpredicted geomagnetic storms.
Aims:
We numerically model and investigate the effects of shearing motion
variations onto the resulting eruptions and we focus in particular on
obtaining a stealth CME in the trailing current sheet of a previous
ejection.
Methods: We used the 2.5D magnetohydrodynamics package
of the code MPI-AMRVAC to numerically simulate consecutive CMEs by
imposing shearing motions onto the inner boundary, which represents,
in our case, the low corona. The initial magnetic configuration
consists of a triple arcade structure embedded into a bimodal solar
wind, and the sheared polarity inversion line is found in the southern
loop system. The mesh was continuously adapted through a refinement
method that applies to current carrying structures, allowing us to
easily track the CMEs in high resolution, without resolving the grid
in the entire domain. We also compared the obtained eruptions with
the observed directions of propagation, determined using a forward
modelling reconstruction technique based on a graduated cylindrical
shell geometry, of an initial multiple coronal mass ejection (MCME)
event that occurred in September 2009. We further analysed the
simulated ejections by tracking the centre of their flux ropes in
latitude and their total speed. Radial Poynting flux computation was
employed as well to follow the evolution of electromagnetic energy
introduced into the system.
Results: Changes within 1% in the
shearing speed result in three different scenarios for the second CME,
although the preceding eruption seems insusceptible to such small
variations. Depending on the applied shearing speed, we thus obtain
a failed eruption, a stealth, or a CME driven by the imposed shear,
as the second ejection. The dynamics of all eruptions are compared
with the observed directions of propagation of an MCME event and a good
correlation is achieved. The Poynting flux analysis reveals the temporal
variation of the important steps of eruptions.
Conclusions:
For the first time, a stealth CME is simulated in the aftermath of a
first eruption, originating from an asymmetric streamer configuration,
through changes in the applied shearing speed, indicating it is not
necessary for a closed streamer to exist high in the corona for such
an event to occur. We also emphasise the high sensitivity of the corona
to small changes in motions at the photosphere, or in our simulations,
at the low corona. ARRAY(0x28d6278)
Title: Coupling the MULTI-VP model with EUHFORIA
Authors: Samara, Evangelia; Magdalenic, Jasmina; Pinto, Rui F.;
Jercic, Veronika; Scolini, Camilla; Rodriguez, Luciano; Poedts, Stefaan
Bibcode: 2020EGUGA..22..966S
Altcode:
The EUropean Heliospheric FORecasting Information Asset (EUHFORIA)
is a new 3D magnetohydrodynamic (MHD) space weather prediction tool
(Pomoell and Poedts, 2018). EUHFORIA models solar wind and coronal
mass ejections (CMEs) all the way from the Sun to 2 AU. It consists
of two different domains; the coronal part, which extends from the
solar surface to 0.1 AU and the heliospheric part, which covers
the spatial domain from 0.1 AU onwards. For the reconstruction of
the global solar corona, the empirical Wang-Sheeley-Arge (WSA, Arge,
2003) model is currently used, in combination with the potential field
source surface (PFSS) model and the Schatten current sheet (SCS) model,
in order to reconstruct the magnetic field up to 0.1 AU and produce the
plasma boundary conditions required by the 3D MHD heliospheric part to
initiate. In the framework of the ongoing validation of the solar wind
modeling with EUHFORIA, we implemented and tested a different coronal
model, the so-called MULTI-VP model (Pinto and Rouillard, 2017). First
results and comparisons of EUHFORIA modeled output at Earth produced
by employing the WSA and MULTI-VP coronal models, will be presented.
Title: Can we explain the low geo-effectiveness of the fast halo
CMEs in 2002 with EUHFORIA?
Authors: Schmieder, Brigitte; Poedts, Stefaan; Verbeke, Christine
Bibcode: 2020EGUGA..22.5543S
Altcode:
In 2002 (Cycle 23), a weak impact on the magnetosphere of the Earth has
been reported for six halo CMEs related to six X-class flares and with
velocities higher than 1000 km/s. The registered Dst minima are all
between -17 nT and -50 nT. A study of the Sun-Earth chain of phenomena
related to these CMEs reveals that four of them have a source at the
limb and two have a source close to the solar disk center (Schmieder
et al., 2020). All of CME magnetic clouds had a low z-component of the
magnetic field, oscillating between positive and negative values.We
performed a set of EUHFORIA simulations in an attempt to explain the
low observed Dst and the observed magnetic fields. We study the degree
of deviation of these halo CMEs from the Sun-Earth axis and as well as
their deformation and erosion due to their interaction with the ambient
solar wind (resulting in magnetic reconnections) according to the input
of parameters and their chance to hit other planets. The inhomogeneous
nature of the solar wind and encounters are also important parameters
influencing the impact of CMEs on planetary magnetospheres.
Title: On the fine structures in interplanetary radio emissions
Authors: Jebaraj, Immanuel Christopher; Magdalenic, Jasmina; Poedts,
Stefaan
Bibcode: 2020EGUGA..22.1025J
Altcode:
Solar radio emission is studied for many decades and a large number of
studies have been dedicated to metric radio emission originating from
the low corona. It is generally accepted that solar radio emission
observed at wavelengths below the metric range is produced by the
coherent plasma emission mechanism. Fine structures seem to be an
intrinsic part of solar radio emission and they are very important
for understanding plasma processes in the solar medium. Extensive
reporting and number of studies of the metric range fine structures
were performed, but studies of fine structures in the interplanetary
domain are quite rare. New and advanced ground-based radio imaging
spectroscopic techniques (e.g. LOFAR, MWA, etc.,) and space-based
observations (Wind/WAVES, STEREO/WAVES A & B, PSP, and SolO in the
future) provide a unique opportunity to study radio fine structures
observed all the way from metric to kilometric range.Radio signatures
of solar eruptive events, such as flares and CMEs, observed in the
interplanetary space are mostly confined to type II (radio signatures
of magneto-hydrodynamic shock waves), and type III bursts(electron
beams propagating along open and quasi-open magnetic field lines). In
this study, we have identified, and analyzed three types of fine
structures present within the interplanetary radio bursts. Namely,
the striae-like fine structures within type III bursts, continuum-like
emission patches, and very slow drifting narrowband structures within
type II radio bursts. Since space-based radio observations are limited
to dynamic spectra, we use the novel radio triangulation technique
employing direction finding measurements from stereoscopic spacecraft
(Wind/WAVES, STEREO/WAVES A & B) to obtain the 3D position of the
radio emission. The novelty of the technique is that it is not dependent
on a density model and in turn can probe the plasma density in the
triangulated radio source positions (Magdalenic et al. 2014). Results
of the study show that locating the radio source helps not only to
understand the generation mechanism of the fine structures but also the
ambient plasma conditions such as e.g. electron density. We found that
fine structures are associated with complex CME/shock wave structures
which interact with the ambient magnetic field structures. We also
discuss the possible relationship between the fine structures, the
broadband emission they are part of, and the solar eruptive events
they are associated with.
Title: Observation-based modelling of magnetised CMEs in the inner
heliosphere with EUHFORIA
Authors: Scolini, Camilla; Pomoell, Jens; Chané, Emmanuel; Poedts,
Stefaan; Rodriguez, Luciano; Kilpua, Emilia; Temmer, Manuela;
Verbeke, Christine; Dissauer, Karin; Veronig, Astrid; Palmerio, Erika;
Dumbović, Mateja
Bibcode: 2020EGUGA..22.1777S
Altcode:
Coronal Mass Ejections (CMEs) are the primary source of strong
space weather disturbances at Earth and other locations in the
heliosphere. Understanding the physical processes involved in their
formation at the Sun, propagation in the heliosphere, and impact
on planetary bodies is therefore critical to improve current space
weather predictions throughout the heliosphere. The capability of CMEs
to drive strong space weather disturbances at Earth and other planetary
and spacecraft locations primarily depends on their dynamic pressure,
internal magnetic field strength, and magnetic field orientation at
the impact location. In addition, phenomena such as the interaction
with the solar wind and other solar transients along the way, or
the pre-conditioning of interplanetary space due to the passage of
previous CMEs, can significantly modify the properties of individual
CMEs and alter their ultimate space weather impact. Investigating
and modeling such phenomena via advanced physics-based heliospheric
models is therefore crucial to improve the space weather prediction
capabilities in relation to both single and complex CME events. In this
talk, we present our progress in developing novel methods to model CMEs
in the inner heliosphere using the EUHFORIA MHD model in combination
with remote-sensing solar observations. We discuss the various
observational techniques that can be used to constrain the initial
CME parameters for EUHFORIA simulations. We present current efforts
in developing more realistic magnetised CME models aimed at describing
their internal magnetic structure in a more realistic fashion. We show
how the combination of these two approaches allows the investigation of
CME propagation and evolution throughout the heliosphere to a higher
level of detail, and results in significantly improved predictions of
CME impact at Earth and other locations in the heliosphere. Finally,
we discuss current limitations and future improvements in the context
of studying space weather events throughout the heliosphere.
Title: The impact of coronal hole characteristics and solar cycle
activity in reconstructing coronal holes with EUHFORIA
Authors: Asvestari, E.; Heinemann, S. G.; Temmer, M.; Pomoell, J.;
Kilpua, E.; Magdalenic, J.; Poedts, S.
Bibcode: 2020JPhCS1548a2004A
Altcode:
Modelling with high accuracy the open magnetic field and the fast solar
wind in the heliosphere is essential for space weather forecasting
purposes. Primary sources of open magnetic field flux are Coronal
Holes (CH), uni-polar regions that appear as dark patches in the
solar corona when observed in X-ray and extreme-ultraviolet (EUV)
images due to having significantly lower density and temperature
to their surroundings. Therefore, when assessing how well the open
magnetic field and the fast solar wind are modelled one can look at
how well the model performs on one of its fundamental functions, that
of reconstructing coronal hole areas. In this study we investigate how
the CH morphology (i.e. latitudinal position of the centre of mass,
area, intensity, elongation) and the solar variability, from high to
low activity periods, can affect the results. We also investigated the
possibility that the model is reconstructing CHs that are systematically
shifted with respect to their observed position. The study is applied
on 15 CHs exhibiting different latitudinal position and geometry. We
compare the modelled CH areas with boundaries obtained by remote sensing
EUV observations using the CATCH tool (Collection of Analysis Tools for
Coronal Holes). We found no apparent effect of the CH characteristics
on the modelling capabilities. In addition, solar cycle activity seems
not to have any effect either. However, we emphasize that our sample
is small and this outcome highlights the need for an extended research.
Title: Real time physics-based solar wind forecasts for SafeSpace
Authors: Pinto, Rui; Kieokaew, Rungployphan; Lavraud, Benoît; Génot,
Vincent; Bouchemit, Myriam; Rouillard, Alexis; Poedts, Stefaan;
Bourdarie, Sébastien; Daglis, Yannis
Bibcode: 2020EGUGA..2215245P
Altcode:
We present the solar wind forecast module to be implemented on the
Sun - interplanetary space - Earth's magnetosphere chain of the
H2020 SafeSpace project. The wind modelling pipeline, developed at
the IRAP, performs real-time robust simulations (forward modelling)
of the physical processes that determine the state of the solar wind
from the surface of the Sun up to the L1 point. The pipeline puts
together different mature research models: determination of the
background coronal magnetic field, computation of many individual
solar wind acceleration profiles (1 to 90 solar radii), propagation
across the heliosphere and formation of CIRs (up to 1 AU or more),
estimation of synthetic diagnostics (white-light and EUV imaging,
in-situ time-series) and comparison to observations and spacecraft
measurements. Different magnotograms sources (WSO, SOLIS, GONG, ADAPT)
can be combined, as well as coronal field reconstruction methods (PFSS,
NLFFF), wind models (MULTI-VP), and heliospheric propagation models
(CDPP/AMDA 1D MHD, ENLIL, EUHFORIA). We provide a web-based service
that continuously supplies a full set of bulk physical parameters
(wind speed, density, temperature, magnetic field, phase speeds) of
the solar wind up to 6-7 days in advance, at a time cadence compatible
with space weather applications.
Title: Low Geo-Effectiveness of Fast Halo CMEs Related to the 12
X-Class Flares in 2002
Authors: Schmieder, B.; Kim, R. -S.; Grison, B.; Bocchialini, K.;
Kwon, R. -Y.; Poedts, S.; Démoulin, P.
Bibcode: 2020JGRA..12527529S
Altcode: 2020arXiv200310777S
It is generally accepted that extreme space weather events tend to be
related to strong flares and fast halo coronal mass ejections (CMEs). In
the present paper, we carefully identify the chain of events from
the Sun to the Earth induced by all 12 X-class flares that occurred
in 2002. In this small sample, we find an unusual high rate (58%) of
solar sources with a longitude larger than 74°. Yet all 12 X-class
flares are associated with at least one CME. The fast halo CMEs (50%)
are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum
values (more than -51 nT), while five (41%) of the 12 X-class flares
are related to solar proton events (SPEs). We conclude that (i) all
12 analyzed solar events, even those associated with fast halo CMEs
originating from the central disk region, and those ICMEs and SPEs
were not very geo-effective. This unexpected result demonstrates that
the suggested events in the chain (fast halo CME, X-class flares,
central disk region, ICME, and SPE) are not infallible proxies for
geo-effectiveness. (ii) The low value of integrated and normalized
southward component of the interplanetary magnetic field (Bz*) may
explain the low geo-effectiveness for this small sample. In fact,
Bz* is well correlated to the weak Dst and low auroral electrojet
activity. Hence, the only space weather impact at Earth in 2002 we
can explain is based on Bz* at L1.
Title: EUHFORIA in the ESA Virtual Space Weather Modelling Centre
Authors: Poedts, Stefaan
Bibcode: 2020EGUGA..22.5259P
Altcode:
The goal of the ESA project "Virtual Space Weather Modelling Centre -
Part 3" (2019-2021) is to further develop the Virtual Space Weather
Modelling Centre (VSWMC), building on the Part 2 prototype system
and focusing on the interaction with the ESA SSA SWE system. A
first, limited version went operational in May 2019 under the H-ESC
umbrella on the ESA SSA SWE Portal. The objective and scopes of this
new project include: the efficient integration of new models and new
model couplings, including daily automated end-to-end (Sun to Earth)
simulations, the further development and wider use of the coupling
toolkit and front-end GUI, making the operational system more robust
and user-friendly. The VSWMC-Part 3 project started on 1 October
2019.EUHFORIA ('European heliospheric forecasting information asset')
is integrated in the VSWMC and will be upgraded with alternative coronal
models (Multi-VP and Wind-Predict) and flux-rope CME models, and new
couplings will be made available, e.g. to more advanced magnetospheric
models and radiation belt models, geo-effects models, and even SEP
models. The first results will be discussed and put into perspective.
Title: Determination of the solar rotation parameters via orthogonal
polynomials
Authors: Mdzinarishvili, T. G.; Shergelashvili, B. M.; Japaridze,
D. R.; Chargeishvili, B. B.; Kosovichev, A. G.; Poedts, S.
Bibcode: 2020AdSpR..65.1843M
Altcode:
Accurate measurements of the solar differential rotation parameters
are necessary for understanding the solar dynamo mechanism. We use the
orthogonalization process to estimate these parameters. The advantage
of the orthogonalization of the data in the tracer motion statistical
analysis is outlined. The differential rotation is represented in
terms of various types of polynomials. We compare the quality of a
set of models of the solar differential rotation using the Akaike
information criterion and choose the best one. Applying the proposed
method, we studied the solar differential rotation and its North-South
asymmetry using observations of coronal holes. A statistical analysis
of observations from the Atmospheric Imaging Assembly (AIA) on Solar
Dynamics Observatory (SDO) reveals the differential rotation pattern
of coronal holes and its North-South asymmetry.
Title: The Virtual Space Weather Modelling Centre
Authors: Poedts, Stefaan; Kochanov, Andrey; Lani, Andrea; Scolini,
Camilla; Verbeke, Christine; Hosteaux, Skralan; Chané, Emmanuel;
Deconinck, Herman; Mihalache, Nicolae; Diet, Fabian; Heynderickx,
Daniel; De Keyser, Johan; De Donder, Erwin; Crosby, Norma B.; Echim,
Marius; Rodriguez, Luciano; Vansintjan, Robbe; Verstringe, Freek;
Mampaey, Benjamin; Horne, Richard; Glauert, Sarah; Jiggens, Piers;
Keil, Ralf; Glover, Alexi; Deprez, Grégoire; Luntama, Juha-Pekka
Bibcode: 2020JSWSC..10...14P
Altcode:
Aims: Our goal is to develop and provide an open end-to-end
(Sun to Earth) space weather modeling system, enabling to combine
("couple") various space weather models in an integrated tool, with
the models located either locally or geographically distributed, so
as to better understand the challenges in creating such an integrated
environment.
Methods: The physics-based models are installed on
different compute clusters and can be run interactively and remotely
and that can be coupled over the internet, using open source "high-level
architecture" software, to make complex modeling chains involving models
from the Sun to the Earth. Visualization tools have been integrated
as "models" that can be coupled to any other integrated model with
compatible output.
Results: The first operational version
of the VSWMC is accessible via the SWE Portal and demonstrates its
end-to-end simulation capability. Users interact via the front-end GUI
and can interactively run complex coupled simulation models and view
and retrieve the output, including standard visualizations, via the
GUI. Hence, the VSWMC provides the capability to validate and compare
model outputs.
Title: Improving Predictions of High-Latitude Coronal Mass Ejections
Throughout the Heliosphere
Authors: Scolini, C.; Chané, E.; Pomoell, J.; Rodriguez, L.;
Poedts, S.
Bibcode: 2020SpWea..1802246S
Altcode:
Predictions of the impact of coronal mass ejections (CMEs) in the
heliosphere mostly rely on cone CME models, whose performances are
optimized for locations in the ecliptic plane and at 1 AU (e.g.,
at Earth). Progresses in the exploration of the inner heliosphere,
however, advocate the need to assess their performances at both higher
latitudes and smaller heliocentric distances. In this work, we perform
3-D magnetohydrodynamics simulations of artificial cone CMEs using
the EUropean Heliospheric FORecasting Information Asset (EUHFORIA),
investigating the performances of cone models in the case of CMEs
launched at high latitudes. We compare results obtained initializing
CMEs using a commonly applied approximated (Euclidean) distance relation
and using a proper (great circle) distance relation. Results show that
initializing high-latitude CMEs using the Euclidean approximation
results in a teardrop-shaped CME cross section at the model inner
boundary that fails in reproducing the initial shape of high-latitude
cone CMEs as a circular cross section. Modeling errors arising from
the use of an inappropriate distance relation at the inner boundary
eventually propagate to the heliospheric domain. Errors are most
prominent in simulations of high-latitude CMEs and at the location
of spacecraft at high latitudes and/or small distances from the
Sun, with locations impacted by the CME flanks being the most error
sensitive. This work shows that the low-latitude approximations commonly
employed in cone models, if not corrected, may significantly affect
CME predictions at various locations compatible with the orbit of
space missions such as Parker Solar Probe, Ulysses, and Solar Orbiter.
Title: CME-CME Interactions as Sources of CME Geoeffectiveness:
The Formation of the Complex Ejecta and Intense Geomagnetic Storm
in 2017 Early September
Authors: Scolini, Camilla; Chané, Emmanuel; Temmer, Manuela; Kilpua,
Emilia K. J.; Dissauer, Karin; Veronig, Astrid M.; Palmerio, Erika;
Pomoell, Jens; Dumbović, Mateja; Guo, Jingnan; Rodriguez, Luciano;
Poedts, Stefaan
Bibcode: 2020ApJS..247...21S
Altcode: 2019arXiv191110817S
Coronal mass ejections (CMEs) are the primary sources of intense
disturbances at Earth, where their geoeffectiveness is largely
determined by their dynamic pressure and internal magnetic field,
which can be significantly altered during interactions with other
CMEs in interplanetary space. We analyze three successive CMEs that
erupted from the Sun during 2017 September 4-6, investigating the
role of CME-CME interactions as a source of the associated intense
geomagnetic storm (Dst_{min}=-142 nT on September 7). To quantify
the impact of interactions on the (geo)effectiveness of individual
CMEs, we perform global heliospheric simulations with the European
Heliospheric Forecasting Information Asset (EUHFORIA) model, using
observation-based initial parameters with the additional purpose of
validating the predictive capabilities of the model for complex CME
events. The simulations show that around 0.45 au, the shock driven by
the September 6 CME started compressing a preceding magnetic ejecta
formed by the merging of two CMEs launched on September 4, significantly
amplifying its Bz until a maximum factor of 2.8 around 0.9
au. The following gradual conversion of magnetic energy into kinetic
and thermal components reduced the Bz amplification until
its almost complete disappearance around 1.8 au. We conclude that a
key factor at the origin of the intense storm triggered by the 2017
September 4-6 CMEs was their arrival at Earth during the phase of
maximum Bz amplification. Our analysis highlights how the
amplification of the magnetic field of individual CMEs in spacetime due
to interaction processes can be characterized by a growth, a maximum,
and a decay phase, suggesting that the time interval between the CME
eruptions and their relative speeds are critical factors in determining
the resulting impact of complex CMEs at various heliocentric distances
(helioeffectiveness).
Title: The effect of drifts on the decay phase of SEP events
Authors: Wijsen, N.; Aran, A.; Sanahuja, B.; Pomoell, J.; Poedts, S.
Bibcode: 2020A&A...634A..82W
Altcode: 2020arXiv200104655W
Aims: We study the effect of the magnetic gradient and
curvature drifts on the pitch-angle dependent transport of solar
energetic particles (SEPs) in the heliosphere, focussing on ∼3-36
MeV protons. By considering observers located at different positions
in the heliosphere, we investigate how drifts may alter the measured
intensity-time profiles and energy spectra. We focus on the decay
phase of solar energetic proton events in which a temporal invariant
spectrum and disappearing spatial intensity gradients are often
observed; a phenomenon known as the "reservoir effect" or the "SEP
flood". We study the effects of drifts by propagating particles both
in nominal and non-nominal solar wind conditions.
Methods:
We used a three-dimensional (3D) particle transport model, solving
the focused transport equation extended with the effect of particle
drifts in the spatial term. Nominal Parker solar wind configurations of
different speeds and a magnetohydrodynamic (MHD) generated solar wind
containing a corotating interaction region (CIR) were considered. The
latter configuration gives rise to a magnetic bottle structure,
with one bottleneck at the Sun and the other at the CIR. We inject
protons from a fixed source at 0.1 AU, the inner boundary of the MHD
model.
Results: When the drift induced particle net-flux is zero,
the modelled intensity-time profiles obtained at different radial
distances along an IMF line show the same intensity fall-off after
the prompt phase of the particle event, which is in accordance with
the SEP flood phenomenon. However, observers magnetically connected
close to the edges of the particle injection site can experience,
as a result of drifts, a sudden drop in the intensities occurring
at different times for different energies such that no SEP flood
phenomenon is established. In the magnetic bottle structure, this
effect is enhanced due to the presence of magnetic field gradients
strengthening the nominal particle drifts. Moreover, anisotropies can
be large for observers that only receive particles through drifts,
illustrating the importance of pitch-angle dependent 3D particle
modelling. We observe that interplanetary cross-field diffusion
can mitigate the effects of particle drifts.
Conclusions:
Particle drifts can substantially modify the decay phase of SEP events,
especially if the solar wind contains compression regions or shock waves
where the drifts are enhanced. This is, for example, the case for our
CIR solar wind configuration generated with a 3D MHD model, where the
effect of drifts is strong. A similar decay rate in different energy
channels and for different observers requires the mitigation of the
effect of drifts. One way to accomplish this is through interplanetary
cross-field diffusion, suggesting thus a way to determine a minimum
value for the cross-field diffusion strength.
Title: A study of the role of CME-CME interactions on CME
geo-effectiveness with EUHFORIA
Authors: Scolini, C.; Poedts, S.; Rodriguez, L.; Temmer, M.; Dumbovic,
M.; Guo, J.; Veronig, A.; Dissauer, K.; Palmerio, E.; Kilpua, K. E. J.;
Pomoell, J.
Bibcode: 2019AGUFMSH43D3368S
Altcode:
Coronal Mass Ejections (CMEs) are the main source of strong space
weather disturbances at Earth and other locations in the solar
system. While their impact is largely determined by their dynamic
pressure and magnetic field, interactions with other CMEs can
significantly alter their individual characteristics and enhance their
(geo-)effectiveness. As observations in the heliosphere are limited,
investigating such phenomena via physics-based models is therefore
crucial to advance our understanding of complex CME events, and to
assess the prediction capabilities at various locations. Here we
present a comprehensive study of the role of CME-CME interactions on
their (geo-)effectiveness, by performing simulations of complex CME
events with the EUHFORIA heliospheric solar wind and CME propagation
model. As a case study, we consider a sequence of 6 CMEs observed during
the unusually active week of 4-10 September 2017. As their source region
moved on the solar disk due to the rotation, CMEs were launched over
a wide range of longitudes, interacting with each other while paving
the way for the propagation of the following ones. CME signatures were
observed at Mars and at Earth, where intense disturbances and space
weather events were triggered by CME-CME interactions. Using input
parameters derived from multi-spacecraft remote-sensing observations
of CMEs and their source region, we perform global simulations of the
event using the spheromak CME model in EUHFORIA, and we investigate how
their interactions affected the evolution of single CME structures and
the in-situ properties at Earth and Mars. Results from this case
study are complemented by a parametric study of CME-CME interactions,
performed by running a set of simulations varying the initial CME
parameters (e.g. speed, waiting time, magnetic field properties,
density…), with the aim of quantifying the effect of such changes on
their propagation and interaction. Results will benchmark our current
prediction capabilities in the case of complex CME events and provide
insights on their large-scale evolution in the heliosphere.
Title: Developing Fast Solar Wind Modeling with EUHFORIA
Authors: Samara, E.; Magdalenic, J.; Rodriguez, L.; Heinemann, S. G.;
Poedts, S.
Bibcode: 2019AGUFMSH41F3328S
Altcode:
The fast component of the solar wind is very important in terms of space
weather. Upon arrival at Earth (or at other planets) , the solar wind
high speed streams (HSSs) can compress the magnetosphere and generate
geomagnetic storms. Moreover, the HSSs and the background solar wind
influence the propagation of CMEs. This work aims to enhance fast
solar wind modeling with EUHFORIA (EUropean Heliospheric FORecasting
Information Asset) by focusing on two different aspects. First, by
focusing on the properties of the HSS sources, the coronal holes (CHs)
observed at the Sun. A statistical overview between insitu features of
the HSSs as detected by ACE satellite at L1 and the characteristics
of the coronal holes from which they originated, indicate which CH
properties are crucial on forming the fast component of the solar wind
at Earth. The second aspect for developing fast solar wind modeling with
EUHFORIA is to test magnetograms from different providers. Magnetograms
constitute the basic source of information for MHD simulations and
preliminary results indicate that the model's outputs can highly vary
because of them. E valuation of the results and assessment of the
goodness of the model depending on the t wo aforementioned aspects ,
is made.
Title: Improving Modelling Areas of Open-Closed Flux in the Corona
Using Remote Sensing Observations
Authors: Asvestari, E.; Heinemann, S.; Temmer, M.; Pomoell, J.;
Kilpua, K. E. J.; Magdalenic, J.; Poedts, S.
Bibcode: 2019AGUFMSH13A..09A
Altcode:
Modelling the open magnetic field in the heliosphere with high
accuracy is essential for space weather forecasting purposes. Primary
source of open magnetic field are Coronal Holes (CH). Therefore, when
assessing how well we model the open magnetic field one needs to test
how well the model performs on one of its fundamental functions, that
of reconstructing coronal hole areas. For our study, we used EUHFORIA
(European heliospheric forecasting information asset) model which
employs an empirical solar wind model that combines the Potential
Field Source Surface (PFSS) and the Schatten Current Sheet (SCS)
models. Two important free parameters of the PFSS and the SCS models
are the source surface height (the outer boundary of the PFSS) and the
height of the inner boundary of SCS. Although, a commonly used value
for the source surface height is that of 2.5 solar radii, a wider range
of allowed heights ranging from 1.5 to 3.25 solar radii exist. Here, we
investigate the optimal heights that one should preselect in the model
aiming for better reconstruction of open flux areas. We vary the source
surface height within the interval [1.4, 3.2]Rs with a step of 0.1Rs,
and the SCS inner boundary height within the interval [1.3, 2.8]Rs with
the same step, where Rs is one solar radius. The study is applied on 15
CH exhibiting different latitudinal position and geometry. We compare
the modelled open flux areas with CH boundaries extracted using remote
sensing EUV observations and CATCH (Collection of analysis tools for
coronal holes). This study indicates that lower values of the two
boundary heights improve the modelling results. EUV image data from
instruments having a wide field of view, such as SUVI on board GOES-R,
and SWAP on board PROBA2, offer unprecedented possibility to actually
observe the heights below which closed loops exist in the corona,
and therefore further constrain the height choices in the model by
providing a lower limit.
Title: Data-driven and observation-based modeling of CMEs in the
inner heliosphere with EUHFORIA
Authors: Pomoell, J.; Kilpua, K. E. J.; Asvestari, E.; Price, D. J.;
Lumme, E.; Scolini, C.; Good, S.; Palmerio, E.; Verbeke, C.; Poedts, S.
Bibcode: 2019AGUFMSH41A..03P
Altcode:
Characterizing the global magnetic structure of interplanetary
coronal mass ejections (ICMEs) remains a major topic in current
solar-terrestrial physics and space weather research. Understanding
the processes responsible for forming the eruption in the low corona
as well as the subsequent dynamical evolution through the heliosphere
are topics of key importance in order to more accurately characterize
these large-scale structures. In this talk, we present our
progress in developing novel methods to model CMEs from the Sun to
Earth. We present modeling results that use imaging observations of
the corona to constrain simplified models of CMEs employed in the
EUHFORIA inner-heliosphere magnetohydrodynamics model. We also show
recent efforts using an alternative methodology in which data-driven
simulations of active region magnetic fields are used to predict the
magnetic field of the erupting structure. Finally, we discuss what
these novel models imply about the evolution and structure of ICMEs.
Title: Solar energetic particles experience EUHFORIA's CMEs in
PARADISE
Authors: Wijsen, N.; Aran, A.; Pomoell, J.; Poedts, S.
Bibcode: 2019AGUFMSH21B..07W
Altcode:
We present the Particle Radiation Asset Directed at Interplanetary
Space Exploration (PARADISE) model, describing the transport of
solar energetic particles (SEPs) in the heliosphere. Our model
solves the time-dependent five-dimensional focused transport
equation stochastically, by propagating energetic particles in a
solar wind generated by the three-dimensional magnetohydrodynamic
model EUHFORIA. This latter model allows the injection of coronal mass
ejections (CMEs) into the ambient solar wind, by using either a cone or
a spheromak model to describe the CME structure. The coupling between
PARADISE and EUHFORIA permits us to study the effect of a solar wind
that deviates strongly from a nominal Parker-like configuration on the
spatial, pitch-angle and energy dependencies of the energetic particle
distribution function. In this study, we propagate particles in a
solar wind containing a single CME. We investigate to what extent our
model is able to reproduce the typical characteristics of time-intensity
profiles observed during a gradual SEP event by an observer positioned
at Earth or at any other location in the heliosphere. In particular,
we focus on the lower range of the SEP energy spectrum (up to a few
MeV), as these particles may still undergo considerable acceleration
at the CME driven shock in interplanetary space. Moreover, we study
how different particle diffusion conditions near the CME driven shock
and in interplanetary space can influence our results, hereby including
both scattering in pitch-angle and spatial diffusion perpendicular to
the magnetic field.
Title: Modelling the angular response of EPD/EPT: Application to
the electron event observed on 21 April 2019
Authors: Pacheco, D.; Aran, A.; Wijsen, N.; Lario, D.; Agueda, N.;
Gomez-Herrero, R.; Poedts, S.; Sanahuja, B.; Wimmer-Schweingruber,
R. F.; Rodriguez-Pacheco, J.
Bibcode: 2019AGUFMSH21D3305P
Altcode:
Directional information of energetic particle intensities observed by
spacecraft in interplanetary space is of paramount importance both to
understand the particle transport processes undergone by the particles,
in their journey from their acceleration sites to the spacecraft, and
to infer properties of the particle sources (such as their intensity
and duration). Following the same methodology as previously used for
the ACE/EPAM, STEREO/SEPT and Helios/E6 energetic particle instruments,
we have modelled the angular response of the Electron Proton Telescope
(EPT) of the Energetic Particle Detector (EPD) on board Solar
Orbiter. We present here how this instrument would have measured the
pitch angle distributions (PADs) during some events that were detected
by the Helios spacecraft, and that we have already modelled (Pacheco
et al. 2019, an references therein). We found that even though Helios
was a spinning spacecraft that gathered information from eight angular
sectors, the EPT fields of view will often offer similar angular
coverage, obtaining, under specific circumstances, better angular
information than Helios when the interplanetary magnetic field points
away from the ecliptic. Finally, we present the modelling of a solar
energetic electron event measured by the Wind spacecraft on 21 April
2019. During this event, Parker Solar Probe (PSP) was locatedat 0.46 AU
and separated ~60º in longitude from Earth. Operational restrictions
provided just a partial detection of this event by PSP. Our models allow
us to deduce the solar near-relativistic electron injection histories at
the Sun and thus reconstruct, under the assumption of various transport
conditions, what the electron intensity-time profiles will look like
at the position of PSP, and what PADs would have been observed by a
detector such as EPD/EPT. Reference: Pacheco et al., A&A,
624, A3, 17pp (2019)
Title: Assessing the Performance of EUHFORIA Modeling the Background
Solar Wind
Authors: Hinterreiter, Jürgen; Magdalenic, Jasmina; Temmer, Manuela;
Verbeke, Christine; Jebaraj, Immanuel Christopher; Samara, Evangelia;
Asvestari, Eleanna; Poedts, Stefaan; Pomoell, Jens; Kilpua, Emilia;
Rodriguez, Luciano; Scolini, Camilla; Isavnin, Alexey
Bibcode: 2019SoPh..294..170H
Altcode: 2019arXiv190707461H
In order to address the growing need for more accurate space-weather
predictions, a new model named EUHFORIA (EUropean Heliospheric
FORecasting Information Asset) was recently developed. We present
the first results of the performance assessment for the solar-wind
modeling with EUHFORIA and identify possible limitations of its present
setup. Using the basic EUHFORIA 1.0.4 model setup with the default input
parameters, we modeled background solar wind (no coronal mass ejections)
and compared the obtained results with Advanced Composition Explorer
(ACE) in-situ measurements. For the purposes of statistical study we
developed a technique of combining daily EUHFORIA runs into continuous
time series. The combined time series were derived for the years 2008
(low solar activity) and 2012 (high solar activity), from which in-situ
speed and density profiles were extracted. We find for the low-activity
phase a better match between model results and observations compared to
the high-activity time interval considered. The quality of the modeled
solar-wind parameters is found to be rather variable. Therefore, to
better understand the results obtained we also qualitatively inspected
characteristics of coronal holes, i.e. the sources of the studied fast
streams. We discuss how different characteristics of the coronal holes
and input parameters to EUHFORIA influence the modeled fast solar wind,
and suggest possibilities for the improvement of the model.
Title: Effect of the solar wind density on the evolution of normal
and inverse coronal mass ejections
Authors: Hosteaux, S.; Chané, E.; Poedts, S.
Bibcode: 2019A&A...632A..89H
Altcode: 2019arXiv191004680H
Context. The evolution of magnetised coronal mass ejections (CMEs)
and their interaction with the background solar wind leading to
deflection, deformation, and erosion is still largely unclear as
there is very little observational data available. Even so, this
evolution is very important for the geo-effectiveness of CMEs.
Aims: We investigate the evolution of both normal and inverse
CMEs ejected at different initial velocities, and observe the effect
of the background wind density and their magnetic polarity on their
evolution up to 1 AU.
Methods: We performed 2.5D (axisymmetric)
simulations by solving the magnetohydrodynamic equations on a radially
stretched grid, employing a block-based adaptive mesh refinement scheme
based on a density threshold to achieve high resolution following the
evolution of the magnetic clouds and the leading bow shocks. All the
simulations discussed in the present paper were performed using the
same initial grid and numerical methods.
Results: The polarity
of the internal magnetic field of the CME has a substantial effect on
its propagation velocity and on its deformation and erosion during its
evolution towards Earth. We quantified the effects of the polarity
of the internal magnetic field of the CMEs and of the density of
the background solar wind on the arrival times of the shock front
and the magnetic cloud. We determined the positions and propagation
velocities of the magnetic clouds and thus also the stand-off distance
of the leading shock fronts (i.e. the thickness of the magnetic sheath
region) and the deformation and erosion of the magnetic clouds during
their evolution from the Sun to the Earth. Inverse CMEs were found
to be faster than normal CMEs ejected in the same initial conditions,
but with smaller stand-off distances. They also have a higher magnetic
cloud length, opening angle, and mass. Synthetic satellite time series
showed that the shock magnitude is not affected by the polarity of
the CME. However, the density peak of the magnetic cloud is dependent
on the polarity and, in case of inverse CMEs, also on the background
wind density. The magnitude of the z-component of the magnetic field
was not influenced by either the polarity or the wind density.
Title: Spreading protons in the heliosphere: a note on cross-field
diffusion effects
Authors: Wijsen, N.; Aran, A.; Pomoell, J.; Poedts, S.
Bibcode: 2019JPhCS1332a2018W
Altcode: 2019arXiv190800769W
We study how a high-speed solar wind stream embedded in a slow solar
wind affects the transport and energy changes of solar energetic protons
in interplanetary space, assuming different levels of cross-field
diffusion. This is done using a particle transport model that computes
directional particle intensities and first order parallel anisotropies
in a background solar wind generated by the magnetohydrodynamic model
EUHFORIA. In particular, we consider a mono-energetic 4 MeV proton
injection over an extended region located at a heliographic radial
distance of 0.1 AU. By using different values for the perpendicular
proton mean free path, we study how cross-field diffusion may
affect the energetic particle spread and intensity profiles near
a high-speed solar wind stream and a corotating interaction region
(CIR). We find that both a strong cross-field diffusion and a solar
wind rarefaction region are capable of dispersing SEPs efficiently,
producing overall low particle intensities which can in some cases
prevent the SEPs from being detected in-situ, since their intensity
may drop below the detected preevent intensity levels. We also discuss
how accelerated particle populations form on the reverse and forward
shock waves, separated by the stream interface inside the CIR. Under
strong levels of cross-field diffusion, particles cross the SI and
hence both accelerated particle populations merge together.
Title: Reconstructing Coronal Hole Areas With EUHFORIA and Adapted
WSA Model: Optimizing the Model Parameters
Authors: Asvestari, E.; Heinemann, S. G.; Temmer, M.; Pomoell, J.;
Kilpua, E.; Magdalenic, J.; Poedts, S.
Bibcode: 2019JGRA..124.8280A
Altcode: 2019arXiv190703337A
The adopted Wang-Sheeley-Arge (WSA) model embedded in EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) is compared to
EUV observations. According to the standard paradigm, coronal holes are
sources of open flux; thus, we use remote sensing EUV observations and
CATCH (Collection of Analysis Tools for Coronal Holes) to extract CH
areas and compare them to the open flux areas modeled by EUHFORIA. From
the adopted WSA model we employ only the Potential Field Source Surface
(PFSS) model for the inner corona and the Schatten Current Sheet
(SCS) model for the outer (PFSS+SCS). The height, Rss, of
the outer boundary of the PFSS, known as the source surface, and the
height, Ri, of the inner boundary of the SCS are important
parameters affecting the modeled CH areas. We investigate the impact
the two model parameters can have in the modeled results. We vary
Rss within the interval [1.4, 3.2]R⊙ with
a step of 0.1R⊙, and Ri within the interval
[1.3, 2.8]R⊙ with the same step, and the condition that
Ri<Rss. This way we have a set of 184 initial
parameters to the model, and we assess the model results for all these
possible height pairs. We conclude that the default heights used so
far fail in modeling accurately CH areas and lower heights need to
be considered.
Title: Evolution of Coronal Mass Ejection Properties in the Inner
Heliosphere: Prediction for the Solar Orbiter and Parker Solar Probe
Authors: Al-Haddad, Nada; Lugaz, Noé; Poedts, Stefaan; Farrugia,
Charles J.; Nieves-Chinchilla, Teresa; Roussev, Ilia I.
Bibcode: 2019ApJ...884..179A
Altcode: 2019arXiv191004811A
The evolution of the magnetic field and plasma quantities inside a
coronal mass ejection (CME) with distance are known from statistical
studies using data from 1 au monitors, planetary missions, Helios,
and Ulysses. This does not cover the innermost heliosphere, below
0.29 au, where no data are yet publicly available. Here, we describe
the evolution of the properties of simulated CMEs in the inner
heliosphere using two different initiation mechanisms. We compare the
radial evolution of these properties with that found from statistical
studies based on observations in the inner heliosphere by Helios and
MESSENGER. We find that the evolution of the radial size and magnetic
field strength is nearly indistinguishable for twisted flux rope
from that of writhed CMEs. The evolution of these properties is also
consistent with past studies, primarily with recent statistical studies
using in situ measurements and with studies using remote observations
of CMEs.
Title: Whistler instability stimulated by the suprathermal electrons
present in space plasmas
Authors: Lazar, M.; López, R. A.; Shaaban, S. M.; Poedts, S.;
Fichtner, H.
Bibcode: 2019Ap&SS.364..171L
Altcode: 2019arXiv191001506L
In the absence of efficient collisions, deviations from thermal
equilibrium of plasma particle distributions are controlled by the
self-generated instabilities. The whistler instability is a notorious
example, usually responsible for the regulation of electron temperature
anisotropy A = T_{\perp }/T_{allel }> 1 (with \perp , allel
respective to the magnetic field direction) observed in space plasmas,
e.g., solar wind and planetary magnetospheres. Suprathermal electrons
present in these environments change the plasma dispersion and stability
properties, with expected consequences on the kinetic instabilities and
the resulting fluctuations, which, in turn, scatter the electrons and
reduce their anisotropy. In order to capture these mutual effects we
use a quasilinear kinetic approach and PIC simulations, which provide
a comprehensive characterization of the whistler instability under the
influence of suprathermal electrons. Analysis is performed for a large
variety of plasma conditions, ranging from low-beta plasmas encountered
in outer corona or planetary magnetospheres to a high-beta solar
wind characteristic to large heliospheric distances. Enhanced by the
suprathermal electrons, whistler fluctuations stimulate the relaxation
of temperature anisotropy, and this influence of suprathermals increases
with plasma beta parameter.
Title: On Polarization of Solar Decameter Spikes
Authors: Shevchuk, M.; Melnik, V.; Dorovskyy, V.; Brazhenko, A.;
Frantsuzenko, A.; Konovalenko, A.; Poedts, S.; Magdalenic, J.
Bibcode: 2019simi.conf...40S
Altcode:
In the present paper an analysis of the polarization properties of the
solar decameter spikes is performed. We found that decameter spikes
can possess both left and right circular polarization which changes
from 0 up to 100% with an average value 50%.
Title: Particle-in-cell Simulations of the Whistler Heat-flux
Instability in Solar Wind Conditions
Authors: López, R. A.; Shaaban, S. M.; Lazar, M.; Poedts, S.; Yoon,
P. H.; Micera, A.; Lapenta, G.
Bibcode: 2019ApJ...882L...8L
Altcode: 2019arXiv190806666L
In collision-poor plasmas from space, e.g., solar wind or stellar
outflows, the heat flux carried by the strahl or beaming electrons is
expected to be regulated by the self-generated instabilities. Recently,
simultaneous field and particle observations have indeed revealed
enhanced whistler-like fluctuations in the presence of counter-beaming
populations of electrons, connecting these fluctuations to the
whistler heat-flux instability (WHFI). This instability is predicted
only for limited conditions of electron beam-plasmas, and has not
yet been captured in numerical simulations. In this Letter we report
the first simulations of WHFI in particle-in-cell setups, realistic
for the solar wind conditions, and without temperature gradients or
anisotropies to trigger the instability in the initiation phase. The
velocity distributions have a complex reaction to the enhanced
whistler fluctuations conditioning the instability saturation by a
decrease of the relative drifts combined with induced (effective)
temperature anisotropies (heating the core electrons and pitch-angle
and energy scattering the strahl). These results are in good agreement
with a recent quasilinear approach, and support therefore a largely
accepted belief that WHFI saturates at moderate amplitudes. In the
anti-sunward direction the strahl becomes skewed with a pitch-angle
distribution decreasing in width as electron energy increases, which
seems to be characteristic of self-generated whistlers and not to
small-scale turbulence.
Title: A Case for Electron-Astrophysics
Authors: Verscharen, Daniel; Wicks, Robert T.; Alexandrova, Olga;
Bruno, Roberto; Burgess, David; Chen, Christopher H. K.; D'Amicis,
Raffaella; De Keyser, Johan; Dudok de Wit, Thierry; Franci, Luca;
He, Jiansen; Henri, Pierre; Kasahara, Satoshi; Khotyaintsev, Yuri;
Klein, Kristopher G.; Lavraud, Benoit; Maruca, Bennett A.; Maksimovic,
Milan; Plaschke, Ferdinand; Poedts, Stefaan; Reynolds, Chirstopher
S.; Roberts, Owen; Sahraoui, Fouad; Saito, Shinji; Salem, Chadi S.;
Saur, Joachim; Servidio, Sergio; Stawarz, Julia E.; Stverak, Stepan;
Told, Daniel
Bibcode: 2019arXiv190802206V
Altcode:
A grand-challenge problem at the forefront of physics is to understand
how energy is transported and transformed in plasmas. This fundamental
research priority encapsulates the conversion of plasma-flow and
electromagnetic energies into particle energy, either as heat or some
other form of energisation. The smallest characteristic scales, at
which electron dynamics determines the plasma behaviour, are the next
frontier in space and astrophysical plasma research. The analysis of
astrophysical processes at these scales lies at the heart of the field
of electron-astrophysics. Electron scales are the ultimate bottleneck
for dissipation of plasma turbulence, which is a fundamental process
not understood in the electron-kinetic regime. Since electrons are the
most numerous and most mobile plasma species in fully ionised plasmas
and are strongly guided by the magnetic field, their thermal properties
couple very efficiently to global plasma dynamics and thermodynamics.
Title: Quasi-linear approach of the whistler heat-flux instability
in the solar wind
Authors: Shaaban, S. M.; Lazar, M.; Yoon, P. H.; Poedts, S.; López,
R. A.
Bibcode: 2019MNRAS.486.4498S
Altcode: 2019arXiv190308005S; 2019MNRAS.tmp..809S
The hot beaming (or strahl) electrons responsible for the main electron
heat flux in the solar wind are believed to be self-regulated by the
electromagnetic beaming instabilities, also known as the heat-flux
instabilities. Here we report the first quasi-linear theoretical
approach of the whistler unstable branch able to characterize the
long-term saturation of the instability as well as the relaxation of
the electron velocity distributions. The instability saturation is not
solely determined by the drift velocities, which undergo only a minor
relaxation, but mainly from a concurrent interaction of electrons with
whistlers that induces (opposite) temperature anisotropies of the core
and beam populations and reduces the effective anisotropy. These results
might be able to (i) explain the low intensity of the whistler heat-flux
fluctuations in the solar wind (although other explanations remain
possible and need further investigation), and (ii) confirm a reduced
effectiveness of these fluctuations in the relaxation and isotropization
of the electron strahl and in the regulation of the electron heat flux.
Title: Multipoint Observations of the June 2012 Interacting
Interplanetary Flux Ropes
Authors: Kilpua, Emilia K. J.; Good, Simon W.; Palmerio, Erika;
Asvestari, Eleanna; Lumme, Erkka; Ala-Lahti, Matti; Kalliokoski,
Milla M. H.; Morosan, Diana E.; Pomoell, Jens; Price, Daniel J.;
Magdalenić, Jasmina; Poedts, Stefaan; Futaana, Yoshifumi
Bibcode: 2019FrASS...6...50K
Altcode:
In this paper we perform a detailed analysis of interplanetary flux
ropes observed between June 15-17, 2012 at Venus and subsequently
at Earth's Lagrange L1 point, while the observation points were
separated by about 0.28 AU in radial distance and 5° in heliographic
longitude. The flux ropes were associated with coronal mass ejections
(CMEs) that erupted from the Sun on June 12-14, 2012 (SOL2012-06-12,
SOL2012-06-13, and SOL2012-06-14). We examine the CME-CME interactions
by using in-situ observations from the almost radially aligned
spacecraft at Venus and L1, as well as by using heliospheric modelling
and imagery. The June 14 CME reached the June 13 CME near the orbit of
Venus and significant interaction occurred before they both reached
Earth. The shock driven by the June 14 CME propagated through the
June 13 CME and the two CMEs coalesced, creating the signatures of one
large, coherent flux rope at L1. We discuss the origin of the strong
interplanetary magnetic fields related to this sequence of events,
the complexity of interpreting solar wind observations in the case of
multiple interacting CMEs, and the coherence of the identified flux
ropes at different observation points.
Title: The evolution of coronal mass ejections in the inner
heliosphere: Implementing the spheromak model with EUHFORIA
Authors: Verbeke, C.; Pomoell, J.; Poedts, S.
Bibcode: 2019A&A...627A.111V
Altcode:
Aims: We introduce a new model for coronal mass ejections (CMEs)
that has been implemented in the magnetohydrodynamics (MHD) inner
heliosphere model EUHFORIA. Utilising a linear force-free spheromak
(LFFS) solution, the model provides an intrinsic magnetic field
structure for the CME. As a result, the new model has the potential
to predict the magnetic components of CMEs at Earth. In this paper,
we present the implementation of the new model and show the capability
of the new model.
Methods: We present initial validation runs
for the new magnetised CME model by considering the same set of events
as used in the initial validation run of EUHFORIA that employed the
Cone model. In particular, we have focused on modelling the CME that
was responsible for creating the largest geomagnetic disturbance (Dst
index). Two scenarios are discussed: one where a single magnetised CME
is launched and another in which we launch all five Earth-directed
CMEs that were observed during the considered time period. Four out
of the five CMEs were modelled using the Cone model.
Results:
In the first run, where the propagation of a single magnetized CME is
considered, we find that the magnetic field components at Earth are
well reproduced as compared to in-situ spacecraft data. Considering a
virtual spacecraft that is separated approximately seven heliographic
degrees from the position of Earth, we note that the centre of the
magnetic cloud is missing Earth and a considerably larger magnetic
field strength can be found when shifting to that location. For the
second run, launching four Cone CMEs and one LFFS CME, we notice that
the simulated magnetised CME is arriving at the same time as in the
corresponding full Cone model run. We find that to achieve this, the
speed of the CME needs to be reduced in order to compensate for the
expansion of the CME due to the addition of the magnetic field inside
the CME. The reduced initial speed of the CME and the added magnetic
field structure give rise to a very similar propagation of the CME
with approximately the same arrival time at 1 au. In contrast to the
Cone model, however, the magnetised CME is able to predict the magnetic
field components at Earth. However, due to the interaction between the
Cone model CMEs and the magnetised CME, the magnetic field amplitude
is significantly lower than for the run using a single magnetised
CME.
Conclusions: We have presented the LFFS model that is
able to simulate and predict the magnetic field components and the
propagation of magnetised CMEs in the inner heliosphere and at Earth. We
note that shifting towards a virtual spacecraft in the neighbourhood of
Earth can give rise to much stronger magnetic field components. This
gives the option of adding a grid of virtual spacecrafts to give a
range of values for the magnetic field components.
Title: Quasilinear approach of the cumulative whistler instability
in fast solar wind: Constraints of electron temperature anisotropy
Authors: Shaaban, S. M.; Lazar, M.; Yoon, P. H.; Poedts, S.
Bibcode: 2019A&A...627A..76S
Altcode: 2019arXiv190406202S
Context. Solar outflows are a considerable source of free energy that
accumulates in multiple forms such as beaming (or drifting) components,
or temperature anisotropies, or both. However, kinetic anisotropies
of plasma particles do not grow indefinitely and particle-particle
collisions are not efficient enough to explain the observed limits
of these anisotropies. Instead, self-generated wave instabilities
can efficiently act to constrain kinetic anisotropies, but the
existing approaches are simplified and do not provide satisfactory
explanations. Thus, small deviations from isotropy shown by the electron
temperature (T) in fast solar winds are not explained yet.
Aims:
This paper provides an advanced quasilinear description of the whistler
instability driven by the anisotropic electrons in conditions typical
for the fast solar winds. The enhanced whistler-like fluctuations
may constrain the upper limits of temperature anisotropy A ≡
T⊥/T∥ > 1, where ⊥, ∥ are defined
with respect to the magnetic field direction.
Methods: We
studied self-generated whistler instabilities, cumulatively driven
by the temperature anisotropy and the relative (counter)drift of
electron populations, for example, core and halo electrons. Recent
studies have shown that quasi-stable states are not bounded by linear
instability thresholds but an extended quasilinear approach is necessary
to describe these quasi-stable states in this case.
Results:
Marginal conditions of stability are obtained from a quasilinear theory
of cumulative whistler instability and approach the quasi-stable states
of electron populations reported by the observations. The instability
saturation is determined by the relaxation of both the temperature
anisotropy and relative drift of electron populations.
Title: Observation-based modelling of magnetised coronal mass
ejections with EUHFORIA
Authors: Scolini, C.; Rodriguez, L.; Mierla, M.; Pomoell, J.;
Poedts, S.
Bibcode: 2019A&A...626A.122S
Altcode: 2019arXiv190407059S
Context. Coronal mass ejections (CMEs) are the primary source of strong
space weather disturbances at Earth. Their geo-effectiveness is largely
determined by their dynamic pressure and internal magnetic fields, for
which reliable predictions at Earth are not possible with traditional
cone CME models.
Aims: We study two well-observed Earth-directed
CMEs using the EUropean Heliospheric FORecasting Information
Asset (EUHFORIA) model, testing for the first time the predictive
capabilities of a linear force-free spheromak CME model initialised
using parameters derived from remote-sensing observations.
Methods: Using observation-based CME input parameters, we performed
magnetohydrodynamic simulations of the events with EUHFORIA, using the
cone and spheromak CME models.
Results: Simulations show that
spheromak CMEs propagate faster than cone CMEs when initialised with
the same kinematic parameters. We interpret these differences as the
result of different Lorentz forces acting within cone and spheromak
CMEs, which lead to different CME expansions in the heliosphere. Such
discrepancies can be mitigated by initialising spheromak CMEs with a
reduced speed corresponding to the radial speed only. Results at Earth
provide evidence that the spheromak model improves the predictions of
B (Bz) by up to 12-60 (22-40) percentage points compared
to a cone model. Considering virtual spacecraft located within ±10°
around Earth, B (Bz) predictions reach 45-70% (58-78%) of the
observed peak values. The spheromak model shows inaccurate predictions
of the magnetic field parameters at Earth for CMEs propagating away
from the Sun-Earth line.
Conclusions: The spheromak model
successfully predicts the CME properties and arrival time in the case
of strictly Earth-directed events, while modelling CMEs propagating
away from the Sun-Earth line requires extra care due to limitations
related to the assumed spherical shape. The spatial variability of
modelling results and the typical uncertainties in the reconstructed
CME direction advocate the need to consider predictions at Earth and at
virtual spacecraft located around it. Movies are available at https://www.aanda.org
Title: Multipoint Study of Successive Coronal Mass Ejections Driving
Moderate Disturbances at 1 au
Authors: Palmerio, Erika; Scolini, Camilla; Barnes, David; Magdalenić,
Jasmina; West, Matthew J.; Zhukov, Andrei N.; Rodriguez, Luciano;
Mierla, Marilena; Good, Simon W.; Morosan, Diana E.; Kilpua, Emilia
K. J.; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2019ApJ...878...37P
Altcode: 2019arXiv190601353P
We analyze in this work the propagation and geoeffectiveness of four
successive coronal mass ejections (CMEs) that erupted from the Sun
during 2013 May 21-23 and were detected in interplanetary space by
the Wind and/or STEREO-A spacecraft. All these CMEs featured critical
aspects for understanding so-called “problem space weather storms”
at Earth. In the first three events a limb CMEs resulted in moderately
geoeffective in situ structures at their target location in terms of the
disturbance storm time (Dst) index (either measured or estimated). The
fourth CME, which also caused a moderate geomagnetic response, erupted
from close to the disk center as seen from Earth, but it was not
visible in coronagraph images from the spacecraft along the Sun-Earth
line and appeared narrow and faint from off-angle viewpoints. Making
the correct connection between CMEs at the Sun and their in situ
counterparts is often difficult for problem storms. We investigate
these four CMEs using multiwavelength and multipoint remote-sensing
observations (extreme ultraviolet, white light, and radio), aided
by 3D heliospheric modeling, in order to follow their propagation in
the corona and in interplanetary space and to assess their impact at
1 au. Finally, we emphasize the difficulties in forecasting moderate
space weather effects that are provoked by problematic and ambiguous
events and the importance of multispacecraft data for observing and
modeling problem storms.
Title: Comparative analysis of solar radio bursts before and during
CME propagation
Authors: Dididze, G.; Shergelashvili, B. M.; Melnik, V. N.; Dorovskyy,
V. V.; Brazhenko, A. I.; Poedts, S.; Zaqarashvili, T. V.; Khodachenko,
M.
Bibcode: 2019A&A...625A..63D
Altcode: 2019arXiv190312279D
Context. As is well known, coronal mass ejection (CME) propagation often
results in the fragmentation of the solar atmosphere on smaller regions
of density (magnetic field) enhancement (depletion). It is expected
that this type of fragmentation may have radio signatures.
Aims: The general aim of the present paper is to perform a comparative
analysis of type III solar and narrow-band type-III-like radio burst
properties before and during CME events, respectively. The main goal is
to analyze radio observational signatures of the dynamical processes
in solar corona. In particular, we aim to perform a comparison of
local plasma parameters without and with CME propagation, based on the
analysis of decameter radio emission data.
Methods: In order to
examine this intuitive expectation, we performed a comparison of usual
type III bursts before the CME with narrow-band type-III-like bursts,
which are observationally detectable on top of the background type IV
radio bursts associated with CME propagation. We focused on the analysis
of in total 429 type III and 129 narrow-band type-III-like bursts. We
studied their main characteristic parameters such as frequency drift
rate, duration, and instantaneous frequency bandwidth using standard
statistical methods. Furthermore, we inferred local plasma parameters
(e.g., density scale height, emission source radial sizes) using known
definitions of frequency drift, duration, and instantaneous frequency
bandwidth.
Results: The analysis reveals that the physical
parameters of coronal plasma before CMEs considerably differ from
those during the propagation of CMEs (the observational periods 2 and
4 with type IV radio bursts associated with CMEs). Local density radial
profiles and the characteristic spatial scales of radio emission sources
vary with radial distance more drastically during the CME propagation
compared to the cases of quasistatic solar atmosphere without CME(s)
(observational periods 1 and 3).
Conclusions: The results of
the work enable us to distinguish different regimes of plasma state
in the solar corona. Our results create a solid perspective from
which to develop novel tools for coronal plasma studies using radio
dynamic spectra.
Title: Investigating the evolution and interactions of the September
2017 CME events with EUHFORIA
Authors: Scolini, Camilla; Rodriguez, Luciano; Temmer, Manuela; Guo,
Jingnan; Dumbovic, Mateja; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2019shin.confE...1S
Altcode:
Coronal Mass Ejections (CMEs) are the primary source of strong
space weather disturbances at Earth and other locations in the
heliosphere. While their (geo-)effectiveness is largely determined
by their dynamic pressure and magnetic field, phenomena such as
the interaction with other transients (CMEs, CIRs…), or the
pre-conditioning of interplanetary space due to preceding CMEs,
can significantly alter the properties of single CME events and
influence their (geo-)effectiveness. Investigating such phenomena
via physics-based models is crucial to improve our understanding of
interacting CME events, and to assess the prediction capability of
extreme space weather events at various locations in the heliosphere. We present a comprehensive analysis of the CME events that erupted
from AR12673 during the unusually active week of September 4-10,
2017, using the EUHFORIA heliospheric model. As AR12673 rotated on
the solar disk, CMEs were launched over a wide range of longitudes,
interacting with each other and paving the way for the propagation
of following CMEs. CME signatures were observed at both Earth and
Mars, and associated particle events were reported at Earth, Mars,
and STEREO-A. At Earth, an intense geomagnetic storm triggered by
a CME sheath interacting with a preceding ejecta was recorded on
September 8, 2017. Using parameters derived from remote-sensing
and multi-spacecraft observations of the CMEs and their source
region, we simulate the events with both traditional cone CME model,
and with a more realistic flux-rope CME model. We investigate how
CME-CME interactions affect the spatial and temporal evolution of CME
shocks, sheaths and ejecta in the heliosphere, and we compare simulation
results with in-situ measurements at Earth and Mars. This study will not
only benchmark current prediction capabilities in the case of complex
CME events, but will also provide better insights on the large-scale
evolution of complex CME events throughout the heliosphere.
Title: Towards a novel multi-fluid coronal model
Authors: Leitner, Peter; Lani, Andrea; Poedts, Stefaan
Bibcode: 2019shin.confE.153L
Altcode:
Based on data-driven PFSS field extrapolations we model the coronal
plasma within the multifluid approximation up to 0.1 AU where our
solution is intended to provide input for the inlet boundary of
the heliospheric code EUHFORIA (EUropean Heliospheric FORecasting
Information Asset). Our coronal model based on the code COOLFluiD
(Computational Object-Oriented Libraries for Fluid Dynamics) which is
developed at the Von Karman Institute and at KU Leuven will finally be
coupled to EUHFORIA in order to replace the simplistic Wang-Sheeley-Arge
(WSA) model currently employed there. This improvement will be
particularly significant for the simulation of coronal mass ejections
whose emergence needs to modeled accurately already below EUHFORIA's
inlet boundary. We initialize our model with PFSS solutions obtained
by the FVM implemented in COOLFluiD, isotropic density and temperature
profiles and a numerical non-isothermal Parker solar wind solution. Our
MHD relaxations are based on the full unreduced MHD equations solved
for the time being in single-fluid approximation.
Title: Developing fast solar wind modeling with EUHFORIA
Authors: Samara, Evangelia; Magdalenic, Jasmina; Rodriguez, Luciano;
Heinemann, Stephan G.; Poedts, Stefaan
Bibcode: 2019shin.confE..81S
Altcode:
The fast component of the solar wind is very important in terms of space
weather. Upon arrival at Earth (or at other planets), the high speed
streams (HSS) can compress the magnetosphere and generate geomagnetic
storms. Moreover, the HSS and the background solar wind influence the
propagation of CMEs. This work aims to enhance the fast solar wind
modeling with EUHFORIA (EUropean Heliospheric FORecasting Information
Asset) by focusing on two different aspects. First, by focusing on the
properties of their sources, the coronal holes (CHs) observed at the
Sun and by providing a statistical overview of their characteristics
between November 2017-March 2019 during which the minimum of Solar Cycle
24 was still in progress. Second, by testing magnetograms from different
providers. Magnetograms constitute the basic source of information for
MHD simulations and modeling results can be highly variable because
of them. Evaluation of the results and assessment of the goodness of
the model depending on the two aforementioned aspects, is made.
Title: Interplanetary spread of solar energetic protons near a
high-speed solar wind stream
Authors: Wijsen, N.; Aran, A.; Pomoell, J.; Poedts, S.
Bibcode: 2019A&A...624A..47W
Altcode: 2019arXiv190309072W
Aims: We study how a fast solar wind stream embedded in a
slow solar wind influences the spread of solar energetic protons in
interplanetary space. In particular, we aim at understanding how the
particle intensity and anisotropy vary along interplanetary magnetic
field (IMF) lines that encounter changing solar wind conditions
such as the shock waves bounding a corotating interaction region
(CIR). Moreover, we study how the intensities and anisotropies vary as
a function of the longitudinal and latitudinal coordinate, and how the
width of the particle intensities evolves with the heliographic radial
distance. Furthermore, we study how cross-field diffusion may alter
these spatial profiles.
Methods: To model the energetic protons,
we used a recently developed particle transport code that computes
particle distributions in the heliosphere by solving the focused
transport equation (FTE) in a stochastic manner. The particles are
propagated in a solar wind containing a CIR, which was generated by the
heliospheric model, EUHFORIA. We study four cases in which we assume a
delta injection of 4 MeV protons spread uniformly over different regions
at the inner boundary of the model. These source regions have the same
size and shape, yet are shifted in longitude from each other, and are
therefore magnetically connected to different solar wind conditions.
Results: The intensity and anisotropy profiles along selected IMF
lines vary strongly according to the different solar wind conditions
encountered along the field line. The IMF lines crossing the shocks
bounding the CIR show the formation of accelerated particle populations,
with the reverse shock wave being a more efficient accelerator than
the forward shock wave. The longitudinal intensity profiles near the
CIR are highly asymmetric in contrast to the profiles obtained in a
nominal solar wind. For the injection regions that do not cross the
transition zone between the fast and slow solar wind, we observe a steep
intensity drop of several orders of magnitude near the stream interface
(SI) inside the CIR. Moreover, we demonstrate that the longitudinal
width of the particle intensity distribution can increase, decrease,
or remain constant with heliographic radial distance, reflecting
the underlying IMF structure. Finally, we show how the deflection of
the IMF at the shock waves and the compression of the IMF in the CIR
deforms the three-dimensional shape of the particle distribution in
such a way that the original shape of the injection profile is lost.
Title: Solar wind suprathermal particle populations
Authors: Lazar, Marian; Shaaban, Shaaban Mohammed; Lopez, Rodrigo;
Poedts, Stefaan; Fichtner, Horst
Bibcode: 2019EGUGA..2116019L
Altcode:
Suprathermal populations are an ubiquitous and still intriguing
component of plasma particles (electrons, protons and heavier ions)
present in the solar wind and planetary atmospheres. The enhanced
suprathermal tails of the observed velocity (or energy) distributions
deviate significantly from a standard Maxwellian specific to thermal
equilibrium, but are well reproduced by the Kappa power-laws. Recent
advances of Kappa modeling have revealed essential properties of
suprathermal populations suggesting major implications from micro- to
macroscopic scales. We discuss a series of new results which enhance
the interpretation of the existing and forthcoming observational data to
understand key features of the solar wind dynamics, e.g., the origin of
the observed wave fluctuations and their role on differential heating
and acceleration.
Title: Multipoint study of successive CMEs driving moderate
disturbances at 1 AU
Authors: Palmerio, Erika; Scolini, Camilla; Barnes, David; Magdalenic,
Jasmina; West, Matthew; Zhukov, Andrei; Rodriguez, Luciano; Mierla,
Marilena; Good, Simon; Morosan, Diana; Kilpua, Emilia; Pomoell, Jens;
Poedts, Stefaan
Bibcode: 2019EGUGA..2117038P
Altcode:
Coronal mass ejections (CMEs) are the major drivers of space weather
effects at 1 AU. From a forecasting perspective, the most significant
CMEs are those erupting from close to the disc centre (as seen from
Earth or their target location) and fully encompassing the solar
disc in coronagraph imagery. Such CMEs are known as front-sided
full halos. However, geomagnetic activity can be driven also by CMEs
erupting from closer to the solar limb and/or having a narrower width
in coronagraph data. Multipoint analysis can give insights on the
impact and geoeffectiveness of such CMEs. In light of these aspects,
we analyse the propagation of four successive coronal mass ejections
(CMEs) that erupted in May 2013 and hit Earth, the STEREO-A spacecraft,
or both. All the CMEs under study are "problematic" from a space weather
forecasting perspective, since the first three CMEs erupted from the
solar limb as seen from their corresponding target location, whilst the
fourth one erupted from close to the disc centre, but was invisible to
coronagraph images from Earth's viewpoint. Nevertheless, all the events
drove moderate disturbances both at Earth and STEREO-A. We analyse the
kinematics of the four CMEs using a combination of remote-sensing data
from the solar disc, solar corona, and inner heliosphere. Moreover,
we use input parameters from coronagraph reconstructions to forecast
the arrival of the CMEs at 1 AU through the EUropean Heliospheric
FORecasting Information Asset (EUHFORIA) model. Finally, we emphasise
the difficulties in forecasting moderate space weather effects provoked
by problematic and ambiguous events.
Title: On the transport of solar energetic protons near and within
a corotating interaction region
Authors: Wijsen, Nicolas; Aran, Angels; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2019EGUGA..2113003W
Altcode:
When solar energetic particles (SEPs) escape their acceleration
site, they propagate through our solar system, guided by the
interplanetary magnetic field (IMF). Upon impacting a satellite,
SEPs upset the microelectronics and software on board, leading in
some cases to a temporary or permanent failure of the satellite.This
highlights the importance of developing models capable of explaining
and predicting the characteristics of SEP events. In this work we
study how the interplanetary transport of SEPs is affected by the
presence of large-scale plasma structures perturbing a nominal solar
wind configuration. Specifically, we focus on the effects of having a
fast solar wind source near the solar equator, producing a corotating
interaction region (CIR) at low heliographic latitudes. Such a structure
affects the IMF, and as a consequence it alters the SEP trajectories. In
addition, such CIR is bounded by two shock waves that are able to
augment the energy of SEPs through first order Fermi acceleration. We
study these effects by coupling a three-dimensional SEP transport model
to the heliospheric model, EUHFORIA. The latter model solves the ideal
magnetohydrodynamic (MHD) equations, providing realistic solar wind
configuration in the heliosphere. This solar wind is then used by our
particle transport model to solve the focused transport equation in a
stochastic manner, thereby providing SEP distributions in the entire
heliosphere. In particular, we look at how the SEP peak-intensity varies
along a set of pre-selected magnetic field lines that are residing in
varying solar wind conditions. In addition, we illustrate how the 3D
structure of the corotating interaction region deforms the original
injection region substantially. Finally, we have also explored the
efficiency of the CIR pair of shocks at accelerating particles by
injecting a seed population of 50 keV protons in the upstream region of
both the forward and reverse shock waves. We obtain that the reverse
shock accelerates these protons up to 2 MeV in 50 hours, whereas the
forward shock needs∼95 hours to accelerate them to 400 keV.
Title: Investigating the evolution and interactions of the September
2017 CME events with EUHFORIA
Authors: Scolini, Camilla; Rodriguez, Luciano; Temmer, Manuela; Guo,
Jingnan; Dumbovic, Mateja; Pomoell, Jens; Poedts, Stefaan
Bibcode: 2019EGUGA..21.1337S
Altcode:
Coronal Mass Ejections (CMEs) and their Interplanetary counterparts
(ICMEs) are the primary source of strong space weather disturbances at
Earth and other places in the heliosphere. Key parameters determining
the geo-effectiveness of CMEs are their plasma dynamic pressure
and internal magnetic field intensity and orientation. In addition,
phenomena such as the interaction with other CME structures along the
way, or the pre-conditioning of interplanetary (IP) space due to the
passage of previous CMEs, can significantly modify the properties of
single CME events and influence their geo-effectiveness. Therefore,
investigating and modeling such phenomena via physics-based heliospheric
models is crucial in order to assess and improve our space weather
prediction capability in relation to complex CME events. In this regard,
we present a comprehensive analysis of the CME events that erupted from
AR 12673 during the unusually active week of September 4-10, 2017, with
the aim of validating for the first time the prediction capabilities
of the EUHFORIA model in the case of complex CME events. As AR 12673
rotated along with the solar disk, CMEs were launched over a wide
range of longitudes, interacting with each other and paving the way
for the propagation of the following CMEs. Following the eruptions,
ICME-related signatures were observed at both Earth and Mars,
while associated particle events were reported at Earth, Mars, and
STEREO-A. In terms of impact on Earth, an intense geomagnetic storm,
triggered by a strong southward magnetic field associated to an ICME
sheath, was recorded on September 8, 2017. In order to study these
CME-CME interactions and their influence on the geo-effectiveness of
single CMEs, we simulate the events using the EUHFORIA model. With
the intent of preserving a predictive approach, we use kinematic,
geometric and magnetic input parameters for the CMEs as derived from
remote-sensing and multi-spacecraft observations of the CMEs and
their source regions. We model CMEs first using an over-simplified
cone model, and then a more realistic flux- rope model so to quantify
the improvement in the prediction of the interplanetary magnetic field
and CME geo-effectiveness at Earth in the latter case. Furthermore,
we investigate the modelling of CME-CME interactions considering the
spatial and temporal evolution of ICMEs in terms of their shocks,
sheaths and ejecta structures in the heliosphere, and we quantify the
impact of such phenomena on the propagation and evolution of single
CME events. Results from this study will not only benchmark our
current prediction capabilities in the case of complex CME events,
but will also provide better insights on the large-scale evolution
and interaction of complex CME events in the inner heliosphere.
Title: Origin of the two shock waves associated with the September
27/28, 2012 event
Authors: Jebaraj, Immanuel Christopher; Magdalenic, Jasmina; Scolini,
Camilla; Rodriguez, Luciano; Poedts, Stefaan; Kilpua, Emilia; Krupar,
Vratislav; Pomoell, Jens; Temmer, Manuela
Bibcode: 2019EGUGA..2116967J
Altcode:
Coronal mass ejections and flares are solar eruptive phenomena
responsible for space weather activities near Earth. They can
accelerate particles, and generate shock waves which are a threat to
our technologies at Earth and in space. Therefore, predicting shock
arrival at Earth has been an important goal for space weather. Space
based radio observations provide the unique opportunity to track shock
waves in the inner heliosphere. We present the study of CME/flare event
on September 27/28, 2012. The GOES C3.1 flare that originated from NOAA
AR 1577 was associated with a full-halo CME (first seen in SOHO/LASCO
C2 field of view at 23:47) and white light shock wave observed by all
three spacecraft STEREO A, STEREO B, and SOHO. The associated radio
event shows a group of type III bursts and two somewhat unusual type II
bursts with significantly different starting frequencies. To understand
the origin of the two shock waves we performed multi-wavelength study,
and perform radio triangulation to get their source position in the
3D space. For the radio triangulation study, we used goniopolarimetric
measurements from STEREO/WAVES and WIND/WAVES instruments. We also did
data-driven modelling of the CME propagation using EUHFORIA cone model
(EUropean Heliospheric FORecasting Information Asset) and validate
the results by comparison with in-situ data. Results of this study
indicate that, although temporal association between the shock and
the CME is good, the low frequency type II burst occurs significantly
higher in the solar corona than the associated CME and has therefore
unclear origin. To understand the origin of the low frequency type
II burst we studied preceding event at 10:20 UT (STEREO A/COR2) on
September 27, 2012. The radio triangulation study shows that the type
II source positions are in the southern solar hemisphere and thus may
be associated to the type II emissions in the radio event succeeding
it. We therefore discuss different possibilities for the origin of
two type II bursts.
Title: Reconstructing coronal holes with EUHFORIA
Authors: Asvestari, Eleanna; Heinemann, Stephan; Pomoell, Jens;
Temmer, Manuela; Kilpua, Emilia; Magdalenic, Jasmina; Poedts, Stefaan
Bibcode: 2019EGUGA..21.8085A
Altcode:
Modelling accurately the ambient solar wind is important for space
weather forecasting. EUHFORIA (European Heliospheric Forecasting
Information Asset) model employs an empirical solar wind model that is
based on the Wang-Sheeley-Arge model. It combines the Potential Field
Source Surface (PFSS) and the Schatten Current Sheet (SCS) models. In
previous studies it was shown that placing the inner boundary of the
SCS model at a radius, Ri, lower than that of the outer boundary of the
PFSS model, Rii, improves the simulation output. Here, we investigate
the capability of the empirical solar wind model adopted in EUHFORIA
to recreate the geometry and size of coronal holes for a large set of
pairs of PFSS and SCS radii. We vary Rii within the interval [1.4,
3.0]Rs with a step of 0.1Rs, and the Ri within the interval [1.3,
2.8]Rs with the same step size. The study is repeated for 12 coronal
holes of different latitudinal position and geometry. We compare the
modelled coronal holes with boundaries obtained by remote sensing
EUV observations using the CATCH tool (Collection of Analysis Tools
for Coronal Holes). Preliminary results of the study indicate that a
previously defined pair of PFSS and SCS radii results in underestimated
coronal hole sizes. It also indicates that different radii sets give
better results for different types of coronal holes.
Title: Initiation of Stealth CMEs: Clues from Numerical Modelling
and In-Situ Comparisons
Authors: Talpeanu, Dana-Camelia; Zuccarello, Francesco P.; Chané,
Emmanuel; Poedts, Stefaan; D'Huys, Elke; Mierla, Marilena; Roussev,
Ilia
Bibcode: 2019EGUGA..21.1210T
Altcode:
Coronal Mass Ejections (CMEs) are huge expulsions of magnetized plasma
from the Sun into the interplanetary medium. A particular class of
CMEs are the so-called stealth CMEs, i.e., solar eruptions that are
clearly distinguished in coronagraph observations, but they don't
have a clear source signature. Observational studies show that about
60% of stealth CMEs are preceded by another CME whose solar origin
could be identified. In order to determine the triggering mechanism
for stealth CMEs we are using the MPI-AMRVAC code developed at KU
Leuven. We simulate consecutive CMEs ejected from the southernmost
part of an initial configuration constituted by three magnetic arcades
embedded in a globally bipolar magnetic field. The first eruption is
driven through shearing motions at the solar surface. The following
eruption is a stealth CME resulting from the reconnection of the coronal
magnetic field. Both CMEs are expelled into a bimodal solar wind. We
analyse the parameters that contribute to the occurrence of the second
CME. We obtain 3 different eruption scenarios and dynamics by changing
the shearing speed with only 1%. The difference between the 3 cases
consists in the characteristics of the second CME, which can be a failed
eruption, a stealth CME, or a CME with a traceable source. Furthermore,
we compare the simulated signatures of the CMEs with the measured
in-situ data from Messenger and ACE spacecraft and obtain a good
correlation in arrival time and magnetic field components. This study
aims to better understand the triggering mechanism of stealth eruptions
and improve the forecasting of their geomagnetic impact.
Title: Plasma heating by magnetoacoustic wave propagation in the
vicinity of a 2.5D magnetic null-point
Authors: Sabri, S.; Poedts, S.; Ebadi, H.
Bibcode: 2019A&A...623A..81S
Altcode:
Context. Magnetohydrodynamic (MHD) waves have significant potential
as a plasma heating mechanism. Finding a suitable wave dissipation
mechanism is a very tough task, given the many observational constraints
on the models, and this has resulted in the development of an important
research community in solar physics. The magnetic field structure has
an important role in the solar corona heating. Here, we investigate
in detail current sheet mode generation via magnetic reconnection
and mode conversion releases some of the free magnetic energy
and produces heating. In addition, energy conversion is discussed
completely. Moreover, nonlinear effects on density variations and,
in turn, mode conversion are pursued.
Aims: In order to assess
the role of magnetoacoustic waves in plasma heating, we have modeled
in detail a fast magneto-acoustic wave pulse near a magnetic null-point
in a finite plasma-β. The behavior of the propagation and dissipation
of the fast magneto-acoustic wave is investigated in the inhomogeneous
magnetically structured solar corona. Particular attention is given
to the dissipation of waves and coronal heating and energy transfer
in the solar corona, focusing on the energy transfer resulting from
the interaction of fast magneto-acoustic waves with 2.5D magnetic
null-points.
Methods: The shock-capturing Godunov-type PLUTO
code was used to solve the ideal MHD set of equations in the context
of wave-plasma energy transfer.
Results: It is shown that
magneto-acoustic waves could be a viable candidate to contribute
significantly to the heating of the solar corona and maintain the solar
corona at a temperature of a few million degrees. The temperature is
not constant in the corona. Coronal heating occurs near magnetic null
points. It is found that magnetic reconnection, phase mixing and mode
conversion contribute to the heating. Moreover, nonlinear fast and
slow magnetoacoustic waves are decoupled except in β = 1 layer.
Title: Particle-in-cell Simulations of Firehose Instability Driven
by Bi-Kappa Electrons
Authors: López, R. A.; Lazar, M.; Shaaban, S. M.; Poedts, S.; Yoon,
P. H.; Viñas, A. F.; Moya, P. S.
Bibcode: 2019ApJ...873L..20L
Altcode:
We report the first results from particle-in-cell simulations of
the fast-growing aperiodic electron firehose instability driven by
the anisotropic bi-Kappa distributed electrons. Such electrons
characterize space plasmas, e.g., solar wind and planetary
magnetospheres. Predictions made by the linear theory for full
wave-frequency and wave-vector spectra of instabilities are confirmed
by the simulations showing that only the aperiodic branch develops at
oblique angles with respect to the magnetic field direction. Angles
corresponding to the peak magnetic field fluctuating power spectrum
increase with the increase in the anisotropy and with the decrease in
the inverse power-law index κ. The instability saturation and later
nonlinear evolutions are also dominated by the oblique fluctuations,
which are enhanced by the suprathermals and trigger a faster relaxation
of the anisotropic electrons. Diffusion in velocity space is stimulated
by the growing fluctuations, which scatter the electrons, starting
with the more energetic suprathermal populations, as appears already
before the saturation. After saturation the fluctuating magnetic field
power shows decay patterns in the wave-vector space and a shift toward
lower angles of propagation.
Title: Firehose instabilities triggered by the solar wind suprathermal
electrons
Authors: Shaaban, S. M.; Lazar, M.; López, R. A.; Fichtner, H.;
Poedts, S.
Bibcode: 2019MNRAS.483.5642S
Altcode: 2018arXiv181106320S; 2019MNRAS.tmp....1S
In collision-poor plasmas from space, e.g. solar wind, terrestrial
magnetospheres, kinetic instabilities are expected to play a major
role in constraining the temperature anisotropy of plasma particles,
but a definitive answer can be given only after ascertaining
their properties in these environments. This study describes the
full spectrum of electron firehose instabilities in the presence
of suprathermal electron populations which are ubiquitous in
space plasmas. Suprathermal electrons stimulate both the periodic
and aperiodic branches, remarkable being the effects shown by the
aperiodic mode propagating obliquely to the ambient magnetic field
which markedly exceeds the growth rates of the parallel (periodic)
branch reported recently in Lazar et al. Derived exclusively in terms
of the plasma parameters, the anisotropy thresholds of this instability
are also lowered in the presence of suprathermal electrons, predicting
an enhanced effectiveness in the solar wind conditions. These results
may also be relevant in various other astrophysical contexts where the
firehose instabilities involve, e.g. solar flares, sites of magnetic
field reconnection, accretion flows or plasma jets leading to shocks
and co-rotating interactions in the heliosphere, interstellar medium,
and Galaxy clusters.
Title: The Interplay of the Solar Wind Core and Suprathermal
Electrons: A Quasilinear Approach for Firehose Instability
Authors: Shaaban, S. M.; Lazar, M.; Yoon, P. H.; Poedts, S.
Bibcode: 2019ApJ...871..237S
Altcode: 2019arXiv190111406S
In the solar wind an equipartition of kinetic energy densities can
be easily established between thermal and suprathermal electrons and
the instability conditions are markedly altered by the interplay
of these two populations. The new thresholds derived here for the
periodic branch of firehose instability shape the limits of temperature
anisotropy reported by observations for both electron populations. This
instability constraint is particularly important for suprathermal
electrons which, by comparison with thermal populations, are even less
controlled by particle-particle collisions. An extended quasilinear
approach to this instability confirms predictions from linear theory
and unveils the mutual effects of thermal and suprathermal electrons
in the relaxation of their temperature anisotropies and the saturation
of growing fluctuations.
Title: Modelling three-dimensional transport of solar energetic
protons in a corotating interaction region generated with EUHFORIA
Authors: Wijsen, N.; Aran, A.; Pomoell, J.; Poedts, S.
Bibcode: 2019A&A...622A..28W
Altcode: 2019arXiv190109596W
Aims: We introduce a new solar energetic particle (SEP) transport
code that aims at studying the effects of different background solar
wind configurations on SEP events. In this work, we focus on the
influence of varying solar wind velocities on the adiabatic energy
changes of SEPs and study how a non-Parker background solar wind can
trap particles temporarily at small heliocentric radial distances
(≲1.5 AU) thereby influencing the cross-field diffusion of SEPs
in the interplanetary space.
Methods: Our particle transport
code computes particle distributions in the heliosphere by solving the
focused transport equation (FTE) in a stochastic manner. Particles are
propagated in a solar wind generated by the newly developed data-driven
heliospheric model, EUHFORIA. In this work, we solve the FTE, including
all solar wind effects, cross-field diffusion, and magnetic-field
gradient and curvature drifts. As initial conditions, we assume a delta
injection of 4 MeV protons, spread uniformly over a selected region at
the inner boundary of the model. To verify the model, we first propagate
particles in nominal undisturbed fast and slow solar winds. Thereafter,
we simulate and analyse the propagation of particles in a solar wind
containing a corotating interaction region (CIR). We study the particle
intensities and anisotropies measured by a fleet of virtual observers
located at different positions in the heliosphere, as well as the global
distribution of particles in interplanetary space.
Results: The
differential intensity-time profiles obtained in the simulations using
the nominal Parker solar wind solutions illustrate the considerable
adiabatic deceleration undergone by SEPs, especially when propagating
in a fast solar wind. In the case of the solar wind containing a CIR,
we observe that particles adiabatically accelerate when propagating in
the compression waves bounding the CIR at small radial distances. In
addition, for r ≳ 1.5 AU, there are particles accelerated by the
reverse shock as indicated by, for example, the anisotropies and
pitch-angle distributions of the particles. Moreover, a decrease in
high-energy particles at the stream interface (SI) inside the CIR is
observed. The compression/shock waves and the magnetic configuration
near the SI may also act as a magnetic mirror, producing long-lasting
high intensities at small radial distances. We also illustrate how the
efficiency of the cross-field diffusion in spreading particles in the
heliosphere is enhanced due to compressed magnetic fields. Finally,
the inclusion of cross-field diffusion enables some particles to cross
both the forward compression wave at small radial distances and the
forward shock at larger radial distances. This results in the formation
of an accelerated particle population centred on the forward shock,
despite the lack of magnetic connection between the particle injection
region and this shock wave. Particles injected in the fast solar wind
stream cannot reach the forward shock since the SI acts as a diffusion
barrier. Movies associated to Figs. 7 and 8 are available at https://www.aanda.org
Title: The Magnetic Morphology of Magnetic Clouds: Multi-spacecraft
Investigation of Twisted and Writhed Coronal Mass Ejections
Authors: Al-Haddad, N.; Poedts, S.; Roussev, I.; Farrugia, C. J.;
Yu, W.; Lugaz, N.
Bibcode: 2019ApJ...870..100A
Altcode:
We present a study about the structure of the magnetic field inside
coronal mass ejections (CMEs) with consideration of the helicity
property of the magnetic field lines. We perform reconstructions and
fittings of the magnetic field of two simulated CMEs: (1) a CME with
writhed magnetic field lines and minimum twist, and (2) a CME with
a twisted flux rope structure. Our aim is to gain insight into the
structure of the CMEs’ magnetic field through comparing the outcome
of the fitting techniques with the actual structure of the simulated
CMEs. Reconstructions are performed at 12 different locations using
the Grad-Shafranov reconstruction technique and a force-free fitting
technique. These locations correspond to different impact parameters,
as well as different longitudinal planes in the CME “legs.” We
find that a flux rope CME and a writhed CME cannot be distinguished
by comparing the best-fit orientation at different locations. We
also find that the reconstructed shapes and impact parameters may
provide some clues about the presence of substantial writhe. Because
of the difficulty for present codes to detect writhe, we conclude that
reconstruction codes and fitting techniques have to be significantly
improved, by taking into consideration the writhe of the magnetic
field lines.
Title: Suprathermal Spontaneous Emissions in κ-distributed Plasmas
Authors: Lazar, M.; Kim, S.; López, R. A.; Yoon, P. H.; Schlickeiser,
R.; Poedts, S.
Bibcode: 2018ApJ...868L..25L
Altcode:
A suprathermal spectral component is identified in the spontaneous
emissions of κ-distributed plasma populations, ubiquitous in
astrophysical setups. Theoretical power spectra are confirmed
by the simulations and capture the dispersion characteristics
of electrostatic and electromagnetic eigenmodes of a quasi-stable
magnetized plasma. Selectively enhanced by the suprathermal emissions
are the fluctuations of fast modes (e.g., Langmuir, fast magnetosonic,
or the low-wavenumber branches of kinetic Alfvén and Bernstein waves)
induced resonantly by the energetic (suprathermal) particles. These
results have an immediate implication in spectroscopic techniques of
in situ or remote diagnosis for the very hot and dense plasmas, e.g.,
close to the Sun, where direct measurements of plasma particles and
their properties are technically impossible. Contrasting patterns
of suprathermal emissions may confirm the coronal origin of the
suprathermal populations observed in the solar wind.
Title: Association between Tornadoes and Instability of Hosting
Prominences
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz; Kukhianidze,
Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina;
Poedts, Stefaan
Bibcode: 2018csc..confE..20M
Altcode:
We studied the dynamics of all prominence tornadoes detected by the
Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011
January 01 to December 31. In total, 361 events were identified
during the whole year, but only 166 tornadoes were traced until the
end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs
in hosting prominences, 83 (50%) caused failed coronal mass ejections
(CMEs) or strong internal motion in the prominences, and only 3 (2%)
finished their lifetimes without any observed activity. Therefore,
almost all prominence tornadoes lead to the destabilization of their
hosting prominences and half of them trigger CMEs. Consequently,
prominence tornadoes may be used as precursors for CMEs and hence for
space weather predictions.
Title: Initiation of Stealth CMEs: Clues from Numerical Modelling
and In-Situ Comparisons
Authors: Talpeanu, Dana-Camelia; Zuccarello, Francesco P.; Chan\xC3,
Emmanuel; Poedts, Stefaan; D'Huys, Elke; Hosteaux, Skralan; Mierla,
Marilena
Bibcode: 2018csc..confE..14T
Altcode:
Coronal Mass Ejections (CMEs) are huge expulsions of magnetized plasma
from the Sun into the interplanetary medium. Stealth CMEs form a
particular subset of CMEs that despite being clearly distinguished
in coronagraph observations, are not associated with clear eruptive
signatures close to the Sun, such as solar flares, coronal dimmings,
EUV waves, or post-flare loop arcades. Observational studies show that
about 60% of stealth CMEs are preceded by another CME whose solar origin
could be identified. The triggering mechanisms for stealth CMEs are
still not well understood processes and in order to determine them,
we are using the MPI-AMRVAC code developed at KU Leuven. We simulate
consecutive CMEs ejected from the southernmost part of an initial
configuration constituted by three magnetic arcades embedded in a
globally bipolar magnetic field. A first eruption is driven through
shearing motions at the solar surface and the stealth CME follows
it after several hours. Both are expelled into a bimodal solar wind,
varying its speed to match the CMEs arrival time at Earth. We analyze
the parameters that contribute to the occurrence of the second CME and
their value ranges whithin which the eruption happens. Furthermore,
we compare the simulated signatures of the two consecutive CMEs with
the in-situ data from ACE spacecraft at 1AU. The aim of this study is
to better understand the triggering mechanism of stealth eruptions,
leading to an improvement in forecasting of their geomagnetic impact.
Title: Ultrahigh-resolution model of a breakout CME embedded in the
solar wind
Authors: Hosteaux, S.; Chané, E.; Decraemer, B.; Talpeanu, D. -C.;
Poedts, S.
Bibcode: 2018A&A...620A..57H
Altcode:
Aims: We investigate the effect of a background solar wind
on breakout coronal mass ejections, in particular, the effect on the
different current sheets and the flux rope formation process.
Methods: We obtained numerical simulation results by solving the
magnetohydrodynamics equations on a 2.5D (axisymmetric) stretched
grid. Ultrahigh spatial resolution is obtained by applying a solution
adaptive mesh refinement scheme by increasing the grid resolution in
regions of high electrical current, that is, by focussing on the maximum
resolution of the current sheets that are forming. All simulations
were performed using the same initial base grid and numerical schemes;
we only varied the refinement level.
Results: A background wind
that causes a surrounding helmet streamer has been proven to have a
substantial effect on the current sheets that are forming and thus
on the dynamics and topology of the breakout release process. Two
distinct ejections occur: first, the top of the helmet streamer
detaches, and then the central arcade is pinched off behind the top
of the helmet streamer. This is different from the breakout scenario
that does not take the solar wind into account, where only the central
arcade is involved in the eruption. In the new ultrahigh-resolution
simulations, small-scale structures are formed in the lateral current
sheets, which later merge with the helmet streamer or reconnect with
the solar surface. We find that magnetic reconnections that occur at
the lateral breakout current sheets deliver the major kinetic energy
contribution to the eruption and not the reconnection at the so-called
flare current sheet, as was seen in the case without background solar
wind. The movies associated to Figs. 3 and A.1 are available at https://www.aanda.org
Title: Clarifying the solar wind heat flux instabilities
Authors: Shaaban, S. M.; Lazar, M.; Poedts, S.
Bibcode: 2018MNRAS.480..310S
Altcode: 2018arXiv180603947S; 2018MNRAS.tmp.1580S
In the solar wind, electron velocity distributions reveal two
countermoving populations that may induce electromagnetic (EM)
beaming instabilities known as heat flux instabilities. Depending
on plasma parameters two distinct branches of whistler and firehose
instabilities can be excited. These instabilities are invoked in many
scenarios, but their interplay is still poorly understood. An exact
numerical analysis is performed to resolve the linear Vlasov-Maxwell
dispersion and characterize these two instabilities, e.g. growth
rates, wave frequencies, and thresholds, enabling to identify their
dominance for conditions typically experienced in space plasmas. Of
particular interest are the effects of suprathermal Kappa-distributed
electrons that are ubiquitous in these environments. The dominance of
whistler or firehose instability is highly conditioned by the beam-core
relative velocity, core plasma beta, and the abundance of suprathermal
electrons. Derived in terms of relative drift velocity the instability
thresholds show an inverse correlation with the core plasma beta for the
whistler modes, and a direct correlation with the core plasma beta for
the firehose instability. Suprathermal electrons reduce the effective
(beaming) anisotropy inhibiting the firehose modes while the whistler
instability is stimulated.
Title: On the Evolution of Pre-Flare Patterns of a 3-Dimensional
Model of AR 11429
Authors: Korsós, M. B.; Poedts, S.; Gyenge, N.; Georgoulis, M. K.;
Yu, S.; Bisoi, S. K.; Yan, Y.; Ruderman, M. S.; Erdélyi, R.
Bibcode: 2018IAUS..335..294K
Altcode: 2018arXiv180100433K
We apply a novel pre-flare tracking of sunspot groups towards improving
the estimation of flare onset time by focusing on the evolution of the
3D magnetic field construction of AR 11429. The 3D magnetic structure
is based on potential field extrapolation encompassing a vertical
range from the photosphere through the chromosphere and transition
region into the low corona. The basis of our proxy measure of activity
prediction is the so-called weighted horizontal gradient of magnetic
field (WGM) defined between spots of opposite polarities
close to the polarity inversion line of an active region. The temporal
variation of the distance of the barycenter of the opposite polarities
is also found to possess potentially important diagnostic information
about the flare onset time estimation as function of height similar
to its counterpart introduced initially in an application at the
photosphere only in Korsós et al. (2015). We apply the photospheric
pre-flare behavioural patterns of sunspot groups to the evolution of
their associated 3D-constructed AR 11429 as function of height. We found
that at a certain height in the lower solar atmosphere the onset time
may be estimated much earlier than at the photosphere or at any other
heights. Therefore, we present a tool and recipe that may potentially
identify the optimum height for flare prognostic in the solar atmosphere
allowing to improve our flare prediction capability and capacity.
Title: Beaming electromagnetic (or heat-flux) instabilities from
the interplay with the electron temperature anisotropies
Authors: Shaaban, S. M.; Lazar, M.; Yoon, P. H.; Poedts, S.
Bibcode: 2018PhPl...25h2105S
Altcode: 2018arXiv180705178S
In space plasmas, kinetic instabilities are driven by the beaming
(drifting) components and/or the temperature anisotropy of charged
particles. The heat-flux instabilities are known in the literature as
electromagnetic modes destabilized by the electron beams (or strahls)
aligned to the interplanetary magnetic field. A new kinetic approach
is proposed here in order to provide a realistic characterization
of heat-flux instabilities under the influence of electrons with
temperature anisotropy. Numerical analysis is based on the kinetic
Vlasov-Maxwell theory for two electron counter-streaming (core and beam)
populations with temperature anisotropies and stationary, isotropic
protons. The main properties of electromagnetic heat-flux instabilities
are found to be markedly changed by the temperature anisotropy of the
electron beam A b = T ⊥ / T ∥
≠ 1 , leading to stimulation of either the whistler branch if A
b > 1 or the firehose branch for A b < 1 . For
a high temperature anisotropy, whistlers switch from heat-flux to a
standard regime, when their instability is inhibited by the beam.
Title: Modeling Coronal Mass Ejections with EUHFORIA: A Parameter
Study of a magnetized Flux Rope Model
Authors: Verbeke, Christine; Poedts, Stefaan; Pomoell, Jens
Bibcode: 2018shin.confE.192V
Altcode:
Coronal Mass Ejections (CMEs) are one of the big influencers on the
coronal and interplanetary dynamics. Understanding their origin and
evolution from the Sun to the Earth is crucial in order to determine
the impact on our Earth and society. One of the key parameters that
determine the geo-effectiveness of the coronal mass ejection is its
internal magnetic configuration. We present a detailed parameter study
of our implemented magnetized flux rope model where we focus on changes
in the input parameters and how these changes affect the characteristics
of the CME at Earth and their evolution in the heliosphere.
Title: Evolution of twisted waves carrying orbital angular momentum:
Application to the Lorentzian (Kappa) distributed non-gyrotropic
plasmas.
Authors: Arshad, Kashif; Poedts, Stefaan; Lazar, Marian
Bibcode: 2018cosp...42E.126A
Altcode:
Twisted waves are usually characterized as waves carrying orbital
angular momentum (OAM), related to the helicity of the wave front,
i.e. vortices. It is demonstrated experimentally with laser beams
having OAM, that light and matter can interact and exchange angular
momentum. About 10-15 years ago, the OAM (a macroscopic property
of light) was rediscovered that can be also transferred from the
light to a gas or plasma, which opens the door to new experiments
and theoretical studies. The appearance of an azimuthal component is
the new parameter, as compared to non-twisted plasmas, due to the
presence of helical electric field perturbation in the plasma. The
propagation of twisted waves in plasmas is predominantly prescribed
by the longitudinal and azimuthal wave numbers. The longitudinal
wave number reflects the variation in the spatial symmetry while the
varying phase of non- planar helical wave fronts is described by the
azimuthal wave number.The study of twisted waves is influenced by
the many recent investigations of orbital angular momentum and its
relevance for the Alfvénic and magnetic tornadoes, the High Frequency
Active Auroral Research Program (HAARP)ionospheric radar facility and
program to study plasma turbulence in the ionosphere of the Earth,
twisted gravitational waves, ultra intense twisted laser beams,
and quantum entanglement of twisted photons, neutrino physics, and
astrophysics in the radio frequency range. In the optical frequency
range, the variety of potential applications such as ultra-fast optical
communication, quantum computing, microscopy and imaging are already
well known. The observed morphologies of twisted modes are spiral,
ring-like or helical, and may describe many phenomena in astrophysical
and terrestrial environments like spiral galaxies, gravitational waves
around rotating black holes, tornados in the solar corona, cometary
tails, etc.The first kinetic studies of twisted waves were performed
for Maxwellian distributed (thermal) plasmas. It is, however, evident
that most of the space plasmas are not in (local) thermal equilibrium,
especially due to presence of superthermal particles in the tails of
the distribution. The velocity (or energy) distributions of these
plasmas are well reproduced by the generalized Lorentzian or Kappa
distribution function. At present, we have investigated properties of
the twisted waves in unmagnetized plasmas. Therefore, twisted Langmuir
and ion acoustic waves are studied for plasma of Kappa distributed
electrons and Maxwellian distributed protons (ions), as reported by
the observations in various space plasma environments (e.g., the solar
corona, planetary magnetospheres, etc.). The study of twisted waves is
then further extended for the dusty plasmas, as dust is ubiquitous in
astrophysical environment, planetary rings and interplanetary media,
comets, interstellar medium, the Eagle nebula, supernova remnants,
Jupiter's dusty rings and Earths mesosphere. These studies lead to the
prediction of instabilities (growth rates and instability windows) for
twisted waves of different types, e.g. the dust ion acoustic (DIA),
and dust acoustic (DA) twisted waves.Mathematically, twisted modes
are well described by the Laguerre-Gaussian (LG) mode function in
cylindrical coordinates, which decomposes the helical electric field
and the perturbed distribution function into planar and non-planar
components described by the longitudinal and azimuthal wave numbers. The
characteristic system of Vlasov-Poisson equations is derived and solved
to obtain the dielectric function for the twisted waves in the presence
of a helical electric field. The approximative analytical and 'exact'
numerical solutions are derived and analyzed to study the dependence
of Landau damping or growth rates on various parameters like the wave
numbers, drift velocities, temperature ratios, dust charging parameters,
spectral indices, etc. The results are physically interpreted and
their relevance for various applications is discussed.
Title: On the effects of suprathermal populations in dusty plasmas:
The case of dust-ion-acoustic waves
Authors: Lazar, M.; Kourakis, I.; Poedts, S.; Fichtner, H.
Bibcode: 2018P&SS..156..130L
Altcode:
Suprathermal populations with energetic distributions deviating
from a standard Maxwellian are ubiquitous in dusty plasmas from
space environments, as a proof that these systems are out of thermal
equilibrium. The excess of free energy may have important implications
in the relaxation processes by the plasma waves and fluctuations,
as well as in their dissipation. In order to emphasize the effects of
suprathermal populations a new realistic interpretation is proposed
on the basis of an advanced Kappa modeling in accord with the
observations. This article is focused on the kinetic description
of dust-modified ion acoustic (DIA) waves in the presence of
Kappa-distributed (suprathermal) particles. Our methodology follows
closely recent considerations on the structural characteristics of
Kappa distributions, contrasting the high-energy tails enhanced by
the suprathermal populations with the Maxwellian (thermal) core of the
distribution. The effects on DIA waves are found to be highly dependent
on the nature of suprathermal particles: both the wave-frequency
and Landau damping rate are inhibited by the suprathermal electrons,
while the suprathermal ions have an opposite influence.
Title: Modeling Coronal Mass Ejections with EUHFORIA: A Parameter
Study of a magnetized Flux Rope Model
Authors: Verbeke, Christine; Poedts, Stefaan; Pomoell, Jens; Scolini,
Camilla
Bibcode: 2018cosp...42E3532V
Altcode:
Coronal Mass Ejections (CMEs) are one of the big influencers on the
coronal and interplanetary dynamics. Understanding their origin and
evolution from the Sun to the Earth is crucial in order to determine
the impact on our Earth and society. One of the key parameters that
determine the geo-effectiveness of the coronal mass ejection is its
internal magnetic configuration. We present a detailed parameter study
of our implemented magnetized flux rope model where we focus on changes
in the input parameters and how these changes affect the characteristics
of the CME at Earth and their evolution in the heliosphere. Recently,
we have implemented a magnetized flux rope model into the inner
heliosphere model EUHFORIA ('EUropean Heliospheric FORecasting
Information Asset'). EUHFORIA is a magnetohydrodynamical forecasting
model of large-scale dynamics from 0.1 AU up to 2 AU. Coronagraph
observations can be used to constrain the kinematics and morphology
of the flux rope. One of the key parameters, the magnetic field, is
difficult to determine directly from observations. In this work, we
approach the problem by conducting a parameter study in which flux ropes
with varying magnetic configurations are simulated. We have studied
the effect of latitude, longitude, toroidal flux and CME speed in a
previous study. Now we also focus on density, half-width and tilt of
the CME and determine the sensitivity of the CME propagation to those
parameters. These parameters are all closely related and will have an
effect on the propagation in multiple ways. We try to disentangle the
various effects.
Title: Quasi-electrostatic twisted waves in Lorentzian dusty plasmas
Authors: Arshad, Kashif; Lazar, M.; Poedts, S.
Bibcode: 2018P&SS..156..139A
Altcode:
The quasi electrostatic modes are investigated in non thermal dusty
plasma using non-gyrotropic Kappa distribution in the presence of
helical electric field. The Laguerre Gaussian (LG) mode function is
employed to decompose the perturbed distribution function and helical
electric field. The modified dielectric function is obtained for the
dust ion acoustic (DIA) and dust acoustic (DA) twisted modes from the
solution of Vlasov-Poisson equation. The threshold conditions for the
growing modes is also illustrated.
Title: Association between Tornadoes and Instability of Hosting
Prominences
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz V.; Kukhianidze,
Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina M.;
Poedts, Stefaan
Bibcode: 2018ApJ...861..112M
Altcode: 2018arXiv180701345M
We studied the dynamics of all prominence tornadoes detected by the
Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011
January 01 to December 31. In total, 361 events were identified
during the whole year, but only 166 tornadoes were traced until the
end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs
in hosting prominences, 83 (50%) caused failed coronal mass ejections
(CMEs) or strong internal motion in the prominences, and only 3 (2%)
finished their lifetimes without any observed activity. Therefore,
almost all prominence tornadoes lead to the destabilization of their
hosting prominences and half of them trigger CMEs. Consequently,
prominence tornadoes may be used as precursors for CMEs and hence for
space weather predictions.
Title: Three-dimensional modelling of solar energetic particle events
with EUHFORIA
Authors: Wijsen, Nicolas; Poedts, Stefaan; Aran, Angels; Pomoell, Jens
Bibcode: 2018cosp...42E3657W
Altcode:
The main sources of solar energetic particles (SEPs) are shock
waves propagating in front of coronal mass ejections (CMEs) and solar
flares. Once particles escape from their acceleration site, they travel
through the heliosphere, spiralling around the interplanetary magnetic
field-lines. On their voyage through space, they may encounter the
Earth where they can e.g., disrupt the microelectronics of satellites
and produce radiation hazard for astronauts in extravehicular
activity. Therefore, it is crucial to understand and thereby build
models capable of predicting the characteristics of SEP events. The
trajectories followed by SEPs in interplanetary space are determined by
the electromagnetic forces acting on the particles. These forces result
from the presence of magnetic fields in the background solar wind,
which are a combination of the large-scale magnetic field originating
from the sun and small-scale magnetic turbulence due to e.g., Alfvén
waves and meandering field lines. One expects thus the properties of SEP
events to be strongly influenced by the varying conditions of the solar
wind. To study these effects, we developed a three-dimensional (3D)
model for the description of SEP events that couples a new Monte Carlo
particle transport code to the newly developed data-driven heliospheric
model, EUHFORIA. The particle transport code computes heliospheric
SEP distributions by solving the focused transport equation with
perpendicular diffusion in a stochastic manner, whereas EUHFORIA solves
the magnetohydrodynamic (MHD) equations, allowing us to obtain complex
solar wind configurations in which we can propagate the energetic
particles. In this talk, we present the first results of the coupling
of the particle code with EUHFORIA, and in particular we focus on the
effects of different background solar wind and scattering conditions
on SEP events observed at different positions in the heliosphere.
Title: Interferometric Observations of the Quiet Sun at 20 and 25
MHz in May 2014
Authors: Melnik, V. N.; Shepelev, V. A.; Poedts, S.; Dorovskyy, V. V.;
Brazhenko, A. I.; Rucker, H. O.
Bibcode: 2018SoPh..293...97M
Altcode: 2018arXiv180608660M
We present the results of solar observations at 20 and 25 MHz with the
Ukrainian T-shaped Radio telescope of the second modification (UTR-2)
in the interferometric session from 27 May to 2 June 2014. In this
case, the different baselines 225, 450, and 675 m between the sections
of the east-west and north-south arms of UTR-2 were used. On 29 May
2014, strong sporadic radio emission consisting of Type III, Type II,
and Type IV bursts was observed. On other days, there was no solar
radio activity in the decameter range. We discuss the observation
results of the quiet Sun. Fluxes and sizes of the Sun in east-west
and north-south directions were measured. The average fluxes were
1050 - 1100 Jy and 1480 - 1570 Jy at 20 and 25 MHz, respectively. The
angular sizes of the quiet Sun in equatorial and polar directions
were 55' and 49' at 20 MHz and 50'
and 42' at 25 MHz. The brightness temperatures of the radio
emission were Tb=5.1 ×105K and Tb=5.7
×105K at 20 and 25 MHz, respectively.
Title: EUHFORIA: European heliospheric forecasting information asset
Authors: Pomoell, Jens; Poedts, S.
Bibcode: 2018JSWSC...8A..35P
Altcode:
The implementation and first results of the new space weather
forecasting-targeted inner heliosphere model "European heliospheric
forecasting information asset" (EUHFORIA) are presented. EUHFORIA
consists of two major components: a coronal model and a heliosphere
model including coronal mass ejections. The coronal model provides
data-driven solar wind plasma parameters at 0.1 AU by constructing
a magnetic field model of the coronal large-scale magnetic field
and employing empirical relations to determine the plasma state
such as the solar wind speed and mass density. These are then used
as boundary conditions to drive a three-dimensional time-dependent
magnetohydrodynamics model of the inner heliosphere up to 2 AU. CMEs
are injected into the ambient solar wind modeled using the cone model,
with their parameters obtained from fits to imaging observations. In
addition to detailing the modeling methodology, an initial validation
run is presented. The results feature a highly dynamic heliosphere
that the model is able to capture in good agreement with in situ
observations. Finally, future horizons for the model are outlined.
Title: A Versatile Numerical Method for the Multi-Fluid Plasma Model
in Partially- and Fully-Ionized Plasmas
Authors: Alvarez-Laguna, A.; Ozak, N.; Lani, A.; Mansour, N. N.;
Deconinck, H.; Poedts, S.
Bibcode: 2018JPhCS1031a2015A
Altcode:
We present an innovative numerical method that solves for the
multi-fluid plasma equations, including the transport, frictional, and
chemical reactions terms, coupled to full Maxwell’s equations. The
numerical method features a scheme for the electromagnetic field with
a proper scaling for the numerical dissipation, a scheme that solves
flows at all speeds regimes (from subsonic to supersonic), and implicit
time integration to tackle the stiffness of the system. Verification
of the numerical scheme is also presented in a wide variety of plasma
conditions.
Title: Generation and evolution of anisotropic turbulence and related
energy transfer in drifting proton-alpha plasmas
Authors: Maneva, Y. G.; Poedts, S.
Bibcode: 2018A&A...613A..10M
Altcode:
The power spectra of magnetic field fluctuations in the solar wind
typically follow a power-law dependence with respect to the observed
frequencies and wave-numbers. The background magnetic field often
influences the plasma properties, setting a preferential direction for
plasma heating and acceleration. At the same time the evolution of the
solar-wind turbulence at the ion and electron scales is influenced
by the plasma properties through local micro-instabilities and
wave-particle interactions. The solar-wind-plasma temperature and
the solar-wind turbulence at sub- and sup-ion scales simultaneously
show anisotropic features, with different components and fluctuation
power in parallel with and perpendicular to the orientation of the
background magnetic field. The ratio between the power of the magnetic
field fluctuations in parallel and perpendicular direction at the
ion scales may vary with the heliospheric distance and depends on
various parameters, including the local wave properties and nonthermal
plasma features, such as temperature anisotropies and relative drift
speeds. In this work we have performed two-and-a-half-dimensional
hybrid simulations to study the generation and evolution of anisotropic
turbulence in a drifting multi-ion species plasma. We investigate
the evolution of the turbulent spectral slopes along and across the
background magnetic field for the cases of initially isotropic and
anisotropic turbulence. Finally, we show the effect of the various
turbulent spectra for the local ion heating in the solar wind.
Title: The Magnetosphere of the Earth under Sub‑Alfvénic Solar
Wind Conditions as Observed on 24 and 25 May 2002
Authors: Chané, Emmanuel; Saur, Joachim; Raeder, Joachim; Neubauer,
Fritz M.; Poedts, Stefaan
Bibcode: 2018tess.conf30178C
Altcode:
On the 24th and 25th of May 2002, the solar wind density at 1 AU was
so low (lower than 0.1 /cc) that the flow became sub-Alfvénic for
intervals that lasted as long as four hours (the Alfvén Mach number
was as low as 0.4). The Earth magnetosphere dramatically changed:
the bow-shock disappeared and two Alfvén wings formed on the flanks
of the magnetosphere. These Alfvén wings are two structures on both
the East and West side of the Earth's magnetosphere, where the solar
wind plasma was decelerated (the deceleration was 30% in one wing
and 60% in the other) and the magnetic field direction changed. The
Alfvén wings reached an extension of 600 Earth radii. We present
observations of the Geotail spacecraft, which are consistent with
Geotail crossing one of these Alfvén wings multiple times. During
this event, the magnetosphere was geomagnetically extremely quiet,
showed no substorm activity and almost no auroral activity. Global
MHD numerical simulations show that the closed field line region was
very symmetric, extending to 20 Earth radii on the day-side and on the
night-side. Whereas the open field lines became highly asymmetric: the
field lines emanating from the northern hemisphere all pointed along
the dawn Alfvén wing, the field lines from the southern hemisphere
all pointed along the other wing. Since November 28, 1963, there were
16 recorded sub-Alfvénic solar wind intervals, lasting for more than
one hour and caused by low solar wind density. Considering the uneven
data coverage, these events occur, on average, every 2.2 years.
Title: Ultra-high Resolution Model of a Breakout CME Embedded in
the Solar Wind
Authors: Hosteaux, Skralan; Chané, Emmanuel; Decraemer, Bieke;
Talpeanu, Dana; Poedts, Stefaan
Bibcode: 2018tess.conf41105H
Altcode:
Photospheric shearing motions are a possible triggering mechanism
for coronal mass ejections (CMEs) by converting free magnetic energy
into kinetic energy via magnetic reconnection. CMEs that erupt in this
manner are called breakout CMEs. Using a solution-dependent adaptive
mesh refinement scheme, we have performed ultra-high resolution 2.5D
MHD simulations of a breakout CME embedded in a bimodal solar wind. This
research was inspired by the work of Karpen et al (2012) and Guidoni et
al. (2016), which discuss ultra-high resolution simulations of breakout
CMEs but without the presence of a background wind. Our results indicate
that the inclusion of a backround solar wind has a substantial effect
on the global evolution of the CME and on the formation and dynamics
of the small scale structures (magnetic islands) in the current sheets
(CSs). Two distinct ejections are observed, namely first the top of
the helmet streamer detaches and then the central arcade gets pinched
off behind the top of the helmet streamer. We show that the breakout
CS splits into two separate CSs, and magnetic islands formed in these
CSs either merge with the detached helmet streamer of reconnect back
with the solar surface. Analyzing the energy balance, it is found that
magnetic reconnection ocurring at the breakout current sheet is the
main kinetic energy contribution to the eruption and not reconnection
at the flare current sheet. We also show that lowering the refinement
level, though having little effect on the overall evolution of the CME,
is of great impact on the behaviour of the magnetic islands.
Title: Sun-to-Earth simulation of the July 12, 2012 geo-effective
CME with EUHFORIA+OpenGGCM
Authors: Scolini, Camilla; Verbeke, Christine; Chané, Emmanuel;
Zuccarello, Francesco; Poedts, Stefaan; Rodriguez, Luciano; Pomoell,
Jens; Cramer, William D.; Raeder, Joachim; Gopalswamy, Nat
Bibcode: 2018tess.conf10903S
Altcode:
In this work we perform a Sun-to-Earth comprehensive analysis of the
July 12, 2012 CME with the aim of testing the space weather predictive
capabilities of the newly developed EUHFORIA heliospheric model
integrated with a flux rope model. In order to achieve this goal,
we make use of a model chain approach by using EUHFORIA outputs at
Earth as input parameters for the OpenGGCM magnetospheric model. We first reconstruct the CME kinematic parameters by means of single-
and multi- spacecraft reconstruction methods based on coronagraphic and
heliospheric CME observations. The magnetic field-related parameters
of the flux-rope are estimated based on imaging observations of the
photospheric and low coronal source region of the eruption. We then
simulate the event with EUHFORIA, using both a cone and a flux-rope CME
model in order to compare the effect of the different CME kinematical
and magnetic input parameters on simulation results at L1. We compare
simulations outputs with in-situ observations of the Interplanetary
CME and we use them as input for the OpenGGCM model, so to investigate
the magnetospheric response to ICME-driven solar wind perturbations
modelled with EUHFORIA. We study the ICME-driven geomagnetic storm
focusing on the predicted geomagnetic activity and compare it with
actual data records. Finally, we discuss the forecasting capabilities
of such kind of approach and its future improvements.
Title: Sun-to-Earth simulations of geo-effective Coronal Mass
Ejections with EUHFORIA: a heliospheric-magnetospheric model chain
approach
Authors: Scolini, Camilla; Verbeke, Christine; Poedts, Stefaan;
Rodriguez, Luciano; Mierla, Marilena; Pomoell, Jens; Cramer, William;
Raeder, Jimmy; Gopalswamy, Nat
Bibcode: 2018EGUGA..20.6441S
Altcode:
In this work we perform a Sun-to-Earth comprehensive analysis of the
July 12, 2012 CME with the aim of testing the space weather predictive
capabilities of the newly developed EUHFORIA heliospheric model
integrated with a flux rope model. In order to achieve this goal,
we make use of a model chain approach by using EUHFORIA outputs at
Earth as input parameters for the OpenGGCM magnetospheric model. We
first reconstruct the CME kinematic parameters by means of single- and
multi- spacecraft reconstruction methods based on coronagraphic and
heliospheric CME observations. The magnetic field-related parameters
of the flux-rope are estimated based on imaging observations of the
photospheric and low coronal source region of the eruption. We then
simulate the event with EUHFORIA, using both a cone and a flux-rope CME
model in order to compare the effect of the different CME kinematical
and magnetic input parameters on simulation results at L1. We compare
simulations outputs with in-situ observations of the Interplanetary
CME and we use them as input for the OpenGGCM model, so to investigate
the magnetospheric response to ICME-driven solar wind perturbations
modelled with EUHFORIA. We study the ICME-driven geomagnetic storm
focusing on the predicted geomagnetic activity and compare it with
actual data records. Finally, we discuss the forecasting capabilities
of such kind of approach and its future improvements.
Title: Validation of the background solar wind modeled by EUHFORIA
Authors: Hinterreiter, Jürgen; Temmer, Manuela; Verbeke, Christine;
Poedts, Stefaan; Pomoell, Jens; Magdalenic, Jasmina; Scolini, Camilla;
Rodriguez, Luciano; Kilpua, Emili; Asvestari, Eleanna
Bibcode: 2018EGUGA..20.6533H
Altcode:
Nowadays, forecasting the arrival time and the geo-effectiveness of CMEs
and the fast solar wind has become of increasing importance. For that
reason, knowledge of the structure and propagation of the background
solar wind is essential. The testing and validation of the performance
of solar wind models is therefore important to assess their reliability
and to further improve the models. This is done for the EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) model within
the CCSOM (Constraining CMEs and Shocks by Observations and Modelling
throughout the inner heliosphere) project [http://sidc.be/ccsom/]. We
validate the modeled background solar wind by comparing the results to
in-situ measurements, in order to make EUHFORIA ready for scientific
exploitation and operational space weather purposes. For this several
established test methods are applied on i) continuous variables of
the solar wind plasma and magnetic field parameters (speed, density,
pressure, Bz), and ii) binary variables based on specific events such
as the arrival time and impact speed of solar wind high speed streams
(HSS). We present first statistical results covering times of low
(2008) and high (2012) solar activity.
Title: Non-thermal velocity distributions in the solar wind
Authors: Pierrard, Viviane; Lazar, Marian; Moschou, Sofia; Poedts,
Stefaan
Bibcode: 2018EGUGA..20.2950P
Altcode:
Velocity distribution functions of plasma particles measured by
spacecraft in the solar wind generally show non-thermal features,
and especially the presence of enhanced suprathermal tails. Such
distributions can well be fitted by different kinds of velocity
distribution functions, such as a sum of two (bi-)Maxwellians with
different temperatures or with (bi-)Kappa distributions decreasing as
a power law of the velocity. The presence of such suprathermal tails
is general in many other space plasmas, which suggests a universal
mechanism for their formation. Using a kinetic model allowing us to
take into account the effects of non-thermal distributions, we show
that the presence of suprathermal populations in space plasmas has
important consequences concerning particle acceleration and plasma
heating, in particular in the solar corona and the solar wind. The
kinetic approach allows us to consider not only electrons and protons,
but also heavier ions. We compare with the evolution of the solar wind
characteristics using measurements of different spacecraft at increasing
radial distances and show how to optimize the boundary conditions to
use in the solar corona to recover observations for typical cases.
Title: From observational evidence to a consistent theory of
suprathermal populations in the solar wind and terrestrial
magnetosphere
Authors: Lazar, Marian; Fichtner, Horst; Poedts, Stefaan; Shaaban,
Shaaban Mohammed; Pierrard, Viviane
Bibcode: 2018EGUGA..2016841L
Altcode:
Suprathermal populations present in space plasmas (e.g., solar wind,
planetary magnetospheres) are usually described by the Kappa (or κ-)
distribution functions. Standard Maxwellian model cannot reproduce the
high-energy tails of the observed distributions, but it is usually
invoked to describe the bulk (core) of the observed distributions,
and as a contrasting limit (κ →∞) to emphasize the effects
of suprathermal particles. However, this limit must be chosen with
caution, otherwise, as in the vast majority of the existing studies,
the comparison does not have the expected relevance. Only predictions
based a realistic interpretation can be confirmed by the observations.
Title: Kinetic Study of twisted waves in non-Gyrotropic Plasmas
Authors: Arshad, Kashif; Lazar, Marian; Poedts, Stefaan
Bibcode: 2018EGUGA..20.9034A
Altcode:
Twisted waves are usually characterized as the waves carrying
orbital angular momentum (OAM). The characteristic parameter of
orbital angular momentum appears due to presence of helical electric
field. The propagation of twisted waves is predominantly defined
by the longitudinal and azimuthal wave numbers for the unmagnetized
case. The longitudinal wave number reflects the variation in the spatial
symmetry while the varying phase of non-planar helical wave fronts
is shown by the azimuthal wave number. The study of twisted waves is
inspired by the recent investigations of orbital angular momentum,
relevance to the Alfvenic and magnetic tornadoes, High Frequency
Active Auroral Research Program (HAARP) ionospheric radar facility,
twisted gravitational waves, ultra intense twisted laser beams, quantum
entanglement of twisted photons, neutrino physics, and astrophysics
in the radio frequency range. In the optical frequency range, it
has potential application such as ultra- fast optical communication,
quantum computing, microscopy and imaging. The observed morphologies
of such modes are spiral, ring like or helical, which is suitable for
the astrophysical and terrestrial environment like spiral galaxies,
gravitational waves around rotating black holes, solar corona, Cometary
tails etc. Therefore, few years ago, the kinetic study of twisted waves
is made for the Maxwellian distributed plasmas. It is evident from the
literature that Maxwellian distribution is not ideal for most of the
space plasmas due to presence of superthermal particle in the tails of
the energy spectrum and some of laboratory plasmas as well. For this
reason, the non-Maxwellian distributed kinetic modeling is developed by
considering non-gyrotropic Generalized Lorentzian or Kappa distribution
function. In this context, the Landau damping is studied for the
twisted Langmuir and ion acoustic waves. The study of twisted waves
is further extended for the dusty plasmas. As dust is ubiquitous in
astrophysical environment, planetary rings and interplanetary media,
Comets, interstellar medium, Eagle nebula, supernovae remnants,
Jupiter's dusty rings and Earth's mesosphere. These studies lead
to the prediction of instabilities for the dust ion acoustic (DIA),
dust acoustic (DA) twisted waves and their threshold conditions along
with the quasi-electrostatic nature of twisted waves. The solutions of
twisted modes can be well defined by the Laguerre Gaussian (LG) mode
function in cylindrical coordinates, which decomposes the perturbed
distribution function and helical electric field into planar and
non-planar components identified by the longitudinal and azimuthal
wave numbers. The Vlasov-Poisson equation is obtained and solved to
obtain the dielectric function for the twisted waves in the presence of
helical electric field. The analytical and exact numerical solution is
also shown to check the dependence of Landau damping and growth rates
on various parameters like normalized wave numbers, normalized drift
velocities, temperature ratios, dust charging parameters, spectral
indices etc.
Title: Stimulated Mirror Instability From the Interplay of Anisotropic
Protons and Electrons, and their Suprathermal Populations
Authors: Shaaban, S. M.; Lazar, M.; Astfalk, P.; Poedts, S.
Bibcode: 2018JGRA..123.1754S
Altcode:
Mirror instability driven by the temperature anisotropy of protons
can offer a plausible explanation for the mirror-like fluctuations
observed in planetary magnetosheaths. In the present paper we
invoke a realistic kinetic approach which can reproduce nonthermal
features of plasma particles reported by the observations, i.e.,
temperature anisotropies and suprathermal populations. Seeking
accuracy, a numerical analysis is performed using an advanced
code named DSHARK, recently proposed to resolve the linear
dispersion and stability for an arbitrary propagation in bi-Kappa
distributed electron-proton plasmas. The stimulating effect of the
anisotropic bi-Maxwellian electrons reported in Remya et al. (2013, https://doi.org/10.1002/jgra.50091)
is markedly enhanced in the presence of suprathermal electrons described
by the bi-Kappa distribution functions. The influence of suprathermal
protons is more temperate, but overall, present results demonstrate
that these sources of free energy provide natural conditions for a
stimulated mirror instability, more efficient than predicted before and
capable to compete with other instabilities (e.g., the electromagnetic
ion-cyclotron instability) and mechanisms of relaxation.
Title: Evidence for Precursors of the Coronal Hole Jets in Solar
Bright Points
Authors: Bagashvili, Salome R.; Shergelashvili, Bidzina M.; Japaridze,
Darejan R.; Kukhianidze, Vasil; Poedts, Stefaan; Zaqarashvili,
Teimuraz V.; Khodachenko, Maxim L.; De Causmaecker, Patrick
Bibcode: 2018ApJ...855L..21B
Altcode: 2018arXiv180300551B
A set of 23 observations of coronal jet events that occurred in coronal
bright points has been analyzed. The focus was on the temporal evolution
of the mean brightness before and during coronal jet events. In the
absolute majority of the cases either single or recurrent coronal jets
(CJs) were preceded by slight precursor disturbances observed in the
mean intensity curves. The key conclusion is that we were able to
detect quasi-periodical oscillations with characteristic periods from
sub-minute up to 3-4 minute values in the bright point brightness that
precedes the jets. Our basic claim is that along with the conventionally
accepted scenario of bright-point evolution through new magnetic
flux emergence and its reconnection with the initial structure of the
bright point and the coronal hole, certain magnetohydrodynamic (MHD)
oscillatory and wavelike motions can be excited and these can take
an important place in the observed dynamics. These quasi-oscillatory
phenomena might play the role of links between different epochs of the
coronal jet ignition and evolution. They can be an indication of the MHD
wave excitation processes due to the system entropy variations, density
variations, or shear flows. It is very likely a sharp outflow velocity
transverse gradients at the edges between the open and closed field line
regions. We suppose that magnetic reconnections can be the source of
MHD waves due to impulsive generation or rapid temperature variations,
and shear flow driven nonmodel MHD wave evolution (self-heating and/or
overreflection mechanisms).
Title: Halo Coronal Mass Ejections during Solar Cycle 24:
reconstruction of the global scenario and geoeffectiveness
Authors: Scolini, Camilla; Messerotti, Mauro; Poedts, Stefaan;
Rodriguez, Luciano
Bibcode: 2018JSWSC...8A...9S
Altcode: 2017arXiv171205847S; 2018JSWSC...8A..09S
In this study we present a statistical analysis of 53 fast
Earth-directed halo CMEs observed by the SOHO/LASCO instrument
during the period Jan. 2009-Sep. 2015, and we use this CME sample
to test the capabilities of a Sun-to-Earth prediction scheme for CME
geoeffectiveness. First, we investigate the CME association with other
solar activity features by means of multi-instrument observations of
the solar magnetic and plasma properties. Second, using coronagraphic
images to derive the CME kinematical properties at 0.1 AU, we propagate
the events to 1 AU by means of the WSA-ENLIL+Cone model. Simulation
results at Earth are compared with in-situ observations at L1. By
applying the pressure balance condition at the magnetopause and a solar
wind-Kp index coupling function, we estimate the expected magnetospheric
compression and geomagnetic activity level, and compare them with global
data records. The analysis indicates that 82% of the CMEs arrived at
Earth in the next 4 days. Almost the totality of them compressed the
magnetopause below geosynchronous orbits and triggered a geomagnetic
storm. Complex sunspot-rich active regions associated with energetic
flares result the most favourable configurations from which geoeffective
CMEs originate. The analysis of related SEP events shows that 74%
of the CMEs associated with major SEPs were geoeffective. Moreover,
the SEP production is enhanced in the case of fast and interacting
CMEs. In this work we present a first attempt at applying a Sun-to-Earth
geoeffectiveness prediction scheme - based on 3D simulations and solar
wind-geomagnetic activity coupling functions - to a statistical set of
potentially geoeffective halo CMEs. The results of the prediction scheme
are in good agreement with geomagnetic activity data records, although
further studies performing a fine-tuning of such scheme are needed.
Title: Modeling Coronal Mass Ejections with EUHFORIA: A Parameter
Study of the Gibson-Low Flux Rope Model using Multi-Viewpoint
Observations
Authors: Verbeke, C.; Asvestari, E.; Scolini, C.; Pomoell, J.; Poedts,
S.; Kilpua, E.
Bibcode: 2017AGUFMSH52A..02V
Altcode:
Coronal Mass Ejections (CMEs) are one of the big influencers on the
coronal and interplanetary dynamics. Understanding their origin and
evolution from the Sun to the Earth is crucial in order to determine
the impact on our Earth and society. One of the key parameters that
determine the geo-effectiveness of the coronal mass ejection is its
internal magnetic configuration. We present a detailed parameter
study of the Gibson-Low flux rope model. We focus on changes in the
input parameters and how these changes affect the characteristics
of the CME at Earth. Recently, the Gibson-Low flux rope model
has been implemented into the inner heliosphere model EUHFORIA,
a magnetohydrodynamics forecasting model of large-scale dynamics
from 0.1 AU up to 2 AU. Coronagraph observations can be used to
constrain the kinematics and morphology of the flux rope. One of
the key parameters, the magnetic field, is difficult to determine
directly from observations. In this work, we approach the problem by
conducting a parameter study in which flux ropes with varying magnetic
configurations are simulated. We then use the obtained dataset to look
for signatures in imaging observations and in-situ observations in
order to find an empirical way of constraining the parameters related
to the magnetic field of the flux rope. In particular, we focus on
events observed by at least two spacecraft (STEREO + L1) in order to
discuss the merits of using observations from multiple viewpoints in
constraining the parameters.
Title: Sun-to-Earth simulations of geo-effective Coronal Mass
Ejections with EUHFORIA: a heliospheric-magnetospheric model chain
approach
Authors: Scolini, C.; Verbeke, C.; Gopalswamy, N.; Wijsen, N.; Poedts,
S.; Mierla, M.; Rodriguez, L.; Pomoell, J.; Cramer, W. D.; Raeder, J.
Bibcode: 2017AGUFMSH31A2716S
Altcode:
Coronal Mass Ejections (CMEs) and their interplanetary counterparts
are considered to be the major space weather drivers. An accurate
modelling of their onset and propagation up to 1 AU represents a
key issue for more reliable space weather forecasts, and predictions
about their actual geo-effectiveness can only be performed by coupling
global heliospheric models to 3D models describing the terrestrial
environment, e.g. magnetospheric and ionospheric codes in the
first place. In this work we perform a Sun-to-Earth comprehensive
analysis of the July 12, 2012 CME with the aim of testing the space
weather predictive capabilities of the newly developed EUHFORIA
heliospheric model integrated with the Gibson-Low (GL) flux rope
model. In order to achieve this goal, we make use of a model chain
approach by using EUHFORIA outputs at Earth as input parameters for the
OpenGGCM magnetospheric model. We first reconstruct the CME kinematic
parameters by means of single- and multi- spacecraft reconstruction
methods based on coronagraphic and heliospheric CME observations. The
magnetic field-related parameters of the flux rope are estimated based
on imaging observations of the photospheric and low coronal source
regions of the eruption. We then simulate the event with EUHFORIA,
testing the effect of the different CME kinematic input parameters on
simulation results at L1. We compare simulation outputs with in-situ
measurements of the Interplanetary CME and we use them as input for
the OpenGGCM model, so to investigate the magnetospheric response to
solar perturbations. From simulation outputs we extract some global
geomagnetic activity indexes and compare them with actual data records
and with results obtained by the use of empirical relations. Finally,
we discuss the forecasting capabilities of such kind of approach and
its future improvements.
Title: <p>Modelling Solar Energetic Particle Propagation in
Realistic Heliospheric Solar Wind Conditions Using a Combined MHD
and Stochastic Differential Equation Approach
Authors: Wijsen, N.; Poedts, S.; Pomoell, J.
Bibcode: 2017AGUFMSH31B2737W
Altcode:
Solar energetic particles (SEPs) are high energy particles originating
from solar eruptive events. These particles can be energised at
solar flare sites during magnetic reconnection events, or in shock
waves propagating in front of coronal mass ejections (CMEs). These
CME-driven shocks are in particular believed to act as powerful
accelerators of charged particles throughout their propagation
in the solar corona. After escaping from their acceleration site,
SEPs propagate through the heliosphere and may eventually reach our
planet where they can disrupt the microelectronics on satellites in
orbit and endanger astronauts among other effects. Therefore it is
of vital importance to understand and thereby build models capable
of predicting the characteristics of SEP events. The propagation of
SEPs in the heliosphere can be described by the time-dependent focused
transport equation. This five-dimensional parabolic partial differential
equation can be solved using e.g., a finite difference method or by
integrating a set of corresponding first order stochastic differential
equations. In this work we take the latter approach to model SEP
events under different solar wind and scattering conditions. The
background solar wind in which the energetic particles propagate is
computed using a magnetohydrodynamic model. This allows us to study
the influence of different realistic heliospheric configurations on
SEP transport. In particular, in this study we focus on exploring the
influence of high speed solar wind streams originating from coronal
holes that are located close to the eruption source region on the
resulting particle characteristics at Earth. Finally, we discuss our
upcoming efforts towards integrating our particle propagation model
with time-dependent heliospheric MHD space weather modelling.
Title: Kinetic Theory of quasi-electrostatic waves in non-gyrotropic
plasmas
Authors: Arshad, K.; Poedts, S.; Lazar, M.
Bibcode: 2017AGUFMSH31C2751A
Altcode:
The orbital angular momentum (OAM) is a trait of helically phased
light or helical (twisted) electric field. Lasers carrying orbital
angular momentum (OAM) revolutionized many scientific and technological
paradigms like microscopy, imaging and ionospheric radar facility to
analyze three dimensional plasma dynamics in ionosphere, ultra-intense
twisted laser pulses, twisted gravitational waves and astrophysics. This
trend has also been investigated in plasma physics. Laguerre-Gaussian
type solutions are predicted for magnetic tornadoes and Alfvénic
tornadoes which exhibit spiral, split and ring-like morphologies. The
ring shape morphology is ideal to fit the observed solar corona,
solar atmosphere and Earth's ionosphere. The orbital angular momentum
indicates the mediation of electrostatic and electromagnetic waves in
new phenomena like Raman and Brillouin scattering. A few years ago, some
new effects have been included in studies of orbital angular momentum
in plasma regimes such as wave-particle interaction in the presence
of helical electric field. Therefore, kinetic studies are carried
out to investigate the Landau damping of the waves and growth of the
instabilities in the presence helical electric field carrying orbital
angular momentum for the Maxwellian distributed plasmas. Recently,
a well suited approach involving a kappa distribution function has
been adopted to model the twisted space plasmas. This leads to the
development of new theoretical grounds for the study of Lorentzian or
kappa distributed twisted Langmuir, ion acoustic, dust ion acoustic and
dust acoustic modes. The quasi-electrostatic twisted waves have been
studied now for the non-gyrotropic dusty plasmas in the presence of the
orbital angular momentum of the helical electric field using Generalized
Lorentzian or kappa distribution function. The Laguerre-Gaussian (LG)
mode function is employed to decompose the perturbed distribution
function and electric field into planar (longitudinal) and non-planar
(azimuthal) components. The modified Vlasov and Poisson equations
are solved to obtain the dielectric function for quasi-electrostatic
twisted modes the non-gyrotropic dusty plasmas. Some numerical and
graphical analysis is also illustrated for the better understanding
of the twisted non-gyrotropic plasmas.
Title: Shaping the solar wind electron temperature anisotropy by
the interplay of core and suprathermal populations
Authors: Shaaban Hamd, S. M.; Lazar, M.; Poedts, S.; Pierrard, V.;
Štverák
Bibcode: 2017AGUFMSH33A2763S
Altcode:
We present the results of an advanced parametrization of the temperature
anisotropy of electrons in the slow solar wind and the electromagnetic
instabilities resulting from the interplay of their thermal core and
suprathermal halo populations. A large set of observational data (from
the Ulysses, Helios and Cluster missions) is used to parametrize
these components and establish their correlations. Comparative
analysis demonstrates for the first time a particular implication
of the suprathermal electrons which are less dense but hotter than
thermal electrons. The instabilities are significantly stimulated
by the interplay of the core and halo populations, leading to lower
thresholds which shape the observed limits of the temperature anisotropy
for both the core and halo populations. This double agreement strongly
suggests that the selfgenerated instabilities play the major role in
constraining the electron anisotropy.
Title: Nonlinear Evolution of Observed Fast Streams in the Solar
Wind - Micro-instabilities and Energy Exchange between Protons and
Alpha Particles
Authors: Maneva, Y. G.; Poedts, S.
Bibcode: 2017AGUFMSH32A..08M
Altcode:
Non-thermal kinetic components such as deformed velocity distributions,
temperature anisotropies and relative drifts between the multiple ion
populations are frequently observed features in the collisionless fast
solar wind streams near the Earth whose origin is still to be better
understood. Some of the traditional models consider the formation
of the temperature anisotropies through the effect of the solar wind
expansion, while others assume in situ heating and particle acceleration
by local fluctuations, such as plasma waves, or by spacial structures,
such as advected or locally generated current sheets. In this study
we consider the evolution of initial ion temperature anisotropies
and relative drifts in the presence of plasma oscillations, such
as ion-cyclotron and kinetic Alfven waves. We perform 2.5D hybrid
simulations to study the evolution of observed fast solar wind plasma
parcels, including the development of the plasma micro-instabilities,
the field-particle correlations and the energy transfer between
the multiple ion species. We consider two distinct cases of highly
anisotropic and quickly drifting protons which excite ion-cyclotron
waves and of moderately anisotropic slower protons, which co-exist
with kinetic Alfven waves. The alpha particles for both cases are
slightly anisotropic in the beginning and remain anisotropic throughout
the simulation time. Both the imposed magnetic fluctuations and the
initial differential streaming decrease in time for both cases, while
the minor ions are getting heated. Finally we study the effects of the
solar wind expansion and discuss its implications for the nonlinear
evolution of the system.
Title: Solar Illumination Control of the Polar Wind
Authors: Maes, L.; Maggiolo, R.; De Keyser, J.; André, M.; Eriksson,
A. I.; Haaland, S.; Li, K.; Poedts, S.
Bibcode: 2017JGRA..12211468M
Altcode:
Polar wind outflow is an important process through which the ionosphere
supplies plasma to the magnetosphere. The main source of energy driving
the polar wind is solar illumination of the ionosphere. As a result,
many studies have found a relation between polar wind flux densities
and solar EUV intensity, but less is known about their relation to
the solar zenith angle at the ionospheric origin, certainly at higher
altitudes. The low energy of the outflowing particles and spacecraft
charging means it is very difficult to measure the polar wind at high
altitudes. We take advantage of an alternative method that allows
estimations of the polar wind flux densities far in the lobes. We
analyze measurements made by the Cluster spacecraft at altitudes from
4 up to 20 RE. We observe a strong dependence on the solar
zenith angle in the ion flux density and see that both the ion velocity
and density exhibit a solar zenith angle dependence as well. We also
find a seasonal variation of the flux density.
Title: The Magnetosphere of the Earth under Sub-Alfvénic Solar Wind
Conditions as Observed on 24 and 25 May 2002
Authors: Chané, Emmanuel; Saur, Joachim; Raeder, Joachim; Neubauer,
Fritz M.; Maynard, Kristofor M.; Poedts, Stefaan
Bibcode: 2017GMS...230....1C
Altcode:
No abstract at ADS
Title: Statistical properties of coronal hole rotation rates: Are
they linked to the solar interior?
Authors: Bagashvili, S. R.; Shergelashvili, B. M.; Japaridze,
D. R.; Chargeishvili, B. B.; Kosovichev, A. G.; Kukhianidze, V.;
Ramishvili, G.; Zaqarashvili, T. V.; Poedts, S.; Khodachenko, M. L.;
De Causmaecker, P.
Bibcode: 2017A&A...603A.134B
Altcode: 2017arXiv170604464B
Context. The present paper discusses results of a statistical study
of the characteristics of coronal hole (CH) rotation in order to
find connections to the internal rotation of the Sun.
Aims:
The goal is to measure CH rotation rates and study their distribution
over latitude and their area sizes. In addition, the CH rotation rates
are compared with the solar photospheric and inner layer rotational
profiles.
Methods: We study CHs observed within ± 60° latitude
and longitude from the solar disc centre during the time span from
the 1 January 2013 to 20 April 2015, which includes the extended peak
of solar cycle 24. We used data created by the spatial possibilistic
clustering algorithm (SPoCA), which provides the exact location and
characterisation of solar coronal holes using SDO/AIA193 Å channel
images. The CH rotation rates are measured with four-hour cadence
data to track variable positions of the CH geometric centre.
Results: North-south asymmetry was found in the distribution of coronal
holes: about 60 percent were observed in the northern hemisphere and
40 percent were observed in the southern hemisphere. The smallest and
largest CHs were present only at high latitudes. The average sidereal
rotation rate for 540 examined CHs is 13.86( ± 0.05)°/d.
Conclusions: The latitudinal characteristics of CH rotation do
not match any known photospheric rotation profile. The CH angular
velocities exceed the photospheric angular velocities at latitudes
higher than 35-40 degrees. According to our results, the CH rotation
profile perfectly coincides with tachocline and the lower layers of
convection zone at around 0.71 R⊙; this indicates that
CHs may be linked to the solar global magnetic field, which originates
in the tachocline region.
Title: Effect of Radiation on Chromospheric Magnetic Reconnection:
Reactive and Collisional Multi-fluid Simulations
Authors: Alvarez Laguna, A.; Lani, A.; Mansour, N. N.; Deconinck,
H.; Poedts, S.
Bibcode: 2017ApJ...842..117A
Altcode:
We study magnetic reconnection under chromospheric conditions in five
different ionization levels from 0.5% to 50% using a self-consistent
two-fluid (ions + neutrals) model that accounts for compressibility,
collisional effects, chemical inequilibrium, and anisotropic heat
conduction. Results with and without radiation are compared, using
two models for the radiative losses: an optically thin radiation loss
function, and an approximation of the radiative losses of a plasma
with photospheric abundances. The results without radiation show that
reconnection occurs faster for the weakly ionized cases as a result of
the effect of ambipolar diffusion and fast recombination. The tearing
mode instability appears earlier in the low ionized cases and grows
rapidly. We find that radiative losses have a stronger effect than was
found in previous results as the cooling changes the plasma pressure
and the concentration of ions inside the current sheet. This affects
the ambipolar diffusion and the chemical equilibrium, resulting in
thin current sheets and enhanced reconnection. The results quantify
this complex nonlinear interaction by showing that a strong cooling
produces faster reconnections than have been found in models without
radiation. The results accounting for radiation show timescales and
outflows comparable to spicules and chromospheric jets.
Title: Dual Maxwellian-Kappa modeling of the solar wind electrons:
new clues on the temperature of Kappa populations
Authors: Lazar, M.; Pierrard, V.; Shaaban, S. M.; Fichtner, H.;
Poedts, S.
Bibcode: 2017A&A...602A..44L
Altcode: 2017arXiv170301459L
Context. Recent studies on Kappa distribution functions invoked in space
plasma applications have emphasized two alternative approaches that
may assume the temperature parameter either dependent or independent of
the power-index κ. Each of them can obtain justification in different
scenarios involving Kappa-distributed plasmas, but direct evidence
supporting either of these two alternatives with measurements from
laboratory or natural plasmas is not available yet.
Aims: This
paper aims to provide more facts on this intriguing issue from direct
fitting measurements of suprathermal electron populations present in
the solar wind, as well as from their destabilizing effects predicted
by these two alternative approaches.
Methods: Two fitting models
are contrasted, namely, the global Kappa and the dual Maxwellian-Kappa
models, which are currently invoked in theory and observations. The
destabilizing effects of suprathermal electrons are characterized on the
basis of a kinetic approach that accounts for the microscopic details of
the velocity distribution.
Results: In order to be relevant, the
model is chosen to accurately reproduce the observed distributions and
this is achieved by a dual Maxwellian-Kappa distribution function. A
statistical survey indicates a κ-dependent temperature of the
suprathermal (halo) electrons for any heliocentric distance. Only
for this approach are the instabilities driven by the temperature
anisotropy found to be systematically stimulated by the abundance of
suprathermal populations, thus lowering the values of κ-index.
Title: Quasi-oscillatory dynamics observed in ascending phase of
the flare on March 6, 2012
Authors: Philishvili, E.; Shergelashvili, B. M.; Zaqarashvili, T. V.;
Kukhianidze, V.; Ramishvili, G.; Khodachenko, M.; Poedts, S.; De
Causmaecker, P.
Bibcode: 2017A&A...600A..67P
Altcode: 2016arXiv161209562P
Context. The dynamics of the flaring loops in active region (AR) 11429
are studied. The observed dynamics consist of several evolution stages
of the flaring loop system during both the ascending and descending
phases of the registered M-class flare. The dynamical properties
can also be classified by different types of magnetic reconnection,
related plasma ejection and aperiodic flows, quasi-periodic oscillatory
motions, and rapid temperature and density changes, among others. The
focus of the present paper is on a specific time interval during the
ascending (pre-flare) phase.
Aims: The goal is to understand
the quasi-periodic behavior in both space and time of the magnetic loop
structures during the considered time interval.
Methods: We have
studied the characteristic location, motion, and periodicity properties
of the flaring loops by examining space-time diagrams and intensity
variation analysis along the coronal magnetic loops using AIA intensity
and HMI magnetogram images (from the Solar Dynamics Observatory).
Results: We detected bright plasma blobs along the coronal loop during
the ascending phase of the solar flare, the intensity variations
of which clearly show quasi-periodic behavior. We also determined
the periods of these oscillations.
Conclusions: Two different
interpretations are presented for the observed dynamics. Firstly, the
oscillations are interpreted as the manifestation of non-fundamental
harmonics of longitudinal standing acoustic oscillations driven by
the thermodynamically non-equilibrium background (with time variable
density and temperature). The second possible interpretation we provide
is that the observed bright blobs could be a signature of a strongly
twisted coronal loop that is kink unstable.
Title: Kinetic theory of twisted waves: Application to space plasmas
having superthermal population of species
Authors: Arshad, Kashif; Poedts, Stefaan; Lazar, Marian
Bibcode: 2017EGUGA..1919650A
Altcode:
Nowadays electromagnetic (EM) fields have various applications in
fundamental research, communication, and home appliances. Even though,
there are still some subtle features of electromagnetic field known to
us a century ago, yet to be utilized. It is because of the technical
complexities to sense three dimensional electromagnetic field. An
important characteristic of electromagnetic field is its orbital angular
momentum (OAM). The angular momentum consists of two distinct parts;
intrinsic part associated with the wave polarization or spin, and the
extrinsic part associated with the orbital angular momentum (OAM). The
orbital angular momentum (OAM) is inherited by helically phased light
or helical (twisted) electric field. The investigations of Allen on
lasers carrying orbital angular momentum (OAM), has initiated a new
scientific and technological advancement in various growing fields,
such as microscopy and imaging, atomic and nano-particle manipulation,
ultra-fast optical communications, quantum computing, ionospheric radar
facility to observe 3D plasma dynamics in ionosphere, photonic crystal
fibre, OAM entanglement of two photons, twisted gravitational waves,
ultra-intense twisted laser pulses and astrophysics. Recently, the
plasma modes are also investigated with orbital angular momentum. The
production of electron vortex beams and its applications are indicated
by Verbeeck et al. The magnetic tornadoes (rotating magnetic field
structures) exhibit three types of morphology i.e., spiral, ring
and split. Leyser pumped helical radio beam carrying OAM into the
Ionospheric plasma under High Frequency Active Auroral Research Program
(HAARP) and characteristic ring shaped morphology is obtained by the
optical emission spectrum of pumped plasma turbulence. The scattering
phenomenon like (stimulated Raman and Brillouin backscattering) is
observed to be responsible for the interaction between electrostatic
and electromagnetic waves through orbital angular momentum. The
ring shape morphology of a beam with orbital angular momentum (OAM)
is ideal for the observation of solar corona around the sun where the
intensity of the beam is minimum at the center, in solar experiments,
and Earth's ionosphere. The twisted plasma modes carrying OAM are mostly
studied either by the fluid theory or Maxwellian distributed Kinetic
Theory. But most of the space plasmas and some laboratory plasmas
have non-thermal distributions due to super-thermal population of
the plasma particles. Therefore the Kinetic Theory of twisted plasma
modes carrying OAM are recently studied using non-thermal (kappa)
distribution of the super-thermal particles in the presence of the
helical electric field and significant change in the damping rates
are observed by tuning appropriate parameters.
Title: Modeling the Sun-To-Earth Evolution of the Magnetic Structure
of Coronal Mass Ejections with EUHFORIA
Authors: Pomoell, Jens; Kilpua, Emilia; Verbeke, Christine; Lumme,
Erkka; Poedts, Stefaan; Palmerio, Erika; Isavnin, Alexey
Bibcode: 2017EGUGA..1911747P
Altcode:
Unraveling the formation and evolution of coronal mass ejections (CMEs)
from the Sun to Earth remains one of the outstanding goals in current
solar-terrestrial physics and space weather research. In particular,
capturing the dynamical evolution of the magnetic field configuration of
CMEs from initiation to in-situ detection is of key importance in order
to determine the geo-effectiveness of the impinging structure. We are in
the process of developing a data-driven modeling pipeline designed to
advance our capability to accurately model this evolution on a routine
basis. Our modeling scheme consists of two major building-blocks: A
non-potential time-dependent model of the coronal magnetic field driven
by a time-sequence of vector magnetograms and a magnetohydrodynamics
model that computes the dynamics in the inner heliosphere from 0.1 AU
up to the orbit of Mars (EUHFORIA). The two models are coupled using
a flux rope model, wherein coronagraph observations are employed to
constrain the kinematics and morphological parameters of the flux rope,
while the magnetic structure is obtained from the coronal model. In
this work, we present our Sun-to-Earth modeling approach to determine
the evolution of the magnetic field structure of CMEs. In addition,
we showcase results of the modeling using well-observed case studies
and comparisons with in-situ observations and discuss future horizons
for our modeling approach.
Title: Instability constraints for the electron temperature anisotropy
in the slow solar wind. Thermal core vs. suprathermal halo
Authors: Lazar, M.; Shaaban, S. M.; Pierrard, V.; Fichtner, H.;
Poedts, S.
Bibcode: 2017arXiv170405311L
Altcode:
This letter presents the results of an advanced parametrization of
the solar wind electron temperature anisotropy and the instabilities
resulting from the interplay of the (bi-)Maxwellian core and (bi-)Kappa
halo populations in the slow solar wind. A large set of observational
data (from the Ulysses, Helios and Cluster missions) is used to
parametrize these components and establish their correlations. The
instabilities are significantly stimulated in the presence of
suprathermals, and the instability thresholds shape the limits of
the temperature anisotropy for both the core and halo populations
re-stating the incontestable role that the selfgenerated instabilities
can play in constraining the electron anisotropy. These results confirm
a particular implication of the suprathermal electrons which are less
dense but hotter than thermal electrons.
Title: EUHFORIA: a solar wind and CME evolution model
Authors: Poedts, Stefaan; Pomoell, Jens
Bibcode: 2017EGUGA..19.7396P
Altcode:
We present the latest results of the new physics-based
forecasting-targeted inner heliosphere model EUHFORIA
('EUropean Heliospheric FORecasting Information Asset') that
we are developing. EUHFORIA consists of a coronal model and a
magnetohydrodynamic (MHD) heliosphere model with CMEs. The aim of the
baseline coronal model is to produce realistic plasma conditions at the
interface radius r = 0.1 AU between the two models thus providing the
necessary input to the time-dependent, three-dimensional MHD heliosphere
model. It uses GONG synoptic line-of-sight magnetograms as input for a
potential (PFSS) field extrapolation of the low-coronal magnetic field
coupled to a current sheet (CS) model of the extended coronal magnetic
field. The plasma variables at the interface radius are determined by
employing semi-empirical considerations based on the properties of the
PFSS+CS field such as the flux tube expansion factor and distance to
nearest coronal hole. The heliosphere model computes the time-dependent
evolution of the MHD variables from the interface radius typically up
to 2 AU. Coronal mass ejections (CMEs) are injected at the interface
radius using a hydrodynamic cone-like model using parameters constrained
from fits to coronal imaging observations. In order to account for the
modification of the heliosphere due to the presence of earlier CMEs,
the standard run scenario includes CMEs launched five days prior to
the start of the forecast, while the duration of the forecast extends
up to seven days. In addition to presenting results of the modeling,
we will highlight our on-going efforts to advance beyond the baseline
in the forecasting pipeline. In particular we discuss our path towards
using magnetized CMEs, the application of a time-dependent coronal
model as well as modeling the transport of solar energetic particles
(SEPs) in the heliosphere. We also discuss the tests with solution AMR
(Adaptive Mesh Refinement) for the background wind and the evolution
of magnetized CME clouds and shock waves.
Title: Solar signatures and eruption mechanism of the August 14,
2010 coronal mass ejection (CME)
Authors: D'Huys, Elke; Seaton, Daniel B.; De Groof, Anik; Berghmans,
David; Poedts, Stefaan
Bibcode: 2017JSWSC...7A...7D
Altcode: 2017arXiv170108814D
On August 14, 2010 a wide-angled coronal mass ejection (CME) was
observed. This solar eruption originated from a destabilized filament
that connected two active regions and the unwinding of this filament
gave the eruption an untwisting motion that drew the attention
of many observers. In addition to the erupting filament and the
associated CME, several other low-coronal signatures that typically
indicate the occurrence of a solar eruption were associated with this
event. However, contrary to what was expected, the fast CME (v >
900 km s-1) was accompanied by only a weak C4.4 flare. We
investigate the various eruption signatures that were observed for this
event and focus on the kinematic evolution of the filament in order to
determine its eruption mechanism. Had this solar eruption occurred just
a few days earlier, it could have been a significant event for space
weather. The risk of underestimating the strength of this eruption based
solely on the C4.4 flare illustrates the need to include all eruption
signatures in event analyses in order to obtain a complete picture of
a solar eruption and assess its possible space weather impact.
Title: Multi-fluid Modeling of Magnetosonic Wave Propagation in
the Solar Chromosphere: Effects of Impact Ionization and Radiative
Recombination
Authors: Maneva, Yana G.; Alvarez Laguna, Alejandro; Lani, Andrea;
Poedts, Stefaan
Bibcode: 2017ApJ...836..197M
Altcode: 2016arXiv161108439M
In order to study chromospheric magnetosonic wave propagation
including, for the first time, the effects of ion-neutral interactions
in the partially ionized solar chromosphere, we have developed a
new multi-fluid computational model accounting for ionization and
recombination reactions in gravitationally stratified magnetized
collisional media. The two-fluid model used in our 2D numerical
simulations treats neutrals as a separate fluid and considers charged
species (electrons and ions) within the resistive MHD approach
with Coulomb collisions and anisotropic heat flux determined by
Braginskiis transport coefficients. The electromagnetic fields are
evolved according to the full Maxwell equations and the solenoidality
of the magnetic field is enforced with a hyperbolic divergence-cleaning
scheme. The initial density and temperature profiles are similar to
VAL III chromospheric model in which dynamical, thermal, and chemical
equilibrium are considered to ensure comparison to existing MHD models
and avoid artificial numerical heating. In this initial setup we
include simple homogeneous flux tube magnetic field configuration and
an external photospheric velocity driver to simulate the propagation of
MHD waves in the partially ionized reactive chromosphere. In particular,
we investigate the loss of chemical equilibrium and the plasma heating
related to the steepening of fast magnetosonic wave fronts in the
gravitationally stratified medium.
Title: How is the Jovian main auroral emission affected by the
solar wind?
Authors: Chané, E.; Saur, J.; Keppens, R.; Poedts, S.
Bibcode: 2017JGRA..122.1960C
Altcode:
The influence of the solar wind on Jupiter's magnetosphere is
studied via three-dimensional global MHD simulations. We especially
examine how solar wind density variations affect the main auroral
emission. Our simulations show that a density increase in the solar
wind has strong effects on the Jovian magnetosphere: the size of
the magnetosphere decreases, the field lines are compressed on the
dayside and elongated on the nightside (this effect can be seen
even deep inside the magnetosphere), and dawn-dusk asymmetries are
enhanced. Our results also show that the main oval becomes brighter
when the solar wind is denser. But the precise response of the main
oval to such a density enhancement in the solar wind depends on the
local time: on the nightside the main oval becomes brighter, while on
the dayside it first turns slightly darker for a few hours and then
also becomes brighter. Once the density increase in the solar wind
reaches the magnetosphere, the magnetopause moves inward, and in less
than 5 h, a new approximate equilibrium position is obtained. But
the magnetosphere as a whole needs much longer to adapt to the new
solar wind conditions. For instance, the total electrical current
closing in the ionosphere slowly increases during the simulation and
it takes about 60 h to reach a new equilibrium. By then the currents
have increased by as much as 45%.
Title: Properties of groups of solar S-bursts in the decameter band
Authors: Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.;
Brazhenko, A.; Poedts, S.; Rucker, H. O.; Panchenko, M.
Bibcode: 2017pre8.conf..369D
Altcode:
On 9 July 2013 from 5:30 UT till 13:28 UT more than 1000 S-bursts
were recorded by the Ukrainian radio telescope UTR-2 operated in the
frequency band 9-32 MHz. All S-bursts were low intensity events with
an average flux of about 10 s.f.u. and a minimum flux as low as 0.2
s.f.u. which made their detection with small instruments practically
impossible. New methods of observations allowed to retrieve the weakest
S-bursts with fluxes comparable to the background level. The durations
and frequency drift rates of these bursts as well as the dependencies
of these parameters on frequency were found. The obtained results
complement the analysis by Morosan et al. [2015] with data at lowest
frequencies accessible for ground-based observations.
Title: Long-period oscillations of active region patterns:
least-squares mapping on second-order curves
Authors: Dumbadze, G.; Shergelashvili, B. M.; Kukhianidze, V.;
Ramishvili, G.; Zaqarashvili, T. V.; Khodachenko, M.; Gurgenashvili,
E.; Poedts, S.; De Causmaecker, P.
Bibcode: 2017A&A...597A..93D
Altcode: 2016arXiv161001509D
Context. Active regions (ARs) are the main sources of variety in
solar dynamic events. Automated detection and identification tools
need to be developed for solar features for a deeper understanding
of the solar cycle. Of particular interest here are the dynamical
properties of the ARs, regardless of their internal structure and
sunspot distribution.
Aims: We studied the oscillatory dynamics
of two ARs: NOAA 11327 and NOAA 11726 using two different methods of
pattern recognition.
Methods: We developed a novel method of
automated AR border detection and compared it to an existing method
for the proof-of-concept. The first method uses least-squares fitting
on the smallest ellipse enclosing the AR, while the second method
applies regression on the convex hull.
Results: After processing
the data, we found that the axes and the inclination angle of the
ellipse and the convex hull oscillate in time. These oscillations
are interpreted as the second harmonic of the standing long-period
kink oscillations (with the node at the apex) of the magnetic flux
tube connecting the two main sunspots of the ARs. We also found that
the inclination angles oscillate with characteristic periods of 4.9
h in AR 11726 and 4.6 h in AR 11327. In addition, we discovered that
the lengths of the pattern axes in the ARs oscillate with similar
characteristic periods and these oscillations might be ascribed to
standing global flute modes.
Conclusions: In both ARs we have
estimated the distribution of the phase speed magnitude along the
magnetic tubes (along the two main spots) by interpreting the obtained
oscillation of the inclination angle as the standing second harmonic
kink mode. After comparing the obtained results for fast and slow
kink modes, we conclude that both of these modes are good candidates
to explain the observed oscillations of the AR inclination angles,
as in the high plasma β regime the phase speeds of these modes
are comparable and on the order of the Alfvén speed. Based on the
properties of the observed oscillations, we detected the appropriate
depth of the sunspot patterns, which coincides with estimations made
by helioseismic methods. The latter analysis can be used as a basis
for developing a magneto-seismological tool for ARs.
Title: Firehose constraints of the bi-Kappa-distributed electrons:
a zero-order approach for the suprathermal electrons in the solar wind
Authors: Lazar, M.; Shaaban, S. M.; Poedts, S.; Štverák, Š.
Bibcode: 2017MNRAS.464..564L
Altcode: 2016MNRAS.tmp.1443L
The increase of temperature predicted by the solar wind expansion
in the direction parallel to the interplanetary magnetic field is
already notorious for not being confirmed by the observations. In
hot and dilute plasmas from space, particle-particle collisions are
not efficient in constraining large deviations from isotropy, but the
resulting firehose instability provides itself plausible limitations
for the temperature anisotropy of both the electron and proton
species. This paper takes into discussion the suprathermal (halo)
electrons, which are ubiquitous in the solar wind, and may be highly
anisotropic and susceptible to the firehose instability. Suprathermals
enhance the high-energy tails of the velocity distributions making
them well described by the Kappa distribution functions, with the
advantage that these are power laws suitable to reproduce either the
entire distribution or only the suprathermal halo tails. New features
of the instability are captured from a linear stability analysis of
bi-Kappa-distributed electrons with the temperature depending on the
power-index κ. This approach enables a realistic interpretation of
non-thermal electrons and their effects on the instability: growth
rates are systematically stimulated and thresholds are lowered with
decreasing the power-index κ. In a zero-order limiting approach of the
halo component (minimizing the effects of a cooler and less anisotropic
core population), the instability thresholds align to the limits of
the temperature anisotropy reported by the observations. These results
provide new and valuable support for an extended implication of the
firehose instability in the relaxation of temperature anisotropy in
collisionless plasmas from space.
Title: Shaping the solar wind temperature anisotropy by the interplay
of electron and proton instabilities
Authors: Shaaban, S. M.; Lazar, M.; Poedts, S.; Elhanbaly, A.
Bibcode: 2017Ap&SS.362...13S
Altcode: 2016arXiv161201012S
A variety of nonthermal characteristics like kinetic, e.g., temperature,
anisotropies and suprathermal populations (enhancing the high energy
tails of the velocity distributions) are revealed by the in-situ
observations in the solar wind indicating quasistationary states of
plasma particles out of thermal equilibrium. Large deviations from
isotropy generate kinetic instabilities and growing fluctuating
fields which should be more efficient than collisions in limiting
the anisotropy (below the instability threshold) and explain the
anisotropy limits reported by the observations. The present paper
aims to decode the principal instabilities driven by the temperature
anisotropy of electrons and protons in the solar wind, and contrast
the instability thresholds with the bounds observed at 1 AU for the
temperature anisotropy. The instabilities are characterized using linear
kinetic theory to identify the appropriate (fastest) instability in
the relaxation of temperature anisotropies A_{e,p} = T_{e,p,perp}/
T _{e,p,allel} ≠1. The analysis focuses on the electromagnetic
instabilities driven by the anisotropic protons (Ap
lessgtr1) and invokes for the first time a dynamical model to capture
the interplay with the anisotropic electrons by correlating the effects
of these two species of plasma particles, dominant in the solar wind. ;
Title: Data-Driven Modeling of the Coronal Magnetic Field: Comparing
Time-Dependent Magnetofrictional Modeling and Nonlinear Force-free
Field Extrapolations
Authors: Pomoell, J.; Lumme, E.; Kilpua, E.; Verbeke, C.; Poedts,
S.; Palmerio, E.; Isavnin, A.
Bibcode: 2016AGUFMSH12B..03P
Altcode:
Accurate modeling of the coronal magnetic field is of key importance for
advancing our understanding of the processes governing the initiation
of coronal mass ejections and their potential for causing severe space
weather. Currently, the most popular models employed in a data-driven
event-based context are time-independent, such as the nonlinear
force-free field (NLFFF) model. From a space-weather perspective,
however, such modeling might not be sufficient, as time-dependent
effects such as rotation, kinking or deflection of the erupting
structure can alter the geo-effectivity of the eruption. In this work,
we employ a time-dependent data-driven magnetofriction-based coronal
model that we have recently developed along with NLFFF modeling. We
study how a time-sequence of NLFFF extrapolations compares to a
time-dependent magnetofrictional computation that is driven by an
electric field inverted from a sequence of photospheric measurements. We
employ both synthetic test cases as well as study well-observed
eruptions. In particular, we focus on discussing the merits of the
two approaches for use in a space weather prediction pipeline.
Title: Solar wind driven instability with non-Maxwellian distribution
functions
Authors: Ehsan, Z.; Poedts, S.; Vranjes, J.; Arshad, K.; Shah, H. A.;
Bourdin, P. A.
Bibcode: 2016AGUFMSH21D2558E
Altcode:
In plasmas with an electron drift current relative to static ions, ion
acoustic waves are subject to the kinetic instability. The instability
threshold however, when one quasi-neutral electron-ion plasma propagates
through another static target plasma, may be well below the ion
acoustic speed of the static plasma. Such a currentless instability
may frequently be driven by the solar wind when it permeates through
another plasma in space. Such kinetic instabilities were previously
studied in the framework of thermodynamically stable plasmas obeying
a Maxwellian behavior. Recently, it has become possible to construct
the distribution function from the empirical data, which is found to
deviate from the Maxwellian due to the presence of high energy tails
and shoulders in the profile of the distribution functions. Here we
study a situation where non-Maxwellian (Lorentzian or kappa) solar
wind plasma interacts with another relatively slow plasma, and then
excites a kinetic instability in the acoustic mode. As a special case,
we also discuss the presence of interstellar dust and discuss dispersion
properties and growth rates of ion/dust acoustic modes quantitatively.
Title: Twofluid Simulations of Propagation of Slow and ALFVÉN Waves
in the Partially Ionized Solar Chromosphere
Authors: Maneva, Y. G.; Poedts, S.; Alvarez Laguna, A.; Lani, A.
Bibcode: 2016AGUFMSH14B..04M
Altcode:
Ion-neutral interactions play crucial role in the energetics and
dynamics of the partially ionized solar chromosphere. To study
the effect of neutrals for the evolution of the chromospheric
plasma, including the transport coefficients, chemical reactions
and possible contribution to wave damping and absorption, we have
developed a multi-fluid simulation tool, which considers ionization
and recombination processes in gravitationally stratified magnetized
collisional media. Recent works have suggested that the vastly dominant
neutrals might over-damp Alfvén waves in the chromosphere, thus
absorbing their energy closer to the solar surface and reducing the
contribution of Alfvén waves generated by the photospheric drivers
to the coronal heating problem. In this study we have driven slow
magnetosonic and Alfvén waves at the photosphere and have followed
their evolution through the chromosphere towards the transition
region. We have investigated the wave energy transfer related to shock
formation, wave absorption and mode conversion in the gravitationally
stratified media, as well as have the distribution of Poynting flux. Our
two-fluid model consists of resistive MHD electrons and ions, which
are chemically and collisionally coupled to a separate fluid population
of neutral hydrogen. The model takes into account Coulomb collisions,
anisotropic heat flux determined by Braginskii's transport coefficients,
as well as impact ionization and radiative recombination. The initial
state represents gravitationally stratified temperature and density
profiles, which satisfy hydrostatic chemical equilibrium, except for
the Lorentz force associated with the external magnetic field. We
study the effects of the initial driver's amplitude and period on the
related plasma energization, as well as the wave-induced changes in
ionization and recombination.
Title: Three-Fluid collisional and reactive magnetic reconnection
with radiative effects in chromospheric conditions
Authors: Alvarez Laguna, A.; Ozak, N. O.; Maneva, Y. G.; Lani, A.;
Kosovichev, A. G.; Mansour, N. N.; Poedts, S.
Bibcode: 2016AGUFMSH21E2566A
Altcode:
The partially ionized chomosphere hosts the interplay of complex
physical phenomena, i.e., collisional processes, non-chemical
equilibrium conditions and non-LTE radiation effects, etc. We study the
magnetic reconnection in different ionization levels under chromospheric
conditions for a multi-fluid, compressible, collisional and reactive
model. We will extend previous work that considers two-fluid models
(plasma + neutrals), to a three-fluid model accounting for electron
dynamics. The model includes chemical reactions of ionization,
recombination and charge exchange collisions. The transport fluxes
consider the anisotropy introduced by the magnetic field in the charged
species. The radiative losses, that are known to play an important role
in the chromosphere, are modeled with an effectively thin radiation
loss function, fitting a three-level Hydrogen atom. In a set of 2-D
computational simulations, we study different ionization levels from
0.5% to 50%, with fixed Lundquist number, analyzing the radiation
effects on the tearing mode instability.
Title: Kinetic Features Observed in the Solar Wind Electron
Distributions
Authors: Pierrard, V.; Lazar, M.; Poedts, S.
Bibcode: 2016AGUFMSH51D2606P
Altcode:
More than 120 000 of velocity distributions measured by Helios,
Cluster and Ulysses in the ecliptic have been analyzed within an
extended range of heliocentric distances from 0.3 to over 4 AU. The
velocity distribution of electrons reveal a dual structure with a
thermal (Maxwellian) core and a suprathermal (Kappa) halo. A detailed
observational analysis of these two components provides estimations
of their temperatures and temperature anisotropies, and we decode any
potential interdependence that their properties may indicate. The
core temperature is found to decrease with the radial distance,
while the halo temperature slightly increases, clarifying an apparent
contradiction in previous observational analysis and providing valuable
clues about the temperature of the Kappa-distributed populations. For
low values of the power-index kappa, these two components manifest a
clear tendency to deviate from isotropy in the same direction, that
seems to confirm the existence of mechanisms with similar effects
on both components, e.g., the solar wind expansion, or the particle
heating by the fluctuations. However, the existence of plasma states
with anti-correlated anisotropies of the core and halo populations and
the increase of their number for high values of the power-index kappa
suggest a dynamic interplay of these components, mediated most probably
by the anisotropy-driven instabilities. Estimating the temperature
of the solar wind particles and their anisotropies is particularly
important for understanding the origin of these deviations from thermal
equilibrium as well as their effects.
Title: Evolution of Anisotropic Turublence in Drifting Proton-Alpha
Plasma - 2.5D Hybrid Simulations
Authors: Maneva, Y. G.; Poedts, S.; Vinas, A. F.
Bibcode: 2016AGUFMSH44A..08M
Altcode:
In-situ measurements from various solar wind spacecraft indicate the
presence of anisotropic turbulence with different spectral slopes
of the magnetic field power spectra in parallel and perpendicular
directions with respect to the orientation of the background magnetic
field. Furthermore, both the parallel and the perpendicular energy
spectra steepen as we reach the dissipation range and we observe
multiple spectral breaks at the ion scales and beyond. The turbulent
dissipation of magnetic field fluctuations at the sub-ion scales is
believed to go into local ion heating and acceleration, so that the
spectral breaks are typically associated with particle energization. The
gained energy can be in the form of anisotropic heating, formation of
non-thermal features in the particle velocity distributions functions,
and redistribution of the differential acceleration between the
different ion populations. To study the relation between the evolution
of the anisotropic turbulent spectra and the particle heating at the ion
and sub-ion scales we perform a series of 2.5D hybrid simulations in
a drifting proton-alpha plasma. We neglect the fast electron dynamics
and treat the electrons as an isothermal fluid electrons, whereas the
protons and the minor population of alpha particles are evolved in a
fully kinetic manner. We start with a given wave spectrum and study
the evolution of the magnetic field spectral slopes as a function of
the parallel and perpendicular wave-numbers. Simultaneously, we track
the particle response and the energy exchange between the parallel
and perpendicular scales in the presence of drifting proton-alpha
population in the collisionless solar wind plasma. The results of
the study show anisotropic behavior of the turbulent power spectra
with steeper slopes along the magnetic field and slower dissipation
in perpendicular direction.
Title: Two-fluid Modeling of Drift Waves in the Solar Atmosphere
Authors: Ozak, N. O.; Alvarez Laguna, A.; Maneva, Y. G.; Poedts, S.
Bibcode: 2016AGUFMSH21E2575O
Altcode:
Wave heating models relying on MHD simulations are commonly used by
solar physicists in the attempt to solve the solar corona heating
problem. However, the MHD equations leave out many important phenomena
that arise from the separate motion of the electrons and ions in
the plasma. In the present work, we develop a 2.5D electron + ion
two-fluid model to investigate the development of drift waves due to
inhomogeneities in the plasma. Specifically, we explore the possibility
of plasma heating by drift waves in solar corona and chromosphere. The
MHD approach is not applicable for modeling drift waves, as they
require separate computations of ion and electron motion. Hence,
our two-fluid model is the first of its kind applied to the study
of drift waves in larger scales. We explore the effect of the scale
of the density inhomogeneity as a driver of the drift waves. Lastly,
we include collisions in the model to study the drift wave instability
and consequent transport effects.
Title: Mixing the Solar Wind Proton and Electron Scales: Effects
of Electron Temperature Anisotropy on the Oblique Proton Firehose
Instability
Authors: Maneva, Y.; Lazar, M.; Viñas, A.; Poedts, S.
Bibcode: 2016ApJ...832...64M
Altcode:
The double adiabatic expansion of the nearly collisionless solar wind
plasma creates conditions for the firehose instability to develop and
efficiently prevent the further increase of the plasma temperature
in the direction parallel to the interplanetary magnetic field. The
conditions imposed by the firehose instability have been extensively
studied using idealized approaches that ignore the mutual effects
of electrons and protons. Recently, more realistic approaches have
been proposed that take into account the interplay between electrons
and protons, unveiling new regimes of the parallel oscillatory
modes. However, for oblique wave propagation the instability develops
distinct branches that grow much faster and may therefore be more
efficient than the parallel firehose instability in constraining the
temperature anisotropy of the plasma particles. This paper reports
for the first time on the effects of electron plasma properties on the
oblique proton firehose (PFH) instability and provides a comprehensive
vision of the entire unstable wave-vector spectrum, unifying the
proton and the smaller electron scales. The plasma β and temperature
anisotropy regimes considered here are specific for the solar wind
and magnetospheric conditions, and enable the electrons and protons to
interact via the excited electromagnetic fluctuations. For the selected
parameters, simultaneous electron and PFH instabilities can be observed
with a dispersion spectrum of the electron firehose (EFH) extending
toward the proton scales. Growth rates of the PFH instability are
markedly boosted by the anisotropic electrons, especially in the oblique
direction where the EFH growth rates are orders of magnitude higher.
Title: The Electron Temperature and Anisotropy in the Solar
Wind. Comparison of the Core and Halo Populations
Authors: Pierrard, V.; Lazar, M.; Poedts, S.; Štverák, Š.;
Maksimovic, M.; Trávníček, P. M.
Bibcode: 2016SoPh..291.2165P
Altcode: 2016arXiv160308392P; 2016SoPh..tmp..121P
Estimating the temperature of solar wind particles and their
anisotropies is particularly important for understanding the origin
of their deviations from thermal equilibrium and the effects this
has. In the absence of energetic events, the velocity distribution
of electrons reveals a dual structure with a thermal (Maxwellian)
core and a suprathermal (kappa) halo. This article presents a
detailed observational analysis of these two components, providing
estimations of their temperatures and temperature anisotropies,
and decoding any potential interdependence that their properties
may indicate. The dataset used in this study includes more than 120
000 of the distributions measured by three missions in the ecliptic
within an extended range of heliocentric distances from 0.3 to over 4
AU. The core temperature is found to decrease with the radial distance,
while the halo temperature slightly increases, clarifying an apparent
contradiction in previous observational analyses and providing valuable
clues about the temperature of the kappa-distributed populations. For
low values of the power-index kappa, these two components manifest a
clear tendency to deviate from isotropy in the same direction, which
seems to confirm the existence of mechanisms with similar effects
on both components, e.g., the solar wind expansion, or the particle
heating by the fluctuations. However, the existence of plasma states
with anticorrelated anisotropies of the core and halo populations
and the increase in their number for high values of the power-index
kappa suggest a dynamic interplay of these components, mediated,
most probably, by the anisotropy-driven instabilities.
Title: A small mission concept to the Sun-Earth Lagrangian L5 point
for innovative solar, heliospheric and space weather science
Authors: Lavraud, B.; Liu, Y.; Segura, K.; He, J.; Qin, G.; Temmer,
M.; Vial, J. -C.; Xiong, M.; Davies, J. A.; Rouillard, A. P.; Pinto,
R.; Auchère, F.; Harrison, R. A.; Eyles, C.; Gan, W.; Lamy, P.;
Xia, L.; Eastwood, J. P.; Kong, L.; Wang, J.; Wimmer-Schweingruber,
R. F.; Zhang, S.; Zong, Q.; Soucek, J.; An, J.; Prech, L.; Zhang,
A.; Rochus, P.; Bothmer, V.; Janvier, M.; Maksimovic, M.; Escoubet,
C. P.; Kilpua, E. K. J.; Tappin, J.; Vainio, R.; Poedts, S.; Dunlop,
M. W.; Savani, N.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard, T.;
DeForest, C.; Webb, D.; Lugaz, N.; Fuselier, S. A.; Dalmasse, K.;
Tallineau, J.; Vranken, D.; Fernández, J. G.
Bibcode: 2016JASTP.146..171L
Altcode:
We present a concept for a small mission to the Sun-Earth Lagrangian L5
point for innovative solar, heliospheric and space weather science. The
proposed INvestigation of Solar-Terrestrial Activity aNd Transients
(INSTANT) mission is designed to identify how solar coronal magnetic
fields drive eruptions, mass transport and particle acceleration that
impact the Earth and the heliosphere. INSTANT is the first mission
designed to (1) obtain measurements of coronal magnetic fields from
space and (2) determine coronal mass ejection (CME) kinematics with
unparalleled accuracy. Thanks to innovative instrumentation at a vantage
point that provides the most suitable perspective view of the Sun-Earth
system, INSTANT would uniquely track the whole chain of fundamental
processes driving space weather at Earth. We present the science
requirements, payload and mission profile that fulfill ambitious science
objectives within small mission programmatic boundary conditions.
Title: Interferometer Observations of Solar Type III Bursts by the
Radio Telescope UTR-2
Authors: Melnik, V.; Shepelev, V.; Brazhenko, A.; Dorovskyy, V.;
Rucker, H.; Poedts, S.
Bibcode: 2016simi.conf...23M
Altcode:
Results of solar radio emission observations by the radio telescopes
UTR-2 (Kharkiv, Ukraine) and URAN-2 (Poltava, Ukraine) in May-June 2014
are discussed. Observations by the radio telescope UTR-2 were carried
out in the interferometer mode using West-East arm of the UTR-2 with
bases 225 m, 450 m and 675 m on May 29 and North-South arm with bases
208 m, 416 m, 624 m, 885 m, 1301m and 1509 m on June 2 at frequencies
20 MHz and 25 MHz. On May 29 some powerful simple type III bursts and
groups of type III bursts were observed against type IV burst. There
were only single weak type III bursts on June 2. Analysis of visibility
functions of radio emission sources at these frequencies was allowed
to find spatial sizes of bursts sources, which changed mainly from 20`
to 22` at 25 MHz and from 24` to 27` at 20 MHz. Also sources distances
at these frequencies were obtained. Radio emissions at frequencies 20
MHz and 25 MHz escaped at distances 2.9RS and 2.6RS, respectively, in
most cases. At these distances radio emissions at frequencies 10 MHz
and 12.5 MHz are generated in the Newkirk corona so the observational
radio emissions are the second harmonics. This fact is confirmed by the
low polarizations of discussed type III bursts. Brightness temperatures
of these bursts were in the range from 2.1x10(9)K to 4.4x10(10)K for
bursts on May 29 and only about 108K for the burst observed on June 2.
Title: The evolution of CMEs with radial distance: Numerical approach
Authors: Al-haddad, Nada; Roussev, Ilia; Nieves-Chinchilla, Teresa;
Poedts, Stefaan; Lugaz, Noé; Farrugia, Charles
Bibcode: 2016cosp...41E..55A
Altcode:
Most of what is known about the evolution of CME properties comes from
statistical studies using data from 1 AU as well as from Helios, and
recently Messenger. However, little is known about the changes of the
CME magnetic field strength and structure during propagation. Here,
we describe the evolution of the properties of simulated CMEs in the
inner heliosphere, for CMEs initiated with writhed as well as twisted
ejecta. We compare the radial evolution of these properties with
that found from previous studies. We find that the evolutions of the
radial size and magnetic field strength are nearly indistinguishable
for twisted flux ropes as compared to writhed CMEs. The evolution of
those properties is also in very good agreement with past studies,
primarily with recent statistical studies using in-situ measurements
and with study using remote observations of CMEs.
Title: Rieger-type Periodicity during Solar Cycles 14-24: Estimation
of Dynamo Magnetic Field Strength in the Solar Interior
Authors: Gurgenashvili, Eka; Zaqarashvili, Teimuraz V.; Kukhianidze,
Vasil; Oliver, Ramon; Ballester, Jose Luis; Ramishvili, Giorgi;
Shergelashvili, Bidzina; Hanslmeier, Arnold; Poedts, Stefaan
Bibcode: 2016ApJ...826...55G
Altcode: 2016arXiv160504162G
Solar activity undergoes a variation over timescales of several months
known as Rieger-type periodicity, which usually occurs near maxima
of sunspot cycles. An early analysis showed that the periodicity
appears only in some cycles and is absent in other cycles. But the
appearance/absence during different cycles has not been explained. We
performed a wavelet analysis of sunspot data from the Greenwich Royal
Observatory and the Royal Observatory of Belgium during cycles 14-24. We
found that the Rieger-type periods occur in all cycles, but they are
cycle dependent: shorter periods occur during stronger cycles. Our
analysis revealed a periodicity of 185-195 days during the weak cycles
14-15 and 24 and a periodicity of 155-165 days during the stronger
cycles 16-23. We derived the dispersion relation of the spherical
harmonics of the magnetic Rossby waves in the presence of differential
rotation and a toroidal magnetic field in the dynamo layer near the
base of the convection zone. This showed that the harmonics of fast
Rossby waves with m = 1 and n = 4, where m (n) indicates the toroidal
(poloidal) wavenumbers, perfectly fit with the observed periodicity. The
variation of the toroidal field strength from weaker to stronger cycles
may lead to the different periods found in those cycles, which explains
the observed enigmatic feature of the Rieger-type periodicity. Finally,
we used the observed periodicity to estimate the dynamo field strength
during cycles 14-24. Our estimations suggest a field strength of ∼40
kG for the stronger cycles and ∼20 kG for the weaker cycles.
Title: Radio Emission of the Quiet Sun at 20 and 25 MHz According
to Interferometer Observations with the UTR-2 Radio Telescope
Authors: Shepeliev, V.; Melnik, V.; Brazhenko, A.; Dorovskyy, V.;
Poedts, S.; Rucker, H.
Bibcode: 2016simi.conf...17S
Altcode:
We report observations of the solar radio emission at frequencies of
20.0 and 25.0 MHz by radio interferometers with different baselines
composed of sections of North-South and East-West arms of the UTR-2
radio telescope. The interferometer measurements were accompanied
with wide band observations within 8–33 MHz with the URAN-2
radio telescope. There was only one day when strong sporadic radio
emission consisting of type III, type II and type IV bursts have been
observed. There was no solar activity in the decameter range on other
days of the observational session. A flux density of the quiet Sun in
that period is estimated to lie within 1050–1100 Jy and 1480–1570
Jy at 20.0 and 25.0 MHz, correspondingly. An angular size of the quiet
Sun in equatorial and polar directions was 55' and 49' at 20.0 MHz and
50' and 42' at 25.0 MHz. Brightness temperatures of solar corona radio
emission was found to be Tb =5.1 105 K and Tb =5.7 105 K at 20.0 and
25.0 MHz, respectively.
Title: The interplay of the solar wind proton core and halo
populations: EMIC instability
Authors: Shaaban, S. M.; Lazar, M.; Poedts, S.; Elhanbaly, A.
Bibcode: 2016JGRA..121.6031S
Altcode:
The kinetic properties of the solar wind protons (ions), like their
temperature anisotropy and the resulting instabilities, are, in
general, investigated considering only the proton core (or thermal)
populations. The implication of the suprathermal halo components is
minimized or just ignored, despite the fact that their presence in
the solar wind is continuously reported by the observations, and
their kinetic energy density may be significant. Whether they are
originating in the corona or solar wind, the energetic particles
may result from acceleration by the plasma turbulence or from the
pitch angle scattering of the streaming protons by the self-generated
fluctuations. The presence of suprathermal protons in the heliosphere
suggests, therefore, a direct implication in resonant interactions,
e.g., Landau and cyclotron, with plasma particles. This paper presents
the results of a first investigation on the interplay of the proton
core and suprathermal halo, when both these two populations may exhibit
temperature anisotropies, which destabilize the electromagnetic ion
(proton) cyclotron (EMIC) modes. These results clearly show that
for conditions typically encountered in the solar wind, the effects
of the suprathermals can be more important than those driven by the
core. Remarkable are also the cumulative effects of the core and halo
components, which change dramatically the instability conditions.
Title: Effects of suprathermal electrons on the proton temperature
anisotropy in space plasmas: Electromagnetic ion-cyclotron instability
Authors: Shaaban, S. M.; Lazar, M.; Poedts, S.; Elhanbaly, A.
Bibcode: 2016Ap&SS.361..193S
Altcode: 2016arXiv160204051S
In collision-poor plasmas from space, e.g., the solar wind and planetary
magnetospheres, the kinetic anisotropy of the plasma particles is
expected to be regulated by the kinetic instabilities. Driven by an
excess of ion (proton) temperature perpendicular to the magnetic
field (T_{perp}>T_{allel}), the electromagnetic ion-cyclotron
(EMIC) instability is fast enough to constrain the proton anisotropy,
but the observations do not conform to the instability thresholds
predicted by the standard theory for bi-Maxwellian models of the
plasma particles. This paper presents an extended investigation
of the EMIC instability in the presence of suprathermal electrons
which are ubiquitous in these environments. The analysis is based
on the kinetic (Vlasov-Maxwell) theory assuming that both species,
protons and electrons, may be anisotropic, and the EMIC unstable
solutions are derived numerically providing an accurate description
for conditions typically encountered in space plasmas. The effects of
suprathermal populations are triggered by the electron anisotropy and
the temperature contrast between electrons and protons. For certain
conditions the anisotropy thresholds exceed the limits of the proton
anisotropy measured in the solar wind considerably restraining the
unstable regimes of the EMIC modes.
Title: Kelvin-Helmholtz Instability in the Solar Wind Plasmas:
16-Momentum Fluid Formalism
Authors: Ismayilli, R. F.; Dzhalilov, N. S.; Shergelashvili, B. M.;
Poedts, S.; Pirguliyev, M. Sh.
Bibcode: 2016AzAJ...11b..15I
Altcode:
We study wave properties and instabilities in magnetized, anisotropic,
collisionless plasma in the fluid approximation using the16 momentum
formalism. In particular, we investigated equations different from the
ideal MHD equations by including evolution equations for the heat fluxes
with different components along the magnetic field S∥ and in the
transverse direction S⊥. In this work, we studied the Kelvin-Helmholtz
instability that occurs in the contact discontinuity interactions of the
slow (350-400km/s), fast (600-850km/s) and CME (900-1200km/s) components
of solar wind, taking into account the pressure anisotropic properties
(p⊥,p∥) of the wind plasma. This instability is investigated by
solving the 16-momentum set of equations based on an assumed geometry.
Title: The Effect of Limited Sample Sizes on the Accuracy of the
Estimated Scaling Parameter for Power-Law-Distributed Solar Data
Authors: D'Huys, Elke; Berghmans, David; Seaton, Daniel B.; Poedts,
Stefaan
Bibcode: 2016SoPh..291.1561D
Altcode: 2016arXiv160506972D; 2016SoPh..tmp...82D
Many natural processes exhibit a power-law behavior. The power-law
exponent is linked to the underlying physical process, and therefore
its precise value is of interest. With respect to the energy content
of nanoflares, for example, a power-law exponent steeper than 2 is
believed to be a necessary condition for solving the enigmatic coronal
heating problem. Studying power-law distributions over several orders
of magnitudes requires sufficient data and appropriate methodology. In
this article we demonstrate the shortcomings of some popular methods in
solar physics that are applied to data of typical sample sizes. We use
synthetic data to study the effect of the sample size on the performance
of different estimation methods. We show that vast amounts of data are
needed to obtain a reliable result with graphical methods (where the
power-law exponent is estimated by a linear fit on a log-transformed
histogram of the data). We revisit published results on power laws for
the angular width of solar coronal mass ejections and the radiative
losses of nanoflares. We demonstrate the benefits of the maximum
likelihood estimator and advocate its use.
Title: Observing the Unobservable: Identification and Characterisation
of Stealth Coronal Mass Ejections
Authors: D'Huys, Elke; Seaton, Daniel B.; Poedts, Stefaan; Berghmans,
David
Bibcode: 2016SPD....4740401D
Altcode:
I will present my doctoral thesis research on stealth CMEs: solar
coronal mass ejections that are clearly observed in coronagraph
data but do not show significant low-coronal or on-disk signatures
of eruption. This lack of coronal signatures makes it challenging to
determine their source region and predict their trajectory throughout
interplanetary space. We identified 40 such events and investigated
their properties both observationally and statistically. We found that
our sample size was insufficient to determine the scaling law for the
CME angular width reliably. We therefore analyzed in general what the
effect is of a limited sample size on the estimation of a power law
parameter. Armed with this knowledge, we returned to our sample of
stealth CMEs, re-analyzed the power law for their angular widths and
compared the results to the power law found for normal CMEs.
Title: Firehose constraints for the solar wind suprathermal electrons
Authors: Lazar, M.; Shaaban, S. M.; Poedts, S.; Štverák, Š.
Bibcode: 2016arXiv160405628L
Altcode:
The indefinite increase of temperature predicted by the solar wind
expansion in the direction parallel to the interplanetary magnetic field
is already notorious for not being confirmed by the observations. In
hot and dilute plasmas from space particle-particle collisions are
not efficient in constraining large deviations from isotropy, but
the resulting firehose instability provides in this case plausible
limitations for the temperature anisotropy of the thermal (core)
populations of both the electron and proton species. The present
paper takes into discussion the suprathermal (halo) electrons,
which are ubiquitous in the solar wind. Less dense but hotter than
the core, suprathermals may be highly anisotropic and susceptible
to the firehose instability. The main features of the instability
are here derived from a first-order theory for conditions specific
to the suprathermal electrons in the solar wind and terrestrial
magnetospheres. Unveiled here, new regimes of the electron firehose
instability may be exclusively controlled by the suprathermals. The
instability is found to be systematically stimulated by the suprathermal
electrons, with thresholds that approach the limits of the temperature
anisotropy reported by the observations. These results represent new
and valuable evidences for the implication of the firehose instability
in the relaxation of the temperature anisotropy in space plasmas.
Title: Shear Instability Analysis of MHD Discontinuities in the
Solar Wind Conditions
Authors: Ismayilli, R. F.; Dzhalilov, N. S.; Shergelashvili, B. M.;
Poedts, S.; Pirguliyev, M. Sh.
Bibcode: 2016AzAJ...11a..23I
Altcode:
We study wave properties and instabilities in magnetized, anisotropic,
collisionless plasma in the fluid approximation using the16 momentum
formalism. In particular, we investigated equations different from
the ideal MHD equations by including evolution equations for the heat
fluxes with different components along the magnetic field S∥ and
S⊥. Main aim of this paper is to study the MHD shear instability that
occurs in the contact surface of interaction of the slow (350-400km/s),
fast (600-850km/s) and CME (900-1200km/s) components of solar wind,
taking in to account the anisotropic properties of the wind plasma. A
preliminary study of the obtained dispersion equation for solar wind
plasma parameters showed that in places of contacts of different streams
having the MHD shear instability properties which highly dependent on
the plasma anisotropy and heat flow along magnetic field. The results
could be used for the interpretation of the observed facts of wave
turbulence in corotating interaction regions (CIR) as well.
Title: The Storm of Decameter Spikes During the Event of 14 June 2012
Authors: Shevchuk, N. V.; Melnik, V. N.; Poedts, S.; Dorovskyy, V. V.;
Magdalenic, J.; Konovalenko, A. A.; Brazhenko, A. I.; Briand, C.;
Frantsuzenko, A. V.; Rucker, H. O.; Zarka, P.
Bibcode: 2016SoPh..291..211S
Altcode: 2015SoPh..tmp..171S
An event on 14 June 2012, observed with the radio telescopes UTR-2
(Kharkov, Ukraine), URAN-2 (Poltava, Ukraine), and NDA (Nançay, France)
during a joint Summer campaign, is analyzed and discussed. The high
solar activity resulted in a storm of spikes, and a storm of Type III
bursts, Type IIIb bursts, and a Type IV burst observed in the decameter
band. During the observed time interval, the average flux of radio
emission changed twice. Using spikes as a tool for diagnostics of
plasma parameters, we followed variations of the coronal temperature
and the coronal magnetic field in the observed time interval. Thus,
in frames of the model described in this article the observed decameter
spikes' durations of 0.3 - 1 seconds correspond to the coronal plasma
temperatures of ≈0.1 -0.6 ×106K. At the same time the
spikes' frequency bandwidths of 25 - 80 kHz give us the magnetic-field
value of about 2 G.
Title: Effects of Electrons on the Electromagnetic Ion Cyclotron
Instability: Solar Wind Implications
Authors: Shaaban, S. M.; Lazar, M.; Poedts, S.; Elhanbaly, A.
Bibcode: 2015ApJ...814...34S
Altcode:
In diffuse plasmas in space, particle-particle collisions are rare
and inefficient, such that a plausible mechanism for constraining
the temperature anisotropy of plasma particles may be provided by
the resulting instabilities. The implication of the electromagnetic
ion-cyclotron (EMIC) instability in the solar wind is still unclear
because this instability is fast enough to relax the proton temperature
anisotropy, but the 1 AU measurements do not conform to the instability
thresholds predicted by the existing theories, which ignore the
kinetic effects of electrons, assuming them to be isotropic. This paper
presents a refined analysis of the EMIC instability in the presence
of a temperature (T) anisotropy of electron (subscript “e”)
population, i.e., {A}{{e}}={T}{{e},\perp
}/{T}{{e},\parallel }\ne 1, enabling the identification
of two distinct regimes of this instability that correspond to an
excess of perpendicular temperature ({A}{{e}}\gt 1) or
an excess of parallel temperature ({A}{{e}}\lt 1). The
growth rates, real frequencies, and threshold conditions are found
to be highly sensitive to the electron temperature anisotropy, and
electrons with {A}{{e}}\gt 1 inhibit the instability,
while for {A}{{e}}\lt 1 the instability growth rates
increase with the electron anisotropy. Moreover, the electron-proton
temperature ratio {θ }T={T}{{e},\parallel
}/{T}{{p},\parallel } becomes an important factor that
stimulates the effect of the anisotropic electrons. The potential
relevance of the new results in the solar wind is analyzed by
contrasting the instability thresholds with the observed limits of
the proton temperature anisotropy.
Title: Dissipation of Parallel and Oblique Alfvén-Cyclotron
Waves—Implications for Heating of Alpha Particles in the Solar Wind
Authors: Maneva, Y. G.; Viñas, Adolfo F.; Moya, Pablo S.; Wicks,
Robert T.; Poedts, Stefaan
Bibcode: 2015ApJ...814...33M
Altcode: 2015arXiv150605318M
We perform 2.5D hybrid simulations with massless fluid electrons and
kinetic particle-in-cell ions to study the temporal evolution of ion
temperatures, temperature anisotropies, and velocity distribution
functions in relation to the dissipation and turbulent evolution
of a broadband spectrum of parallel and obliquely propagating
Alfvén-cyclotron waves. The purpose of this paper is to study the
relative role of parallel versus oblique Alfvén-cyclotron waves in
the observed heating and acceleration of alpha particles in the fast
solar wind. We consider collisionless homogeneous multi-species plasma,
consisting of isothermal electrons, isotropic protons, and a minor
component of drifting α particles in a finite-β fast stream near the
Earth. The kinetic ions are modeled by initially isotropic Maxwellian
velocity distribution functions, which develop nonthermal features and
temperature anisotropies when a broadband spectrum of low-frequency
nonresonant, ω ≤ 0.34 Ωp, Alfvén-cyclotron waves
is imposed at the beginning of the simulations. The initial plasma
parameter values, such as ion density, temperatures, and relative drift
speeds, are supplied by fast solar wind observations made by the Wind
spacecraft at 1 AU. The imposed broadband wave spectra are left-hand
polarized and resemble Wind measurements of Alfvénic turbulence in
the solar wind. The imposed magnetic field fluctuations for all cases
are within the inertial range of the solar wind turbulence and have
a Kraichnan-type spectral slope α = -3/2. We vary the propagation
angle from θ = 0° to θ = 30° and θ = 60°, and find that the
heating of alpha particles is most efficient for the highly oblique
waves propagating at 60°, whereas the protons exhibit perpendicular
cooling at all propagation angles.
Title: Simulations of the Earth's magnetosphere embedded in
sub-Alfvénic solar wind on 24 and 25 May 2002
Authors: Chané, E.; Raeder, J.; Saur, J.; Neubauer, F. M.; Maynard,
K. M.; Poedts, S.
Bibcode: 2015JGRA..120.8517C
Altcode:
During 24 and 25 May 2002, the solar wind conditions at Earth's orbit
were very unusual: the density was extremely low (below 0.1/cc) and,
as a result, the flow was subfast and sub-Alfvénic (the Alfvén Mach
number was as low as 0.4 in the rest frame of the Earth). Consequently,
the Earth's bow shock disappeared and two Alfvén wings formed
on the flanks of the magnetosphere. These two long structures
(estimated extension of 600 RE for this event) affect the
incoming plasma as follows: the velocity is reduced and the magnetic
field rotates. In the present study, global magnetohydrodynamical
simulations of the magnetosphere are performed for such upstream
solar wind conditions. The simulations show how the magnetosphere
configuration dramatically changes when the sub-Alfvénic solar wind
reaches the magnetosphere: the dayside magnetopause expands up to 20
RE, and on the nightside the position of the last closed
magnetic field line diminishes to 20 RE. As a result the
closed magnetic field line region becomes very symmetric. The open field
line configuration also changes such that field lines emanating from the
Northern Hemisphere all point in the direction of the dawn Alfvén wing
(around 8:00 LT), while the field lines from the Southern Hemisphere
all point in direction of the other wing (around 22:00 LT). During the
formation of the Alfvén wings, the tail lobes completely disappeared
and the auroral activity greatly diminished, i.e., the magnetosphere
becomes geomagnetically quiet.
Title: iSPHERE - A New Approach to Collaborative Research and Cloud
Computing
Authors: Al-Ubaidi, T.; Khodachenko, M. L.; Kallio, E. J.; Harry,
A.; Alexeev, I. I.; Vázquez-Poletti, J. L.; Enke, H.; Magin, T.;
Mair, M.; Scherf, M.; Poedts, S.; De Causmaecker, P.; Heynderickx,
D.; Congedo, P.; Manolescu, I.; Esser, B.; Webb, S.; Ruja, C.
Bibcode: 2015EPSC...10..211A
Altcode:
The project iSPHERE (integrated Scientific Platform for HEterogeneous
Research and Engineering) that has been proposed for Horizon 2020
(EINFRA-9- 2015, [1]) aims at creating a next generation Virtual
Research Environment (VRE) that embraces existing and emerging
technologies and standards in order to provide a versatile platform
for scientific investigations and collaboration. The presentation
will introduce the large project consortium, provide a comprehensive
overview of iSPHERE's basic concepts and approaches and outline
general user requirements that the VRE will strive to satisfy. An
overview of the envisioned architecture will be given, focusing on
the adapted Service Bus concept, i.e. the "Scientific Service Bus"
as it is called in iSPHERE. The bus will act as a central hub for
all communication and user access, and will be implemented in the
course of the project. The agile approach [2] that has been chosen
for detailed elaboration and documentation of user requirements,
as well as for the actual implementation of the system, will be
outlined and its motivation and basic structure will be discussed. The
presentation will show which user communities will benefit and which
concrete problems, scientific investigations are facing today, will be
tackled by the system. Another focus of the presentation is iSPHERE's
seamless integration of cloud computing resources and how these will
benefit scientific modeling teams by providing a reliable and web
based environment for cloud based model execution, storage of results,
and comparison with measurements, including fully web based tools for
data mining, analysis and visualization. Also the envisioned creation
of a dedicated data model for experimental plasma physics will be
discussed. It will be shown why the Scientific Service Bus provides
an ideal basis to integrate a number of data models and communication
protocols and to provide mechanisms for data exchange across multiple
and even multidisciplinary platforms.
Title: Destabilizing effects of the suprathermal populations in the
solar wind
Authors: Lazar, M.; Poedts, S.; Fichtner, H.
Bibcode: 2015A&A...582A.124L
Altcode:
Context. Suprathermal populations are ubiquitous in the solar wind,
indicating plasma states out of thermal equilibrium, and an excess of
free energy expected to enhance the kinetic instabilities. However,
recent endeavors to disclose the effects of these populations on the
electromagnetic instabilities driven by the temperature anisotropy do
not confirm this expectation, but mainly show that these instabilities
are inhibited by the suprathermals.
Aims: In an attempt to
clarify the effect of the suprathermals, we propose to revisit the
existing models for the anisotropic velocity distributions of plasma
particles and to provide an alternative comparative analysis that
unveils the destabilizing effects of the suprathermal populations.
Methods: Suprathermal tails of the observed distributions are
best fitted by the Kappa power laws (with the bi-Kappa variant to
model temperature anisotropies), which are nearly Maxwellian at low
speeds (thermal core) and decrease as a power law at high speeds
(suprathermal halo). To unveil the destabilizing effects of the
suprathermal populations, the existing methods (A) compare Kappa
and Maxwellian distributions of the same effective temperature,
while the alternative comparative method (B) proposed in this paper
allows for an increase of the effective temperature with increasing
the suprathermal populations. Both of these two methods are invoked
here to quantify and compare the effects of suprathermal electrons
on the electromagnetic electron-cyclotron (EMEC) instability, driven
by the temperature anisotropy Te,⊥>Te,∥
of the electrons (where ∥,⊥ are directions with respect to the
magnetic field).
Results: Only the Maxwellian limit of lower
effective temperature shapes the Kappa model at low energies (method
B), enabling a realistic comparison between the Maxwellian core and
the global best-fitting Kappa, which incorporates both the core and
suprathermal tails. In this case, the EMEC instability is found to be
markedly and systematically enhanced by the suprathermal populations
for any level of the temperature anisotropy. The results of the present
study may provide valuable premises for a realistic description of
the suprathermal populations and their destabilizing effects for the
whole spectrum of kinetic instabilities in the solar wind.
Title: Dynamics of a Solar Prominence Tornado Observed by SDO/AIA
on 2012 November 7-8
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz V.; Kukhianidze,
Vasil; Ramishvili, Giorgi; Shergelashvili, Bidzina; Veronig, Astrid;
Poedts, Stefaan
Bibcode: 2015ApJ...810...89M
Altcode: 2015arXiv150806788M
We study the detailed dynamics of a solar prominence tornado using
time series of 171, 304, 193, and 211 Å spectral lines obtained by
the Solar Dynamics Observatory/Atmospheric Imaging Assembly during
2012 November 7-8. The tornado first appeared at 08:00 UT, November 07,
near the surface, gradually rose upwards with the mean speed of ∼1.5
km s-1 and persisted over 30 hr. Time-distance plots show
two patterns of quasi-periodic transverse displacements of the tornado
axis with periods of 40 and 50 minutes at different phases of the
tornado evolution. The first pattern occurred during the rising phase
and can be explained by the upward motion of the twisted tornado. The
second pattern occurred during the later stage of evolution when the
tornado already stopped rising and could be caused either by MHD kink
waves in the tornado or by the rotation of two tornado threads around
a common axis. The later hypothesis is supported by the fact that the
tornado sometimes showed a double structure during the quasi-periodic
phase. 211 and 193 Å spectral lines show a coronal cavity above
the prominence/tornado, which started expansion at ∼13:00 UT and
continuously rose above the solar limb. The tornado finally became
unstable and erupted together with the corresponding prominence as
coronal mass ejection (CME) at 15:00 UT, November 08. The final stage
of the evolution of the cavity and the tornado-related prominence
resembles the magnetic breakout model. On the other hand, the kink
instability may destabilize the twisted tornado, and consequently
prominence tornadoes can be used as precursors for CMEs.
Title: Fine and Superfine Structure of the Decameter-Hectometer Type
II Burst on 7 June 2011
Authors: Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.;
Brazhenko, A. I.; Panchenko, M.; Poedts, S.; Mykhaylov, V. A.
Bibcode: 2015SoPh..290.2031D
Altcode: 2015SoPh..tmp...92D; 2015arXiv150806801D
The characteristics of a type II burst with a herringbone structure
observed both with ground-based radio telescopes (UTR-2 and URAN-2)
and space-borne spectrometers (STEREO-A and B) are discussed. The burst
was recorded on 7 June 2011 in the frequency band 3 - 33 MHz. It was
characterized by extremely rich fine structure. Statistical analysis
of more than 300 herringbone sub-bursts constituting the burst was
performed separately for the positively (reverse) and negatively
(forward) drifting sub-bursts. The sense and the degree of circular
polarization of the herringbone sub-bursts were measured in a wide
frequency band (16 - 32 MHz). A second-order fine frequency structure
of the herringbone sub-bursts was observed and studied for the first
time. Using STEREO/COR1 and SOHO/LASCO-C2 images, we determined the
direction and radial speed of the coronal mass ejection responsible
for the studied type II burst. The possible location of the type II
burst source on the flank of the shock was found.
Title: Evolution of non-flux rope CMEs
Authors: Al-Haddad, Nada; Farrugia, Charles; Poedts, Stefaan;
Lugaz, Noé
Bibcode: 2015shin.confE.170A
Altcode:
Distinguishing CMEs with writhed magnetic field from those with
twisted field using in-situ measurements has been shown to be nearly
unfeasible. This work aims to address this problem with a new approach:
studying the evolution of two simulated CMEs in the inner heliosphere,
a CME with writhe structure and another with twist structure. We
compare the radial evolution of the properties of these CMEs with
that found from statistical studies based on observations in the inner
heliosphere by Helios and Messenger. We found that the evolution of the
radial size and magnetic field strength is nearly indistinguishable
for twisted flux rope as compared to writhed CMEs. The evolution of
these properties is also in very good agreement with past studies,
primarily with recent statistical studies using in-situ measurements
and with study using remote observations of CMEs.
Title: Modelling large solar proton events with the shock-and-particle
model. Extraction of the characteristics of the MHD shock front at
the cobpoint
Authors: Pomoell, Jens; Aran, Angels; Jacobs, Carla; Rodríguez-Gasén,
Rosa; Poedts, Stefaan; Sanahuja, Blai
Bibcode: 2015JSWSC...5A..12P
Altcode:
We have developed a new version of a model that combines a
two-dimensional Sun-to-Earth magnetohydrodynamic (MHD) simulation of the
propagation of a CME-driven shock and a simulation of the transport of
particles along the interplanetary magnetic field (IMF) line connecting
the shock front and the observer. We assume that the shock-accelerated
particles are injected at the point along the shock front that
intersects this IMF line, i.e. at the cobpoint. Novel features of the
model are an improved solar wind model and an enhanced fully automated
algorithm to extract the necessary plasma characteristics from the
shock simulation. In this work, the new algorithms have been employed
to simulate the 2000 April 4 and the 2006 December 13 SEP events. In
addition to quantifying the performance of the new model with respect
to results obtained using previous versions of the shock-and-particle
model, we investigate the semi-empirical relation between the injection
rate of shock-accelerated particles, Q, and the jump in speed across
the shock, VR, known as the Q(VR) relation. Our results show that
while the magnetic field and density compression at the shock front
is markedly different than in our previous modeling, the evolution
of VR remains largely similar. As a result, we confirm that a simple
relation can still be established between Q and VR, which enables the
computation of synthetic intensity-time profiles at any location in
interplanetary space. Furthermore, the new shock extraction tool is
found to yield improved results being in general more robust. These
results are important not only with regard to efforts to develop
coupled magnetohydrodynamic and particle simulation models, but also
to improve space weather related software tools that aim to predict
the peak intensities, fluences and proton intensity-time profiles of
SEP events (such as the SOLPENCO tool).
Title: Formation and evolution of coronal rain observed by SDO/AIA
on February 22, 2012
Authors: Vashalomidze, Z.; Kukhianidze, V.; Zaqarashvili, T. V.;
Oliver, R.; Shergelashvili, B.; Ramishvili, G.; Poedts, S.; De
Causmaecker, P.
Bibcode: 2015A&A...577A.136V
Altcode: 2015arXiv150403471V
Context. The formation and dynamics of coronal rain are currently not
fully understood. Coronal rain is the fall of cool and dense blobs
formed by thermal instability in the solar corona towards the solar
surface with acceleration smaller than gravitational free fall.
Aims: We aim to study the observational evidence of the formation of
coronal rain and to trace the detailed dynamics of individual blobs.
Methods: We used time series of the 171 Å and 304 Å spectral lines
obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamic Observatory (SDO) above active region AR 11420 on February 22,
2012.
Results: Observations show that a coronal loop disappeared
in the 171 Å channel and appeared in the 304 Å line more than one hour
later, which indicates a rapid cooling of the coronal loop from 1 MK to
0.05 MK. An energy estimation shows that the radiation is higher than
the heat input, which indicates so-called catastrophic cooling. The
cooling was accompanied by the formation of coronal rain in the form
of falling cold plasma. We studied two different sequences of falling
blobs. The first sequence includes three different blobs. The mean
velocities of the blobs were estimated to be 50 km s-1,
60 km s-1 and 40 km s-1. A polynomial fit shows
the different values of the acceleration for different blobs, which are
lower than free-fall in the solar corona. The first and second blob move
along the same path, but with and without acceleration, respectively. We
performed simple numerical simulations for two consecutive blobs, which
show that the second blob moves in a medium that is modified by the
passage of the first blob. Therefore, the second blob has a relatively
high speed and no acceleration, as is shown by observations. The
second sequence includes two different blobs with mean velocities of
100 km s-1 and 90 km s-1, respectively.
Conclusions: The formation of coronal rain blobs is connected with
the process of catastrophic cooling. The different acceleration of
different coronal rain blobs might be due to the different values in
the density ratio of blob to corona. All blobs leave trails, which
might be a result of continuous cooling in their tails. Two
movies attached to Fig. 1 are available in electronic form at http://www.aanda.org
Title: Numerical Simulations of a Flux Rope Ejection
Authors: Pagano, P.; Mackay, D. H.; Poedts, S.
Bibcode: 2015JApA...36..123P
Altcode: 2015JApA..tmp...19P
Coronal mass ejections (CMEs) are the most violent phenomena observed
on the Sun. One of the most successful models to explain CMEs is the
flux rope ejection model, where a magnetic flux rope is expelled from
the solar corona after a long phase along which the flux rope stays
in equilibrium while magnetic energy is being accumulated. However,
still many questions are outstanding on the detailed mechanism of the
ejection and observations continuously provide new data to interpret
and put in the context. Currently, extreme ultraviolet (EUV) images
from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
Observatory (SDO) are providing new insights into the early phase
of CME evolution. In particular, observations show the ejection of
magnetic flux ropes from the solar corona and how they evolve into
CMEs. However, these observations are difficult to interpret in terms
of basic physical mechanisms and quantities, thus, we need to compare
equivalent quantities to test and improve our models. In our work,
we intend to bridge the gap between models and observations with our
model of flux rope ejection where we consistently describe the full
life span of a flux rope from its formation to ejection. This is done
by coupling the global non-linear force-free model (GNLFFF) built to
describe the slow low- β formation phase, with a full MHD simulation
run with the software MPI-AMRVAC, suitable to describe the fast MHD
evolution of the flux rope ejection that happens in a heterogeneous β
regime. We also explore the parameter space to identify the conditions
upon which the ejection is favoured (gravity stratification and
magnetic field intensity) and we produce synthesised AIA observations
(171 Å and 211 Å). To carry this out, we run 3D MHD simulation in
spherical coordinates where we include the role of thermal conduction
and radiative losses, both of which are important for determining the
temperature distribution of the solar corona during a CME. Our model
of flux rope ejection is successful in realistically describing the
entire life span of a flux rope and we also set some conditions for
the backgroud solar corona to favour the escape of the flux rope, so
that it turns into a CME. Furthermore, our MHD simulation reproduces
many of the features found in the AIA observations.
Title: Decameter U-burst Harmonic Pair from a High Loop
Authors: Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Bubnov,
I. N.; Gridin, A. A.; Shevchuk, N. V.; Rucker, H. O.; Poedts, S.;
Panchenko, M.
Bibcode: 2015SoPh..290..181D
Altcode:
The results of the first observations of solar sporadic radio emission
within 10 - 70 MHz by the Giant Ukrainian Radio Telescope (GURT)
are presented and discussed. Observations in such a wide range of
frequencies considerably facilitate the registration of harmonic
pairs. The solar U-burst harmonic pair observed on 8 August 2012 is
analyzed. The burst key features were determined. Among them, the time
delay between the fundamental and harmonic emissions was of special
interest. The fundamental emission was delayed for 7 s with respect
to the harmonic emission. A model for explaining the occurrence of
such a delay is proposed, in which the emission source is located
inside a magnetic loop containing plasma of increased density. In this
case, the delay appears due to the difference in group velocities of
electromagnetic waves at the fundamental and the harmonic frequencies.
Title: Constraints for the aperiodic O-mode streaming instability
Authors: Lazar, M.; Schlickeiser, R.; Poedts, S.; Stockem, A.;
Vafin, S.
Bibcode: 2015PhPl...22a2102L
Altcode: 2014arXiv1411.1508L
In plasmas, where the thermal energy density exceeds the magnetic
energy density (β∥ > 1), the aperiodic ordinary mode
(O-mode) instability is driven by an excess of parallel temperature
A = T⊥/T∥ < 1 (where ∥ and ⊥ denote
directions relative to the uniform magnetic field). When stimulated by
parallel plasma streams, the instability conditions extend to low beta
states, i.e., β∥ < 1, and recent studies have proven
the existence of a new regime, where the anisotropy threshold decreases
steeply with lowering β∥ → 0 if the streaming velocity
is sufficiently high. However, the occurrence of this instability is
questionable especially in the low-beta plasmas, where the electrostatic
two-stream instabilities are expected to develop much faster in the
process of relaxation of the counterstreams. It is therefore proposed
here to identify the instability conditions for the O-mode below those
required for the onset of the electrostatic instability. A hierarchy of
these two instabilities is established for both the low β∥
< 1 and large β∥ > 1 plasmas. The conditions where
the O-mode instability can operate efficiently are markedly constrained
by the electrostatic instabilities especially in the low-beta plasmas.
Title: Towards realistic parametrization of the kinetic anisotropy
and the resulting instabilities in space plasmas. Electromagnetic
electron-cyclotron instability in the solar wind
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.; Dumitrache, C.
Bibcode: 2015MNRAS.446.3022L
Altcode:
Measured in situ, the particle velocity distributions in the solar wind
plasma reveal two distinct components: a Maxwellian (thermal) core, and
a less dense but hotter suprathermal halo with a power-law distribution
described by Lorentzian/Kappa distribution function. Despite this
evidence, the existing attempts to parametrize anisotropic distributions
and the resulting wave instabilities are limited to idealized models,
which either ignore the suprathermal populations, or minimize the core,
assuming it is cold. Here, a more realistic approach is identified,
combining an isotropic Maxwellian core and an anisotropic bi-Kappa
halo. This model is relevant at large heliocentric distances and
for the slow winds, when the field-aligned strahl is less pronounced
and kinetic energy densities in the core and halo are comparable. A
comparative study with the cold-core-based model is performed on
the electron whistler-cyclotron instability driven by the anisotropic
halo. Derived exactly numerically, the instability thresholds and growth
rates confirm the expectation that cyclotron instabilities are inhibited
by the core thermal spread. This effect is enhanced by the increase of
the halo-core relative density with heliocentric distance, suggesting
that local conditions for this instability to develop at large radial
distances in the solar wind are less favourable than predicted before.
Title: Kinetic Effects in Parametric Instabilities of Finite Amplitude
Alfven Waves in a Drifting Multi-Species Plasma
Authors: Maneva, Y. G.; Araneda, J. A.; Poedts, S.
Bibcode: 2014AGUFMSH33A4144M
Altcode:
We consider parametric instabilities of finite-amplitude large-scale
Alfven waves in a low-beta collisionless multi-species plasma,
consisting of fluid electrons, kinetic protons and a drifting
population of minor ions. Complementary to many theoretical studies,
relying on fluid or multi-fluid approach, in this work we present the
solutions of the parametric instability dispersion relation, including
kinetic effects in the parallel direction, along the ambient magnetic
field. This provides us with the opportunity to predict the importance
of some wave-particle interactions like Landau damping of the daughter
ion-acoustic waves for the given pump wave and plasma conditions. We
apply the dispersion relation to plasma parameters, typical for low-beta
collisionless solar wind close to the Sun. We compare the analytical
solutions to the linear stage of hybrid numerical simulations and
discuss the application of the model to the problems of preferential
heating and differential acceleration of minor ions in the solar corona
and the fast solar wind. The results of this study provide tools for
prediction and interpretation of the magnetic field and particles data
as expected from the future Solar Orbiter and Solar Probe Plus missions.
Title: Three-Dimensional Magnetic Reconnection Under Low Chromospheric
Conditions Using a Two-Fluid Weakly Ionized Reactive Plasma Model
Authors: Alvarez Laguna, A.; Lani, A.; Poedts, S.; Mansour, N. N.;
Kosovichev, A. G.
Bibcode: 2014AGUFMSH23A4151A
Altcode:
Magnetic reconnection is a physical process enabling for the conversion
of so-called free (non-potential) magnetic energy into kinetic and
thermal energy by breaking the flux conservation law that exists for
ideal (i.e. perfectly conducting) plasmas. This ubiquitous phenomenon in
magnetized plasma plays an important role in the Sun's chromosphere as
likely being responsible for transient plasma phenomena such as solar
flares, spicules and chromospheric jets. In this work, we present
a computational model that simulates magnetic reconnection under
low chromospheric conditions using a two-fluid (plasma + neutrals)
approach introduced by Leake et al. (2012). This model considers
non-equilibrium partial ionization effects including ionization,
recombination reactions and scattering collisions while simulating
the interplay between the charged particles with the electromagnetic
field. Previous 2D simulations showed that the dynamics of ions
and neutrals are decoupled during the reconnection process. Also,
the effect of the chemical non-equilibrium in the reconnection region
plays a crucial role, yielding faster reconnection rates. We extended
these simulations to study different 3D configurations in order to
analyze the impact of non-equilibrium partial ionization effects on
the neutral sheet configuration(s) and the reconnection rate of more
realistic geometries. The results are compared with the two-dimensional
simulations.
Title: Implication of Kappa models in realistic parameterization
of the kinetic anisotropy and the resulting instabilities in space
plasmas
Authors: Pierrard, V.; Poedts, S.; Lazar, M.
Bibcode: 2014AGUFMSH41A4115P
Altcode:
Direct in-situ measurements of the velocity distributions of
plasma particles in the solar wind reveal two distinct components:
a Maxwellian (thermal) core, and a less dense but hotter halo in
the high-energy (suprathermal) tails of the distribution, which
are well-described by Kappa power-laws. Despite these evidences,
the present attempts to parameterize the observed anisotropy and the
resulting plasma wave instabilities are limited to idealized models
of the distributions. These are, for instance, simplified models which
ignore the suprathermal populations, or minimize the role of the core,
assuming this component is cold, and model only the suprathermal tails
with a Kappa distribution function. It is worthwhile to asses to which
extent these models are relevant in realistic situations. Here, we
present a comparative analysis with more realistic approaches, which
combine a Maxwellian core, and one or two Kappa distributed components
(the halo and the field-aligned strahl in the fast wind). A comparison
is provided for the particular case of the cyclotron instabilities,
which enables us to emphasize the effects produced by the thermal spread
of plasma particles from the core, and extend approaching complex
situations frequently observed in the solar wind, when both the core
and halo populations are anisotropic. Correlated with the radial profile
of Kappa components in the heliosphere, these effects help us to build
a realistic picture on the role played by these instabilities in major
processes like heating and energy dissipation in the solar wind.
Title: Jupiter's Main Auroral Emission for Different Solar Wind
Conditions
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2014AGUFMSM24B..09C
Altcode:
We study the temporal change of Jupiter's magnetosphere and aurora due
to changing solar wind conditions. In particular, we examine how the
the main auroral emission is affected by the solar wind density. Using
three dimensional global MHD simulations, we perform three different
runs, with: 1) quiet solar wind conditions (ram pressure of 0.05 nPa),
2) disturbed solar wind conditions (ram pressure of 0.17 nPa), and 3)
very disturbed solar wind conditions (ram pressure of 0.34 nPa). We show
that the response of the main auroral emission depends on local time:
at noon, the main oval is only weakly affected by the variations in
the solar wind; whereas on the night side, the main emission becomes
brighter when the solar wind ram pressure increases. For instance,
10 hours after the high density solar wind reached the magnetosphere,
the peak in parallel electrical current on the night side is 20% and 40%
stronger for the disturbed and very disturbed solar wind conditions,
respectively. The main auroral emission begins to change three hours
after the solar wind density enhancement strikes the bow-shock and it
takes approximately three days for the magnetosphere to adjust to the
new solar wind conditions. The total electrical current flowing out
of the ionosphere is then 30% (50%) higher for the (very) disturbed
solar wind conditions than for the quiet solar wind conditions. In
addition, for the three simulations, a localized enhancement of the
main oval emission is periodically observed around noon local time
(inside the main oval discontinuity). A very similar enhancement
has already been observed with the Hubble Space Telescope in Far-UV
images by Palmaerts et al. (JGR, under review). In our simulations,
the localized peak is not caused by fluctuations in the solar wind,
but is always associated with a region of negative radial velocity
in the equatorial plane at the position where the corotation breaks
down. The shearing motions associated with this negative radial velocity
region produce strong gradients for Bz in the azimuthal direction,
which causes an enhancement of the electrical current.
Title: The interplay of Kappa and core populations in the solar wind:
Electromagnetic electron cyclotron instability
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.
Bibcode: 2014JGRA..119.9395L
Altcode:
Recently, a realistic parameterization was proposed for the
kinetic anisotropy and the resulting instabilities in the solar
wind plasma. This parameterization is based on observations of the
particle velocity distribution, which always comprises a Maxwellian
population at low energies, viz. the core, and a suprathermal halo
in the tail of the distribution which is best described by the
Kappa (power law) models. The cyclotron instability, driven by an
anisotropic electron halo, was found to be inhibited by the finite
thermal spread in the core, and this effect is highly dependent on
the halo-core relative density. In this paper, the interplay between
the Kappa and Maxwellian populations is further investigated for
more complex (less idealized) situations when both the core and halo
temperatures are anisotropic. Growth of this instability is markedly
stimulated by the core anisotropy. The wave numbers that are stable
for an isotropic core become unstable even for small anisotropies of
this population. Just a modest increase of the core anisotropy from
Ac=T⊥/T∥=1.2 to 2 causes the growth
rates to enhance by 1 order of magnitude, and the range of unstable
wave numbers to extend considerably. When the anisotropies in the core
and halo are comparable, the growth rate exhibits two distinct peaks,
the first driven by the halo at lower wave numbers and the second driven
by the core. However, the first peak is inhibited by the suprathermal
populations, while the second peak is sustained, suggesting a more
intricate connection between the core and Kappa populations.
Title: Erratum: "Observational Evidence of Torus Instability as
Trigger Mechanism for Coronal Mass Ejections: The 2011 August 4
Filament Eruption" (2014, ApJ,
785, 88)
Authors: Zuccarello, F. P.; Seaton, D. B.; Filippov, B.; Mierla, M.;
Poedts, S.; Rachmeler, L. A.; Romano, P.; Zuccarello, F.
Bibcode: 2014ApJ...795..175Z
Altcode:
No abstract at ADS
Title: Observational Characteristics of Coronal Mass Ejections
without Low-coronal Signatures
Authors: D'Huys, E.; Seaton, D. B.; Poedts, S.; Berghmans, D.
Bibcode: 2014ApJ...795...49D
Altcode: 2014arXiv1409.1422D
Solar eruptions are usually associated with a variety of phenomena
occurring in the low corona before, during, and after the onset of
eruption. Though easily visible in coronagraph observations, so-called
stealth coronal mass ejections (CMEs) do not obviously exhibit any
of these low-coronal signatures. The presence or absence of distinct
low-coronal signatures can be linked to different theoretical models
to establish the mechanisms by which the eruption is initiated
and driven. In this study, 40 CMEs without low-coronal signatures
occurring in 2012 are identified. Their observational and kinematic
properties are analyzed and compared to those of regular CMEs. Solar
eruptions without clear on-disk or low-coronal signatures can lead to
unexpected space weather impacts, since many early warning signs for
significant space weather activity are not present in these events. A
better understanding of their initiation mechanism(s) will considerably
improve the ability to predict such space weather events.
Title: Solar Wind Electron Strahls Associated with a High-Latitude
CME: Ulysses Observations
Authors: Lazar, M.; Pomoell, J.; Poedts, S.; Dumitrache, C.; Popescu,
N. A.
Bibcode: 2014SoPh..289.4239L
Altcode: 2014SoPh..tmp...97L; 2014arXiv1405.5690L
Counterstreaming beams of electrons are ubiquitous in coronal mass
ejections (CMEs) - although their existence is not unanimously accepted
as a necessary and/or sufficient signature of these events. We continue
the investigation of a high-latitude CME registered by the Ulysses
spacecraft on 18 - 19 January 2002 (Dumitrache, Popescu, and Oncica,
Solar Phys. 272, 137, 2011), by surveying the solar-wind electron
distributions associated with this event. The temporal evolution of
the pitch-angle distributions reveals populations of electrons that
are distinguishable through their anisotropy, with clear signatures of
i) electron strahls, ii) counter-streaming in the magnetic clouds and
their precursors, and iii) unidirectionality in the fast wind preceding
the CME. The analysis of the counter-streams inside the CME allows us
to elucidate the complexity of the magnetic-cloud structures embedded
in the CME and to refine the borders of the event. Identifying such
strahls in CMEs, which preserve properties of the low β [<1] coronal
plasma, gives more support to the hypothesis that these populations are
remnants of the hot coronal electrons that escape from the electrostatic
potential of the Sun into the heliosphere.
Title: 3D Global Magnetohydrodynamic Simulations of the Solar
Wind/Earth's Magnetosphere Interaction
Authors: Yalim, M. S.; Poedts, S.
Bibcode: 2014ASPC..488..192Y
Altcode:
In this paper, we present results of real-time 3D global
magnetohydrodynamic (MHD) simulations of the solar wind interaction
with the Earth's magnetosphere using time-varying data from the NASA
Advanced Composition Explorer (ACE) satellite during a few big magnetic
storm events of the previous and current solar cycles, namely the 06
April 2000, 20 November 2003 and 05 April 2010 storms. We introduce
a numerical magnetic storm index and compare the geo-effectiveness of
these events in terms of this storm index which is a measure for the
resulting global perturbation of the Earth's magnetic field. Steady
simulations show that the upstream solar wind plasma parameters enter
the low-β switch-on regime for some time intervals during a magnetic
storm causing a complex dimpled bow shock structure. We also investigate
the traces of such bow shock structures during time-dependent
simulations of the events. We utilize a 3D, implicit, parallel,
unstructured grid, compressible finite volume ideal MHD solver with
an anisotropic grid adaptation technique for the computer simulations.
Title: Overstability of acoustic waves in strongly magnetized
anisotropic magnetohydrodynamic shear flows
Authors: Uchava, E. S.; Shergelashvili, B. M.; Tevzadze, A. G.;
Poedts, S.
Bibcode: 2014PhPl...21h2902U
Altcode: 2014arXiv1407.6943U
We present a linear stability analysis of the perturbation modes in
anisotropic magnetohydrodynamic (MHD) flows with velocity shear and
strong magnetic field. Collisionless or weakly collisional plasma
is described within the 16-momentum MHD fluid closure model that
takes into account not only the effect of pressure anisotropy but
also the effect of anisotropic heat fluxes. In this model, the low
frequency acoustic wave is revealed into a standard acoustic mode
and higher frequency fast thermo-acoustic and lower frequency slow
thermo-acoustic waves. It is shown that thermo-acoustic waves become
unstable and grow exponentially when the heat flux parameter exceeds
some critical value. It seems that velocity shear makes thermo-acoustic
waves overstable even at subcritical heat flux parameters. Thus, when
the effect of heat fluxes is not profound acoustic waves will grow
due to the velocity shear, while at supercritical heat fluxes the
flow reveals compressible thermal instability. Anisotropic thermal
instability should be also important in astrophysical environments,
where it will limit the maximal value of magnetic field that a low
density ionized anisotropic flow can sustain.
Title: Simulating AIA observations of a flux rope ejection
Authors: Pagano, P.; Mackay, D. H.; Poedts, S.
Bibcode: 2014A&A...568A.120P
Altcode: 2014arXiv1407.8397P
Context. Coronal mass ejections (CMEs) are the most violent phenomena
observed on the Sun. Currently, extreme ultraviolet (EUV) images from
the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
Observatory (SDO) are providing new insights into the early phase of
CME evolution. In particular, observations now show the ejection of
magnetic flux ropes from the solar corona and how they evolve into
CMEs. While this is the case, these observations are difficult to
interpret in terms of basic physical mechanisms and quantities. To fully
understand CMEs we need to compare equivalent quantities derived from
both observations and theoretical models. This will aid in bridging the
gap between observations and models.
Aims: To this end, we aim
to produce synthesised AIA observations from simulations of a flux rope
ejection. To carry this out we include the role of thermal conduction
and radiative losses, both of which are important for determining the
temperature distribution of the solar corona during a CME.
Methods: We perform a simulation where a flux rope is ejected from
the solar corona. From the density and temperature of the plasma in
the simulation we synthesise AIA observations. The emission is then
integrated along the line of sight using the instrumental response
function of AIA.
Results: We sythesise observations of AIA in
the channels at 304 Å, 171 Å, 335 Å, and 94 Å. The synthesised
observations show a number of features similar to actual observations
and in particular reproduce the general development of CMEs in the low
corona as observed by AIA. In particular we reproduce an erupting and
expanding arcade in the 304 Å and 171 Å channels with a high density
core.
Conclusions: The ejection of a flux rope reproduces many
of the features found in the AIA observations. This work is therefore
a step forward in bridging the gap between observations and models, and
can lead to more direct interpretations of EUV observations in terms of
flux rope ejections. We plan to improve the model in future studies in
order to perform a more quantitative comparison. Movies associated
with Figs. 3, 9, and 10 are available in electronic form at http://www.aanda.org
Title: Writhe vs. twist as a dominating feature of ICMEs' magnetic
field
Authors: Al-Haddad, Nada; Poedts, Stefaan; Farrugia, Charles J.;
Lugaz, Noé
Bibcode: 2014shin.confE...6A
Altcode:
The magnetic field configuration in coronal mass ejections (CMEs) has
been the subject of a number of recent studies that aimed to understand
its morphology through various methods: with different magnetic field
fitting and reconstruction codes using in situ measurements at 1 AU,
with numerical simulations and with remote-sensing observations by
STEREO and SDO. With most of these methods, it is assumed that CMEs
consist of a twisted magnetic flux rope. We have previously shown how
sheared magnetic field lines in a CME may be mistaken for a twisted flux
rope when observed in situ by a single spacecraft, due to the limitation
of reconstruction methods. Here, we present our most recent study on
this subject. We study the ability of multi-spacecraft measurements to
distinguish between different structures of the CME magnetic field. We
do so by comparing reconstruction obtained using measurements of
a simulated writhed CME to that obtained using measurements of a
twisted flux rope for different spacecraft location with respect to
the CME direction of propagation. We also discuss how these two types
of structures may evolve as they propagate in the inner heliosphere
and whether sheared or writhed field lines have been detected before.
Title: Variation of Proton Flux Profiles with the Observer's Latitude
in Simulated Gradual SEP Events
Authors: Rodríguez-Gasén, R.; Aran, A.; Sanahuja, B.; Jacobs, C.;
Poedts, S.
Bibcode: 2014SoPh..289.1745R
Altcode: 2013arXiv1310.4651R; 2013SoPh..tmp..288R
We studied the variation of the shape of the proton intensity-time
profiles in simulated gradual Solar Energetic Particle (SEP) events
with the relative observer's position in space with respect to the
main direction of propagation of an interplanetary (IP) shock. Using a
three-dimensional (3D) magnetohydrodynamic (MHD) code to simulate such
a shock, we determined the evolution of the downstream-to-upstream
ratios of the plasma variables at its front. Under the assumption of
an existing relation between the normalized ratio in speed across the
shock front and the injection rate of shock-accelerated particles, we
modelled the transport of the particles and obtained the proton flux
profiles to be measured by a grid of 18 virtual observers located at
0.4 and 1.0 AU, with different latitudes and longitudes with respect
to the shock nose. The differences among flux profiles are the result
of the way each observer establishes a magnetic connection with the
shock front, and we found that changes in the observer's latitude may
result in intensity changes of up to one order of magnitude at the
two radial distances considered here. The peak intensity variation
with the radial distance for the pair of observers located at the
same angular position was also derived. This is the first time that
the latitudinal dependence of the peak intensity with the observer's
heliocentric radial distance has been quantified within the framework
of gradual SEP event simulations.
Title: Solar Decameter Spikes
Authors: Melnik, V. N.; Shevchuk, N. V.; Konovalenko, A. A.; Rucker,
H. O.; Dorovskyy, V. V.; Poedts, S.; Lecacheux, A.
Bibcode: 2014SoPh..289.1701M
Altcode: 2013SoPh..tmp..281M
We analyze and discuss the properties of decameter spikes observed in
July - August 2002 by the UTR-2 radio telescope. These bursts have
a short duration (about one second) and occur in a narrow frequency
bandwidth (50 - 70 kHz). They are chaotically located in the dynamic
spectrum. Decameter spikes are weak bursts: their fluxes do not
exceed 200 - 300 s.f.u. An interesting feature of these spikes
is the observed linear increase of the frequency bandwidth with
frequency. This dependence can be explained in the framework of the
plasma mechanism that causes the radio emission, taking into account
that Langmuir waves are generated by fast electrons within a narrow
angle θ≈13∘ - 18∘ along the direction
of the electron propagation. In the present article we consider the
problem of the short lifetime of decameter spikes and discuss why
electrons generate plasma waves in limited regions.
Title: Observational Evidence of Torus Instability as Trigger
Mechanism for Coronal Mass Ejections: The 2011 August 4 Filament
Eruption
Authors: Zuccarello, F. P.; Seaton, D. B.; Mierla, M.; Poedts, S.;
Rachmeler, L. A.; Romano, P.; Zuccarello, F.
Bibcode: 2014ApJ...785...88Z
Altcode: 2014arXiv1401.5936Z
Solar filaments are magnetic structures often observed in the solar
atmosphere and consist of plasma that is cooler and denser than their
surroundings. They are visible for days—even weeks—which suggests
that they are often in equilibrium with their environment before
disappearing or erupting. Several eruption models have been proposed
that aim to reveal what mechanism causes (or triggers) these solar
eruptions. Validating these models through observations represents a
fundamental step in our understanding of solar eruptions. We present
an analysis of the observation of a filament eruption that agrees with
the torus instability model. This model predicts that a magnetic flux
rope embedded in an ambient field undergoes an eruption when the axis of
the flux rope reaches a critical height that depends on the topology of
the ambient field. We use the two vantage points of the Solar Dynamics
Observatory (SDO) and the Solar TErrestrial RElations Observatory to
reconstruct the three-dimensional shape of the filament, to follow
its morphological evolution, and to determine its height just before
eruption. The magnetograms acquired by SDO/Helioseismic and Magnetic
Imager are used to infer the topology of the ambient field and to derive
the critical height for the onset of the torus instability. Our analysis
shows that the torus instability is the trigger of the eruption. We also
find that some pre-eruptive processes, such as magnetic reconnection
during the observed flares and flux cancellation at the neutral line,
facilitated the eruption by bringing the filament to a region where
the magnetic field was more vulnerable to the torus instability.
Title: Electrostatic plasma instabilities driven by neutral gas
flows in the solar chromosphere
Authors: Gogoberidze, G.; Voitenko, Y.; Poedts, S.; De Keyser, J.
Bibcode: 2014MNRAS.438.3568G
Altcode: 2013arXiv1312.5767G; 2014MNRAS.tmp..148G
We investigate electrostatic plasma instabilities of Farley-Buneman
(FB) type driven by quasi-stationary neutral gas flows in the solar
chromosphere. The role of these instabilities in the chromosphere
is clarified. We find that the destabilizing ion thermal effect is
highly reduced by the Coulomb collisions and can be ignored for the
chromospheric FB-type instabilities. In contrast, the destabilizing
electron thermal effect is important and causes a significant reduction
of the neutral drag velocity triggering the instability. The resulting
threshold velocity is found as function of chromospheric height. Our
results indicate that the FB-type instabilities are still less efficient
in the global chromospheric heating than the Joule dissipation of
the currents driving these instabilities. This conclusion does not
exclude the possibility that the FB-type instabilities develop in
the places where the cross-field currents overcome the threshold
value and contribute to the heating locally. Typical length-scales
of plasma density fluctuations produced by these instabilities
are determined by the wavelengths of unstable modes, which are
in the range 10-102 cm in the lower chromosphere and
102-103 cm in the upper chromosphere. These
results suggest that the decimetric radio waves undergoing scattering
(scintillations) by these plasma irregularities can serve as a tool
for remote probing of the solar chromosphere at different heights.
Title: Magnetohydrodynamic study on the effect of the gravity
stratification on flux rope ejections
Authors: Pagano, Paolo; Mackay, Duncan H.; Poedts, Stefaan
Bibcode: 2014IAUS..300..197P
Altcode:
Coronal Mass Ejections (CMEs) are one of the most violent phenomena
found on the Sun. One model to explain their occurrence is the flux rope
ejection model where these magnetic structures firt form in the solar
corona then are ejected to produce a CME. We run simulations coupling
two models. The Global Non-Linear Force-Free Field (GNLFFF) evolution
model to follow the quasi-static formation of a flux rope and MHD
simulations for the production of a CME through the loss of equilibrium
and ejection of this flux rope in presence of solar gravity and density
stratification. Our realistic multi-beta simulations describe the CME
following the flux rope ejection and highlight the decisive role played
by the gravity stratification on the CME propagation speed.
Title: Shearing motions and torus instability in the 2010 April 3
filament eruption
Authors: Zuccarello, F. P.; Romano, P.; Zuccarello, F.; Poedts, S.
Bibcode: 2014IAUS..300..475Z
Altcode:
The magnetic field evolution of active region NOAA 11059 is studied
in order to determine the possible causes and mechanisms that led to
the initiation of the 2010 April 3 coronal mass ejection (CME). We find (1) that the magnetic configuration of the active region
is unstable to the torus instability and (2) that persistent shearing
motions characterized the negative polarity, resulting in a southward,
almost parallel to the meridians, drift motion of the negative magnetic
field concentrations. We conclude that these shearing motions
increased the axial field of the filament eventually bringing the
flux rope axis to a height where the onset condition for the torus
instability was satisfied.
Title: Instability of the parallel electromagnetic modes in Kappa
distributed plasmas - II. Electromagnetic ion-cyclotron modes
Authors: Lazar, M.; Poedts, S.
Bibcode: 2014MNRAS.437..641L
Altcode: 2013MNRAS.tmp.2559L
The low-frequency fluctuations of the interplanetary magnetic
field are frequently attributed to electromagnetic ion-cyclotron
(EMIC) waves generated either locally and self-consistently by the
temperature anisotropy of ions, or in the corona and transported by the
super-Alfvénic solar wind. This paper conducts a refined analysis of
the EMIC instability in the presence of suprathermal populations. The
anisotropic distributions are modelled with two different power-law
distributions functions, the additive bi-Kappa (BK) and the more general
product-bi-Kappa (PBK) distribution function. EMIC solutions are derived
exactly numerically for the full range of the plasma parameters,
including conditions relevant for the solar wind and magnetospheric
plasmas. Accurate physical correlations are provided between the maximum
growth rates and the instability threshold conditions. The expectation
that the instability might be stimulated by the suprathermals is
confirmed by both Kappa models, but in a complementary way: while
the instability thresholds are lowered by the BK model, at higher
anisotropies the growth rates are enhanced only by the PBK model.
Title: The ESA Virtual Space Weather Modelling Centre - Phase 1
Authors: Poedts, Stefaan
Bibcode: 2014cosp...40E2576P
Altcode:
The ESA ITT project (AO/1-6738/11/NL/AT) to develop Phase 1 of a
Virtual Space Weather Modelling Centre has the following objectives
and scope: 1. The construction of a long term (~10 yrs) plan for
the future development of a European virtual space weather modelling
centre consisting of a new ‘open’ and distributed framework for the
coupling of physics based models for space weather phenomena; 2. The
assessment of model capabilities and the amount of work required to
make them operational by integrating them in this framework and the
identification of computing and networking requirements to do so. 3. The
design of a system to enable models and other components to be installed
locally or geographically distributed and the creation of a validation
plan including a system of metrics for testing results. The consortium
that took up this challenge involves: 1)the Katholieke Universiteit
Leuven (Prime Contractor, coordinator: Prof. S. Poedts); 2) the Belgian
Institute for Space Aeronomy (BIRA-IASB); 3) the Royal Observatory of
Belgium (ROB); 4) the Von Karman Institute (VKI); 5) DH Consultancy
(DHC); 6) Space Applications Services (SAS). The project started on May
14 2012, and will finish in May 2014. Thus, by the time of the meeting,
both Phase 1A and Phase 1B (the development of the prototype) will be
finished. The final report will be presented incl. the architecture
decisions made, the framework, the current models integrated already
as well as the model couplers installed. The prototype VSWMC will
be demonstrated.
Title: The Electron Firehose and Ordinary-Mode Instabilities in
Space Plasmas
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.; Ibscher, D.
Bibcode: 2014SoPh..289..369L
Altcode: 2013arXiv1307.0768L
Self-generated wave fluctuations are particularly interesting in the
solar wind and magnetospheric plasmas, where Coulomb collisions are rare
and cannot explain the observed states of quasi-equilibrium. Linear
theory predicts that firehose and ordinary-mode instabilities
can develop under the same conditions, which makes it challenging
to separate the role of these instabilities in conditioning the
space-plasma properties. The hierarchy of these two instabilities is
reconsidered here for nonstreaming plasmas with an electron-temperature
anisotropy T∥>T⊥, where ∥ and ⊥ denote
directions with respect to the local mean magnetic field. In addition
to the previously reported comparative analysis, here the entire 3D
wave-vector spectrum of the competing instabilities is investigated,
with a focus on the oblique firehose instability and the relatively
poorly known ordinary-mode instability. Results show a dominance of the
oblique firehose instability with a threshold lower than the parallel
firehose instability and lower than the ordinary-mode instability. For
stronger anisotropies, the ordinary mode can grow faster, with maximum
growth rates exceeding those of the oblique firehose instability. In
contrast to previous studies that claimed a possible activity of the
ordinary-mode in the low β [< 1] regimes, here it is rigorously
shown that only the high β [> 1] regimes are susceptible to these
instabilities.
Title: Variations in EUV Irradiance: Comparison between LYRA, ESP,
and SWAP Integrated Flux
Authors: Yalim, Mehmet Sarp; Poedts, Stefaan
Bibcode: 2014AdAst2014E..15Y
Altcode: 2014AdAst2014....1Y
The Sun Watcher Using Active Pixel System Detector and Image Processing
(SWAP) telescope and Large Yield Radiometer (LYRA) are the two Sun
observation instruments on-board PROBA2. SWAP extreme ultraviolet
images, if presented in terms of the integrated flux over solar disk,
in general, correlate well with LYRA channel 2-4 (zirconium filter) and
channels QD and 18 of EVE/ESP on-board SDO between 2010 and 2013. Hence,
SWAP can be considered as an additional radiometric channel. We compare
in detail LYRA channel 2-4 and SWAP integrated flux in July 2010
and in particular during the solar eclipse that occurred on July 11,
2010. During this eclipse, the discrepancy between the two data channels
can be explained to be related to the occultation of active region
11087 by the Moon. In the second half of July 2010, LYRA channel 2-4
and SWAP integrated flux deviate from each other, but these differences
can also be explained in terms of features appearing on the solar disk
such as coronal holes and active regions. By additionally comparing with
timeline of EVE/ESP, we can preliminarily interpret these differences
in terms of the difference between the broad bandpass of LYRA channel
2-4 and the, relatively speaking, narrower bandpass of SWAP.
Title: The Magnetic Field Structure of Writhed ICMEs vs. Twisted ICMEs
Authors: Al-haddad, Nada; Farrugia, Charles; Poedts, Stefaan;
Lugaz, Noé
Bibcode: 2014cosp...40E..47A
Altcode:
The magnetic field configuration in coronal mass ejections (CMEs) has
been the subject of a number of recent studies that aimed to understand
its morphology through various methods: with different magnetic field
fitting and reconstruction codes using in situ measurements at 1 AU,
with numerical simulations and with new remote-sensing observations
by STEREO and SDO, among other methods. With most of these methods,
it is assumed that CMEs consist of a twisted magnetic flux rope. We
have previously shown how sheared magnetic field lines in a CME may
be mistaken for a twisted flux rope when observed in situ by a single
spacecraft, due to the limitation of reconstruction methods. Here,
we present our most recent study in this subject, where we study the
ability of multi-spacecraft measurements to determine the structure
of a CME's magnetic field. We do so by comparing the reconstructed
magnetic field of obtained using measurements of a simulated writhed
CME to that obtained using measurements of a twisted flux rope. We also
discuss how these two types of structures may evolve as they propagate
in the inner heliosphere and whether sheared or writhed field lines
have been detected before.
Title: On the Influence of the Solar Wind Density on the Jovian Main
Auroral Emission
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2013AGUFMSM11E..06C
Altcode:
The influence of the solar wind density on Jupiter's main auroral
emission is studied with our three dimensional global MHD model. We
perform three simulations: in the first one, we maintain quiet solar
wind conditions during the whole run [ram pressure of 0.05 nPa, see Joy,
2002]; in the second one, we suddenly increase the solar wind density
to mimic a transition from quiet to disturbed solar wind conditions
[ram pressure of 0.17 nPa, see Joy, 2002]; in the third simulation,
the solar wind conditions vary from quiet to strongly disturbed [ram
pressure of 0.34 nPa]. The field aligned electric current pointing away
from the ionosphere is used as a proxy to determine the position and
the brightness of the aurorae. The effect of the solar wind density
on the main auroral emission strongly varies with local time. 10 hours
after the high density solar wind reached the bow shock, around 10:00LT,
where the main emission discontinuity is located [Radioti et al., 2008],
the peak in the emission becomes weaker for the disturbed and for the
strongly disturbed cases; but the main emission also becomes wider. This
results in a total emission 5% and 17% brighter at 10:00LT for the
disturbed and strongly disturbed cases, respectively. On the night
side, the peaks in the emission intensity are approximately 20% and 40%
brighter for the disturbed and strongly disturbed cases, respectively;
and the emission width does not change significantly. The main auroral
emission begins to change three hours after the solar wind density
enhancement strikes the Jovian bow-shock. The main auroral emission
intensification is mainly caused by a modification of the thermal
pressure pattern, due to the new location of the magnetopause. As
a result, the plasma azimuthal velocity changes, which modifies the
strength of the radial electric currents in the equatorial plane and
the main auroral emission.
Title: Global Simulations of the Magnetosphere under Sub-Alfvénic
Solar Wind Conditions. (Invited)
Authors: Chané, E.; Raeder, J.; Saur, J.; Neubauer, F. M.; Poedts, S.
Bibcode: 2013AGUFMSM44A..05C
Altcode:
During 24 and 25 May 2002 the solar wind density at Earth was so low
(below 0.1 ç) that the flow was sub-fast and sub-Alfvénic (Alfvén
Mach number as low as 0.4 in the rest frame of the Earth). Due to these
unusual solar wind conditions, the Earth's bow-shock disappeared and
two Alfvén wings formed on the flanks of the magnetosphere (see Chané
et al., 2012). These Alfvén wings are two long structures (estimated
extension of 600 Re for this event), where the solar wind plasma
is decelerated and the magnetic field direction changes (estimated
deceleration of 30% in one wing and 60% in the other wing for this
event). In the present study, we perform global numerical simulations
of the magnetosphere for such incoming solar wind conditions. The
simulations show how the magnetosphere configuration dramatically
changes when the sub-Alfvénic solar wind reaches the magnetosphere:
Whereas the day side magnetopause expends up to 20 Re, the position
of the last closed field line on the night side diminishes to 20
Re. As a result the closed magnetic field line region becomes very
symmetric. The open field line configuration also changes drastically:
while the field lines emanating from the northern hemisphere all
point in the direction of the dawn Alfvén wing (around 8:00LT), the
field lines from the southern hemisphere all point in the other wing
(around 22:00LT). During the formation of the Alfvén wings, the lobes
completely disappeared and the auroral activity greatly diminished.
Title: Effect of gravitational stratification on the propagation of
a CME
Authors: Pagano, P.; Mackay, D. H.; Poedts, S.
Bibcode: 2013A&A...560A..38P
Altcode: 2013arXiv1310.6960P
Context. Coronal mass ejections (CMEs) are the most violent phenomenon
found on the Sun. One model that explains their occurrence is the
flux rope ejection model. A magnetic flux rope is ejected from the
solar corona and reaches the interplanetary space where it interacts
with the pre-existing magnetic fields and plasma. Both gravity and
the stratification of the corona affect the early evolution of the
flux rope.
Aims: Our aim is to study the role of gravitational
stratification on the propagation of CMEs. In particular, we assess how
it influences the speed and shape of CMEs and under what conditions
the flux rope ejection becomes a CME or when it is quenched.
Methods: We ran a set of MHD simulations that adopt an eruptive
initial magnetic configuration that has already been shown to be
suitable for a flux rope ejection. We varied the temperature of
the backgroud corona and the intensity of the initial magnetic
field to tune the gravitational stratification and the amount of
ejected magnetic flux. We used an automatic technique to track the
expansion and the propagation of the magnetic flux rope in the MHD
simulations. From the analysis of the parameter space, we evaluate the
role of gravitational stratification on the CME speed and expansion.
Results: Our study shows that gravitational stratification plays a
significant role in determining whether the flux rope ejection will
turn into a full CME or whether the magnetic flux rope will stop in
the corona. The CME speed is affected by the background corona where
it travels faster when the corona is colder and when the initial
magnetic field is more intense. The fastest CME we reproduce in
our parameter space travels at ~850 km s-1. Moreover,
the background gravitational stratification plays a role in the side
expansion of the CME, and we find that when the background temperature
is higher, the resulting shape of the CME is flattened more.
Conclusions: Our study shows that although the initiation mechanisms
of the CME are purely magnetic, the background coronal plasma plays
a key role in the CME propagation, and full MHD models should be
applied when one focuses especially on the production of a CME from
a flux rope ejection. Movies are available in electronic form at
http://www.aanda.org
Title: SoFAST: Automated Flare Detection with the PROBA2/SWAP
EUV Imager
Authors: Bonte, K.; Berghmans, D.; De Groof, A.; Steed, K.; Poedts, S.
Bibcode: 2013SoPh..286..185B
Altcode: 2012SoPh..tmp..288B
The Sun Watcher with Active Pixels and Image Processing (SWAP)
EUV imager onboard PROBA2 provides a non-stop stream of coronal
extreme-ultraviolet (EUV) images at a cadence of typically 130
seconds. These images show the solar drivers of space-weather, such
as flares and erupting filaments. We have developed a software tool
that automatically processes the images and localises and identifies
flares. On one hand, the output of this software tool is intended
as a service to the Space Weather Segment of ESA's Space Situational
Awareness (SSA) program. On the other hand, we consider the PROBA2/SWAP
images as a model for the data from the Extreme Ultraviolet Imager (EUI)
instrument prepared for the future Solar Orbiter mission, where onboard
intelligence is required for prioritising data within the challenging
telemetry quota. In this article we present the concept of the software,
the first statistics on its effectiveness and the online display in
real time of its results. Our results indicate that it is not only
possible to detect EUV flares automatically in an acquired dataset,
but that quantifying a range of EUV dynamics is also possible. The
method is based on thresholding of macropixelled image sequences. The
robustness and simplicity of the algorithm is a clear advantage for
future onboard use.
Title: Properties of the complex type II burst with rich herringbone
structure within 3-33 MHz
Authors: Dorovskyy, V. V.; Melnik, V. M.; Konovalenko, O. O.;
Brazhenko, A. I.; Panchenko, M.; Rucker, H. O.; Poedts, S.;
Stanislavsky, A. A.; Mykhaylov, V. A.
Bibcode: 2013RRPRA..18..107D
Altcode:
Characteristics of the type II burst with "herringbone" structure
observed on 7 June 2011 within 3-33 MHz are considered. The burst
was recorded both by the two ground-based radiotelescopes (UTR-2,
URAN-2) and the spaceborne STEREO radio receivers. For the first time, a
detailed statistical analysis of main parameters of the herringbone sub-
bursts of type II (duration and frequency drift rate) was performed at
decameter wavelengths separately for those positively and negatively
drifting ones. Another new result within these frequencies is the
measured degree of circular polarization of fine structure type II
bursts. A fine frequency, structure of the sub-bursts herringbone
was found to be, similar to the so-called "fringes" in the solar
S-bursts. From the characteristic wave-like oscillations of the type
II back-bone the parameters of coronal streamers intersected by the
shock wave were derived. Using the observational data from the STEREO
and SOHO spacecraft, the speed and direction of the associated CME
propagation were detected. From the ground-based radio observations the
radial speed of type II burst source was found. As a result, possible
location of the type II burst source was determined. In addition,
the geoeffectiveness of the discussed solar event was estimated.
Title: Electromagnetic electron whistler-cyclotron instability in
bi-Kappa distributed plasmas
Authors: Lazar, M.; Poedts, S.; Michno, M. J.
Bibcode: 2013A&A...554A..64L
Altcode:
Context. Recent studies of the electromagnetic electron
whistler-cyclotron instability in anisotropic bi-Kappa distributed
plasmas claim that the instability threshold conditions do not depend on
the power index, κe, of the electron distribution function,
but that the maximum growth rate (γm) strongly depends on
this parameter. But these two statements contradict each other because
the instability threshold conditions are derived with respect to the
threshold levels of the maximum growth rates (e.g.,γm/Ω
= 10-1,10-2, etc.).
Aims: This paper
proposes to clarify this inconsistency, refining the analysis of the
electron-whistler cyclotron instability. In anisotropic plasmas far
from Maxwellian equilibrium, this instability represents one of the most
plausible constraints for the electron temperature anisotropy Te,
⊥ > Te, ∥, (where ∥ and ⊥ denote directions
relative to the local stationary magnetic field).
Methods: In the
context of a suprathermal solar wind, where the electron populations
are well fitted by the advanced Kappa distribution functions, these
models are expected to provide a more realistic description for the
critical stability conditions. The unstable solutions are derived
exactly numerically, providing accurate physical correlations between
the maximum growth rates and the threshold conditions.
Results:
Thresholds of the temperature anisotropy are derived for the full
range of values of the plasma beta including both the solar wind and
magnetospheric plasma conditions. The lowest thresholds, which are
the most relevant for the marginal stability, are found to decrease
with the increase in density of the suprathermal populations. This
result is correlated with an opposite effect on the corresponding
growth rates (at low anisotropies), because their maximum values are
enhanced in the presence of suprathermal electrons. The new marginal
thresholds calculated with a bi-Kappa model are expected to provide
better predictions for the limits of the temperature anisotropy in
the solar wind.
Title: Magnetohydrodynamic simulations of the ejection of a magnetic
flux rope
Authors: Pagano, P.; Mackay, D. H.; Poedts, S.
Bibcode: 2013A&A...554A..77P
Altcode:
Context. Coronal mass ejections (CME's) are one of the most violent
phenomena found on the Sun. One model to explain their occurrence is
the flux rope ejection model. In this model, magnetic flux ropes form
slowly over time periods of days to weeks. They then lose equilibrium
and are ejected from the solar corona over a few hours. The contrasting
time scales of formation and ejection pose a serious problem for
numerical simulations.
Aims: We simulate the whole life span
of a flux rope from slow formation to rapid ejection and investigate
whether magnetic flux ropes formed from a continuous magnetic field
distribution, during a quasi-static evolution, can erupt to produce a
CME.
Methods: To model the full life span of magnetic flux ropes
we couple two models. The global non-linear force-free field (GNLFFF)
evolution model is used to follow the quasi-static formation of a flux
rope. The MHD code ARMVAC is used to simulate the production of a CME
through the loss of equilibrium and ejection of this flux rope.
Results: We show that the two distinct models may be successfully
coupled and that the flux rope is ejected out of our simulation box,
where the outer boundary is placed at 2.5 R⊙. The plasma
expelled during the flux rope ejection travels outward at a speed of
100 km s-1, which is consistent with the observed speed of
CMEs in the low corona.
Conclusions: Our work shows that flux
ropes formed in the GNLFFF can lead to the ejection of a mass loaded
magnetic flux rope in full MHD simulations. Coupling the two distinct
models opens up a new avenue of research to investigate phenomena where
different phases of their evolution occur on drastically different
time scales. Movies are available in electronic form at http://www.aanda.org
Title: Numerical Simulations of Dome-Shaped EUV Waves from Different
Active-Region Configurations
Authors: Selwa, M.; Poedts, S.; DeVore, C. R.
Bibcode: 2013SoPh..284..515S
Altcode:
Recently, 3D STEREO observations explained the 3D structure of EUV
waves. Patsourakos and Vourlidas (Astrophys. J.700, L182, 2009), Veronig
et al. (Astrophys. J.716, L57, 2010) and Selwa, Poedts, and DeVore
(Astrophys. J.747, L21, 2012) reported on the dome-shaped EUV waves
resulting from different events. Here, we model, by means of 3D MHD
simulations, the formation of dome-shaped EUV waves in rotating active
regions (ARs). The numerical simulations are initialized with idealized
(multi-)dipolar coronal (low β) configurations. Next, we apply a
sheared rotational motion to the central parts of all the positive and
negative flux regions at the photospheric boundary. As a result, the
flux tubes connecting the flux sources become twisted. We find that in
all the studied configurations of idealized ARs, the rotating motion
results in a dome-shaped structure originating from the AR. However,
the shape of the dome depends on the initial configuration (topology of
the AR). The initial stage of the wave evolution consists of multiple
fronts that later merge together forming a single wave. The observed
EUV wave propagates nearly isotropically on the disk and also in the
upward direction. We remark that the initial stage of the evolution
is determined by the driver and not caused by a magnetic reconnection
event. At a later stage, however, the wave propagates freely. We study
the different wave properties resulting from different driver speeds
and find that independent of the initial AR topology the 3D dome-shaped
wave is excited in the system. The symmetry of the 3D dome depends on
the topology of the AR and on the duration of the driver. The EUV wave
triggered is independent of the temporal profile of the driver. However,
the properties of the wave (speed, sharpness of the cross-section,
etc.) depend on the type of the trigger.
Title: Magnetic Field Configuration Models and Reconstruction Methods
for Interplanetary Coronal Mass Ejections
Authors: Al-Haddad, N.; Nieves-Chinchilla, T.; Savani, N. P.;
Möstl, C.; Marubashi, K.; Hidalgo, M. A.; Roussev, I. I.; Poedts,
S.; Farrugia, C. J.
Bibcode: 2013SoPh..284..129A
Altcode: 2012arXiv1209.6394A
This study aims to provide a reference for different magnetic field
models and reconstruction methods for interplanetary coronal mass
ejections (ICMEs). To understand the differences in the outputs of
these models and codes, we analyzed 59 events from the Coordinated
Data Analysis Workshop (CDAW) list, using four different magnetic
field models and reconstruction techniques; force-free fitting,
magnetostatic reconstruction using a numerical solution to the
Grad-Shafranov equation, fitting to a self-similarly expanding
cylindrical configuration and elliptical, non-force-free fitting. The
resulting parameters of the reconstructions for the 59 events are
compared statistically and in selected case studies. The ability of a
method to fit or reconstruct an event is found to vary greatly; this
depends on whether the event is a magnetic cloud or not. We find that
the magnitude of the axial field is relatively consistent across models,
but that the axis orientation of the ejecta is not. We also find that
there are a few cases with different signs of the magnetic helicity
for the same event when we leave the boundaries free to vary, which
illustrates that this simplest of parameters is not necessarily always
clearly constrained by fitting and reconstruction models. Finally, we
examine three unique cases in depth to provide a comprehensive idea of
the different aspects of how the fitting and reconstruction codes work.
Title: Forecasting the Earth's radiation belts and modelling solar
energetic particle events: Recent results from SPACECAST
Authors: Horne, Richard B.; Glauert, Sarah A.; Meredith, Nigel P.;
Koskinen, Hannu; Vainio, Rami; Afanasiev, Alexandr; Ganushkina,
Natalia Y.; Amariutei, Olga A.; Boscher, Daniel; Sicard, Angelica;
Maget, Vincent; Poedts, Stefaan; Jacobs, Carla; Sanahuja, Blai; Aran,
Angels; Heynderickx, Daniel; Pitchford, David
Bibcode: 2013JSWSC...3A..20H
Altcode:
High-energy charged particles in the van Allen radiation belts and in
solar energetic particle events can damage satellites on orbit leading
to malfunctions and loss of satellite service. Here we describe some
recent results from the SPACECAST project on modelling and forecasting
the radiation belts, and modelling solar energetic particle events. We
describe the SPACECAST forecasting system that uses physical models that
include wave-particle interactions to forecast the electron radiation
belts up to 3 h ahead. We show that the forecasts were able to reproduce
the >2 MeV electron flux at GOES 13 during the moderate storm of 7-8
October 2012, and the period following a fast solar wind stream on 25-26
October 2012 to within a factor of 5 or so. At lower energies of 10 -
a few 100 keV we show that the electron flux at geostationary orbit
depends sensitively on the high-energy tail of the source distribution
near 10 RE on the nightside of the Earth, and that the
source is best represented by a kappa distribution. We present a
new model of whistler mode chorus determined from multiple satellite
measurements which shows that the effects of wave-particle interactions
beyond geostationary orbit are likely to be very significant. We also
present radial diffusion coefficients calculated from satellite data at
geostationary orbit which vary with Kp by over four orders
of magnitude. We describe a new automated method to determine the
position at the shock that is magnetically connected to the Earth for
modelling solar energetic particle events and which takes into account
entropy, and predict the form of the mean free path in the foreshock,
and particle injection efficiency at the shock from analytical theory
which can be tested in simulations.
Title: Modeling Jupiter's magnetosphere: Influence of the internal
sources
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2013JGRA..118.2157C
Altcode:
We introduce a new model to study Jupiter's magnetosphere and how it
interacts with the solar wind. We first derive a set of one-fluid
MHD equations to consistently include the ion-neutral collisions
in Jupiter's ionosphere and the mass loading in the Io torus. The
mass loading and the subsequent radial mass transport in Jupiter's
magnetosphere leads to a deviation from full corotation of the
magnetospheric plasma. Ion-neutral collisions in Jupiter's ionosphere
and subsequent transport of angular momentum out into the magnetosphere
acts to spin up the magnetosphere's plasma. Our model explicitly
includes mass loading in the Io plasma torus and an inner boundary
region, which represents the effects of Jupiter's ionosphere. We present
the results of five model runs where different mass loading rates and
ionospheric conductances are used. For these model runs, we consider
an antiparallel interplanetary magnetic field and a strong solar
wind dynamic pressure, resulting in a compressed magnetosphere. The
results are compared with analytical models, in situ measurements, and
remote-sensing observations. Our azimuthal velocity profiles and the
position of the corotation breakdown are in quantitative agreement with
theoretical predictions by Hill (1979, 2001) and Saur et al., (2004a),
and Voyager observations. The total current flowing into and out of
the ionosphere is 48.7 MA, which is in agreement with estimates from
measurements and analytical models. Using the field aligned electric
current j∥ to determine the position of the aurorae, we
find that our main auroral oval is associated, as expected, with the
position of the corotation breakdown (between 20.6 RJ and
30.1 RJ for the different model runs). The discontinuity
in the main oval observed by Radioti et al. (2008) is also present
in our results, where it is caused by an asymmetry in the pressure
distribution, due to the interaction between the rotating plasma and
the magnetopause.
Title: SWIFF: Space weather integrated forecasting framework
Authors: Lapenta, Giovanni; Pierrard, Viviane; Keppens, Rony; Markidis,
Stefano; Poedts, Stefaan; Šebek, Ondřej; Trávníček, Pavel M.;
Henri, Pierre; Califano, Francesco; Pegoraro, Francesco; Faganello,
Matteo; Olshevsky, Vyacheslav; Restante, Anna Lisa; Nordlund, Åke;
Trier Frederiksen, Jacob; Mackay, Duncan H.; Parnell, Clare E.;
Bemporad, Alessandro; Susino, Roberto; Borremans, Kris
Bibcode: 2013JSWSC...3A..05L
Altcode:
SWIFF is a project funded by the Seventh Framework Programme of the
European Commission to study the mathematical-physics models that
form the basis for space weather forecasting. The phenomena of space
weather span a tremendous scale of densities and temperature with
scales ranging 10 orders of magnitude in space and time. Additionally
even in local regions there are concurrent processes developing at
the electron, ion and global scales strongly interacting with each
other. The fundamental challenge in modelling space weather is the
need to address multiple physics and multiple scales. Here we present
our approach to take existing expertise in fluid and kinetic models to
produce an integrated mathematical approach and software infrastructure
that allows fluid and kinetic processes to be modelled together. SWIFF
aims also at using this new infrastructure to model specific coupled
processes at the Solar Corona, in the interplanetary space and in the
interaction at the Earth magnetosphere.
Title: The role of streamers in the deflection of coronal mass
ejections: comparison between STEREO 3D reconstructions and numerical
simulations
Authors: Zuccarello, F. P.; Bemporad, A.; Jacobs, C.; Mierla, M.;
Poedts, S.; Zuccarello, F.
Bibcode: 2012AGUFMSH31A2200Z
Altcode:
On 2009 September 21, a filament eruption and the associated Coronal
Mass Ejection (CME) was observed by the %coronographs on board of the
STEREO spacecraft. The CME originated from the southern hemisphere and
showed a deflection of about 15o towards the heliospheric
current sheet (HCS) during the propagation in the COR1 field-of-view
(FOV). The CME source region was near the central meridian, but no
on-disk CME signatures could be seen from the Earth. The aim of this
paper is to provide a physical explanation for the strong deflection
of the CME observed on 2009 September 21. The two-sided view of the
STEREO spacecraft allows us to reconstruct the three dimensional (3D)
travel path of the CME and the evolution of the CME source region. The
observations are combined with a magnetohydrodynamic (MHD) simulation,
starting from a magnetic field configuration closely resembling the
extrapolated potential field for that date. %The amount of helicity
injected in the coronal volume is similar in both the observation
and the simulation. By applying localized shearing motions, a CME is
initiated in the simulation, showing a similar non-radial evolution,
structure, and velocity as the observed event. The CME gets deflected
towards the current sheet of the larger northern helmet streamer, due
to an imbalance in the magnetic pressure and tension forces and finally
it gets into the streamer. This study shows that during solar minima,
even CMEs originating from high latitude can be easily deflected towards
the heliospheric current sheet, eventually resulting in geoeffective
events. How rapidly they undergo this latitudinal migration depends
on the strength of both the large scale coronal magnetic field and
the magnetic flux of the erupting filament.
Title: Global Simulations of the Jovian Magnetosphere
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2012AGUFMSM51A2293C
Altcode:
We present global numerical simulations of the interactions between
the solar wind and Jupiter's magnetosphere. In our model, an inner
boundary region representing the effects of Jupiter's ionosphere
(ion-neutral collisions) and the mass-loading associated with the Io
torus are explicitly included. To test the quality of our model, the
results of four simulations performed on a relatively coarse mesh, using
different mass-loading rates and different ionospheric conductances are
compared with analytical models, in situ measurements and remote-sensing
observations. Our azimuthal velocity profiles and the position of the
corotation break-down are in good quantitative agreement with Hill
[1979, 2001], with profiles calculated with the model of Saur et
al. [2004], and with Voyager observations [McNutt et al., 1981]. In
addition, one simulation is performed on a high resolution mesh. The
position of the corotation break-down in the equatorial plane maps,
as expected, to the main auroral oval in the ionosphere with a clearly
visible corotation enforcing current system. The dawn dusk asymmetry
(Khurana, 2004) is also visible in the simulations, with a thicker
current sheet on the dusk side and with faster azimuthal plasma flows on
the dawn side. Finally, our simulations reproduce the discontinuity in
Jupiter's main auroral oval in the prenoon sector observed by Radioti
et al. (2008).
Title: Magnetic Field Structure in ICMEs: Comparison and Validity
of Different Models
Authors: Al-haddad, N. A.; Nieves-Chinchilla, T.; Savani, N. P.;
Moestl, C.; Marubashi, K.; Hidalgo, M. A.; Roussev, I. I.; Poedts,
S.; Farrugia, C. J.; Jacobs, C.
Bibcode: 2012AGUFMSH31A2202A
Altcode:
In an attempt to understand the magnetic configuration of Interplanetary
Coronal Mass Ejections (ICMEs) and magnetic clouds (MCs), several
magnetic field reconstruction codes and fitting models have been
developed. These methods are required to determine the ICMEs' physical
(e.g., magnetic field strength) and geometrical (e.g. orientation)
parameters, which are derived using different assumptions. In order to
understand the dissimilarities of these codes, we use four magnetic
field fitting models (Grad-Shafranov, force-free fitting with and
without expansion, elliptical cross-section model) to fit 59 ejecta
(24 MCs and 35 non-MC ejecta), and study the resulting correlations
for the the axial magnetic field strength and the orientation of
these ejecta. We show that the axial magnetic field strength is
relatively well determined for different models but not necessarily
the orientation of the ejecta axis. We then set an example to show the
validity of these models by performing the reconstruction of synthetic
satellite measurements obtained from a simulation with writhed (but
not twisted) field lines. We analyze how multi-spacecraft situations
with different separation may help us distinguish between writhed and
twisted magnetic field.
Title: Influence of the interplanetary shock on the radial dependence
of solar energetic particle intensities
Authors: Aran, A.; Jacobs, C.; Sanahuja, B.; Lario, D.; Poedts, S.;
Jiggens, P.
Bibcode: 2012AGUFMSH21A2173A
Altcode:
The inclusion of a travelling shock as a source of energetic
particles during gradual solar energetic particle (SEP) events is
a key element to assess the radiation encountered by a mission in
the inner heliosphere. We have developed, in the frame of the Solar
Energetic Particle Environment Model (SEPEM) project, a two dimensional
magnetohydrodynamic model to describe the shock propagation from
4 solar radii up to 1.6 AU. The outputs of this model are used to
simulate the transport of SEPs from the shock front up to a given
observer. The combination of the shock and particle transport models
allows us to study the influence of both the shock properties and the
observer's magnetic connection on the radial and longitudinal variation
of proton peak intensities and fluences in gradual SEP events. We have
simulated the propagation of four shocks characterized by two different
transit times to 1 AU and two angular widths (narrow and wide). Two
sets of seven spacecraft are placed along two nominal interplanetary
magnetic field lines at radial distances ranging from 0.2 AU to 1.6
AU. The observers at 1 AU are located at central meridian and western
positions with respect to the launch direction of the shocks. We
calculate the resulting synthetic proton time-intensity profiles at
several energies (5.0 < E < 200 MeV) measured by each virtual
spacecraft. By tracking the shock from close to the Sun, we obtain the
peak intensity of high-energy particles at the prompt component of the
SEP events, without assuming ad-hoc conditions for particle injection
at the corona. We discuss how the resulting power-law dependences of
the peak intensities (and fluences) on the observer's radial distance
vary with the particle energy, the characteristics of the shock, and
the different evolving conditions for particle injection at the point
of the shock front that magnetically connects to the observers. This
information may contribute to improve the understanding of the peak
intensities and fluences that missions like Solar Orbiter will measure
during SEP events.
Title: Numerical modeling of the initiation of coronal mass ejections
in active region NOAA 9415
Authors: Zuccarello, F. P.; Meliani, Z.; Poedts, S.
Bibcode: 2012AGUFMSH33E..02Z
Altcode:
Coronal mass ejections (CMEs) and solar flares are the main drivers of
the space weather. Understanding how these events can occur and what
conditions might lead to eruptive events is of crucial relevance for up
to date and reliable space weather forecasting. The aim of the present
paper is to present a numerical magnetohydrodynamic (MHD) data-driven
model suitable for the simulation of the CME initiation and their early
evolution. Starting from a potential magnetic field extrapolation of
the active region (AR) NOAA 9415, we solve the full set of ideal MHD
equations in a non-zero plasma-β environment. We investigate the
response of the solar corona when photospheric motions, resembling
the ones observed for AR 9415, are applied at the inner boundary. As
a consequence of the applied twisting motions a force-free magnetic
field configuration, having the same chirality as the investigated
active region, is obtained. As a response to the converging shearing
motions a flux rope is formed that quickly propagates outwards,
carrying away, against the gravitational attraction by the Sun,
the plasma confined inside the flux rope. Moreover, a compressed
leading edge propagating at a speed of about 550 km s-1
and preceding the CME is formed. The presented simulation shows that
both the initial magnetic field configuration and the plasma-magnetic
field interaction are relevant for a more comprehensive understanding
of the CME initiation and early evolution phenomenon.
Title: Observational Evidence of Alfvén Wings at the Earth
Authors: Poedts, S.; Chané, E.; Saur, J.; Neubauer, F. M.; Raeder, J.
Bibcode: 2012AGUFMSM12A..01P
Altcode:
We present observational evidence of a sub-fast and sub-Alfvénic
solar wind in the near Earth orbit during 24 and 25 May 2002, where
the Alfvén Mach number was as low as 0.4 in the rest frame of the
Earth. The low Alfvén Mach number was caused by a very low solar wind
plasma density (below 0.1 /cc) and four spacecraft provided independent
and consistent measurements of this low density. For such solar wind
conditions, theory predicts that the Earth's bow-shock disappears
and that two Alfvén wings form on the flanks. These Alfvén wings
are two long structures (we estimated an extension of 600 Re), where
the solar wind plasma is decelerated and the magnetic field direction
changes (we calculated a deceleration of 30% in one wing and 60% in
the other wing). We produce data from the Geotail spacecraft, which
are consistent with Geotail entering the foot region of one of the
Alfvén wings. Although Alfvén wings have already been observed at
several moons in the solar system (e.g. Io, Europa, Enceladus), this is
the first observational evidence of Alfvén wings at the Earth. During
this sub-Alfvénic time interval, the magnetosphere was geomagnetically
extremely quiet and there was almost no auroral activity.
Title: Study of Multiple Coronal Mass Ejections at Solar Minimum
Conditions
Authors: Bemporad, A.; Zuccarello, F. P.; Jacobs, C.; Mierla, M.;
Poedts, S.
Bibcode: 2012SoPh..281..223B
Altcode: 2012SoPh..tmp..153B
The aim of this work is to provide a physical explanation for the
genesis of multiple coronal mass ejections (CMEs) in an asymmetric
coronal field configuration. We analyze STEREO observations of a
multiple eruption and compare the results from the data analysis with
predictions provided by magnetohydrodynamic (MHD) simulations. To this
end, the multiple CMEs (MCMEs) observed on 21 - 22 September 2009 were
selected. Both eruptions originated from the same source region and
showed approximately the same latitudinal deflection, by more than
15 degrees, toward the heliospheric current sheet (HCS) during their
propagation in the COR1 field of view. Numerical MHD simulations of
the MCMEs have been performed, starting from an asymmetric coronal
field configuration that mimics the potential field source surface
extrapolation for 21 September 2009. The results demonstrate that,
by shearing the footpoints at the base of the southern arcade,
we were able to reproduce the observed dynamics of the MCMEs. Both
CMEs are deflected toward the HCS due to an imbalance in the magnetic
pressure and tension forces; the global field strength turns out to
be a crucial parameter in order to release two subsequent eruptions,
and hence to reproduce the observed evolution.
Title: Preface
Authors: Nakariakov, V. M.; Georgoulis, M. K.; Poedts, S.; van
Driel-Gesztelyi, L.; Mandrini, C. H.; Leibacher, J.
Bibcode: 2012SoPh..280..295N
Altcode: 2012SoPh..tmp..226N
No abstract at ADS
Title: A Numerical Study of the Response of the Coronal Magnetic
Field to Flux Emergence
Authors: Jacobs, C.; Poedts, S.
Bibcode: 2012SoPh..280..389J
Altcode: 2012SoPh..tmp...25J
Large-scale solar eruptions, known as coronal mass ejections (CMEs),
are regarded as the main drivers of space weather. The exact trigger
mechanism of these violent events is still not completely clear;
however, the solar magnetic field indisputably plays a crucial role in
the onset of CMEs. The strength and morphology of the solar magnetic
field are expected to have a decisive effect on CME properties, such
as size and speed. This study aims to investigate the evolution of a
magnetic configuration when driven by the emergence of new magnetic
flux in order to get a better insight into the onset of CMEs and
their magnetic structure. The three-dimensional, time-dependent
equations for ideal magnetohydrodynamics are numerically solved
on a spherical mesh. New flux emergence in a bipolar active region
causes destabilisation of the initial stationary structure, finally
resulting in an eruption. The initial magnetic topology is suitable
for the `breakout' CME scenario to work. Although no magnetic flux rope
structure is present in the initial condition, highly twisted magnetic
field lines are formed during the evolution of the system as a result
of internal reconnection due to the interaction of the active region
magnetic field with the ambient field. The magnetic energy built up in
the system and the final speed of the CME depend on the strength of
the overlying magnetic field, the flux emergence rate, and the total
amount of emerged flux. The interaction with the global coronal field
makes the eruption a large-scale event, involving distant parts of
the solar surface.
Title: Numerical Modeling of the Initiation of Coronal Mass Ejections
in Active Region NOAA 9415
Authors: Zuccarello, F. P.; Meliani, Z.; Poedts, S.
Bibcode: 2012ApJ...758..117Z
Altcode:
Coronal mass ejections (CMEs) and solar flares are the main drivers
of weather in space. Understanding how these events occur and what
conditions might lead to eruptive events is of crucial importance
for up to date and reliable space weather forecasting. The aim
of this paper is to present a numerical magnetohydrodynamic (MHD)
data-inspired model suitable for the simulation of the CME initiation
and their early evolution. Starting from a potential magnetic field
extrapolation of the active region (AR) NOAA 9415, we solve the full
set of ideal MHD equations in a non-zero plasma-β environment. As a
consequence of the applied twisting motions, a force-free-magnetic
field configuration is obtained, which has the same chirality as
the investigated AR. We investigate the response of the solar corona
when photospheric motions resembling the ones observed for AR 9415 are
applied at the inner boundary. As a response to the converging shearing
motions, a flux rope is formed that quickly propagates outward, carrying
away the plasma confined inside the flux rope against the gravitational
attraction by the Sun. Moreover, a compressed leading edge propagating
at a speed of about 550 km s-1 and preceding the CME is
formed. The presented simulation shows that both the initial magnetic
field configuration and the plasma-magnetic-field interaction are
relevant for a more comprehensive understanding of the CME initiation
and early evolution phenomenon.
Title: Observational evidence of Alfvén wings at the Earth
Authors: Chané, E.; Saur, J.; Neubauer, F. M.; Raeder, J.; Poedts, S.
Bibcode: 2012JGRA..117.9217C
Altcode: 2012JGRA..11709217C
The solar wind at the orbit of the Earth is usually strongly
super-Alfvénic and super-fast, causing a bow-shock to be formed
upstream of the Earth's magnetosphere. We here present observational
evidence that during 24 and 25 May 2002, the solar wind at the Earth
was sub-Alfvénic (with an Alfvén Mach number as low as 0.4 in the
rest frame of the Earth) and was therefore sub-fast for time periods
of up to four hours. The low Alfvén Mach number implies that the
Earth's bow-shock disappeared and two Alfvén wings formed. These
Alfvén wings are two structures on both the East and West side of
the Earth's magnetosphere, where the solar wind plasma is decelerated
and the magnetic field direction changes. We present observations of
the Geotail spacecraft, which are consistent with Geotail entering
the foot of one of these Alfvén wings. We estimate that these wings
reached an extension of 600 RE. Even though Alfvén wings
are present at several moons in the solar system (e.g., Io, Europa,
Enceladus) and are likely to occur at some extrasolar planets, this
is the first time that they are observed at the Earth. We also study
how the Earth is affected by this transition from a super-fast to a
sub-Alfvénic environment and how the Alfvén wings are affected by the
constantly varying solar wind. The sub-Alfvénic solar wind is due to
very low density in the solar wind. While the solar wind Alfvén Mach
number was very low, the magnetosphere was geomagnetically extremely
quiet. Whereas the SYM-H index indicates a recovery phase from a small
to moderate magnetic storm; the AL and AU indices show no substorm
activity. In addition, there was almost no auroral activity.
Title: The role of streamers in the deflection of coronal mass
ejections
Authors: Zuccarello, F. P.; Bemporad, A.; Jacobs, C.; Mierla, M.;
Poedts, S.; Zuccarello, F.
Bibcode: 2012IAUS..286..134Z
Altcode:
On 2009 September 21, a filament eruption and the associated Coronal
Mass Ejection (CME) was observed by the STEREO spacecraft. The CME
originated from the southern hemisphere and showed a deflection of about
15° towards the heliospheric current sheet (HCS) during its propagation
in the COR1 field-of-view (FOV). The aim of this paper is to provide a
physical explanation for the strong deflection of the CME. We first use
the STEREO observations in order to reconstruct the three dimensional
(3D) trajectory of the CME. Starting from a magnetic configuration that
closely resembles the potential field extrapolation for that date, we
performed numerical magneto-hydrodynamics (MHD) simulations. By applying
localized shearing motions, a CME is initiated in the simulation,
showing a similar non-radial evolution, structure, and velocity as the
observed event. The CME gets deflected towards the current sheet of the
larger northern helmet streamer, due to an imbalance in the magnetic
pressure and tension forces and finally it gets into the streamer and
propagates along the heliospheric current sheet.
Title: Magnetic Field Configuration Models and Reconstruction Methods:
a comparative study
Authors: Al-haddad, Nada; Möstl, Christian; Roussev, Ilia;
Nieves-Chinchilla, Teresa; Poedts, Stefaan; Hidalgo, Miguel Angel;
Marubashi, Katsuhide; Savani, Neel
Bibcode: 2012cosp...39...32A
Altcode: 2012cosp.meet...32A
This study aims to provide a reference to different magnetic
field models and reconstruction methods. In order to understand the
dissimilarities of those models and codes, we analyze 59 events from the
CDAW list, using four different magnetic field models and reconstruction
techniques; force- free reconstruction (Lepping et al.(1990); Lynch et
al.(2003)), magnetostatic reconstruction, referred as Grad-Shafranov
(Hu & Sonnerup(2001); Mostl et al.(2009)), cylinder reconstruction
(Marubashi & Lepping(2007)), elliptical, non-force free (Hidalgo et
al.(2002)). The resulted parameters of the reconstructions, for the 59
events are compared, statistically, as well as in more details for some
cases. The differences between the reconstruction codes are discussed,
and suggestions are provided as how to enhance them. Finally we look
at 2 unique cases under the microscope, to provide a comprehensive
idea of the different aspects of how the fitting codes work.
Title: Magnetic Field Configuration Models and Reconstruction Methods
Authors: Al-Haddad, Nada; Nieves-Chinchilla, Teresa; Savani, Neel;
Mostl, Christian; Marubashi, Katsuhide; Hidalgo, Miguel Angel; Roussev,
Ilia; Poedts, Stefaan; Farrugia, Charles J.
Bibcode: 2012shin.confE.155A
Altcode:
The goal of this study is to provide a reference to different magnetic
field models and reconstruction methods for interplanetary coronal
mass ejections (ICMEs). In order to understand the differences of
those models and codes, we analyze 59 events from the CDAW list, using
four different magnetic field models and reconstruction techniques;
force-free fitting (Goldstein, 1983; Lepping, Burlaga, and Jones,
1990), magnetostatic reconstruction referred to as Grad-Shafranov
(Hu and Sonnerup, 2001), self-similar expanding cylinder fitting
(Marubashi and Lepping, 2007), elliptical, non-force free fitting
(Hidalgo, 2003). The resulting parameters of the reconstructions for
the 59 events are compared, statistically, as well as in selected case
studies. The ability of a method to fit or reconstruct an event is found
to vary greatly: the Grad-Shafranov reconstruction is successful for
most magnetic clouds (MCs) but for less than 10% of the non- MC ICMEs;
the other three methods provide a successful fit for more than 80% of
the events, independently of their nature. The differences between the
reconstruction and fitting methods are discussed, and suggestions are
provided as how to reduce them. We find that the magnitude of the axial
field is relatively consistent across models but not the orientation
of the axis of the ejecta. We also find that there are a few cases
for which different signs of helicity are found for the same event,
illustrating that this simplest of the parameters is not necessarily
always well constrained by fitting and reconstruction models. Finally,
we look at 3 unique cases in depth to provide a comprehensive idea of
the different aspects of how the fitting and reconstruction codes work.
Title: Numerical modeling of the initiation of coronal mass ejections
in active region NOAA 9415
Authors: Zuccarello, Francesco Paolo; Meliani, Z.; Poedts, S.
Bibcode: 2012shin.confE..37Z
Altcode:
Coronal mass ejections (CMEs) and solar flares are the main drivers of
the space weather. Understanding how these events can occur and what
conditions might lead to eruptive events is of crucial relevance for up
to date and reliable space weather forecasting. The aim of the present
paper is to present a numerical magnetohydrodynamic (MHD) data-driven
model suitable for the simulation of the CME initiation and their early
evolution. Starting from a potential magnetic field extrapolation of
the active region (AR) NOAA 9415, we solve the full set of ideal MHD
equations in a non-zero plasma-beta environment. We investigate the
response of the solar corona when photospheric motions, resembling
the ones observed for AR 9415, are applied at the inner boundary. As a
consequence of the applied twisting motions a force-free magnetic field
configuration having the same chirality as the investigated active
region is obtained. As a response to the converging shearing motions
a flux rope is formed and quickly propagates outwards, carrying away,
against the gravitational attraction by the Sun, the plasma confined
inside the flux rope. Moreover, a compressed leading edge propagating
at a speed of about 550 km/s and preceding the CME is also formed. The
presented simulation shows that both the initial magnetic field
configuration and the plasma-magnetic field interaction are relevant
for a more comprehensive understanding of the CME initiation and early
evolution phenomenon.
Title: Self-heating of Corona by Electrostatic Fields Driven by
Sheared Flows
Authors: Saleem, H.; Ali, S.; Poedts, S.
Bibcode: 2012ApJ...748...90S
Altcode: 2012arXiv1201.0580S
A mechanism for self-heating of the solar corona is discussed. It
is shown that the free energy available in the form of sheared flows
gives rise to unstable electrostatic perturbations which accelerate and
heat particles. The electrostatic perturbations can occur through two
processes, viz., by a purely growing sheared flow-driven instability
and/or by a sheared flow-driven drift wave. These processes can occur
throughout the corona and, hence, this self-heating mechanism could
be very important for coronal heating. These instabilities can give
rise to local perturbed electrostatic potentials phiv1 of
up to 100 volts within 3 × 10-2 to a few seconds time,
if the (dimensionless) initial perturbation is assumed to be about
1%, that is, ephiv1/Te ~= 10-2. The
wavelengths in the direction perpendicular to the external magnetic
field B 0 vary from about 10 m to 1 m in our model. The
purely growing instability creates electrostatic fields by sheared
flows even if there is no density gradient, whereas a density gradient
is crucial for the occurrence of the drift wave instability. The
purely growing instability develops a small real frequency as well in
the two-ion coronal plasma. In the solar corona, very low frequency
(of the order of 1 Hz) drift dissipative waves can also occur due to
electron-ion collisions.
Title: Dome-shaped EUV Waves from Rotating Active Regions
Authors: Selwa, M.; Poedts, S.; DeVore, C. R.
Bibcode: 2012ApJ...747L..21S
Altcode:
Recent STEREO observations enabled the study of the properties of EUV
waves in more detail. They were found to have a three-dimensional (3D)
dome-shaped structure. We investigate, by means of 3D MHD simulations,
the formation of EUV waves as the result of the interaction of twisted
coronal magnetic loops. The numerical simulation is initialized with
an idealized dipolar active region and is performed under coronal (low
β) conditions. A sheared rotational motion is applied to the central
parts of both the positive and negative flux regions at the photosphere
so that the flux tubes in between them become twisted. We find that
the twisting motion results in a dome-shaped structure followed in
space by a dimming and in time by an energy release (flare). The
rotation of the sunspots is the trigger of the wave which initially
consists of two fronts that later merge together. The resulting EUV
wave propagates nearly isotropically on the disk and ~2 times faster in
the upward direction. The initial stage of the evolution is determined
by the driver, while later the wave propagates freely with a nearly
Alfvénic speed.
Title: Suprathermal Particle Populations in the Solar Wind and Corona
Authors: Lazar, M.; Schlickeiser, R.; Poedts, S.
Bibcode: 2012esw..book..241L
Altcode:
No abstract at ADS
Title: The role of photospheric shearing motions in a filament
eruption related to the 2010 April 3 coronal mass ejection
Authors: Zuccarello, F. P.; Romano, P.; Zuccarello, F.; Poedts, S.
Bibcode: 2012A&A...537A..28Z
Altcode:
Context. Coronal mass ejections (CMEs) are huge expulsion of solar
plasma and magnetic field in the interplanetary medium. Understanding
the physics that lies beyond the CME initiation is one of the most
fascinating research questions. Several models have been proposed
to explain the initiation of CMEs. However, which model better
explains the different aspects of the initiation process and the
early evolution of the CMEs is a subject of ongoing discussion.
Aims: We investigate the magnetic field evolution of NOAA 11059
in order to provide a further contribution to our understanding of
the possible causes and mechanisms that lead to the initiation of
the geoeffective CME that occurred on 2010 April 3.
Methods:
Using KSO Hα images we determine the chirality of the active region
and some properties of the filament that eventually erupted. Using
SOHO/MDI line-of-sight magnetograms we investigate the magnetic
configuration of NOAA 11059 by means of both linear force free and
potential field extrapolations. We also determine the photospheric
velocity maps using the Differential Affine Velocity Estimator
(DAVE).
Results: We find that the magnetic configuration of
the active region is unstable to the torus instability. Moreover,
we find that persistent shearing motions characterized the negative
polarity, resulting in a southward, almost parallel to the meridians,
drift motion of the negative magnetic field concentrations.
Conclusions: We conclude that persistent and coherent shearing motions
played a significant role in facilitating the eruption. These shearing
motions increased the axial field of the filament eventually bringing
the fluxrope axis to a height where the onset condition for the torus
instability was satisfied. Our observations show that both the magnetic
configuration of the system and the photopsheric dynamics that preceded
the event, were favourable for the eruption to occur.
Title: Modeling Space Plasma Dynamics with Anisotropic Kappa
Distributions
Authors: Lazar, M.; Pierrard, V.; Poedts, S.; Schlickeiser, R.
Bibcode: 2012ASSP...33...97L
Altcode: 2012msdp.book...97L; 2012arXiv1204.0363L
Space plasmas are collisionpoor and kinetic effects prevail leading
to wave fluctuations, which transfer the energy to small scales:
wave-particle interactions replace collisions and enhance dispersive
effects heating particles and producing suprathermal populations
observed at any heliospheric distance in the solar wind. At large
distances collisions are not efficient, and the selfgenerated
instabilities constrain the solar wind anisotropy including the thermal
core and the suprathermal components. The generalized power-laws of
Kappa-type are the best fitting model for the observed distributions
of particles, and a convenient mathematical tool for modeling their
dynamics. But the anisotropic Kappa models are not correlated with
the observations leading, in general, to inconsistent effects. This
review work aims to reconcile some of the existing Kappa models with
the observations.
Title: Self-heating in kinematically complex magnetohydrodynamic flows
Authors: Osmanov, Zaza; Rogava, Andria; Poedts, Stefaan
Bibcode: 2012PhPl...19a2901O
Altcode: 2012arXiv1211.4149O
The non-modal self-heating mechanism driven by the velocity shear
in kinematically complex magnetohydrodynamic (MHD) plasma flows
is considered. The study is based on the full set of MHD equations
including dissipative terms. The equations are linearized and unstable
modes in the flow are looked for. Two different cases are specified
and studied: (a) the instability related to an exponential evolution of
the wave vector and (b) the parametric instability, which takes place
when the components of the wave vector evolve in time periodically. By
examining the dissipative terms, it is shown that the self-heating
rate provided by viscous damping is of the same order of magnitude
as that due to the magnetic resistivity. It is found that the heating
efficiency of the exponential instability is higher than that of the
parametric instability.
Title: The Role of Streamers in the Deflection of Coronal Mass
Ejections: Comparison between STEREO Three-dimensional Reconstructions
and Numerical Simulations
Authors: Zuccarello, F. P.; Bemporad, A.; Jacobs, C.; Mierla, M.;
Poedts, S.; Zuccarello, F.
Bibcode: 2012ApJ...744...66Z
Altcode:
On 2009 September 21, a filament eruption and the associated
coronal mass ejection (CME) were observed by the Solar Terrestrial
Relations Observatory (STEREO) spacecraft. The CME originated from the
southern hemisphere and showed a deflection of about 15° toward the
heliospheric current sheet (HCS) during the propagation in the COR1
field of view. The CME source region was near the central meridian,
but no on-disk CME signatures could be seen from the Earth. The aim
of this paper is to provide a physical explanation for the strong
deflection of the CME observed on 2009 September 21. The two-sided view
of the STEREO spacecraft allows us to reconstruct the three-dimensional
travel path of the CME and the evolution of the CME source region. The
observations are combined with a magnetohydrodynamic simulation,
starting from a magnetic field configuration closely resembling the
extrapolated potential field for that date. By applying localized
shearing motions, a CME is initiated in the simulation, showing a
similar non-radial evolution, structure, and velocity as the observed
event. The CME gets deflected toward the current sheet of the larger
northern helmet streamer due to an imbalance in the magnetic pressure
and tension forces and finally gets into the streamer. This study shows
that during solar minima, even CMEs originating from high latitude can
be easily deflected toward the HCS, eventually resulting in geoeffective
events. How rapidly they undergo this latitudinal migration depends
on the strength of both the large-scale coronal magnetic field and
the magnetic flux of the erupting filament.
Title: A polytropic model for the solar wind
Authors: Jacobs, C.; Poedts, S.
Bibcode: 2011AdSpR..48.1958J
Altcode:
The solar wind fills the heliosphere and is the background medium in
which coronal mass ejections propagate. A realistic modelling of the
solar wind is therefore essential for space weather research and for
reliable predictions. Although the solar wind is highly anisotropic,
magnetohydrodynamic (MHD) models are able to reproduce the global,
average solar wind characteristics rather well. The modern computer
power makes it possible to perform full three dimensional (3D)
simulations in domains extending beyond the Earth's orbit, to include
observationally driven boundary conditions, and to implement even
more realistic physics in the equations. In general, MHD models for
the solar wind often make use of additional source and sink terms
in order to mimic the observed solar wind parameters and/or they
hide the not-explicitly modelled physical processes in a reduced
or variable adiabatic index. Even the models that try to take as
much as possible physics into account, still need additional source
terms and fine tuning of the parameters in order to produce realistic
results. In this paper we present a new and simple polytropic model
for the solar wind, incorporating data from the ACE spacecraft to set
the model parameters. This approach allows to reproduce the different
types of solar wind, where the simulated plasma variables are in good
correspondence with the observed solar wind plasma near 1 AU.
Title: The MI-coupling in global simulations of the Jovian and
Kronian magnetospheres
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2011AGUFMSM11A2013C
Altcode:
A new model of the interactions between the solar wind and the
magnetospheres of Jupiter and Saturn is presented. It differs from
other models by explicitly introducing the Magnetosphere-Ionosphere
coupling via an extended ionospheric region, located inside the
simulation domain, where ion-neutral collisions are included in the
MHD equations. Since the MI-coupling is included inside the simulation
domain (above the inner boundary), the current system is closed inside
the simulation domain and the boundary conditions do not interfere
with the MI-coupling. This ionospheric region, even though not an
accurate representation of the Jovian ionosphere, is characterized
through its Pedersen conductance and imposes through its coupling
with the magnetosphere good results at magnetospheric locations
where the corotation breaks down and further outside. In addition, the
mass-loading caused by Io or Enceladus is introduced in an axi-symmetric
toroidal region where a ionization source term is added to the MHD
equations. With this model, two key parameters of the giant planets
magnetospheres can be controlled: namely the ionospheric conductance and
the mass-loading associated with Io or Enceladus. To test our model,
numerical experiments are performed where the ionospheric conductance
and the mass-loading are changed; the results are then compared with
measurements and analytical models. For Jupiter's magnetosphere, for
example, the position of the corotation break-down and the azimuthal
velocity profile are in good agreement with analytical models. We do
not observe any spurious supercorotation (as often seen in global MHD
simulations of Jupiter's magnetosphere). The density profiles and radial
velocity profiles are also compared with observations and theory and
give satisfactory results. As expected by theory, in our simulations,
the position of the corotation break-down maps to the main auroral
emission. Since the current systems are closed inside the ionospheric
region above the inner boundary no current is lost or gained through
this boundary; the total current flowing through the ionosphere (39.6
MA) agrees with estimates from measurements and analytical models.
Title: Multi-Spacecraft Reconstruction of the Magnetic Fields InICMEs
with Writhe Structure
Authors: Al-haddad, N. A.; Roussev, I. I.; Jacobs, C.; Moestl, C.;
Lugaz, N.; Poedts, S.; Farrugia, C. J.
Bibcode: 2011AGUFMSH51A1995A
Altcode:
The structure of magnetic clouds' (MCs) magnetic field can be
reconstructed from in situ measurements under certain assumptions
(2.5-D, temporal invariance, force-free, etc...). Typically,
the reconstructions yield in helically twisted flux rope. In a
previous work, we have shown how recon-structing the magnetic field
of synthetic in situ measurements from coronal mass ejections (CMEs)
with writhed field lines structure, can yield a structure of a helically
twisted flux rope. Here, we investigate the cases of multi-spacecraft
measurements. We study different cases of two and three spacecraft at
different orientation with respect to the CME axis. We analyze how the
different separation and orientation can help us distinguish between
writhed and twisted magnetic field.
Title: Magnetic clouds in the solar wind: a numerical assessment of
analytical models
Authors: Dalakishvili, G.; Kleimann, J.; Fichtner, H.; Poedts, S.
Bibcode: 2011A&A...536A.100D
Altcode: 2011arXiv1109.3790D
Context. Magnetic clouds (MCs) are "magnetized plasma clouds" moving in
the solar wind. MCs transport magnetic flux and helicity away from the
Sun. These structures are not stationary but feature temporal evolution
as they propagate in the solar wind. Simplified analytical models are
frequently used to describe MCs, and they fit certain observational
data well.
Aims: The goal of the present study is to numerically
investigate the validity of an analytical model that is widely used
to describe MCs, and to determine under which conditions this model's
implied assumptions cease to be valid.
Methods: A numerical
approach is applied. Analytical solutions derived in previous studies
are implemented in a 3D magnetohydrodynamic simulation code as initial
conditions. Besides the standard case in which MCs only expand and
propagate in the solar wind, the case of an MC rotating around its
axis of symmetry is also considered, and the resulting influence on
the MC's dynamics is studied.
Results: Initially, the analytical
model represents the main observational features of the MCs. However,
these characteristics prevail only if the structure moves with a
velocity close to the velocity of the background flow. In this case an
MC's evolution can quite accurately be described using an analytic,
self-similar approach. The dynamics of the magnetic structures that
move with a velocity significantly above or below that of the velocity
of the solar wind is investigated in detail.
Conclusions:
Comparison of the numerical results with observational data indicates
reasonable agreement especially for the intermediate case, in which
the MC's bulk velocity and the velocity of the background flow are
equal. In this particular case, analytical solutions obtained on the
basis of a self-similar approach indeed describe the MC's evolution
quite accurately. In general, however, numerical simulations are
necessary to investigate the evolution as a function of a wide range
of the parameters, which define the initial conditions.
Title: Proton firehose instability in bi-Kappa distributed plasmas
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.
Bibcode: 2011A&A...534A.116L
Altcode:
Context. Protons or heavier ions with anisotropic velocity distributions
and non-thermal departure from Maxwellian, are frequently reported in
the magnetosphere and at different altitudes in the solar wind. These
observations are sustained by an extended number of mechanisms of
acceleration in any direction with respect to the interplanetary
magnetic field. However, the observed anisotropy is not large and
most probably constrained by the kinetic instabilities.
Aims:
An excess of parallel kinetic energy, T∥/T⊥
> 1 (where ∥ and ⊥ denote directions relative to the background
magnetic field) drives a proton firehose mode to grow, limiting any
further increase in the anisotropy according to the observations. The
effects of suprathermal populations on the principal characteristics
of the proton firehose instability are investigated.
Methods:
For low-collisional plasmas, the dispersion approach is based on the
fundamental kinetic Vlasov-Maxwell equations. The anisotropy of plasma
distributions including suprathermal populations is modeled by bi-Kappa
functions, and the new dispersion relations are derived in terms of
the modified plasma dispersion function (for Kappa distributions),
and analytical approximations of this function.
Results: Growth
rates of the proton firehose solutions and threshold conditions are
provided in analytical forms for different plasma regimes. The proton
firehose instability needs a larger anisotropy and a larger parameter
β∥ to occur in a Kappa-distributed plasma. A precise
numerical evaluation shows that the growth rates are, in general, lower
and the wave frequency is only slightly affected, but the influence of
suprathermal populations is essentially dependent on both the proton
and electron anisotropies. Departures from the standard dispersion of
a Maxwellian plasma can eventually be used to evaluate the presence
of suprathermal populations in solar flares and the magnetosphere.
Title: On the Internal Structure of the Magnetic Field in Magnetic
Clouds and Interplanetary Coronal Mass Ejections: Writhe versus Twist
Authors: Al-Haddad, N.; Roussev, I. I.; Möstl, C.; Jacobs, C.; Lugaz,
N.; Poedts, S.; Farrugia, C. J.
Bibcode: 2011ApJ...738L..18A
Altcode:
In this study, we test the flux rope paradigm by performing a
"blind" reconstruction of the magnetic field structure of a simulated
interplanetary coronal mass ejection (ICME). The ICME is the result
of a magnetohydrodynamic numerical simulation and does not exhibit
much magnetic twist, but appears to have some characteristics of a
magnetic cloud, due to a writhe in the magnetic field lines. We use the
Grad-Shafranov technique with simulated spacecraft measurements at two
different distances and compare the reconstructed magnetic field with
that of the ICME in the simulation. While the reconstructed magnetic
field is similar to the simulated one as seen in two dimensions,
it yields a helically twisted magnetic field in three dimensions. To
further verify the results, we perform the reconstruction at three
different position angles at every distance point, and all results
are found to be in agreement. This work demonstrates that the current
paradigm of associating magnetic clouds with flux ropes may have to
be revised.
Title: On the Internal Structure of the Magnetic Field in Magnetic
Clouds and Interplanetary Coronal Mass Ejections: Writhe Vs. Twist
Authors: Al-Haddad, Nada; Alhaddad, N.; Jacobs, C.; Mostl, C.; Savani,
N.; Roussev, I.; Lugaz, N.; Farrugia, C.; Poedts, S.
Bibcode: 2011shin.confE.134A
Altcode:
In a previous work, we have shown how reconstructing the magnetic
field of synthetic in situ measurements from coronal mass ejections
(CMEs) with writhed field lines structure, can yield a structure of
a twisted flux rope. We used the Grad-Shafranov (GS) magnetic field
reconstruction method,to reconstruct the magnetic field. To further
verify the results, here, we reconstruct the magnetic field using
the Force-Free reconstruction method on the same data as before,
and compare the results with those obtained from the previous work.
Title: Weak and Strong MHD Turbulence
Authors: Gogoberidze, G.; Mahajan, S.; Poedts, S.; Akhalkatsi, M.
Bibcode: 2011AIPC.1356...67G
Altcode:
The general conditions for the weak and strong regimes of incompressible
magnetohydrodynamic turbulence are derived and studied in the framework
of the direct interaction approximation. It is shown that in the
framework of the weak turbulence theory, the autocorrelation and
cascade timescales are always of the same order of magnitude. This
means that, contrary to the general belief, any model of turbulence
which implies a large number of collisions among wave packets for an
efficient energy cascade (such as the Iroshnikov-Kraichnan model),
does not represent a model of weak turbulence.
Title: Models of Imbalanced MHD Turbulence
Authors: Gogoberidze, G.; Poedts, S.; Akhalkatsi, M.
Bibcode: 2011AIPC.1356...75G
Altcode:
The relation between the energy imbalances and the dissipation rate
imbalances is derived for the model of strong MHD turbulence which
implies incoherent straining imposed by subdominant waves on a dominant
wave packet and a pinning of the spectra of counter propagating Alfvén
waves at the dissipation scale. The comparison of the obtained result
to the results of recent numerical simulations shows that the fitting
is poor both for the weakly and strongly imbalanced cases.
Title: Models for coronal mass ejections
Authors: Jacobs, Carla; Poedts, Stefaan
Bibcode: 2011JASTP..73.1148J
Altcode:
Coronal mass ejections (CMEs) play a key role in space weather. The
mathematical modelling of these violent solar phenomena can contribute
to a better understanding of their origin and evolution and as such
improve space weather predictions. We review the state-of-the-art in
CME simulations, including a brief overview of current models for
the background solar wind as it has been shown that the background
solar wind affects the onset and initial evolution of CMEs quite
substantially. We mainly focus on the attempt to retrieve the
initiation and propagation of CMEs in the framework of computational
magnetofluid dynamics (CMFD). Advanced numerical techniques and large
computer resources are indispensable when attempting to reconstruct
an event from Sun to Earth. Especially the simulations developed in
dedicated event studies yield very realistic results, comparable with
the observations. However, there are still a lot of free parameters in
these models and ad hoc source terms are often added to the equations,
mimicking the physics that is not really understood yet in detail.
Title: Why should the latitude of the observer be considered when
modeling gradual proton events? An insight using the concept of
cobpoint
Authors: Rodríguez-Gasén, R.; Aran, A.; Sanahuja, B.; Jacobs, C.;
Poedts, S.
Bibcode: 2011AdSpR..47.2140R
Altcode:
The shape of flux profiles of gradual solar energetic particle (SEP)
events depends on several not well-understood factors, such as the
strength of the associated shock, the relative position of the observer
in space with respect to the traveling shock, the existence of a
background seed particle population, the interplanetary conditions for
particle transport, as well as the particle energy. Here, we focus
on two of these factors: the influence of the shock strength and
the relative position of the observer. We performed a 3D simulation
of the propagation of a coronal/interplanetary CME-driven shock in
the framework of ideal MHD modeling. We analyze the passage of this
shock by nine spacecraft located at ∼0.4 AU (Mercury’s orbit)
and at different longitudes and latitudes. We study the evolution of
the plasma conditions in the shock front region magnetically connected
to each spacecraft, that is the region of the shock front scanned by
the “cobpoint” (Heras et al., 1995), as the shock propagates away
from the Sun. Particularly, we discuss the influence of the latitude
of the observer on the injection rate of shock-accelerated particles
and, hence, on the resulting proton flux profiles to be detected by
each spacecraft.
Title: Magnetic helicity balance during a filament eruption that
occurred in active region NOAA 9682
Authors: Zuccarello, F. P.; Romano, P.; Zuccarello, F.; Poedts, S.
Bibcode: 2011A&A...530A..36Z
Altcode:
Context. Photospheric shear plasma flows in active regions may be
responsible for the magnetic helicity injection in the solar corona not
only during the energy storage process before a solar eruption, but also
during and after the release of the free magnetic energy caused by the
eruption. Indeed, after a filament eruption or expansion the magnetic
torque imbalance can induce shear flows that can be responsible for yet
another injection of magnetic helicity into the corona.
Aims:
We investigated the magnetic helicity balance in an active region
where a confined solar eruption occurred. This was done to verify a
possible relationship between the filament expansion and the helicity
transport at its footpoints. We aimed to verify if this variation in
the helicity transport rate could be interpreted as a consequence of
the magnetic torque imbalance caused by the tube expansion, as proposed
by Chae et al. (2003, J. Kor. Astron. Soc., 36, 33).
Methods:
We used 171ÅTRACE data to measure some geometrical parameters of
the new magnetic system produced by a filament eruption that occurred
on 2001 November 1 in active region NOAA 9682. We used MDI full disk
line-of-sight magnetogram data to measure the accumulation of magnetic
helicity in the corona before and after the event.
Results:
From the measured expansion factor in the magnetic arcade, visible
at 171 Åduring the eruption, we estimated that the resulting torque
imbalance at the photosphere ought to lead to the injection of negative
helicity following the eruption. We compared this with measurements
of the helicity injection using photospheric velocity and magnetogram
data.
Conclusions: In contradiction to the expectations from
the Chae et al. model, the helicity injection after the eruption was
positive. We offer the alternative interpretation that the helicity
injection resulted from torque of the opposite sign, generated as the
filament lost its negative helicity through magnetic reconnection with
its surroundings.
Title: Validation of CME Detection Software (CACTus) by Means of
Simulated Data, and Analysis of Projection Effects on CME Velocity
Measurements
Authors: Bonte, K.; Jacobs, C.; Robbrecht, E.; De Groof, A.; Berghmans,
D.; Poedts, S.
Bibcode: 2011SoPh..270..253B
Altcode: 2011SoPh..tmp...52B; 2011SoPh..tmp...72B
In the context of space weather forecasting, an automated detection
of coronal mass ejections (CMEs) becomes more and more important
for efficiently handling a large data flow which is expected from
recently-launched and future solar missions. In this paper we validate
the detection software package "CACTus" by applying the program to
synthetic data from our 3D time-dependent CME simulations instead of
observational data. The main strength of this study is that we know
in advance what should be detected. We describe the sensitivities
and strengths of automated detection, more specific for the CACTus
program, resulting in a better understanding of CME detection on one
hand and the calibration of the CACTus software on the other hand,
suggesting possible improvements of the package. In addition, the
simulation is an ideal tool to investigate projection effects on CME
velocity measurements.
Title: Acceleration of dust particles by vortex ring
Authors: Ehsan, Zahida; Tsintsadze, N. L.; Vranjes, J.; Khan, R.;
Poedts, S.
Bibcode: 2011JPlPh..77..155E
Altcode:
It is shown that nonlinear interaction between large amplitude
circularly polarized EM wave and dusty plasma leads to a non-stationary
ponderomotive force, which in turn produces a vortex ring and magnetic
field. Then the ensuing vortex ring in the direction of propagation
of the pump wave can accelerate the micron-size dust particles, which
are initially at rest and eventually form a non-relativistic dust
jet. This effect is purely non-stationary and unlike linear vortices,
dust particles do not rotate here. Specifically, it is pointed out that
the vortex ring or closed filament can become potential candidate for
the acceleration of dust in tokamak plasmas.
Title: Investigation of dynamics of self-similarly evolving magnetic
clouds
Authors: Dalakishvili, G.; Rogava, A.; Lapenta, G.; Poedts, S.
Bibcode: 2011A&A...526A..22D
Altcode: 2010arXiv1010.3573D
Context. Magnetic clouds (MCs) are “magnetized plasma clouds” moving
in the solar wind. MCs transport magnetic flux and helicity away from
the Sun. These structures are not stationary but experience temporal
evolution. Simplified MC models are usually considered.
Aims: We
investigate the dynamics of more general, radially expanding MCs. They
are considered as cylindrically symmetric magnetic structures with
low plasma β.
Methods: We adopt both a self-similar approach
method and a numerical approach.
Results: We demonstrate that
the forces are balanced in the considered self-similarly evolving,
cylindrically symmetric magnetic structures. Explicit analytical
expressions for magnetic field, plasma velocity, density, and
pressure within MCs are derived. These solutions are characterized by
conserved values of magnetic flux and helicity. We also investigate
the dynamics of self-similarly evolving MCs by means of the numerical
code “Graale”. In addition, their expansion in a medium of higher
density and higher plasma β is studied. It is shown that the physical
parameters of the MCs maintain their self-similar character throughout
their evolution.
Conclusions: After comparing different
self-similar and numerical solutions, we are able to conclude that
the evolving MCs are quite adequately described by our self-similar
solutions - they retain their self-similar, coherent nature for quite
a long time and over large distances from the Sun.
Title: Instability of the parallel electromagnetic modes in Kappa
distributed plasmas - I. Electron whistler-cyclotron modes
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.
Bibcode: 2011MNRAS.410..663L
Altcode: 2010MNRAS.tmp.1552L
The electron cyclotron emissions represent a useful tool in the
diagnostics of fusion plasmas and space plasma fluctuations. The
instability which enhances the whistler-cyclotron modes is driven
in the presence of an ambient regular magnetic field by an excess of
transverse kinetic energy of plasma particles. Previous studies have
modelled the anisotropic particles with a bi-Maxwellian or a bi-Kappa
distribution function and found a suppression of this instability in
the presence of suprathermal tails. Here, the anisotropic plasma is
modelled with a product-bi-Kappa distribution, with the advantage that
this distribution function enables the use of two different spectral
indices in the main directions, κ∥≠κ⊥,
and permits further characterization of kappa populations and their
excitations. The exact numerical values of the growth rates and the
instability threshold are derived and contrasted with those for a
simple bi-Kappa and a bi-Maxwellian, using plasma parameters and
magnetic fields relevant for the solar and terrestrial environments.
Title: Trend of photospheric magnetic helicity flux in active regions
generating halo CMEs
Authors: Zuccarello, F. P.; Smyrli, A.; Romano, P.; Poedts, S.
Bibcode: 2010AGUFMSH43B1817Z
Altcode:
Coronal Mass Ejections (CMEs) are very energetic events initiated
in the solar atmosphere, resulting in the expulsion of magnetized
plasma clouds that propagate into interplanetary space. It has been
proposed that CMEs can play an important role in shedding magnetic
helicity, avoiding its endless accumulation in the corona. We therefore
investigated the behavior of magnetic helicity accumulation in sites
where the initiation of CMEs occurred, in order to determine whether and
how changes in magnetic helicity accumulation are temporally correlated
with CME occurrence. After identifying the active regions (AR) where
the CMEs were initiated by means of a double cross-check based on the
flaring-eruptive activity and the use of SOHO/EIT difference images,
we use MDI magnetograms to calculate magnetic flux evolution magnetic,
helicity injection rate and magnetic helicity injection in 10 active
regions that gave rise to 12 halo CMEs observed during the period
February 2000 - June 2003. No unique behavior in magnetic helicity
injection accompanying halo CME occurrence is found. In fact, in
some cases there is an abrupt change in helicity injection timely
correlated with the CME event, while in some others no significant
variation is recorded. However, our analysis show that the most
significant changes in magnetic flux and magnetic helicity injection
are associated with impulsive CMEs rather than gradual CMEs. Moreover,
the most significant changes in magnetic helicity are observed when
X-class flares or eruptive filaments occur, while the occurrence of
flares of class C or M seems not to affect significantly the magnetic
helicity accumulation. Finally, this study shows that magnetic
helicity accumulation in our sample of ARs generating halo CMEs has
sudden and abrupt changes only in 40 % of the cases examined and that
a correlation between the helicity injection changes and the nature
(gradual or impulsive) of the CMEs seems to exist.
Title: CME and Flare Initiation Challenge
Authors: Lapenta, G.; Bettarini, L.; Poedts, S.; Soteria Team
Bibcode: 2010AGUFMSH23B1848L
Altcode:
We propose a challenge aimed at testing the difference among different
mathematical models and numerical codes in predicting the initiation
and subsequent initial phases of evolution of CMEs and flares. This
activity stems from the EC-funded collaborative project SOTERIA
(soteria-space.eu) but is open to the world-wide solar community. We
propose different modeling challenges in 2D and in 3D and we present our
first sets of results obtained with different models and codes. The
goal is primarily that of zeroing in on the different outcomes
of different choices of dissipations, compressibility, beyond-MHD
models in determining the role of the different processes of magnetic
reconnection and their impact on the onset and evolution of flares and
CMEs. We hope the scientific community will be interested and pick
up the challenge. Clearly, modifications to the challenge are still
possible based on the input from the community.
Title: 0.5 - 165 MeV proton and 102 - 312 keV electron injections
during the 2006 December 13 SEP event
Authors: Aran, A.; Agueda, N.; Jacobs, C.; Lario, D.; Sanahuja, B.;
Poedts, S.; Marsden, R. G.
Bibcode: 2010AGUFMSH33A1824A
Altcode:
The last large solar energetic particle event of solar cycle 23 was
observed on 2006 December 13. The origin of this event was associated
with a X3.4 flare from AR10930 at S06W23 and a fast (> 1700 km/s)
halo CME. A long-lasting type III and a metric type II radio burst were
also recorded. We combine proton observations from ACE/EPAM, SOHO/ERNE
and STEREO/IMPACT (24 energy channels from 0.5 to 165 MeV) to model
the proton differential intensities measured during this event. We
simulate both the propagation of the CME-driven shock (from 4 solar
radii to 1 AU) and the transport of shock-accelerated protons along the
upstream interplanetary magnetic field lines. Near-relativistic (102
- 312 keV) electron observations by ACE/EPAM during the early phase
of the event are used to constrain the electron transport conditions
along the field lines and deduce, via a Monte Carlo transport model,
the electron injection profile close to the Sun. The best-fit electron
injection profile shows one prompt component consistent with the timing
and duration of both the radio type III and the hard X-ray bursts and
a second delayed injection component timely associated with the type
II radio burst. From the proton modelling we quantify the injection
rate of shock accelerated protons and show that most of the >
50 MeV protons are injected when the shock is still close to the Sun
(i.e. within 42 solar radii). We compare the inferred electron and
proton injections and discuss the possible contribution of flare-related
particles in the early phase of the event.
Title: Observational and numerical study of the 25 July 2004 event
Authors: Soenen, A.; Jacobs, C.; Poedts, S.; van Driel-Gesztelyi,
L.; Torok, T.; Lapenta, G.
Bibcode: 2010AGUFMSH23B1843S
Altcode:
We study the 25 July 2004 event. By analyzing SOHO EIT images we
establish a basic understanding of the large-scale interaction going
on during this event. Magnetic reconnection between the expanding
CME and the Southern hemispheric active regions (AR) will connect the
leading polarities of the two ARs, lead to brightening in the ARs and
transport CME field line foot points to distant ARs (observable as
dimming at the foot points).We reproduce the large scale interactions
during this event using three-dimensional magneto-hydrodynamic (MHD)
simulations. We superimpose a magnetic source region that resembles
the SOHO MDI images on a basic wind model. By emerging new flux at the
centre of this region we initiate a Coronal Mass Ejection (CME). We
monitor the evolution of this CME and study its interaction with the
source region.
Title: A Model to study Jupiter's Magnetosphere and the
Ionosphere-Magnetosphere Coupling
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2010AGUFMSM51B1784C
Altcode:
In our MHD model of Jupiter's magnetosphere, the
magnetosphere-ionosphere coupling is consistently modelled by
introducing ion-neutral collisions in an extended ionosphere in the MHD
equations. Furthermore, the implementation of a production source term
in the equations mimics the mass-loading of the Io torus. Consequently,
two very important parameters for the Jovian magnetosphere, namely
the ionospheric Pedersen conductance and the Io torus mass-loading,
can be controlled in our model. In order to quantify the accuracy of
our simulations, we compare the azimuthal velocity profiles with the
semi-analytical models of Hill (1979, 2001) and Saur et al. (2004)
when these two parameters vary. Our simulation results are in very
good agreement with these models. In addition, the parallel currents
in the ionosphere are used as a proxy parameter to study the aurorae
in our simulations. We observe that the shape of the main oval is
strongly affected by the location of both, the co-rotation break-down
and the magnetopause.
Title: Drift waves in the corona: heating and acceleration of ions
at frequencies far below the gyrofrequency
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2010MNRAS.408.1835V
Altcode: 2010MNRAS.tmp.1222V; 2010arXiv1007.4726V
In the solar corona, several mechanisms of the drift wave instability
can make the mode grow to amplitudes at which particle acceleration and
stochastic heating by the drift wave take place. The stochastic heating,
well known from laboratory plasma physics where it has been confirmed
in numerous experiments, has been completely ignored in past studies
of coronal heating. However, in the present study and in our very
recent works it has been shown that the inhomogeneous coronal plasma
is, in fact, a perfect environment for fast growing drift waves. As
a matter of fact, the large growth rates are typically of the same
order as the wave frequency. The consequent heating rates may exceed
the required values for sustained coronal heating by several orders of
magnitude. Some aspects of these phenomena are investigated here. In
particular, the analysis of the particle dynamics within the growing
wave is compared with the corresponding fluid analysis. While both
of them predict the stochastic heating, the threshold for the heating
obtained from the single particle analysis is higher. The explanation
for this effect is given.
Title: Kinetic Instability of Drift-Alfvén Waves in Solar Corona
and Stochastic Heating
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2010ApJ...719.1335V
Altcode: 2010arXiv1007.4973V
The solar atmosphere is structured and inhomogeneous, both horizontally
and vertically. The omnipresence of coronal magnetic loops implies
gradients of the equilibrium plasma quantities such as the density,
magnetic field, and temperature. These gradients are responsible for
the excitation of drift waves that grow both within the two-component
fluid description (both in the presence of collisions and without
it) and within the two-component kinetic descriptions (due to purely
kinetic effects). In this work, the effects of the density gradient
in the direction perpendicular to the magnetic field vector are
investigated within the kinetic theory, in both electrostatic (ES)
and electromagnetic (EM) regimes. The EM regime implies the coupling
of the gradient-driven drift wave with the Alfvén wave. The growth
rates for the two cases are calculated and compared. It is found that,
in general, the ES regime is characterized by stronger growth rates,
as compared with the EM perturbations. Also discussed is the stochastic
heating associated with the drift wave. The released amount of energy
density due to this heating should be more dependent on the magnitude
of the background magnetic field than on the coupling of the drift and
Alfvén waves. The stochastic heating is expected to be much higher
in regions with a stronger magnetic field. On the whole, the energy
release rate caused by the stochastic heating can be several orders
of magnitude above the value presently accepted as necessary for a
sustainable coronal heating. The vertical stratification and the very
long wavelengths along the magnetic loops imply that a drift-Alfvén
wave, propagating as a twisted structure along the loop, in fact
occupies regions with different plasma-β and, therefore, may have
different (EM-ES) properties, resulting in different heating rates
within just one or two wavelengths.
Title: Side Magnetic Reconnections Induced by Coronal Mass Ejections:
Observations and Simulations
Authors: Bemporad, A.; Soenen, A.; Jacobs, C.; Landini, F.; Poedts, S.
Bibcode: 2010ApJ...718..251B
Altcode:
Over the last few years coronagraphic and spectroscopic observations
have demonstrated that small-scale eruptions, such as "jets," "narrow
coronal mass ejections (CMEs)," "mini CMEs," "streamer puffs," "streamer
detachments," and others, occur ubiquitously on the Sun. Nevertheless,
the origin of small-scale eruptive events and how these are interrelated
with larger scale CMEs have been poorly investigated so far. In this
work, we study a series of small-scale side eruptions that occurred
during and after a large-scale CME. Observations show that a CME can
be associated not only with a single reconnection process, leading to
the large-scale phenomenon, but also with many other side reconnections
occurring at different locations and times around the main flux rope,
possibly induced by the CME expansion in the surrounding corona. White
light and EUV observations of a slow CME acquired by the SOHO/LASCO and
SOHO/UVCS instruments are analyzed here to characterize the locations
of side reconnections induced by the CME. The magnetic reconnection
rate M has been estimated from the UVCS data from the ratio between
the inflows and outflows observed around the reconnection region, and
from the LASCO data from the observed aperture angles between the slow
mode shocks (SMSs) associated with the reconnection. It turns out that
M ~= 0.05 at the heliocentric distance of 1.8 R sun, while
between ~2.5 and 5.5 R sun, M values progressively decrease
with time/altitude from M ~ 1 down to M ~ 0.3. Such large values of
M are theoretically acceptable only if flux pile-up reconnection is
envisaged. The observed occurrence of multiple reconnections associated
with a CME is verified by numerical simulations of an eruption occurring
within multiple helmet streamers. The simulations confirm that small
side reconnections are a consequence of CME expansion against the
surrounding coronal streamers. The simulated and observed evolution of
aperture angles between the SMSs are in good agreement as well. These
results demonstrate the effect of the global coronal magnetic field
in the occurrence of small-scale eruptions due to lateral reconnection
in a preceding CME event.
Title: Self-heating and its possible relationship to chromospheric
heating in slowly rotating stars
Authors: Rogava, Andria; Osmanov, Zaza; Poedts, Stefaan
Bibcode: 2010MNRAS.404..224R
Altcode: 2010MNRAS.tmp..464R; 2009arXiv0909.5400R
The efficiency of non-modal self-heating by acoustic wave perturbations
is examined. Considering different kinds of kinematically complex
velocity patterns, we show that non-modal instabilities arising in
these inhomogeneous flows may lead to significant amplification of
acoustic waves. Subsequently, the presence of viscous dissipation
damps these amplified waves and causes the energy transfer back to the
background flow in the form of heat; viz. closes the `self-heating'
cycle and contributes to the net heating of the flow patterns and the
chromospheric network as a whole. The acoustic self-heating depends only
on the presence of kinematically complex flows and dissipation. It is
argued that together with other mechanisms of non-linear nature the
self-heating may be a probable additional mechanism of non-magnetic
chromospheric heating in the Sun and other solar-type stars with slow
rotation and extended convective regions.
Title: Global MHD Simulations of Jupiter's Magnetosphere: Study of
the Ionosphere-Magnetosphere Coupling.
Authors: Chané, Emmanuel; Saur, Joachim; Poedts, Stefaan
Bibcode: 2010EGUGA..12.4691C
Altcode:
We present a new MHD model of the Jovian magnetosphere with a consistent
coupling between the ionosphere and the magnetosphere (obtained via
the introduction in the MHD equations of ion-neutral collisions in
an extended ionosphere). In addition, the mass-loading caused by the
Io torus is included in the model via the inclusion of a production
source term in the MHD equations. This model allows us to control the
Pedersen conductance of the ionosphere and the amount of mass-loading
in the Io torus. To demonstrate the accuracy of the model, we verify
whether the position of the corotation break-down changes according
to the theory (Hill, 1979) when these two parameters are changed. Our
simulations show, as expected, that the corotation break-down occurs
further from the planet for a higher Pedersen conductance or for a
lower mass-loading.
Title: Advanced Magnetohydrodynamics
Authors: Goedbloed, J. P.; Keppens, Rony; Poedts, Stefaan
Bibcode: 2010adma.book.....G
Altcode:
Preface; Part III. Flow and Dissipation: 12. Waves and instabilities of
stationary plasmas; 13. Shear flow and rotation; 14. Resistive plasma
dynamics; 15. Computational linear MHD; Part IV. Toroidal Plasmas:
16. Static equilibrium of toroidal plasmas; 17. Linear dynamics of
static toroidal plasmas; 18. Linear dynamics of stationary toroidal
plasmas; Part V. Nonlinear Dynamics: 19. Computational nonlinear MHD;
20. Transonic MHD flows and shocks; 21. Ideal MHD in special relativity;
Appendices; References; Index.
Title: Nonresonant electromagnetic instabilities in space plasmas:
interplay of Weibel and firehose instabilities
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.
Bibcode: 2010AIPC.1216..280L
Altcode:
In coronal outflows and solar winds, the presence of the interplanetary
magnetic field and heat fluxes combined with jets and shock waves give
rise to important thermal anisotropies and energetic counterstreaming
motions of plasma shells. Such anisotropic structures of plasma
quickly lead to the onset of the kinetic electromagnetic instabilities
which are dependent solely on bulk properties of the plasma and not
on resonant interaction with charged particles. Here the interplay
between the Weibel and firehose instabilities, both driven by an excess
of kinetic energy in the direction of the ambient magnetic field, is
considered. Their growth rates and thresholds are evaluated and compared
for the electron temperature anisotropies in the solar wind. It is shown
that the instability of the Weibel-type, which is improperly known as
the ``oblique firehose'' instability, is the most efficient mechanism
of isotropisation limiting the increase of particle velocity anisotropy
and thus confirming the observations. These instabilities can explain
the origin of interplanetary magnetic field fluctuations, which are
expected to enhance along the temperature anisotropy thresholds.
Title: Consistent Self-Similar Magnetohydrodynamics Evolution of
Coronal Transients
Authors: Shapakidze, David; Debosscher, Arnold; Rogava, Andria;
Poedts, Stefaan
Bibcode: 2010ApJ...712..565S
Altcode:
The self-similar model of coronal transients by B. C. Low is
reconsidered. Due to a modification of the basic set of the initial
assumptions of the model, a new class of more consistent solutions is
found. The main advantage of these new solutions is that they do not
contain areas with a physically inconsistent negative pressure. Instead,
the novel solutions are derived on the basis of a special prescription
for the thermal pressure of the transients that guarantees, by design,
its positiveness throughout the whole evolution domain. The possible
importance of these solutions for understanding the physics of the
transient interplanetary coronal mass ejections (ICMEs; originating from
the Sun), and magnetic clouds as a subclass of these, is discussed. A
practical example is cited illustrating the application of our analytic
results to describe some properties of real ICMEs. Some directions
and scopes for further research are outlined.
Title: Resonant Weibel instability in counterstreaming plasmas with
temperature anisotropies
Authors: Lazar, M.; Dieckmann, M. E.; Poedts, S.
Bibcode: 2010JPlPh..76...49L
Altcode: 2009JPlPh..76...49L
The Weibel instability, driven by a plasma temperature anisotropy,
is non-resonant with plasma particles: it is purely growing in
time, and does not oscillate. The effect of a counterstreaming
plasma is examined. In a counterstreaming plasma with an excess
of transverse temperature, the Weibel instability arises along the
streaming direction. Here it is proved that for large wave-numbers the
instability becomes resonant with a finite real (oscillation) frequency,
ωr ≠ 0. When the plasma flows faster, with a bulk velocity
larger than the parallel thermal velocity, the instability becomes
dominantly resonant. This new feature of the Weibel instability can
be relevant for astrophysical sources of non-thermal emissions and
the stability of counterflowing plasma experiments.
Title: Modeling of Local Magnetic Field Enhancements within Solar
Flux Ropes
Authors: Romashets, E.; Vandas, M.; Poedts, S.
Bibcode: 2010SoPh..261..271R
Altcode: 2010SoPh..tmp....7R
To model and study local magnetic-field enhancements in a solar flux
rope we consider the magnetic field in its interior as a superposition
of two linear (constant α) force-free magnetic-field distributions,
viz. a global one, which is locally similar to a part of the
cylinder, and a local torus-shaped magnetic distribution. The newly
derived solution for a toroid with an aspect ratio close to unity is
applied. The symmetry axis of the toroid and that of the cylinder may or
may not coincide. Both the large and small radii of the toroid are set
equal to the cylinder's radius. The total magnetic field distribution
yields a flux tube which has a variable diameter with local minima and
maxima. In principle, this approach can be used for the interpretation
and analysis of solar-limb observations of coronal loops.
Title: Simulation of a multi-spacecraft detected gradual SEP event
by using a shock-and-particle model starting at 4 solar radii
Authors: Rodriguez-Gasen, Rosa; Jacobs, Carla; Aran, Angels; Sanahuja,
Blai; Poedts, Stefaan
Bibcode: 2010cosp...38.4210R
Altcode: 2010cosp.meet.4210R
Particle intensity-time profiles of a gradual SEP event observed by
spacecraft located a different heliolongitudes close to the ecliptic
plane, even being at a similar distance from the Sun, have shown
different shapes. To model this variability we present the simulation of
an event observed by the Helios 1 and 2 and IMP8/ISEE-3 spacecraft. We
have developed under the Solar Energetic Particle Event Modeling (SEPEM)
project a new shock-and-particle model that combines a 2D MHD code
(in the ecliptic plane) and a particle transport code. With this model
we can track the traveling shock from 4 solar radii. This allows us
to determine the injection rate of shock accelerated particles from
close to the Sun, where the bulk of high energy particles often are
accelerated. We have simulated the shock propagation by fitting the time
of shock arrivals and jumps in plasma observed at each of the spacecraft
and we have reproduced the proton intensities measured by these vantage
observers. We draw conclusions on the influence of the relative position
of the observer (with respect to the leading direction of the traveling
shock), on the injection rate of shock-accelerated particles, and on
the particles transport conditions found for each spacecraft. We also
discuss the forecasting capability of the relation between the injection
rate of shock accelerated particles and the jump in speed across the
shock front that we have found in SEP events previously modeled.
Title: Influence of the interplanetary shock on the heliocentric
radial variations of gradual SEP events
Authors: Aran, Angels; Jacobs, Carla; Sanahuja, Blai; Poedts, Stefaan;
Lario, David; Rodriguez-Gasen, Rosa
Bibcode: 2010cosp...38.4157A
Altcode: 2010cosp.meet.4157A
The inclusion of a travelling shock as a source of energetic particles
during gradual solar ener-getic particle (SEP) events is a key
element to assess the radiation encountered by a mission in the inner
heliosphere. We have developed, in the frame of the Solar Energetic
Particle Envi-ronment Model (SEPEM) project, a new two dimensional
(2D) magnetohydrodynamic (MHD) model to describe the shock propagation
from 4 solar radii up to 1.6 AU. The outputs of this model are used
to simulate the transport of SEPs from the shock front up to a given
observer. The combination of the shock and particle transport models
allows us to study the influence of both the shock properties and the
observer's magnetic connection on the radial and longitudinal variation
of proton peak intensities and fluences in gradual SEP events. We
have simulated the propagation of six shocks characterized by three
different transit times to 1 AU and two different angular widths
(narrow and wide). Two sets of spacecraft are placed along two nominal
interplanetary magnetic field lines in the undisturbed solar wind but
at different radial distances from the Sun. The two observers at 1 AU
are located at central meridian and western positions with respect
to the nose of each shock. For each spacecraft, synthetic proton
time-intensity profiles at several energies (1.0 < E < 128 MeV)
are produced. By tracking the shock from close to the Sun, we obtain the
peak intensity of high energy particles at the prompt component of the
SEP events, without assuming ad-hoc conditions for particle injection
at the corona. We discuss how the resulting power-law dependences of
the peak intensities (and fluences) on the observer's radial distance
vary with the particle energy, the characteristics of the shock, and the
different evolving conditions for particle injection at the cobpoint.
Title: Counterstreaming magnetized plasmas with kappa distributions -
II. Perpendicular wave propagation
Authors: Lazar, M.; Tautz, R. C.; Schlickeiser, R.; Poedts, S.
Bibcode: 2010MNRAS.401..362L
Altcode: 2009MNRAS.tmp.1517L
The analysis of the stability and the dispersion properties of a
counterstreaming plasma system with kappa distributions are extended
here with the investigation of perpendicular instabilities. Purely
growing filamentation (Weibel-like) modes propagating perpendicular to
the background magnetic field can be excited in streaming plasmas with
or without an excess of parallel temperature. In this case, however,
the effect of suprathermal tails of kappa populations is opposite to
that obtained for parallel waves: the growth rates can be higher and the
instability faster than for Maxwellian plasmas. The unstable wavenumbers
also extend to a markedly larger broadband making this instability
more likely to occur in space plasmas with anisotropic distributions
of kappa-type. The filamentation instability of counterstreaming
magnetized plasmas could provide a plausible mechanism for the origin of
two-dimensional transverse magnetic fluctuations detected at different
altitudes in the solar wind.
Title: SEPEM -Solar Energetic Particle Environment Modelling
Authors: Crosby, Norma Bock; Glover, Alexi; Aran, Angels; Bonnevie,
Cédric; Dyer, Clive; Gabriel, Steve; Hands, Alex; Heynderickx, Daniel;
Jacobs, Carla; Jiggens, Piers; King, David; Lawrence, Gareth; Poedts,
Stefaan; Sanahuja, Blai; Truscott, Pete
Bibcode: 2010cosp...38.4225C
Altcode: 2010cosp.meet.4225C
The ESA Solar Energetic Particle Environment Modelling (SEPEM) project
is currently under development and this presentation highlights the
work done so far and the final developments. The full release of SEPEM
will take place during the second half of 2010. The main objectives
of SEPEM are to create new engineering models and tools to address
current and future needs, as well as simulate past events and future
scenarios. SEPEM moves beyond mission integrated fluence statistics to
peak flux statistics and durations of high flux periods. Furthermore
SEPEM integrates effects tools to allow calculation of single event
upset rate and radiation background for a variety of scenarios. SEPEM
also improves existing physics-based shock-particle propaga-tion models
to predict the expected event-time profiles at non-Earth locations
[SOLPENCO2]. The main outputs of SEPEM is the creation of a standard
solar energetic particle dataset and a user-friendly webserver with
access to the models being developed under this project.
Title: Simulations of SEP events: does the latitude of the observer
play a significant role on the proton flux profiles?
Authors: Rodriguez-Gasen, Rosa; Aran, Angels; Sanahuja, Blai; Jacobs,
Carla; Poedts, Stefaan
Bibcode: 2010cosp...38.4209R
Altcode: 2010cosp.meet.4209R
Two observers located at 1 AU and with the same heliocentric longitude,
detecting the same CME-driven shock, would not necessarily measure
the same particle flux profile if they have different latitude with
respect to the incoming disturbance. The reason is that their magnetic
connection with the front of the shock may scan different regions on
the shock front with different conditions for particle acceleration,
and hence the observed flux profiles will differ. To study how relevant
these changes can be, we simulate the propagation of two CME-driven
shocks (slow and fast) from the Sun up to several observers placed at
different radial distances, and at different longitudes and latitudes
(i.e., different angular positions with respect to the nose of the
shock). We derive the plasma conditions at the point on the shock
front where the magnetic connection of the observer is established as
derived from the 3D MHD CME/shock propagation simulation. We study the
influence of the position of the observer on the proton flux profiles
to be detected by each observer by assuming a relationship between
the plasma jump in speed at the shock front (while expanding from the
Sun up to each observer) and the injection rate of shock accelerated
particles. We discuss these results in terms of the latitude of the
observers.
Title: Electric fields in solar magnetic structures due to
gradient-driven instabilities: heating and acceleration of particles
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2009MNRAS.400.2147V
Altcode: 2009arXiv0909.0585V; 2009MNRAS.tmp.1466V
The electrostatic instabilities driven by the gradients of the density,
temperature and magnetic field are discussed in their application
to solar magnetic structures. Strongly growing modes are found for
some typical plasma parameters. These instabilities (i) imply the
presence of electric fields that can accelerate the plasma particles
in both perpendicular and parallel directions with respect to the
magnetic field vector, and (ii) can stochastically heat ions. The
perpendicular acceleration is to the leading order determined by
the E × B drift acting equally on both ions and electrons, while the
parallel acceleration is most effective on electrons. The experimentally
confirmed stochastic heating is shown to act mainly in the direction
perpendicular to the magnetic field vector and acts stronger on heavier
ions. The energy release rate and heating may exceed for several orders
of magnitude the value accepted as necessary for a self-sustained
heating in the solar corona. The energy source for both the acceleration
and the heating is stored in the mentioned background gradients.
Title: Global MHD simulations of Jupiter's magnetosphere: study of
the ionosphere-magnetosphere coupling
Authors: Chané, E.; Saur, J. S.; Poedts, S.
Bibcode: 2009AGUFMSM23B1610C
Altcode:
In the Jovian magnetosphere, the corotation enforcing current system
plays a major role and controls the main oval auroral emissions. This
current system is composed of: 1) radially outward currents in
the equatorial plane, where the closed field lines of Jupiter are
deformed by the subcorotating plasma; 2) Pedersen currents in the
ionosphere pointing to the equator; 3) field aligned (Birkeland)
currents closing the system. In this study, we present a MHD model
specially designed to perform three dimensional global simulations of
the Jovian magnetosphere and to reproduce the corotation enforcing
current system. In this model, a consistent coupling between the
ionosphere and the magnetosphere is obtained via the introduction of
ion-neutral collisions in the ionosphere and the mass-loading caused
by Io (~1000 kg/s) is simulated via a production source term. This
model will allow us to understand the influence of the solar wind on
the current systems of Jupiter's magnetosphere and to study how the
ion-neutral collision frequency in the ionosphere and the mass-loading
at the orbit of Io affect the position of the corotation break-down in
our simulations. The first results indicate that a northward IMF tends
to lead to an open magnetosphere while a southward IMF does not. In
addition, the corotation breaks down at larger radial distances for high
Pedersen conductivities in the ionosphere (controlled in our model by
the ion-neutral collision frequency) or for a weaker mass-loading at
Io; as predicted by Hill (1979).
Title: Farley-Buneman Instability in the Solar Chromosphere
Authors: Gogoberidze, G.; Voitenko, Y.; Poedts, S.; Goossens, M.
Bibcode: 2009ApJ...706L..12G
Altcode: 2009arXiv0902.4426G
The Farley-Buneman instability (FBI) is studied in the partially
ionized plasma of the solar chromosphere taking into account the
finite magnetization of the ions and Coulomb collisions. We obtain the
threshold value for the relative velocity between ions and electrons
necessary for the instability to develop. It is shown that Coulomb
collisions play a destabilizing role in the sense that they enable the
instability even in the regions where the ion magnetization is larger
than unity. By applying these results to chromospheric conditions, we
show that the FBI cannot be responsible for the quasi-steady heating
of the solar chromosphere. However, we do not exclude the instability
development locally in the presence of strong cross-field currents
and/or strong small-scale magnetic fields. In such cases, FBI should
produce locally small-scale, ~0.1-3 m, density irregularities in the
solar chromosphere. These irregularities can cause scintillations of
radio waves with similar wave lengths and provide a tool for remote
chromospheric sensing.
Title: Characteristics of magnetised plasma flow around stationary
and expanding magnetic clouds
Authors: Dalakishvili, G.; Poedts, S.; Fichtner, H.; Romashets, E.
Bibcode: 2009A&A...507..611D
Altcode:
Aims: Studies of interplanetary magnetic clouds have shown that the
characteristics of the region ahead of these objects, which are moving
away from the Sun in the solar wind, play a role in determining their
geo-efficiency, i.e. the kind and the degree of their effects on the
Earth environment. Therefore, our main goal is to model and study
the plasma parameters in the vicinity of interplanetary magnetic
clouds.
Methods: To this end we present a model in which
the magnetic clouds are immersed in a magnetised plasma flow with a
homogeneous magnetic field. We first calculate the resulting distortion
of the external magnetic field and then determine the plasma velocity
by employing the frozen-in condition.
Results: Subsequently,
the plasma density and pressure are expressed as functions of the
magnetic field and the velocity field.
Conclusions: The plasma
flow parameters are determined by solving the time-independent ideal
MHD equations for both the stationary regime and for the case of an
expanding cylindrical magnetic cloud, thus extending previous results
that appeared in the literature.
Title: Models of Solar Wind Structures and Their Interaction with
the Earth's Space Environment
Authors: Watermann, J.; Wintoft, P.; Sanahuja, B.; Saiz, E.; Poedts,
S.; Palmroth, M.; Milillo, A.; Metallinou, F. -A.; Jacobs, C.;
Ganushkina, N. Y.; Daglis, I. A.; Cid, C.; Cerrato, Y.; Balasis, G.;
Aylward, A. D.; Aran, A.
Bibcode: 2009SSRv..147..233W
Altcode:
The discipline of “Space Weather” is built on the scientific
foundation of solar-terrestrial physics but with a strong orientation
toward applied research. Models describing the solar-terrestrial
environment are therefore at the heart of this discipline,
for both physical understanding of the processes involved and
establishing predictive capabilities of the consequences of these
processes. Depending on the requirements, purely physical models,
semi-empirical or empirical models are considered to be the most
appropriate. This review focuses on the interaction of solar
wind disturbances with geospace. We cover interplanetary space,
the Earth’s magnetosphere (with the exception of radiation belt
physics), the ionosphere (with the exception of radio science), the
neutral atmosphere and the ground (via electromagnetic induction
fields). Space weather relevant state-of-the-art physical and
semi-empirical models of the various regions are reviewed. They include
models for interplanetary space, its quiet state and the evolution of
recurrent and transient solar perturbations (corotating interaction
regions, coronal mass ejections, their interplanetary remnants, and
solar energetic particle fluxes). Models of coupled large-scale solar
wind-magnetosphere-ionosphere processes (global magnetohydrodynamic
descriptions) and of inner magnetosphere processes (ring current
dynamics) are discussed. Achievements in modeling the coupling between
magnetospheric processes and the neutral and ionized upper and middle
atmospheres are described. Finally we mention efforts to compile
comprehensive and flexible models from selections of existing modules
applicable to particular regions and conditions in interplanetary
space and geospace.
Title: Magnetic helicity and active filament configuration
Authors: Romano, P.; Zuccarello, F.; Poedts, S.; Soenen, A.;
Zuccarello, F. P.
Bibcode: 2009A&A...506..895R
Altcode:
Context: The role of magnetic helicity in active filament formation
and destabilization is still under debate.
Aims: Although active
filaments usually show a sigmoid shape and a twisted configuration
before and during their eruption, it is unclear which mechanism leads
to these topologies. In order to provide an observational contribution
to clarify these issues, we describe a filament evolution whose
characteristics seem to be directly linked to the magnetic helicity
transport in corona.
Methods: We applied different methods to
determine the helicity sign and the chirality of the filament magnetic
field. We also computed the magnetic helicity transport rate at the
filament footpoints.
Results: All the observational signatures
provided information on the positive helicity and sinistral chirality of
the flux rope containing the filament material: its forward S shape,
the orientation of its barbs, the bright and dark threads at 195
Å. Moreover, the magnetic helicity transport rate at the filament
footpoints showed a clear accumulation of positive helicity.
Conclusions: The study of this event showed a correspondence between
several signatures of the sinistral chirality of the filament and
several evidences of the positive magnetic helicity of the filament
magnetic field. We also found that the magnetic helicity transported
along the filament footpoints showed an increase just before the
change of the filament shape observed in Hα images. We argued that
the photospheric regions where the filament was rooted might be the
preferential ways where the magnetic helicity was injected along
the filament itself and where the conditions to trigger the eruption
were yielded.
Title: Modelling the initiation of coronal mass ejections: magnetic
flux emergence versus shearing motions
Authors: Zuccarello, F. P.; Jacobs, C.; Soenen, A.; Poedts, S.;
van der Holst, B.; Zuccarello, F.
Bibcode: 2009A&A...507..441Z
Altcode:
Context: Coronal mass ejections (CMEs) are enormous expulsions of
magnetic flux and plasma from the solar corona into the interplanetary
space. These phenomena release a huge amount of energy. It is generally
accepted that both photospheric motions and the emergence of new
magnetic flux from below the photosphere can put stress on the system
and eventually cause a loss of equilibrium resulting in an eruption.
Aims: By means of numerical simulations we investigate both emergence
of magnetic flux and shearing motions along the magnetic inversion
line as possible driver mechanisms for CMEs. The pre-eruptive region
consists of three arcades with alternating magnetic flux polarity,
favouring the breakout mechanism.
Methods: The equations of ideal
magnetohydrodynamics (MHD) were advanced in time by using a finite
volume approach and solved in spherical geometry. The simulation domain
covers a meridional plane and reaches from the lower solar corona
up to 30 R_⊙. When we applied time-dependent boundary conditions
at the inner boundary, the central arcade of the multiflux system
expands, leading to the eventual eruption of the top of the helmet
streamer. We compare the topological and dynamical evolution of the
system when driven by the different boundary conditions. The available
free magnetic energy and the possible role of magnetic helicity in the
onset of the CME are investigated.
Results: In our simulation
setup, both driving mechanisms result in a slow CME. Independent of the
driving mechanism, the overall evolution of the system is the same: the
actual CME is the detatched helmet streamer. However, the evolution of
the central arcade is different in the two cases. The central arcade
eventually becomes a flux rope in the shearing case, whereas in the
flux emergence case there is no formation of a flux rope. Furthermore,
we conclude that magnetic helicity is not crucial to a solar eruption.
Title: The role of lateral magnetic reconnection in solar eruptive
events
Authors: Soenen, A.; Bemporad, A.; Jacobs, C.; Poedts, S.
Bibcode: 2009AnGeo..27.3941S
Altcode:
On 10-11 December 2005 a slow CME occurred in between two coronal
streamers in the Western Hemisphere. SOHO/MDI magnetograms show a
multipolar magnetic configuration at the photosphere consisting of a
complex of active regions located at the CME source and two bipoles
at the base of the lateral coronal streamers. White light observations
reveal that the expanding CME affects both of the lateral streamers and
induces the release of plasma within or close to them. These transient
phenomena are possibly due to magnetic reconnections induced by the
CME expansion that occurs either inside the streamer current sheet or
between the CME flanks and the streamer. Our observations show that
CMEs can be associated to not only a single reconnection process
at a single location in the corona, but also to many reconnection
processes occurring at different times and locations around the flux
rope. Numerical simulations are used to demonstrate that the observed
lateral reconnections can be reproduced. The observed secondary
reconnections associated to CMEs may facilitate the CME release by
globally decreasing the magnetic tension of the corona. Future CME
models should therefore take into account the lateral reconnection
effect.
Title: Acoustic oscillations in the field-free, gravitationally
stratified cavities under solar bipolar magnetic canopies
Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.;
Poedts, S.
Bibcode: 2009A&A...505..763K
Altcode: 2009arXiv0905.2302K
Aims: The main goal here is to study the dynamics of the gravitationally
stratified, field-free cavities in the solar atmosphere, located
under small-scale, cylindrical magnetic canopies, in response to
explosive events in the lower-lying regions (due to granulation,
small-scale magnetic reconnection, etc.).
Methods: We derive
the two-dimensional Klein-Gordon equation for isothermal density
perturbations in cylindrical coordinates. The equation is first solved
by a standard normal mode analysis to obtain the free oscillation
spectrum of the cavity. Then, the equation is solved in the case of
impulsive forcing associated to a pressure pulse specified in the lower
lying regions.
Results: The normal mode analysis shows that the
entire cylindrical cavity of granular dimensions tends to oscillate
with frequencies of 5-8 mHz and also with the atmospheric cut-off
frequency. Furthermore, the passage of a pressure pulse, excited
in the convection zone, sets up a wake in the cavity oscillating
with the same cut-off frequency. The wake oscillations can resonate
with the free oscillation modes, which leads to an enhanced observed
oscillation power.
Conclusions: The resonant oscillations of
these cavities explain the observed power halos near magnetic network
cores and active regions.
Title: The universally growing mode in the solar atmosphere: coronal
heating by drift waves
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2009MNRAS.398..918V
Altcode: 2009MNRAS.tmp.1020V; 2009arXiv0906.2071V
The heating of the plasma in the solar atmosphere is discussed within
both frameworks of fluid and kinetic drift wave theory. We show that
the basic ingredient necessary for the heating is the presence of
density gradients in the direction perpendicular to the magnetic field
vector. Such density gradients are a source of free energy for the
excitation of drift waves. We use only well-established basic theory,
verified experimentally in laboratory plasmas. Two mechanisms of the
energy exchange and heating are shown to take place simultaneously:
one due to the Landau effect in the direction parallel to the magnetic
field, and another one, stochastic heating, in the perpendicular
direction. The stochastic heating (i) is due to the electrostatic nature
of the waves, (ii) is more effective on ions than on electrons, (iii)
acts predominantly in the perpendicular direction, (iv) heats heavy
ions more efficiently than lighter ions and (v) may easily provide a
drift wave-heating rate that is orders of magnitude above the value
that is presently believed to be sufficient for the coronal heating,
that is ~=6 × 10-5Jm-3 s-1 for active
regions and ~=8 × 10-6Jm-3 s-1 for
coronal holes. This heating acts naturally through well-known effects
that are, however, beyond the current standard models and theories.
Title: Solar nanoflares and other smaller energy release events as
growing drift waves
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2009PhPl...16i2902V
Altcode: 2009arXiv0909.1689V
Rapid energy releases (RERs) in the solar corona extend over many
orders of magnitude, the largest (flares) releasing an energy of
1025 J or more. Other events, with a typical energy that
is a billion times less, are called nanoflares. A basic difference
between flares and nanoflares is that flares need a larger magnetic
field and thus occur only in active regions, while nanoflares can appear
everywhere. The origin of such RERs is usually attributed to magnetic
reconnection that takes place at altitudes just above the transition
region. Here we show that nanoflares and smaller similar RERs at
least in some cases can be explained within the drift wave theory as a
natural stage in the kinetic growth of the drift wave. In this scenario,
a growing mode with a sufficiently large amplitude leads to stochastic
heating that can provide an energy release of over 1016 J.
Title: Limits for the Firehose Instability in Space Plasmas
Authors: Lazar, M.; Poedts, S.
Bibcode: 2009SoPh..258..119L
Altcode:
Electromagnetic instabilities in high-β plasmas, where β is the
ratio of the kinetic plasma energy to the magnetic energy, have a
broad range of astrophysical applications. The presence of temperature
anisotropies T∥/T⊥>1 (where ∥ and
⊥ denote directions relative to the background magnetic field)
in solar flares and the solar wind is sustained by the observations
and robust acceleration mechanisms that heat plasma particles in
the parallel direction. The surplus of parallel kinetic energy
can excite either the Weibel-like instability (WI) of the ordinary
mode perpendicular to the magnetic field or the firehose instability
(FHI) of the circularly polarized waves at parallel propagation. The
interplay of these two instabilities is examined. The growth rates and
the thresholds provided by the kinetic Vlasov - Maxwell theory are
compared. The WI is the fastest growing one with a growth rate that
is several orders of magnitude larger than that of the FHI. These
instabilities are however inhibited by the ambient magnetic field
by introducing a temperature anisotropy threshold. The WI admits a
larger anisotropy threshold, so that, under this threshold, the FHI
remains the principal mechanism of relaxation. The criteria provided
here by describing the interplay of the WI and FHI are relevant for
the existence of these two instabilities in any space plasma system
characterized by an excess of parallel kinetic energy.
Title: Diamagnetic current does not produce an instability in the
solar corona
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2009A&A...503..591V
Altcode:
Context: The solar atmosphere contains density irregularities of various
sizes embedded in magnetic fields. In the case of a density gradient
perpendicular to the magnetic field vector, the plasma supports drift
waves that are usually growing as a result of the free energy stored
in the density gradient.
Aims: Some basic features of the drift
wave are discussed here and, in particular, the gyro-viscosity stress
tensor effects and the properties of the diamagnetic drift. Also,
the recently proposed “new” instability due to the diamagnetic
drift is checked.
Methods: This analysis involves a calculation
that considers some terms missing in previous calculations that
have appeared in the literature.
Results: It is shown that the
diamagnetic drift, which is essential for the recently proposed new
physical phenomenon, cannot contribute to the flux in the continuity
equation. Moreover, the part of the ion polarization drift contribution
to the ion flux cancels out exactly with the contribution of the part
of the stress tensor drift to the same flux.
Conclusions: Thus,
the ion diamagnetic current does not produce an instability in the
solar corona.
Title: GRADSPH: A parallel smoothed particle hydrodynamics code for
self-gravitating astrophysical fluid dynamics
Authors: Vanaverbeke, S.; Keppens, R.; Poedts, S.; Boffin, H.
Bibcode: 2009CoPhC.180.1164V
Altcode:
We describe the algorithms implemented in the first version of
GRADSPH, a parallel, tree-based, smoothed particle hydrodynamics
code for simulating self-gravitating astrophysical systems written
in FORTRAN 90. The paper presents details on the implementation
of the Smoothed Particle Hydro (SPH) description, where a gridless
approach is used to model compressible gas dynamics. This is done in
the conventional SPH way by means of ‘particles’ which sample
fluid properties, exploiting interpolating kernels. The equations
of self-gravitating hydrodynamics in the SPH framework are derived
self-consistently from a Lagrangian and account for variable
smoothing lengths (‘GRAD-h’) terms in both the hydrodynamic
and gravitational acceleration equations. A Barnes-Hut tree is
used for treating self-gravity and updating the neighbour list of
the particles. In addition, the code updates particle properties
on their own individual timesteps and uses a basic parallelisation
strategy to speed up calculations on a parallel computer system with
distributed memory architecture. Extensive tests of the code in one
and three dimensions are presented. Finally, we describe the program
organisation of the publicly available 3D version of the code, as well
as details concerning the structure of the input and output files
and the execution of the program. Catalogue identifier: AECX_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECX_v1_0.html
Program obtainable from: CPC Program Library, Queen's University,
Belfast, N. Ireland Licensing provisions: Standard CPC licence,
http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed
program, including test data, etc.: 11 123 No. of bytes in distributed
program, including test data, etc.: 1 561 909 Distribution
format: tar.gz Programming language: Fortran 90/MPI Computer:
HPC cluster Operating system: Unix Has the code been vectorised or
parallelised?: Yes RAM: 56 Mwords with 1.2 million particles on 1 CPU
Word size: 32 bits Classification: 12 Nature of problem: Evolution of
a self-gravitating fluid. Solution method: Hydrodynamics is described
using SPH, self-gravity using the Barnes-Hut tree method. Running time:
The test case provided with the distribution takes less than 10 minutes
for 500 time steps on 10 processors.
Title: Numerical simulations of homologous coronal mass ejections
in the solar wind
Authors: Soenen, A.; Zuccarello, F. P.; Jacobs, C.; Poedts, S.;
Keppens, R.; van der Holst, B.
Bibcode: 2009A&A...501.1123S
Altcode:
Context: Coronal mass ejections (CMEs) are enormous expulsions of
magnetic flux and plasma from the solar corona. Most scientists agree
that a coronal mass ejection is the sudden release of magnetic free
energy stored in a strongly stressed field. However, the exact reason
for this sudden release is still highly debated.
Aims: In an
initial multiflux system in steady state equilibrium, containing
a pre-eruptive region consisting of three arcades with alternating
magnetic flux polarity, we study the initiation and early evolution
properties of a sequence of CMEs by shearing a region slightly
larger than the central arcade.
Methods: We solve the ideal
magnetohydrodynamics (MHD) equations in an axisymmetrical domain
from the solar surface up to 30 R_⊙. The ideal MHD equations are
advanced in time over a non uniform grid using a modified version of
the Versatile Advection Code (VAC).
Results: By applying shearing
motions on the solar surface, the magnetic field is energised and
multiple eruptions are obtained. Magnetic reconnection first opens the
overlying field and two new reconnections sites set in on either side
of the central arcade. After the disconnection of the large helmet top,
the system starts to restore itself but cannot return to its original
configuration as a new arcade has already started to erupt. This process
then repeats itself as we continue shearing.
Conclusions: The
simulations reported in the present paper, demonstrate the ability to
obtain a sequence of CMEs by shearing a large region of the central
arcade or by shearing a region that is only slightly larger than
the central arcade. We show, be it in an axisymmetric configuration,
that the breakout model can not only lead to confined eruptions but
also to actual coronal mass ejections provided the model includes a
realistic solar wind model.
Title: Three frontside full halo coronal mass ejections with a
nontypical geomagnetic response
Authors: Rodriguez, L.; Zhukov, A. N.; Cid, C.; Cerrato, Y.; Saiz,
E.; Cremades, H.; Dasso, S.; Menvielle, M.; Aran, A.; Mandrini, C.;
Poedts, S.; Schmieder, B.
Bibcode: 2009SpWea...7.6003R
Altcode:
Forecasting potential geoeffectiveness of solar disturbances (in
particular, of frontside full halo coronal mass ejections) is important
for various practical purposes, e.g., for satellite operations, radio
communications, global positioning system applications, power grid,
and pipeline maintenance. We analyze three frontside full halo coronal
mass ejections (CMEs) that occurred in the year 2000 (close to the
activity maximum of solar cycle 23), together with associated solar
and heliospheric phenomena as well as their impact on the Earth's
magnetosphere. Even though all three were fast full halos (with plane
of the sky speeds higher than 1100 km/s), the geomagnetic response
was very different for each case. After analyzing the source regions
of these halo CMEs, it was found that the halo associated with the
strongest geomagnetic disturbance was the one that initiated farther
away from disk center (source region at W66); while the other two CMEs
originated closer to the central meridian but had weaker geomagnetic
responses. Therefore, these three events do not fit into the general
statistical trends that relate the location of the solar source and
the corresponding geoeffectivity. We investigate possible causes of
such a behavior. Nonradial direction of eruption, passage of the Earth
through a leg of an interplanetary flux rope, and strong compression
at the eastern flank of a propagating interplanetary CME during its
interaction with the ambient solar wind are found to be important
factors that have a direct influence on the resulting north-south
interplanetary magnetic field (IMF) component and thus on the CME
geoeffectiveness. We also find indications that interaction of two CMEs
could help in producing a long-lasting southward IMF component. Finally,
we are able to explain successfully the geomagnetic response using
plasma and magnetic field in situ measurements at the L1 point. We
discuss the implications of our results for operational space weather
forecasting and stress the difficulties of making accurate predictions
with the current knowledge and tools at hand.
Title: A new paradigm for solar coronal heating
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2009EL.....8639001V
Altcode: 2009arXiv0904.4546V
The solar coronal heating problem refers to the question why the
temperature of the Sun's corona is more than two orders of magnitude
higher than that of its surface. Almost 70 years after the discovery,
this puzzle is still one of the major challenges in astrophysics. The
current basic paradigm of coronal heating is unable to explain all the
observational features of heating. Here we argue that a new paradigm
is required to solve the puzzle in a self-consistent manner. The
alternative approach is based on the kinetic theory of drift waves. We
show that, with qualitative and quantitative arguments, the drift
waves have the potential to satisfy all coronal heating requirements.
Title: Numerical simulations of the solar corona and Coronal Mass
Ejections
Authors: Poedts, Stefaan; Jacobs, Carla; van der Holst, Bart; Chané,
Emmanuel; Keppens, Rony
Bibcode: 2009EP&S...61..599P
Altcode: 2009EP&S...61L.599P
Numerical simulations of Coronal Mass Ejections (CMEs) can provide a
deeper insight in the structure and propagation of these impressive
solar events. In this work, we present our latest results of numerical
simulations of the initial evolution of a fast CME. For this purpose,
the equations of ideal MagnetoHydroDynamics (MHD) have been solved on
a three-dimensional (3D) mesh by means of an explicit, finite volume
solver, where the simulation domain ranges from the lower solar corona
up to 30 R e. In order to simulate the propagation of a
CME throughout the heliosphere, a magnetic flux rope is superposed on
top of a stationary background solar (MHD) wind with extra density
added to the flux rope. The flux rope is launched by giving it an
extra initial velocity in order to get a fast CME forming a 3D shock
wave. The magnetic field inside the initial flux rope is described in
terms of Bessel functions and possesses a high amount of twist.
Title: The Role of Lateral Magnetic Reconnections in Solar Eruptive
Events
Authors: Soenen, Alexander; Poedts, S.; Bemporad, A.
Bibcode: 2009SPD....40.2210S
Altcode:
On December 10-11, 2005 a slow CME occurred in between two coronal
streamers in the Western hemisphere. SOHO/MDI magnetograms show a
multipolar magnetic configuration at the photosphere consisting of a
complex of active regions located at the CME source and two bi-poles
at the base of the lateral coronal streamers. White light observations
reveal that the expanding CME affects both of the lateral streamers and
induces the release of plasma within or close to them. These transient
phenomena are possibly due to magnetic reconnections induced by the
CME expansion that occurs either inside the streamer current sheet or
between the CME flanks and the streamer. Our observations show
that CMEs can be associated to not only a single reconnection process
at a single location in the corona, but also to many reconnection
processes occurring at different times and locations around the flux
rope. Numerical simulations are used to demonstrate that the observed
lateral reconnections can be reproduced. These simulations suggest that
the shear to be applied to the erupting arcade decreases as the number
of lateral induced reconnections increases. The observed secondary
reconnections associated to CMEs facilitate the CME release by globally
decreasing the magnetic tension of the corona. Future CME models should
therefore take into account the lateral reconnection effect.
Title: A New Paradigm for Coronal Heating!
Authors: Vranjes, Jovo; Poedts, S.
Bibcode: 2009SPD....40.1201V
Altcode:
The solar coronal heating problem refers to the question why the
temperature of the Sun's corona is more than two orders of magnitude
higher than that of its surface. Almost 70 years after the discovery,
this puzzle is still one of the major challenges in astrophysics. The
current basic paradigm of coronal heating is unable to explain all
the observational features of the heating. As a matter of fact,
a coronal heating model must fulfill a lot of requirements. First
of all, it should be consistent with the measured energy losses in
the solar corona due to conduction and radiation, i.e. it should 1)
not only provide the right amount of energy but 2) do so at the right
times scales, e.g. about 5x10**3 J/(m**2s) in active regions. Moreover,
it should 3) include the source of the required energy, and 4) work
everywhere in the corona, i.e. for all magnetic structures (with
different heating requirements). Furthermore, it should be able 5)
to explain the observed temperature anisotropy (Tperp >
Tpar), 6) be more effective on ions than on electrons
(Ti > Te), and 7) heat heavier ions more
efficiently than lighter ions. None of the proposed heating mechanisms
so far even claimed to fulfil all these model requirements. Here we argue that a new paradigm is required to solve the puzzle
in a self-consistent manner. The alternative approach is based on the
kinetic theory which provides a microscopic description of the plasma
processes, including those on the dissipation length scale. We also
show, with qualitative and quantitative arguments, that the drift waves
that are characteristic of this new model have the potential to satisfy
all the above-mentioned requirements for a coronal heating mechanism.
Title: Magnetic Flux Emergence and Shearing Motions as Trigger
Mechanisms for Coronal Mass Ejections
Authors: Poedts, S.; Soenen, A.; Zuccarello, F. P.; Jacobs, C.;
van der Holst, B.
Bibcode: 2009AIPC.1121...99P
Altcode:
We study the initiation and early evolution of coronal mass ejections
(CMEs) in the framework of numerical ideal magnetohydrodynamics
(MHD). The magnetic field of the active region possesses a topology in
order for the ``breakout'' model to work. An initial multi-flux system
in steady equilibrium containing a pre-eruptive region consisting of
three arcades with alternating flux polarity is kept in place by the
magnetic tension of the overlying closed magnetic field of the helmet
streamer. Both foot point shearing and magnetic flux emergence are used
as a triggering mechanism in this model. The boundary conditions cause
the central arcade to expand and lead to the eventual ejection of the
top of the helmet streamer. We compare the topological and dynamical
evolution of the two triggering mechanisms and find that the overall
evolution of the systems are similar.
Title: Simulations of the Jovian magnetosphere
Authors: Chané, E.; Saur, J.; Poedts, S.
Bibcode: 2009EGUGA..11.9833C
Altcode:
The rapidly rotating magnetosphere of Jupiter is the largest single
structure of the Solar system. Unlike the magnetosphere of the Earth,
which is mostly filled with plasma originating from the Solar wind,
the plasma of the Jovian magnetosphere emanates from an internal
source: the Galilean moon Io. Due to its volcanism, Io continually
supply the Jovian magnetosphere with heavy plasma: approximately 1000
kilograms of plasma is provided by Io every second. As a result of the
coupling of the Jovian magnetosphere to its ionosphere, this plasma
is accelerated up to approximately the corotation speed. In addition,
due to the centrifugal force, the plasma is slowly driven away from
Jupiter. When the plasma is too far from the planet to be accelerated
efficiently by the Lorentz force, it tends to sub-corotate and it
deforms the magnetic field lines of Jupiter, producing a electric
current system which couples Jupiter's magnetosphere with its ionosphere
and produces aurorae. Consequently, internal transport due to Io's
plasma production seems to be one of the main processes causing the
main auroral oval of Jupiter. On the other hand, the importance of
the solar wind (which controls the aurorae on Earth) remains unclear
for Jupiter. In this study, the interactions between the solar wind
and the Jovian magnetosphere are studied by means of global three
dimensional magnetohydrodynamic (MHD) simulations. The ionization of
the neutrals in the Io torus are reproduced by a mass loading source
term in the MHD equations confined in a toroidal region located at 5.9
Rj from the centre of the planet. The influence of the incoming solar
wind on the current systems of the Jovian magnetosphere is studied in
an parameter study.
Title: The Internal Structure of Coronal Mass Ejections: Are all
Regular Magnetic Clouds Flux Ropes?
Authors: Jacobs, C.; Roussev, I. I.; Lugaz, N.; Poedts, S.
Bibcode: 2009ApJ...695L.171J
Altcode:
In this Letter, we investigate the internal structure of a coronal mass
ejection (CME) and its dynamics by invoking a realistic initiation
mechanism in a quadrupolar magnetic setting. The study comprises a
compressible three-dimensional magnetohydrodynamics simulation. We
use an idealized model of the solar corona, into which we superimpose
a quadrupolar magnetic source region. By applying shearing motions
resembling flux emergence at the solar boundary, the initial equilibrium
field is energized and it eventually erupts, yielding a fast CME. The
simulated CME shows the typical characteristics of a magnetic cloud
(MC) as it propagates away from the Sun and interacts with a bimodal
solar wind. However, no distinct flux rope structure is present
in the associated interplanetary ejection. In our model, a series
of reconnection events between the eruptive magnetic field and the
ambient field results in the creation of significant writhe in the
CME's magnetic field, yielding the observed rotation of the magnetic
field vector, characteristic of an MC. We demonstrate that the magnetic
field lines of the CME may suffer discontinuous changes in their mapping
on the solar surface, with footpoints subject to meandering over the
course of the eruption due to magnetic reconnection. We argue that CMEs
with internal magnetic structure such as that described here should
also be considered while attempting to explain in situ observations
of regular MCs at L1 and elsewhere in the heliosphere.
Title: Cosmological Effects of Weibel-Type Instabilities
Authors: Lazar, M.; Schlickeiser, R.; Wielebinski, R.; Poedts, S.
Bibcode: 2009ApJ...693.1133L
Altcode:
New arguments are given here in favor of Weibel-type instabilities
as one of the most plausible sources of the cosmological magnetic
field. The Weibel instability has recently been proposed as one of the
secondary mechanisms of relaxation for the large interpenetrating
formations of galactic and intergalactic plasma. Here, these
investigations are extended to counterstreaming plasmas which have,
in addition, intrinsic temperature anisotropies, and where any form
of the Weibel-type instability can be excited. This can be a simple
filamentation instability due to the relative motion of counterstreaming
plasmas, or a Weibel-like instability when it is generated by an excess
of transverse temperature with respect to the streaming direction. But
it can also be a cumulative filamentation/Weibel instability when the
plasma is hotter along the streaming direction. Such plasma systems
are relevant for the relative motions of filaments and sheets of
galaxies, and are expected to exist at large scales and any age of our
Universe. For such counterstreaming plasmas with internal temperature
anisotropies, any Weibel-type instability mentioned before can become
the primary wave relaxation mechanism of the plasma anisotropy,
because it develops easily faster than the principal competitor,
which is the two-stream electrostatic instability. The estimations
made here for typical parameters of intergalactic plasmas, provide
micro-Gauss levels of the magnetic field of Weibel type, which are
consistent with magnetic field values, 10-7-10-5
G, derived from Faraday rotation measure of the linearly polarized
emission of galactic or extragalactic sources.
Title: Linking two consecutive nonmerging magnetic clouds with their
solar sources
Authors: Dasso, S.; Mandrini, C. H.; Schmieder, B.; Cremades, H.; Cid,
C.; Cerrato, Y.; Saiz, E.; Démoulin, P.; Zhukov, A. N.; Rodriguez,
L.; Aran, A.; Menvielle, M.; Poedts, S.
Bibcode: 2009JGRA..114.2109D
Altcode: 2009JGRA..11402109D; 2012arXiv1212.5546D
On 15 May 2005, a huge interplanetary coronal mass ejection (ICME) was
observed near Earth. It triggered one of the most intense geomagnetic
storms of solar cycle 23 (Dst peak = -263 nT). This
structure has been associated with the two-ribbon flare, filament
eruption, and coronal mass ejection originating in active region 10759
(NOAA number). We analyze here the sequence of events, from solar wind
measurements (at 1 AU) and back to the Sun, to understand the origin
and evolution of this geoeffective ICME. From a detailed observational
study of in situ magnetic field observations and plasma parameters
in the interplanetary (IP) medium and the use of appropriate models
we propose an alternative interpretation of the IP observations,
different to those discussed in previous studies. In our view, the
IP structure is formed by two extremely close consecutive magnetic
clouds (MCs) that preserve their identity during their propagation
through the interplanetary medium. Consequently, we identify two
solar events in Hα and EUV which occurred in the source region
of the MCs. The timing between solar and IP events, as well as the
orientation of the MC axes and their associated solar arcades are in
good agreement. Additionally, interplanetary radio type II observations
allow the tracking of the multiple structures through inner heliosphere
and pin down the interaction region to be located midway between the
Sun and the Earth. The chain of observations from the photosphere to
interplanetary space is in agreement with this scenario. Our analysis
allows the detection of the solar sources of the transients and explains
the extremely fast changes of the solar wind due to the transport of
two attached (though nonmerging) MCs which affect the magnetosphere.
Title: On the combination of ACE data with numerical simulations to
determine the initial characteristics of a CME
Authors: Chané, E.; Poedts, S.; van der Holst, B.
Bibcode: 2008A&A...492L..29C
Altcode:
Aims: Our goal is to combine the Advanced Composition Explorer (ACE)
data with numerical simulations to determine the initial characteristics
of the halo coronal mass ejection (CME), which was observed on
April 4, 2000.
Methods: The evolution of a CME from the Sun
to 1 AU is simulated in the framework of 2.5 D (axi-symmetric) ideal
Magnetohydrodynamics (MHD). The initial parameters of the CME model
are adjusted to reproduce the ACE data as accurately as possible. The
initial parameters leading to the best fit are then assumed to be the
most plausible initial parameters of the CME event.
Results:
Once the ACE data and the transit time were successfully reproduced,
we concluded that, at 1.5 R_⊙, the CME had a maximal magnetic
field strength of 2.5 × 10-4 T and a total mass of 6.7 ×
1012 kg, and the CME linear speed up to 30 R_⊙ was 1524
km s-1.
Title: Initiation of Coronal Mass Ejections by Magnetic Flux Emergence
in the Framework of the Breakout Model
Authors: Zuccarello, F. P.; Soenen, A.; Poedts, S.; Zuccarello, F.;
Jacobs, C.
Bibcode: 2008ApJ...689L.157Z
Altcode:
The possible role of magnetic flux emergence in the initiation of
coronal mass ejections (CMEs) is investigated in the framework of the
breakout model. The ideal MHD equations are solved numerically on a
spherical, axisymmetric (2.5-dimensional) domain. An initial multiflux
system in steady equilibrium containing a pre-eruptive region consisting
of three arcades with alternating magnetic flux polarity is kept in
place by the magnetic tension of the overlying closed magnetic field of
a helmet streamer. The emergence of new magnetic flux in the central
arcade is simulated by means of a time-dependent boundary condition
on the vector potential applied at the solar base. Height-time plots
of the ejected material, as well as time evolution of the magnetic,
kinetic and internal energy in the entire domain as functions of flux
emergence rate, are produced. The results show that the emergence of
new magnetic flux in the central arcade triggers a CME. The obtained
eruption corresponds to a slow CME, and conversion of magnetic energy
into kinetic energy is observed.
Title: Acoustic oscillations in a field-free cavity under solar
small-scale bipolar magnetic canopy
Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.;
Poedts, S.
Bibcode: 2008AnGeo..26.2983K
Altcode: 2008arXiv0801.2877K
Observations show the increase of high-frequency wave power near
magnetic network cores and active regions in the solar lower
atmosphere. This phenomenon can be explained by the interaction
of acoustic waves with a magnetic field. We consider small-scale,
bipolar, magnetic field canopy structure near the network cores and
active regions overlying field-free cylindrical cavities of the
photosphere. Solving the plasma equations we get the analytical
dispersion relation of acoustic oscillations in the field-free
cavity area. We found that the m=1 mode, where m is azimuthal wave
number, cannot be trapped under the canopy due to energy leakage
upwards. However, higher (m≥2) harmonics can be easily trapped
leading to the observed acoustic power halos under the canopy.
Title: Counterstreaming magnetized plasmas with kappa distributions -
I. Parallel wave propagation
Authors: Lazar, M.; Schlickeiser, R.; Poedts, S.; Tautz, R. C.
Bibcode: 2008MNRAS.390..168L
Altcode: 2008MNRAS.tmp.1041L
Non-thermal particle distributions of kappa type are frequently
encountered in collisionless plasmas from space. The electromagnetic
emissions coming from space are believed to originate in the
counterstreaming structures of plasmas, which are ubiquitous in many
astrophysical systems. Here, we investigate the dispersion properties
and the stability of a counterstreaming plasma system with temperature
anisotropies modelled by a bi-kappa distribution function. The
numerical evaluation of parallel modes shows growth rates lower than
those obtained for Maxwellian plasmas, with a strong dependence on
the spectral index of the particle distribution function. If all other
parameters are known, measuring the instability growth time can provide
a possible tool for the determination of the spectral index κ.
Title: Radiative Relaxation of Space Plasma Anisotropies
Authors: Lazar, M.; Poedts, S.; Schlickeiser, R.
Bibcode: 2008ESPM...12.3.71L
Altcode:
Anisotropic charge particle distributions are ubiquitous in space
plasma. The solar wind originates in the near-Sun region where corona
is heated and the plasma is accelerated to supersonic speeds in both
a quasistatic form and the episodic events of coronal mass ejection
(CME). Energetic flows of charge particles penetrate the space plasma
leading to complex formations of counterstreaming plasmas. In such
plasma systems the particle velocity distributions are anisotropic,
and, therefore, unstable against the excitation of the electromagnetic
instabilities of Weibel (or filamentation) type. Here it is shown that,
for counterstreaming plasmas with non-thermal populations of Lorentzian
type, typically encountered in magnetized interplanetary plasmas,
these instabilities become the primary relaxation mechanism of the
plasma system. In this case, the electromagnetic fields measured by
the space probes can be used to determine space plasma parameters and
the magnetic field.
Title: Numerical Modeling of the Initiation of Coronal Mass Ejections
Authors: Jacobs, C.; Lugaz, N.; Poedts, S.; Roussev, I.
Bibcode: 2008ESPM...12.3.56J
Altcode:
Coronal Mass Ejections (CMEs) are large expulsions of solar material
that involve large disturbances in the structure of the solar corona and
in the solar wind. There is general consensus that stressed magnetic
field structures are present in the CME source region at the time
of eruption. The different theoretical models with regard to CME
initiation all have in common the existence of magnetic flux ropes,
either present in the solar atmosphere before the CME lift-off, or
created during the eruption. Some of the models, like the magnetic
'breakout', presume a specific magnetic topology of the pre-eruption
coronal field. In this research, the initiation of CMEs is studied
in the framework of computational ideal magnetohydrodynamics (MHD). A
multipolar flux system is energized through photospheric motions of the
magnetic foot points. We investigate the interplanetary propagation
and magnetic field structure of CMEs originating from regions with
different magnetic topology.
Title: Magnetic flux emergence and shearing motions as CME trigger
mechanisms
Authors: Poedts, S.; Soenen, A.; Zuccarello, F. P.; Jacobs, C.;
van der Hoist, B.
Bibcode: 2008AIPC.1043..291P
Altcode:
We present recent developments in the mathematical modeling and
numerical simulations of the initiation and interplanetary evolution
of CMEs in the framework of ideal magneto-hydrodynamics (MHD). In
earlier work, we reconstructed simple, axisymmetric (2.5D) solar
wind models for the quiet Sun. Next, we mimicked fast CME events
by superposing high-density plasma blobs on the background wind and
launching them in a given direction at a certain speed, enabling the
study of the evolution of the fast CME shocks, their effects on the
coronal field and background solar wind. Here, more realistic CME onset
models are presented to investigate the possible role of magnetic foot
point shearing and magnetic flux emergence/disppearence as triggering
mechanisms of the instability. In particular, the well-known breakout
model has been superposed on a solar wind model and it is shown that
both foot point shearing and magnetic flux emergence can be used as
a triggering mechanism in this model.
Title: Parametric Study of Breakout Coronal Mass Ejections in the
Solar Wind
Authors: Soenen, A.; Poedts, S.; van der Holst, B.
Bibcode: 2008ESPM...12.3.57S
Altcode:
We present the results of a parametric study on the initiation and
early evolution properties of Coronal Mass Ejections (CMEs). Our
mathematical model is based on the breakout model which we embedded
in a 2.5D axisymmetric solar wind in the framework of numerical ideal
magnetohydrodynamics (MHD). The initial results used as a basis for this
parametric study were published by B. van der Holst et al. (2007). In
this paper the authors describe how the initial, steady equilibrium
containing a pre-eruptive region consisting of three arcades with
alternating magnetic flux polarity and correspondingly three neutral
lines on the photosphere can produce a CME by shearing part of the
central arcade. They conclude that the breakout CME propagation through
the solar wind consists of two major phases. The original breakout
model phase closely follows the scenario described by Antiochos et
al. (1999). However, at a certain moment the breakout reconnection, on
the leading edge of the rising central arcade and a flare reconnection
below, stops and two new reconnections spots are formed on the flanks
of the erupting central arcade. These ultimately disconnect the top
of the overlying helmet streamer from the Sun. We investigate the
influence of the magnetic field strength and size of the central arcade
on the CME velocity and look at the effect of changing the sheartime
or shear velocity. The effect of the background solar wind model on
these simulations is also investigated. The results of changes to
these parameters are analyzed by looking at their effect on properties
like current density, relative density, kinetic and magnetic energy,
and helicity.
Title: Drift Mode Driven by Shear Plasma Flow in Solar Atmosphere
Authors: Vranjes, J.; Poedts, S.; Saleem, H.
Bibcode: 2008ESPM...12.3.21V
Altcode:
The solar atmosphere contains at any moment a large number of spicules
comprising plasma that moves towards the upper layers with typical axial
velocities of 20-30 km/s. It is expected that these flows as well as the
plasma density are inhomogeneous in the perpendicular direction. The
presence of such a density gradient implies the existence of drift
waves, while the inhomogeneity of the flow velocity can cause the
growth of such modes. In this work the stability of the drift waves
will be discussed within the two-fluid theory taking into account the
ion temperature and the stress tensor effects. An analytical linear
normal mode analysis is used within the local approximation. A detailed
derivation of the hot ion contribution is performed. A dispersion
equation is derived and the stability/instability conditions are
discussed in detail for the parameter range appropriate for solar
spicules. The drift mode appears to be highly unstable for typical
spicule characteristic lengths of the density and the shear flow
gradients, i.e., in the range of a few hundred meters up to a few
kilometers, yielding wave frequencies of the order of a few Hz. The
waves and the instabilities develop at reasonable time scales regarding
the life times of spicules that are measured in minutes.
Title: Modelling the Initiation of Coronal Mass Ejections by Magnetic
Flux Emergence
Authors: Zuccarello, F. P.; Soenen, A.; Poedts, S.
Bibcode: 2008ESPM...12.3.55Z
Altcode:
The possible role of magnetic flux emergence as triggering mechanism
for the initiation of Coronal Mass Ejections (CMEs) is studied in the
framework of the ideal magnetohydrodynamics (MHD) model. The full MHD
equations are solved numerically on a spherical, axisymmetric (2.5D)
domain. All simulations are performed with a modified version
of the Versatile Advection Code (VAC) (Toth 1996). The magnetic field
of the solution is maintained divergence-free at machine precision by
exploiting an approach similar to that of Balsara and Spicer (1999):
instead of storing the magnetic field components on a staggered
mesh, we use the vector potential components in the nodes. In
order to get satisfactorily solar wind properties, the Manchester
et al. (2004) source term is implemented in the energy equation and
gravity is taken into account as well in the model. Finally,
a magnetic vector potential is superimposed at the inlet boundary of
the Parker wind solution so that, when the steady state is reached,
the Antiochos et al. (1999) triple arcade 'break out' magnetic
field configuration (symmetric with respect to the equator) of a
helmet streamers is obtained. When the steady state has been
reached, we impose a magnetic flux emergence at the inlet boundary
that is linearly growing in time during a time interval of ? t =
24 hours. After this time the vector potential at the solar base is
again fixed. Due to the magnetic flux emergence at the solar base,
extra radial magnetic field, is built up near the neutral line of the
central arcade that expands outward. This generates an extra upward
magnetic pressure force. As a consequence, the central flux system
expands outward. Also the overlying field expands and, therefore,
the downward magnetic tension increases. As a result, the X-point is
flattened. When the distance between the central expanding arcade
field and the overlying streamer field is of the order of the grid
resolution, the (numerical) reconnection between these fields sets
in. A flux rope is formed and, later, accelerated. Height-time
and velocity-height plots of the ejected material are produced. The
obtained eruption corresponds to a slow CME. The time evolution of
the magnetic energy, kinetic energy and internal energy in the entire
domain shows that magnetic energy is converted into kinetic energy,
as expected. The energy evolution plots show, however, that only a
small amount of magnetic energy is released in the system, so that the
system evolves to a higher energy state. We think that the explanation
of this behavior lies in the role of the magnetic helicity, which we
neglected by only emerging radial magnetic field. In conclusion,
we stress that by imposing a reasonable (Romano et al. (2007)) flux
emergence rate, in a large but realistic active region (with, of course,
model dimensionality limitations), quite realistic velocity profiles
and energetics of slow CMEs are obtained.
Title: Flux of Alfven Waves in the Solar Photosphere
Authors: Vranjes, J.; Poedts, S.; Pandey, B. P.; de Pontieu, B. P.
Bibcode: 2008ESPM...12.3.10V
Altcode:
The convective motions in the solar photosphere, resulting in the foot
point motion of different magnetic structures in the solar atmosphere,
are frequently proposed as the source for the excitation of Alfven
waves, which are assumed to propagate towards the chromosphere
and corona resulting finally in the heating of these layers by the
dissipation of this wave energy. However, the photosphere is a) very
weakly ionized, and, b) the dynamics of the plasma particles in this
region is heavily influenced by the plasma-neutral collisions. The
purpose of this work is to check the consequences of these two
facts on the above scenario and their effects on the electromagnetic
waves. Standard plasma theory is used and the wave physics of the weakly
ionized photosphere is discussed. The magnetization and the collision
frequencies of the plasma constituents are quantitatively examined. It is shown that the ions and electrons in the photosphere are
both un-magnetized; their collision frequency with neutrals is much
larger than the gyro-frequency. This implies that eventual Alfven-type
electromagnetic perturbations must involve the neutrals as well. This
has the following consequences. i) In the presence of perturbations,
the whole fluid (plasma + neutrals) moves. ii) The Alfven velocity
includes the total (plasma + neutrals) density and is thus considerably
smaller compared to the collision-less case. iii) The perturbed velocity
of a unit volume, which now includes both plasma and neutrals, becomes
much smaller compared to the ideal (collision-less) case. iv) Finally,
when the effects of partial ionization and collisions are consistently
taken into account, the corresponding wave energy flux for the given
parameters becomes orders of magnitude smaller compared to the ideal
case.
Title: Magnetic field generation at ion acoustic time scale
Authors: Vranjes, J.; Saleem, H.; Poedts, S.
Bibcode: 2008POBeo..84..503V
Altcode:
Ion acoustic wave in an inhomogeneous plasma naturally couples with
a transverse electromagnetic perturbations. Due to this coupling
the ion acoustic mode becomes electromagnetic. There appears a lower
frequency cut off of the ion acoustic wave, the wave becomes dispersive
and backward.
Title: Coupled gas acoustic and ion acoustic waves in weakly ionized
plasma
Authors: Vranjes, J.; Pandey, B. P.; Poedts, S.
Bibcode: 2008POBeo..84..507V
Altcode:
Gas acoustic and ion acoustic modes are investigated in a collisional,
weakly ionized plasma in the presence of un-magnetized ions and
magnetized electrons. In such a plasma, an ion acoustic mode, driven by
an electron flow along the magnetic field lines, can propagate almost
at any angle with respect to the ambient field lines as long as the
electrons are capable of participating in the perturbations by moving
only along the field lines. The electron-ion collisions are shown to
modify the previously obtained angle dependent instability threshold
for the driving electron flow. The inclusion of the neutral dynamics
implies an additional neutral sound mode which couples to the current
driven ion acoustic mode, and these two modes can interchange their
identities in certain parameter regimes.
Title: Growing drift-cyclotron modes in the hot solar atmosphere
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2008A&A...482..653V
Altcode: 2008arXiv0806.0071V
Context: The ion cyclotron (IC) wave has been discussed in the
literature in the context of the solar coronal heating. This is partly
due to the necessity of explaining the observed preferential heating in
the direction perpendicular to magnetic field lines. Observations have
also shown the existence of filamentary density structures of various
cross sections in the solar atmosphere. The presence of the related
density gradients implies the possibility for the development of drift
wave (DW) instability.
Aims: The frequencies of the two modes
(IC and DW) are usually well separated, however, they can become close
to each other for short inhomogeneity scale lengths of the equilibrium
density. In this case, the drift wave can effectively couple to the ion
cyclotron mode, and in the present work we want to demonstrate this
coupling in the parameter domain relevant for the solar corona.
Methods: Well-known analytical results which follow from the kinetic
theory are used and the dispersion equation, which describes coupled
ion cyclotron and drift waves, is solved numerically.
Results:
The numerical results obtained by using the values for the plasma
density, magnetic field and temperature applicable to the solar
corona clearly show the coupling and the instability (growing)
of the two modes. The coupling happens at very short wavelengths,
that are of the order of the ion gyro radius, and for characteristic
scale lengths of the equilibrium density that are altitude dependent
and may become of the order of only a few meters.
Conclusions:
The demonstrated instability of the two coupled modes (driven by the
equilibrium density gradient) is obtained by using a rigorous kinetic
theory model and for realistic parameter values. The physical mechanism
which is behind the coupling is simple and is expected to take place
throughout the solar atmosphere and the solar wind which contain a
variety of very elongated density structures of various sizes. The mode
grows on account of the density gradient, it is essentially an ion mode,
and its further dissipation should result in an increased ion heating.
Title: Modeling of the magnetic field in the magnetosheath region
Authors: Romashets, E. P.; Poedts, S.; Vandas, M.
Bibcode: 2008JGRA..113.2203R
Altcode:
In recent years, many advanced numerical techniques and codes have
been developed to calculate the location of the bow shock and the
magnetohydrodynamic parameters in the sheath region for various types
of inflows and obstacle shapes. Some of these methods are applicable
to the Earth's magnetosphere. On the other hand, only a few attempts
have been made to describe the problem analytically. In this paper,
we consider the discontinuities at the bow shock surface and at the
magnetopause as boundary conditions for the construction of the magnetic
field in the region between these two surfaces. The locations and the
(parabolic) shapes of the two surfaces are specified depending on the
solar wind parameters, viz. velocity, density, temperature, and magnetic
field. In the inner magnetosphere, i.e., below the magnetopause,
the magnetic field is considered as given by a modified dipole. The
solution is derived in parabolic coordinates.
Title: Energy flux of Alfvén waves in weakly ionized plasma
Authors: Vranjes, J.; Poedts, S.; Pandey, B. P.; de Pontieu, B.
Bibcode: 2008A&A...478..553V
Altcode: 2008arXiv0805.4591V
Context: The overshooting convective motions in the solar photosphere,
resulting in the foot point motion of different magnetic structures
in the solar atmosphere, are frequently proposed as the source for the
excitation of Alfvén waves, which are assumed to propagate towards the
chromosphere and corona resulting finally in the heating of these layers
by the dissipation of this wave energy. However, the photosphere is a)
very weakly ionized, and, b) the dynamics of the plasma particles in
this region is heavily influenced by the plasma-neutral collisions.
Aims: The purpose of this work is to check the consequences
of these two facts on the above scenario and their effects on the
electromagnetic waves.
Methods: Standard plasma theory is used
and the wave physics of the weakly ionized photosphere is discussed. The
magnetization and the collision frequencies of the plasma constituents
are quantitatively examined.
Results: It is shown that the ions
and electrons in the photosphere are both un-magnetized; their collision
frequency with neutrals is much larger than the gyro-frequency. This
implies that eventual Alfvén-type electromagnetic perturbations must
involve the neutrals as well. This has the following consequences: i)
in the presence of perturbations, the whole fluid (plasma + neutrals)
moves; ii) the Alfvén velocity includes the total (plasma + neutrals)
density and is thus considerably smaller compared to the collision-less
case; iii) the perturbed velocity of a unit volume, which now includes
both plasma and neutrals, becomes much smaller compared to the ideal
(collision-less) case; and iv) the corresponding wave energy flux
for the given parameters becomes much smaller compared to the ideal
case.
Conclusions: The wave energy flux through the photosphere
becomes orders of magnitude smaller, compared to the ideal case, when
the effects of partial ionization and collisions are consistently
taken into account.
Title: Magnetic clouds seen at different locations in the heliosphere
Authors: Rodriguez, L.; Zhukov, A. N.; Dasso, S.; Mandrini, C. H.;
Cremades, H.; Cid, C.; Cerrato, Y.; Saiz, E.; Aran, A.; Menvielle,
M.; Poedts, S.; Schmieder, B.
Bibcode: 2008AnGeo..26..213R
Altcode:
We analyze two magnetic clouds (MCs) observed in different points
of the heliosphere. The main aim of the present study is to provide
a link between the different aspects of this phenomenon, starting
with information on the origins of the MCs at the Sun and following
by the analysis of in-situ observations at 1 AU and at Ulysses. The
candidate source regions were identified in SOHO/EIT and SOHO/MDI
observations. They were correlated with H-α images that were obtained
from ground-based observatories. Hints on the internal magnetic field
configuration of the associated coronal mass ejections are obtained
from LASCO C2 images. In interplanetary space, magnetic and plasma
moments of the distribution function of plasma species (ACE/Ulysses)
were analyzed together with information on the plasma composition,
and the results were compared between both spacecraft in order to
understand how these structures interact and evolve in their cruise
from the Sun to 5 AU. Additionally, estimates of global magnitudes of
magnetic fluxes and helicity were obtained from magnetic field models
applied to the data in interplanetary space. We have found that these
magnetic characteristics were well kept from their solar source, up to
5 AU where Ulysses provided valuable information which, together with
that obtained from ACE, can help to reinforce the correct matching of
solar events and their interplanetary counterparts.
Title: Determination of the cobpoint evolution using 3D MHD
simulations for the propagation of CME-driven shocks
Authors: Rodriguez-Gasen, Rosa; Aran, Angels; Sanahuja, Blai; Jacobs,
Carla; Poedts, Stefaan
Bibcode: 2008cosp...37.2637R
Altcode: 2008cosp.meet.2637R
Particle flux profile of large solar energetic particle (SEP) events
depends on several factors, such as the strength and geometry of the
associated CME-driven shock, the relative position of the observer
with respect to the leading direction of the travelling shock,
the conditions for the particle acceleration, the injection and
the transport throughout the interplanetary space, and the particle
energy. In this study we focus on two of these factors: the influence of
the shock and the relative position of the observer. We performed a 3D
simulation of the propagation of a coronal/interplanetary CME-driven
shock from the Sun up to 1 AU in the framework of ideal MHD using
the Versatile Advection Code (Toth et al., 1996). Three spacecrafts
are located at 1 AU at different longitudes with respect to the nose
of the shock. We study the evolution of the plasma conditions in the
shock front region magnetically connected to each spacecraft, that is,
the region of the shock front scanned by the cobpoint (Heras et al.,
1995) as the shock propagates away from the Sun. The conclusions
about the influence of these changing conditions on the injection
rate of shock-accelerated particles are presented. References Toth,
G. A General Code for Modelling MHD flows on Parallel Computers:
Versatile Advection Code, Astrophys. Lett. and Comm., 34, 245,
1996. Heras, A.M., Sanahuja, B., Lario, D., et al. Three low-energy
particle events: modeling the influence of the parent interplanetary
shock. Astrophys. J. 445, 497-508, 1995.
Title: Advances in Solar Energetic Particle Statistical and Physical
Modelling as part of the SEPEM Study.
Authors: Crosby, Norma Bock; Glover, Alexi; Gabriel, Stephen; Jiggens,
Piers; Sanahuja, Blai; Aran, Angels; Poedts, Stefaan; Jacobs, Carla;
Truscott, Pete; Hands, Alex; Dyer, Clive; King, David; Stegen, Koen;
Bijloos, Geert
Bibcode: 2008cosp...37..605C
Altcode: 2008cosp.meet..605C
Many of the currently used standard models of the solar energetic
particle environment were developed based on results published more than
15 years ago. Modern user requirements, as well as recent observational
data and scientific advances mean that these standards are currently in
need of review and updating. Incorporating recent scientific results and
a complete set of well calibrated data the ESA Solar Energetic Particle
Environment Modelling (SEPEM) project is working towards creating new
engineering models and tools to address current and future needs. The
objectives of the SEPEM project are to move beyond a model generating
only mission integrated fluence statisics to include peak flux
statistics, durations of high flux periods and other outputs suitable
for SEU rate and radiation background calculations. Databases of ion
species and their fluxes will also be integrated into tools for SEU and
background calculation so that past events and future scenarios can be
simulated. This study is also working to improve existing physics-based
shock-acceleration models to predict the expected event-time profiles
at non-Earth locations (near-Sun, Mercury, Venus, Mars,...) with a
view to obtaining a new model of helio-radial dependence of events. A
further output of SEPEM for the user community will be a user-friendly
webserver with access to the models being developed under this project.
Title: Numerical Simulations of the Jovian Magnetosphere: Influence
of the Solar Wind
Authors: Chané, E.; Poedts, S.; Saur, J.
Bibcode: 2007AGUFMSM53A1080C
Altcode:
The Earth and the jovian magnetospheres are shaped by the solar
wind, displaying gigantic magnetic tails on the night side. Due to
the intrinsic variability of the solar wind, the global shape of
the Earth magnetosphere fluctuates with time; the influence of the
solar wind velocity, density, pressure and other characteristics were
extensively studied and are now more or less understood. On the other
hand, the interactions between the jovian magnetosphere and the solar
wind are still poorly comprehended. The extremely strong internal
magnetic field, the fast rotation and the presence of the Io torus
(included in our model by the mean of a source term) are specific to
Jupiter and should lead to a magnetosphere hardly comparable with
the magnetosphere of the Earth. In order to study this phenomena,
we performed three dimensional numerical simulations of the jovian
magnetosphere in the framework of magnetohydrodynamics. We present
here an extensive parameters study showing the response of the jovian
magnetosphere to different solar wind parameters.
Title: Simulation of a Breakout Coronal Mass Ejection in the
Solar Wind
Authors: van der Holst, B.; Jacobs, C.; Poedts, S.
Bibcode: 2007ApJ...671L..77V
Altcode:
The initiation and evolution of coronal mass ejections (CMEs) is studied
by means of the breakout model embedded in a 2.5D axisymmetric solar
wind in the framework of numerical magnetohydrodynamics (MHD). The
initial, steady equilibrium contains a pre-eruptive region consisting
of three arcades with alternating magnetic flux polarity and with
correspondingly three neutral lines on the photosphere. The magnetic
tension of the overlying closed magnetic field of the helmet streamer
keeps this structure in place. The most crucial part of the initial
breakout topology is the existence of an X-point on the leading edge of
the central arcade. By shearing part of this arcade, the reconnection
with the overlying streamer field is turned on. The initial phase
of the erupting arcade then closely follows the original breakout
scenario. The breakout reconnection opens the overlying field in an
energetically efficient way leading to an ever faster eruption. However,
from a certain moment two new reconnections set in on the sides of
the erupting central arcade and the breakout reconnection stops. The
consequence of this change in reconnection location is twofold: (1)
the lack of breakout reconnection so that the breakout plasmoid fails
to become a fast CME; and (2) an eventual disconnection of the large
helmet top resulting in a slow CME.
Title: Plasma flows around magnetic obstacles in the solar wind
Authors: Romashets, E.; Poedts, S.
Bibcode: 2007A&A...475.1093R
Altcode:
Context: Recent numerical simulations and data analysis have shown
that the area in front of magnetic clouds is very important from the
point of view of its geo-efficiency. This area has very complicated
magnetic and plasma structures. It is necessary to describe the plasma
parameter distributions in the vicinity of magnetic clouds and other
stable structures in the solar wind. Assuming that the magnetic field
around the object is determined or measured, the velocity field is
calculated from the frozen-in equation, while the density and pressure
are given by explicit formulas expressing P and ρ as functions of only
{B} and {V}. An alternative method is to solve the full system of MHD
equations numerically, but even in this case the analytical estimates
determined here are also useful when formulating initial and boundary
conditions.
Aims: The aim is to treat the region in front of
interplanetary magnetic clouds in terms of analytical functions for
a detailed consideration of general phenomena and also for particular
phenomena of specific clouds.
Methods: First, the velocity and
magnetic field distributions satisfying the boundary conditions and
the frozen-in condition are determined. Next, the plasma density and
pressure are calculated.
Results: The three-dimensional plasma
parameter distributions are found for the general case of an inclined
cylindrical cloud.
Title: Amplification of compressional magnetohydrodynamic waves in
systems with forced entropy oscillations
Authors: Shergelashvili, Bidzina M.; Maes, Christian; Poedts, Stefaan;
Zaqarashvili, Teimuraz V.
Bibcode: 2007PhRvE..76d6404S
Altcode: 2007arXiv0709.0846S
The propagation of compressional MHD waves is studied for an externally
driven system. It is assumed that the combined action of the external
sources and sinks of the entropy results in the harmonic oscillation
of the entropy (and temperature) in the system. It is found that with
the appropriate resonant conditions fast and slow waves get amplified
due to the phenomenon of parametric resonance. In addition, it is shown
that the considered waves are mutually coupled as a consequence of the
nonequilibrium state of the background medium. The coupling is strongest
when the plasma β≈1 . The proposed formalism is sufficiently general
and can be applied to many dynamical systems, both under terrestrial
and astrophysical conditions.
Title: Numerical simulations of the initiation and the IP evolution
of coronal mass ejections
Authors: Jacobs, C.; Poedts, S.; van der Holst, B.; Dubey, G.;
Keppens, R.
Bibcode: 2007AIPC..934..101J
Altcode:
We present recent results from numerical simulations of the initiation
and interplanetary (IP) evolution of Coronal Mass Ejections (CMEs)
in the framework of ideal magnetohydrodynamics (MHD). As a first step,
the magnetic field in the lower corona and the background solar wind
are reconstructed. Both simple, axisymmetric (2.5D) solar wind models
for the quiet sun as more complicated 3D solar wind models taking
into account the actual coronal field through magnetogram data are
reconstructed. In a second step, fast CME events are mimicked by
superposing high-density plasma blobs on the background wind and
launching them in a given direction at a certain speed. In this way,
the evolution of the CME can be modeled and its effects on the coronal
field and background solar wind studied. In addition, more realistic
CME onset models have been developed to investigate the possible role of
magnetic foot point shearing and magnetic flux emergence/disappearence
as triggering mechanisms of the instability. Parameter studies of such
onset models reveal the importance of the background wind model that
is used and of the initiation parameters, such as the amount and the
rate of the magnetic flux emergence or the region and the amount of
foot point shearing.
Title: Overreflection and Generation of Gravito-Alfvén Waves in
Solar-Type Stars
Authors: Rogava, Andria; Gogoberidze, Grigol; Poedts, Stefaan
Bibcode: 2007ApJ...664.1221R
Altcode: 2007arXiv0704.3919R
The dynamics of linear perturbations is studied in magnetized plasma
shear flows with a constant shearing rate and with gravity-induced
stratification. The general set of linearized equations is derived,
and the two-dimensional case is considered in detail. The Boussinesq
approximation is used in order to examine relatively small scale
perturbations of low-frequency modes: gravito-Alfvén waves (GAWs)
and entropy-mode (EM) perturbations. It is shown that for flows
with arbitrary shearing rate, there exists a finite time interval of
nonadiabatic evolution of the perturbations. The nonadiabatic behavior
manifests itself in a twofold way, viz., by the overreflection of the
GAWs and by the generation of GAWs from EM perturbations. It is shown
that these phenomena act as efficient transformers of the equilibrium
flow energy into the energy of the perturbations for moderate and high
shearing rate solar plasma flows. Efficient generation of GAWs by EM
perturbations takes place for shearing rates about an order of magnitude
smaller than necessary for development of a shear instability. The
latter fact could have important consequences for the problem of
angular momentum redistribution within the Sun and solar-type stars.
Title: The jovian magnetosphere: numerical simulations.
Authors: Chané, E.; Poedts, S.
Bibcode: 2007epsc.conf..755C
Altcode:
We present numerical simulations of the jovian magnetosphere in the
framework of three-dimensional magnetohydrodynamics. An extensive
parameters study is presented; showing the influence of the solar wind
density, velocity, and magnetic field. The results of simulations
with a time-dependent solar wind are also shown and the response of
the jovian magnetosphere to these variations is studied.
Title: Observational evidence favors a resistive wave heating
mechanism for coronal loops over a viscous phenomenon
Authors: Van Doorsselaere, T.; Andries, J.; Poedts, S.
Bibcode: 2007A&A...471..311V
Altcode:
Context: How coronal loops are heated to their observed temperatures
is the subject of a long standing debate.
Aims: Observational
evidence exists that the heating in coronal loops mainly occurs near the
loop footpoints. In this article, analytically and numerically obtained
heating profiles produced by resonantly damped waves are compared to
the observationally estimated profiles.
Methods: To do that,
the predicted heating profiles are fitted with an exponential heating
function, which was also used to fit the observations. The results
of both fits, the estimated heating scale heights, are compared to
determine the viability of resonant absorption as a heating mechanism
for coronal loops.
Results: Two results are obtained. It is shown
that any wave heating mechanism (i.e. not just resonant absorption)
should be dominated by a resistive (and not a viscous) phenomenon in
order to accomodate the constraint of footpoint heating. Additionally
it is demonstrated that the analytically and numerically estimated
heating scale heights for the resonant absorption damping mechanism
fit the observations very well.
Title: Unstable drift mode driven by shear plasma flow in solar
spicules
Authors: Saleem, H.; Vranjes, J.; Poedts, S.
Bibcode: 2007A&A...471..289S
Altcode:
Context: The lower solar atmosphere contains at any moment a large
number of spicules comprising plasma that moves towards the upper
layers with typical axial velocities of 20{-}30 km s-1. It
is expected that these flows as well as the plasma density are
inhomogeneous in the perpendicular direction. The presence of such
a density gradient implies the existence of drift waves, while
the inhomogeneity of the flow velocity can cause the growth of such
modes.
Aims: The stability of the drift waves will be discussed
within the two-fluid theory taking into account the ion temperature and
the stress tensor effects.
Methods: An analytical linear normal
mode analysis is used within the local approximation.
Results:
A detailed derivation of the hot ion contribution is performed. A
dispersion equation is derived and the stability/instability conditions
are discussed in detail for the parameter range appropriate for solar
spicules. The drift mode appears to be highly unstable for typical
spicule characteristic lengths of the density and the shear flow
gradients, i.e. in the range of a few hundred meters up to a few
kilometers, yielding wave frequencies of the order of a few Hz.
Conclusions: Hence, the waves and the instabilities develop at
reasonable time scales regarding the life times of spicules that are
measured in minutes.
Title: Quantifying Shear-induced Wave Transformations in the
Solar Wind
Authors: Gogoberidze, Grigol; Rogava, Andria; Poedts, Stefaan
Bibcode: 2007ApJ...664..549G
Altcode: 2007astro.ph..3527G
The possibility of velocity shear-induced linear transformations of
different magnetohydrodynamic waves in the solar wind is studied
both analytically and numerically. A quantitative analysis of the
wave transformation processes for all possible plasma-β regimes is
performed. By applying the obtained criteria for effective wave coupling
to the solar wind parameters, we show that velocity shear-induced
linear transformations of Alfvén waves into magnetoacoustic waves
could effectively take place for the relatively low frequency Alfvén
waves in the energy-containing interval. The obtained results are in
a good qualitative agreement with the observed features of density
perturbations in the solar wind.
Title: Comparison between 2.5D and 3D simulations of coronal mass
ejections
Authors: Jacobs, C.; van der Holst, B.; Poedts, S.
Bibcode: 2007A&A...470..359J
Altcode:
Context: The shocks and magnetic clouds related to Coronal Mass
Ejections (CMEs) in the solar corona and interplanetary space (IP)
play an important role in the study of space weather. In order to study
the evolution of these IP shocks, numerical simulations of a simplified
CME model were performed.
Aims: In an earlier study, the effect
of the background wind on the evolution of interplanetary shock waves
was investigated, where the computations were carried out under the
assumption of axial symmetry. The assumption of axial symmetry might be
a good approach for the solar corona under conditions of solar minimum,
but for the study of CMEs this assumption is definitely no longer valid
as CMEs possess clearly a fully three dimensional (3D) structure. From
this perspective, the previous simulations were repeated, but now in a
three dimensional set-up in order to point out the differences between
the 2.5D and 3D simulations and to check the quality and reliability
of the 2.5D simulations.
Methods: The computations were performed
in the framework of ideal magnetohydrodynamics (MHD) and to advance the
ideal MHD equations in time a parallel finite volume code with explicit
upwind solver was used. The shock waves are generated in a similar way
in both the 3D and 2.5D simulations, namely by a simple density-blob
model. The 3D and 2.5D simulations are all performed with the same
numerical methods and on comparable grids, such that the differences
between the simulations are purely due to the dimensionality of the
problem, and/or the initial parameters for the CME generation.
Results: Three different axisymmetric simulations of CME propagation
are compared with the fully three dimensional computation. The 2.5D
simulations differ from each other in the parameters used for CME
initiation. In a first simulation, the same initial parameters as for
the 3D case were taken, in a second simulation the initial amount of
mass in the 2.5D and 3D CME was the same, and in a third simulation
they had a comparable amount of momentum. It turned out that the latter
one compared best with the 3D results.
Conclusions: As 2.5D
computations are computationally much cheaper than 3D computations,
we conclude that the 2.5D simulations of the CME evolution are a good
first approach and resemble well the 3D result, provided that the
appropriate initiation parameters are chosen.
Title: Numerical Simulations of the Initiation and the IP Evolution
of Coronal Mass Ejections
Authors: Poedts, Stefaan; van der Holst, B.; Jacobs, C.; Chane, E.;
Dubey, G.; Keppens, R.
Bibcode: 2007AAS...210.2925P
Altcode: 2007BAAS...39..141P
We present recent results from numerical simulations of the initiation
and IP evolution of CMEs in the framework of ideal magnetohydrodynamics
(MHD). As a first step, the magnetic field in the lower corona and the
background solar wind are reconstructed. Both simple, axi-symmetric
(2.5D) solar wind models for the quiet sun as more complicated
3D solar wind models taking into account the actual coronal field
through magnetogram data are reconstructed. In a second step,
2.5D fast CME events are mimicked by superposing high-density plasma
blobs on the background wind and launching them in a given direction
at a certain speed. In this way, the evolution of the CME can be
modeled and its effects on the coronal field and background solar
wind studied. In addition, more realistic CME onset models have
been developed to investigate the possible role of magnetic foot
point shearing and magnetic flux emergence/disppearence as triggering
mechanisms of the instability. Parameter studies of such onset models
reveal the importance of the background wind model that is used and
of the initiation parameters, such as the amount and the rate of the
magnetic flux emergence or the region and the amount of foot point
shearing. Last but not least, a simulation of the evolution of
a 3D CME and its magnetic cloud superposed on a 3D solar wind model
is presented and discussed. In this simulation the CME is mimicked
by superposing a magnetic flux rope on top of a stationary background
solar wind with extra density and velocity added to the flux rope. The
magnetic field inside the initial flux rope is described in terms of
Bessel functions and possesses a high amount of twist. Its effect on
the evolution of the CME is studied.
Title: Modeling of the three-dimensional motion of toroidal magnetic
clouds in the inner heliosphere
Authors: Romashets, E.; Vandas, M.; Poedts, S.
Bibcode: 2007A&A...466..357R
Altcode:
Context: The motion of a magnetic cloud through the heliosphere
is governed by three main forces, viz. the diamagnetic force, the
drag force, and gravity. Some recently derived formulas enabling the
calculation of the ambient magnetic field around a toroidal magnetic
cloud are applied to calculate the diamagnetic force acting on the
cloud and to determine the cloud dynamics.
Aims: The aim is to
determine the three dimensional velocity profiles and the trajectory
of the magnetic cloud, as well as the evolution of the orientation of
the cloud axis from the calculated moment of the force.
Methods:
The method applied in this study consists of three steps. First, the
r-component of the magnetic field at r=2.5 Rs is derived
from a spherical harmonic analysis. Next, the field distribution in the
entire heliosphere, including the spiral structure, is reconstructed
in a way that is consistent with this boundary condition at r=2.5
Rs as well as with actual measurements at 1 AU. Then,
a toroid is launched at a point obtained from solar observations of
a specific event and the initial size, orientation, and velocity of
this toroid is estimated from these observational data as well.
Results: The three dimensional velocity profiles and the trajectory of
the magnetic cloud, as well as the evolution of the orientation of the
cloud axis have been determined for a toroidally shaped cloud moving in
the interplanetary medium taking into account a spiral magnetic field.
Title: MHD seismology of coronal loops using the period and damping
of quasi-mode kink oscillations
Authors: Arregui, I.; Andries, J.; Van Doorsselaere, T.; Goossens,
M.; Poedts, S.
Bibcode: 2007A&A...463..333A
Altcode:
Aims:We combine the magnetohydrodynamic (MHD) theory of resonantly
damped quasi-mode kink oscillations with observational estimates of
the period and damping of transverse coronal loop oscillations to
extract information on physical parameters in oscillating loops.
Methods: A numerical study of the quasi-mode period and damping,
in one-dimensional fully non-uniform flux tubes, is used to obtain
equilibrium models that reproduce the observed periods and damping
rates. This scheme is applied to 11 loop oscillation events.
Results: When only the damping rate is used, the valid equilibrium
models form a one-dimensional solution curve in the two-dimensional
parameter space (density contrast, transverse inhomogeneity
length-scale). Lower limits to the transverse inhomogeneity are
obtained in the limit of high contrast loops. When both the period and
the damping rate are used, the equilibrium Alfvén speed (or Alfvén
travel time) comes into play. The valid equilibrium models then form
a one-dimensional solution curve in the three-dimensional parameter
space (density contrast, transverse inhomogeneity length-scale, Alfvén
speed or Alfvén travel time). The projection of these solutions onto
the Alfvén speed axis is found to be constrained to a rather limited
interval. Upper limits to the internal Alfvén speed are derived for
9 of the 11 analysed events.
Title: Simulating CME Initiation and Evolution: State-of-the-art
Authors: Poedts, S.; van der Holst, B.; Jacobs, C.; Chané, E.; Dubey,
G.; Kimpe, D.
Bibcode: 2007ASSL..344...39P
Altcode:
A review is given of some recent results on CME initiation and
evolution simulations obtained at the Centre for Plasma Astrophysics
(CPA, K.U.Leuven) on the background of the international developments
in this very dynamic field
Title: Comment on ``Heating of the Solar Corona by Dissipative
Alfvén Solitons''
Authors: Vranjes, J.; Poedts, S.; Pandey, B. P.
Bibcode: 2007PhRvL..98d9501V
Altcode:
A Comment on the Letter by K. Stasiewicz, Phys. Rev. Lett. 96, 175003
(2006)PRLTAO0031-900710.1103/PhysRevLett.96.175003. The authors of
the Letter offer a Reply.
Title: Analysis of the effect of neutral flow on the waves in the
solar photosphere
Authors: Petrović, D.; Vranjes, J.; Poedts, S.
Bibcode: 2007A&A...461..277P
Altcode:
Context: The solar surface and photosphere are covered by a network of
convective motions of a mainly neutral fluid. Such a neutral motion
drags the tiny plasma population along, which results in drifts of
the plasma species due to the magnetic field. These drifts can, in
turn, excite and amplify plasma perturbations, which is the subject
of the present work.
Aims: The behaviour of electromagnetic
waves is discussed for a weakly ionized plasma with a neutral flow,
in a magnetization regime in which an electron drift exists relative
to the ions. This drift across the magnetic field is caused by the
neutral flow.
Methods: Using a standard normal mode approach,
the linear dynamics of small perturbations propagating obliquely to
the equilibrium magnetic field lines is investigated. In the regime
of strong perturbations, in which the convective derivatives in the
electron and ion momentum equations are within the same order of
magnitude as the time derivatives, a nonlinear analysis is performed
by considering spatial scales at which the effects due to collisions
can be neglected.
Results: A dispersion relation describing the
coupled, drift-driven, and dispersive Alfvén modes is obtained for
a strongly collisional plasma. The results are applied to the solar
photosphere. Without electron drift due to the frequent collisions, the
real part of the (kinetic) Alfvén wave frequency practically vanishes;
i.e., the KAW is completely damped. It is shown that the KAW is much
less damped in the presence of the electron drift. However, the kinetic
Alfvén wave cannot be destabilized by this drift. The instability of
the drift-driven mode (Farley-Buneman type) is shown to develop when
the electron drift exceeds a certain threshold. At spatial scales far
exceeding the mean free path of the particles, the non-linear effects
result in a self-organization in the form of traveling double vortices.
Title: The initiation of coronal mass ejections by magnetic flux
emergence
Authors: Dubey, G.; van der Holst, B.; Poedts, S.
Bibcode: 2006A&A...459..927D
Altcode:
Aims.The initiation of solar Coronal Mass Ejections (CMEs) is studied
in the framework of computational Magneto-Hydro-Dynamics (MHD).
Methods: .The initial configuration includes a magnetic flux rope
that is embedded in a gravitationally stratified solar atmosphere
with a background dipole magnetic field in spherical, axi-symmetric
geometry. The flux rope is in equilibrium due to an image current below
the photosphere. An emerging magnetic flux triggering mechanism is used
to make this equilibrium configuration unstable.
Results: . When
the magnetic flux emerges within the filament below the flux rope this
results in a catastrophic behavior similar to earlier, more simple
models. As a result, the flux rope rises and a current sheet forms
below it. It is shown that the magnetic reconnection in the current
sheet below the flux rope in combination with the outward curvature
forces results in a fast ejection of the flux rope as observed for solar
CMEs. We have done a parameter study of the effect of the flux emergence
rate on the velocity and the acceleration of the resulting CMEs.
Title: Growing drift-Alfvén modes in collisional solar plasma
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2006A&A...458..635V
Altcode:
Context: .Solar plasmas are structured and stratified both vertically
and horizontally. The presence of density gradients and magnetic
fields results in an additional wave which can be electrostatic (the
drift wave) and electromagnetic (the drift-Alfvén wave).
Aims:
. The stability is discussed of the drift-Alfvén wave which is driven
by the equilibrium density gradient, in both unbounded and bounded,
collisional solar plasmas, including the effects of both hot ions and
a finite ion Larmor radius. The density gradient in combination with
the electron collisions with heavier plasma species is the essential
source of the instability of the electrostatic drift mode which is
coupled to the dispersive Alfvén mode.
Methods: .An analytical
linear normal mode analysis is used for the description of the waves
in spatially unlimited plasma. In the application to the magnetic
structures the complex eigen-modes and the corresponding complex
discrete eigen-frequencies in cylindric, radially inhomogeneous,
collisional and bounded plasma are derived and discussed.
Results: .A detailed derivation of the hot ion (the finite ion Larmor
radius) contribution is performed within the two fluid model. In
the analysis of modes in an unbounded plasma the exchange of identity
between the electrostatic and electromagnetic modes is demonstrated. Due
to this, the frequency of the electromagnetic part of the mode becomes
very different compared to the case without the density gradient. In
the case of a bounded plasma the dispersion properties of modes involve
a discrete poloidal mode number, and eigen-functions in terms of Bessel
functions with discrete zeros at the boundary. The results are applied
to coronal and chromospheric plasmas.
Title: Initiation of CMEs by Magnetic Flux Emergence
Authors: Dubey, Govind; van der Holst, Bart; Poedts, Stefaan
Bibcode: 2006JApA...27..159D
Altcode:
The initiation of solar Coronal Mass Ejections (CMEs) isstudied in
the framework of numerical magnetohydrodynamics (MHD). The initial
CME model includes a magnetic flux rope in spherical, axisymmetric
geometry. The initial configuration consists of a magnetic flux rope
embedded in a gravitationally stratified solar atmosphere with a
background dipole magnetic field. The flux rope is in equilibrium due
to an image current below the photosphere. An emerging flux triggering
mechanism is used to make this equilibrium system unstable. When the
magnetic flux emerges within the filament below the flux rope, this
results in a catastrophic behavior similar to previous models. As a
result, the flux rope rises and a current sheet forms below it. It is
shown that the magnetic reconnection in the current sheet below the
flux rope in combination with the outward curvature forces results in
a fast ejection of the flux rope as observed for solar CMEs.We have
done a parametric study of the emerging flux rate.
Title: On the Effect of the Background Solar Wind on CME's Initiated
by Flux Emergence
Authors: Dubey, G.; Poedts, S.; van der Holst, B.; Gryp, M.
Bibcode: 2006ESASP.617E.125D
Altcode: 2006soho...17E.125D
No abstract at ADS
Title: CME Modeling: An a Posteriori Approach
Authors: Chané, E.; Poedts, S.; van der Holst, B.
Bibcode: 2006ESASP.617E.120C
Altcode: 2006soho...17E.120C
No abstract at ADS
Title: 3D Evolution of a "Density-Driven" CME Event
Authors: Jacobs, C.; Poedts, S.; van der Holst, B.
Bibcode: 2006ESASP.617E.140J
Altcode: 2006soho...17E.140J
No abstract at ADS
Title: Time Dependent Simulations of 2D Coronal Loop Models
Authors: van Doorsselaere, T.; Poedts, S.; Andries, J.; Arregui, I.
Bibcode: 2006ESASP.617E.113V
Altcode: 2006soho...17E.113V
No abstract at ADS
Title: Seismology of Coronal Loops Using the Period and Damping of
Quasi-Mode Kink Oscillations
Authors: Arregui, I.; Andries, J.; Van Doorsselaere, T.; Goossens,
M.; Poedts, S.
Bibcode: 2006ESASP.617E..81A
Altcode: 2006soho...17E..81A
No abstract at ADS
Title: Ion Sound in Highly Collisional, Partially Ionized Plasma
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2006ESASP.617E.116V
Altcode: 2006soho...17E.116V
No abstract at ADS
Title: On the Motion of Toroidal Magnetic Clouds in the Solar Corona
and Inner Heliosphere
Authors: Romashets, E.; Vandas, M.; Poedts, S.
Bibcode: 2006ESASP.617E.144R
Altcode: 2006soho...17E.144R
No abstract at ADS
Title: Collisional instability of the drift wave in multi-component
plasmas
Authors: Vranjes, J.; Pandey, B. P.; Poedts, S.
Bibcode: 2006P&SS...54..695V
Altcode:
The collisional instability of the drift wave in a multi-component
plasma is investigated. It is shown that when the electron and ion
density gradients are different, e.g., due to the presence of a static
third component or due to neutral drag effects, the drift mode becomes
unstable. The instability is caused by the simultaneous action of
the electron collisions with all other plasma species and the spatial
difference of the density of the plasma components. This instability
may be expected as a natural consequence of the stratification of a
multi-component plasma placed in an external gravity field where it
can operate for any amount of charge on heavy particles. Therefore it
could develop in weakly ionized cold interstellar regions for example,
when the heavy particles, i.e. charged grains, are a few tens of Å
in size, and carry typically ±1,±2 charge. In the solar atmosphere,
it may appear in the weakly ionized photospheric layers due to the
convective motion of the neutral component.
Title: Nonmodal Cascade in the Compressible Solar Atmosphere:
Self-Heating, an Alternative Way to Enhance Wave Heating
Authors: Shergelashvili, Bidzina M.; Poedts, Stefaan; Pataraya,
Avtandil D.
Bibcode: 2006ApJ...642L..73S
Altcode:
The nonmodal self-heating mechanism recently proposed by Rogava is
applied to the medium of solar coronal holes with an inhomogeneous
plasma flow along the magnetic field lines. The viscosity force is
assumed to be anisotropic. The efficiency of the nonmodal cascade
process is examined for different sets of environmental parameters
and for different wave parameters. It is concluded that the proposed
mechanism can serve as an alternative mechanism for explaining the
significant heat production in the lower corona, even when only laminar
values of the viscosity coefficients are taken into account.
Title: The effect of the solar wind on CME triggering by magnetic
foot point shearing
Authors: Jacobs, C.; Poedts, S.; van der Holst, B.
Bibcode: 2006A&A...450..793J
Altcode:
Context: .Photospheric motions and a sheared configuration of the
magnetic field are often considered as precursors of violent solar
phenomena such as flares and Coronal Mass Ejections (CMEs). Therefore,
in many numerical CME initiation studies shearing of the magnetic foot
points is used as a mechanism to make the magnetic field unstable
and to trigger the CME event.
Aims: .From that point of view
we decided to do a parameter study that investigates the effect of
the different initiation parameters, in particular the effect of the
shear flow velocity. Moreover, the simulations were performed on three
different background solar wind models. In this way, both effects of
the background wind and the initiation parameters on the CME evolution
are quantified.
Methods: .The results are obtained by means of
a finite volume, explicit solver to advance the equations of ideal
magnetohydrodynamics. All simulations involve the same numerical grid,
the same numerical technique and similar boundary conditions, so that
the results can be compared in an unequivocal way.
Results: .The
foot points of the magnetic field lines are sheared by introducing an
extra longitudinal flow profile on the solar surface with a maximum
velocity ranging from 3 km s-1 to 9 km s-1. The
temporal evolution of the magnetic energy, the velocity of the flux
rope, and the magnetic helicity show a dependence on the maximum shear
velocity as well as on the background wind model.
Title: Unstable kinetic Alfvén wave in partially ionized plasma
Authors: Vranjes, J.; Petrovic, D.; Poedts, S.; Kono, M.; Čadež,
V. M.
Bibcode: 2006P&SS...54..641V
Altcode:
The stability of kinetic Alfven waves is discussed for a partially
ionized plasma with a flux of ionizing electrons which balance the
plasma particle losses. Accidental electromagnetic perturbations are
shown to be unstable due to the energy change of ionizing electrons.
Title: Inverse and normal coronal mass ejections: evolution up to 1 AU
Authors: Chané, E.; van der Holst, B.; Jacobs, C.; Poedts, S.;
Kimpe, D.
Bibcode: 2006A&A...447..727C
Altcode:
Simulations of Coronal Mass Ejections (CMEs) evolving in the
interplanetary (IP) space from the Sun up to 1 AU are performed in
the framework of ideal magnetohydrodynamics (MHD) by the means of a
finite volume, explicit solver. The aim is to quantify the effect of
the initiation parameters, such as the initial magnetic polarity,
on the evolution and on the geo-effectiveness of CMEs. The CMEs
are simulated by means of a very simple model: a high density and
high pressure magnetized plasma blob is superposed on a background
steady state solar wind model with an initial velocity and launch
direction. The simulations show that the initial magnetic polarity
substantially affects the IP evolution of the CMEs influencing
the propagation velocity, the shape, the trajectory and even the
geo-effectiveness. We also tried to reproduce the physical values
(density, velocity, and magnetic field) observed by the ACE spacecraft
after the halo CME event that occurred on April 4, 2000.
Title: Quasi-mode damping in two-dimensional fully non-uniform
coronal loops
Authors: Arregui, I.; Van Doorsselaere, T.; Andries, J.; Goossens,
M.; Poedts, S.
Bibcode: 2006RSPTA.364..529A
Altcode:
No abstract at ADS
Title: Low Frequency Waves in Spatially Bounded Plasma
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2005ESASP.600E.104V
Altcode: 2005dysu.confE.104V; 2005ESPM...11..104V
No abstract at ADS
Title: CME Modeling: the a Posteriori Approach
Authors: Chané, E.; Poedts, S.; van der Holst, B.
Bibcode: 2005ESASP.600E.154C
Altcode: 2005dysu.confE.154C; 2005ESPM...11..154C
No abstract at ADS
Title: Triggering CMES by Magnetic Foot Point Shearing: a Parameter
Study
Authors: Jacobs, C.; Poedts, S.; van der Holst, B.
Bibcode: 2005ESASP.600E.158J
Altcode: 2005ESPM...11..158J; 2005dysu.confE.158J
No abstract at ADS
Title: Seismology of Coronal Loops Using Resonant Absorption
Authors: Arregui, I.; van Doorsselaere, T.; Andries, J.; Goossens,
M.; Poedts, S.
Bibcode: 2005ESASP.600E..21A
Altcode: 2005dysu.confE..21A; 2005ESPM...11...21A
No abstract at ADS
Title: Non-Modal Self-Heating of the Solar Atmosphere: AN Alternative
way to Enhance the Wave Heating Process
Authors: Shergelashvili, B. M.; Poedts, S.; Pataraya, A. D.
Bibcode: 2005ESASP.600E..98S
Altcode: 2005ESPM...11...98S; 2005dysu.confE..98S
No abstract at ADS
Title: Electrostatic Modes in Partially Ionized Plasma
Authors: Vranjes, J.; Poedts, S.
Bibcode: 2005ESASP.600E..68V
Altcode: 2005ESPM...11...68V; 2005dysu.confE..68V
No abstract at ADS
Title: The Dynamic Sun: Challenges for Theory and Observations
Authors: Danesy, D.; Poedts, S.; de Groof, A.; Andries, J.
Bibcode: 2005ESASP.600E....D
Altcode: 2005dysu.confE....D; 2005ESPM...11.....D
No abstract at ADS
Title: Building a Time Dependent Code to Simulate Oscillations of
Line-Tied Coronal Loops
Authors: van Doorsselaere, T.; Poedts, S.; Arregui, I.; Andries, J.
Bibcode: 2005ESASP.600E..83V
Altcode: 2005dysu.confE..83V; 2005ESPM...11...83V
No abstract at ADS
Title: Collisional Drift Instability in Plasmas with Inelastic
Collisions
Authors: Petrovic, D.; Vranjes, J.; Poedts, S.
Bibcode: 2005ESASP.600E..67P
Altcode: 2005dysu.confE..67P; 2005ESPM...11...67P
No abstract at ADS
Title: Transient Amplification of Disturbances in the Solar
Atmosphere: a Mechanism for CME Initiation?
Authors: Shergelashvili, B. M.; Poedts, S.; Pataraya, A. D.
Bibcode: 2005ESASP.600E.165S
Altcode: 2005ESPM...11..165S; 2005dysu.confE.165S
No abstract at ADS
Title: Multiwavelength Analysis of Downflows Along AN Off-Limb Loop
Authors: de Groof, A.; Müller, D. A. N.; Poedts, S.
Bibcode: 2005ESASP.600E..29D
Altcode: 2005ESPM...11...29D; 2005dysu.confE..29D
No abstract at ADS
Title: Downflows Along AN Off-Limb Loop Seen both in 30.4NM and Hα
Authors: de Groof, A.; Müller, D. A. N.; Poedts, S.
Bibcode: 2005ESASP.596E..36D
Altcode: 2005ccmf.confE..36D
No abstract at ADS
Title: Dynamics of Coronal Loop Oscillations Recent Improvements
and Computational Aspects
Authors: van Doorsselaere, T.; Arregui, I.; Andries, J.; Goossens,
M.; Poedts, S.
Bibcode: 2005SSRv..121...79V
Altcode:
We will discuss the observed, heavily damped transversal oscillations
of coronal loops. These oscillations are often modeled as transversal
kink oscillations in a cylinder. Several features are added to the
classical cylindrical model. In our models we include loop curvature,
longitudinal density stratification, and highly inhomogeneous radial
density profiles. In this paper, we will first give an overview of
recently obtained results, both analytically and numerically. After
that, we shed a light on the computational aspects of the modeling
process. In particular, we will focus on the parallellization of the
numerical codes.
Title: Detailed comparison of downflows seen both in EIT 30.4 nm
and Big Bear Hα movies
Authors: de Groof, A.; Bastiaensen, C.; Müller, D. A. N.; Berghmans,
D.; Poedts, S.
Bibcode: 2005A&A...443..319D
Altcode:
An EIT shutterless campaign was conducted on 11 July 2001 and provided
120 high-cadence (68 s) 30.4 nm images of the north-eastern quarter
of the Sun. Systematic intensity variations are seen which appear
to propagate along an off-disk loop-like structure. In this paper we
study the nature of these intensity variations by confronting the EIT
observations studied in De Groof et al. (2004, A&A, 415, 1141)
with simultaneous Hα images from Big Bear Solar Observatory. With
the goal to carefully co-register the two image sets, we introduce a
technique designed to compare data of two different instruments. The
image series are first co-aligned and later overplotted in order to
visualize and compare the behaviour of the propagating disturbances
in both data sets. Since the same intensity variations are seen in
the EIT 30.4 nm and in the Hα images, we confirm the interpretation
of De Groof et al. (2004, A&A, 415, 1141) that we are observing
downflows of relatively cool plasma. The origin of the downflows is
explained by numerical simulations of "catastrophic cooling" in a
coronal loop which is heated predominantly at its footpoints.
Title: Modelling of Solar Wind, CME Initiation and CME Propagation
Authors: van der Holst, B.; Poedts, S.; Chané, E.; Jacobs, C.; Dubey,
G.; Kimpe, D.
Bibcode: 2005SSRv..121...91V
Altcode:
Simulations of coronal mass ejections (CMEs) evolving in the
interplanetary (IP) space from the Sun up to 1 AU are performed in
the framework of ideal magnetohydrodynamics (MHD) by the means of
a finite-volume, explicit solver. The aim is to quantify the effect
of the background solar wind and of the CME initiation parameters,
such as the initial magnetic polarity, on the evolution and on
the geo-effectiveness of CMEs. First, three different solar wind
models are reconstructed using the same numerical grid and the same
numerical scheme. Then, different CME initiation models are considered:
Magnetic foot point shearing and magnetic flux emergence. For the
fast CME evolution studies, a very simple CME model is considered:
A high-density and high-pressure magnetized plasma blob is superposed
on a background steady state solar wind model with an initial velocity
and launch direction. The simulations show that the initial magnetic
polarity substantially affects the IP evolution of the CMEs influencing
the propagation velocity, the shape, the trajectory (and thus, the
geo-effectiveness).
Title: Foreword: Computing in Space and Astrophysical Plasmas
Authors: Goossens, Marcel; Poedts, Stefaan; Voitenko, Yuriy; Chian,
Abraham C. -L.
Bibcode: 2005SSRv..121....1G
Altcode:
No abstract at ADS
Title: Dynamics of Coronal Loop Oscillations
Authors: van Doorsselaere, T.; Arregui, I.; Andries, J.; Goossens,
M.; Poedts, S.
Bibcode: 2005ESASP.596E..44V
Altcode: 2005ccmf.confE..44V
No abstract at ADS
Title: Quantitative Study of Initiation and Evolution of CMEs in
Different Wind Models
Authors: Poedts, S.; Chané, E.; van der Holst, B.; Jacobs, C.; Dubey,
G.; Kimpe, D.
Bibcode: 2005ESASP.592..301P
Altcode: 2005ESASP.592E..45P; 2005soho...16E..45P
No abstract at ADS
Title: Triggering CMEs by Magnetic Flux Emergence
Authors: Dubey, G.; Poedts, S.; van der Holst, B.
Bibcode: 2005ESASP.592..637D
Altcode: 2005soho...16E.125D; 2005ESASP.592E.125D
No abstract at ADS
Title: Solar coronal loop oscillations: theory of resonantly damped
oscillations and comparison with observations
Authors: Goossens, M.; Andries, J.; Arregui, I.; Doorsselaere, T. V.;
Poedts, S.
Bibcode: 2005AIPC..784..114G
Altcode:
One of the proposed damping mechanisms of coronal transverse loop
oscillations in the kink mode is resonant absorption as a result
of the spatial variation of the Alfvén velocity in the equilibrium
configuration. Analytical expressions for the period and the damping
time exist for 1-D cylindrical equilibrium models with thin non-uniform
transitional layers. Comparison with observations indicates that the
assumption of thin non-uniform transitional layers is not a very
accurate approximation of reality. This contributions starts with
a short review of observations on transverse oscillations in solar
coronal loops. Then it presents results on periods and damping times
of resonantly damped kink mode oscillations for (i) fully non-uniform
1-D cylindrical equilibrium models in which the equilibrium quantities
vary in the radial direction across the magnetic field from the centre
of the loop up to its boundary and (ii) non-uniform 2-D cylindrical
equilibrium models in which the equilibrium quantities vary both in the
radial direction across the magnetic field and in the axial direction
along the magnetic field. An important point is that the periods and
damping times obtained for these fully non-uniform models can differ
substantially from those obtained for thin non-uniform transitional
layers. This contribution then reports on a consistency test between
theory and observations showing that there is a very good agreement
within the observational inaccuracies.
Title: CME Triggering by Magnetic Footpoint Shearing
Authors: Jacobs, C.; Poedts, S.; van der Holst, B.
Bibcode: 2005ESASP.592..641J
Altcode: 2005ESASP.592E.126J; 2005soho...16E.126J
No abstract at ADS
Title: On the effect of the inhomogeneous subsurface flows on the
high degree solar p-modes
Authors: Shergelashvili, B. M.; Poedts, S.
Bibcode: 2005A&A...438.1083S
Altcode: 2005astro.ph..4314S
The observed power spectrum of high-degree solar p-modes (ℓ>200)
shows discrepancies with the power spectrum predicted by the
stochastic excitement and damping theory. In an attempt to explain these
discrepancies, the present paper is concerned with the influence of the
observed subsurface flows on the trapped acoustic modes (p-modes). The
effect of these inhomogeneous background flows is investigated by
means of a non-modal analysis and a multi-layer model. It is shown
that the rotational and meridional components of the velocity field
change the wavelengths of the oscillation modes which, in turn,
results in modifications of the corresponding modal frequencies. The
magnitudes of the frequency residuals depend on the spatial scales of
the modes and on the gradients of the different components of the flow
velocity. Together with other mechanisms (e.g. the scattering of modes
by the large-scale convection), the non-modal effect of the variation of
the frequencies in time may contribute: 1) to the observed widening of
the corresponding peaks in the observed power spectrum with increasing
angular degree; 2) to the partial dissipation of spectral power, and,
as a result; 3) to the discrepancies between the predicted and the
observed power spectrum of solar p-modes.
Title: ``Swing Absorption'' of fast magnetosonic waves in
inhomogeneous media
Authors: Shergelashvili, B. M.; Zaqarashvili, T. V.; Poedts, S.;
Roberts, B.
Bibcode: 2005A&A...433...15S
Altcode:
A&A, 429, 767-777 (2005), DOI: 10.1051/0004-6361:20041494
Title: On the effect of the initial magnetic polarity and of the
background wind on the evolution of CME shocks
Authors: Chané, E.; Jacobs, C.; van der Holst, B.; Poedts, S.;
Kimpe, D.
Bibcode: 2005A&A...432..331C
Altcode:
The shocks and magnetic clouds caused by Coronal Mass Ejections (CMEs)
in the solar corona and interplanetary (IP) space play an important
role in the study of space weather. In the present paper, numerical
simulations of some simple CME models were performed by means of
a finite volume, explicit solver to advance the equations of ideal
magnetohydrodynamics. The aim is to quantify here both the effect of
the background wind model and of the initial polarity on the evolution
of the IP CMEs and the corresponding shocks. To simulate the CMEs,
a high density-pressure plasma blob is superposed on different steady
state solar wind models. The evolution of an initially non-magnetized
plasma blob is compared with that of two magnetized ones (with
both normal and inverse polarity) and the differences are analysed
and quantified. Depending on the launch angle of the CME and the
polarity of the initial flux rope, the velocity of the shock front
and magnetic cloud is decreased or increased. Also the spread angle
of the CME and the evolution path of the CME in the background solar
wind is substantially different for the different CME models and the
different wind models. A quantitative comparison of these simulations
shows that these effects can be quite substantial and can clearly
affect the geo-effectiveness and the arrival time of the events.
Title: On the effect of the background wind on the evolution of
interplanetary shock waves
Authors: Jacobs, C.; Poedts, S.; Van der Holst, B.; Chané, E.
Bibcode: 2005A&A...430.1099J
Altcode:
The propagating shock waves in the solar corona and interplanetary
(IP) space caused by fast Coronal Mass Ejections (CMEs) are simulated
numerically and their structure and evolution is studied in the
framework of ideal magnetohydrodynamics (MHD). Due to the presence
of three characteristic velocities and the anisotropy induced by the
magnetic field, the CME shocks generated in the lower corona can have
a complex structure and topology including secondary shock fronts,
over-compressive and compound shocks, etc. The evolution of these
CME shocks is followed during their propagation in IP space up to
r=30 R_⊙. Here, particular attention is given to the effect of
the background solar wind on the evolution parameters of the fast
CME shocks, i.e. shock speed, deformation of the leading shock front
and the CME plasma, stand-off distance of the leading shock front,
direction, spread angle, etc. First, different ``frequently used''
solar wind models are reconstructed with the same numerical code,
the same numerical technique on exactly the same numerical grid (and
thus the same numerical dissipation), the same boundary conditions,
and the same normalization. Then, a simple CME model is superposed on
three different solar wind models, again using exactly the same initial
conditions. The result is a fair comparison and thus an objective study
of the effect of the background wind on the CME shock evolution. This
effect is surprisingly substantial and can be quantified due to the
uniformity of the normalization of the used models and simulation
techniques.
Title: ``Swing Absorption'' of fast magnetosonic waves in
inhomogeneous media
Authors: Shergelashvili, B. M.; Zaqarashvili, T. V.; Poedts, S.;
Roberts, B.
Bibcode: 2005A&A...429..767S
Altcode: 2004astro.ph..8114S
The recently suggested swing interaction between fast magnetosonic
and Alfvén waves (Zaqarashvili & Roberts \cite{paper1}) is
generalized to inhomogeneous media. We show that the fast magnetosonic
waves propagating across an applied non-uniform magnetic field can
parametrically amplify the Alfvén waves propagating along the field
through the periodical variation of the Alfvén speed. The resonant
Alfvén waves have half the frequency and the perpendicular velocity
polarization of the fast waves. The wavelengths of the resonant
waves have different values across the magnetic field, due to the
inhomogeneity in the Alfvén speed. Therefore, if the medium is
bounded along the magnetic field, then the harmonics of the Alfvén
waves, which satisfy the condition for onset of a standing pattern,
have stronger growth rates. In these regions the fast magnetosonic
waves can be strongly ``absorbed'', their energy going in transversal
Alfvén waves. We refer to this phenomenon as ``Swing Absorption''. This
mechanism can be of importance in various astrophysical situations.
Title: The Effect of Curvature on Quasi-Modes in Coronal Loops
Authors: van Doorsselaere, T.; Debosscher, A.; Andries, J.; Poedts, S.
Bibcode: 2004ESASP.575..448V
Altcode: 2004soho...15..448V
No abstract at ADS
Title: Detection of Long Periodwaves in the Polar Coronal Holes
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Poedts, S.
Bibcode: 2004ESASP.575..136B
Altcode: 2004soho...15..136B
No abstract at ADS
Title: The Mechanism of Swing Absorption of Fast Magnetosonic Waves
in Inhomogeneous Media
Authors: Shergelashvili, B. M.; Zaqarashvili, T. V.; Poedts, S.;
Roberts, B.
Bibcode: 2004ESASP.575..431S
Altcode: 2004astro.ph.10277S; 2004soho...15..431S
The recently suggested swing interaction between fast magnetosonic and
Alfvén waves (2002) is generalized to inhomogeneous media. We show that
the fast magnetosonic waves propagating across an applied non-uniform
magnetic field can parametrically amplify the Alfvén waves propagating
along the field through the periodical variation of the Alfvén
speed. The resonant Alfvén waves have half the frequency and the
perpendicular velocity polarization of the fast waves. The wavelengths
of the resonant waves have different values across the magnetic field,
due to the inhomogeneity in the Alfvén speed. Therefore, if the medium
is bounded along the magnetic field, then the harmonics of the Alfvén
waves, which satisfy the condition for onset of a standing pattern,
have stronger growth rates. In these regions the fast magnetosonic
waves can be strongly 'absorbed', their energy going in transversal
Alfvén waves. We refer to this phenomenon as 'Swing Absorption'. This
mechanism can be of importance in various astrophysical situations.
Title: Is the Solar Corona Nonmodally Self-Heated
Authors: Shergelashvili, B. M.; Rogava, A. D.; Poedts, S.
Bibcode: 2004ESASP.575..437S
Altcode: 2004astro.ph.10279S; 2004soho...15..437S
Recently it was pointed out that nonmodally (transiently and/or
adiabatically) pre-amplified waves in shear flows, undergoing
subsequent viscous damping, can ultimately heat the ambient flow. The
key ingredient of this process is the ability of waves to grow, by
extracting energy from the spatially inhomogeneous mean flow. In this
paper we examine this mechanism in the context of the solar coronal
plasma flows. "Self-heating" (SH) processes are examined when both
viscous damping and magnetic resistivity are at work. We show that if
the plasma viscosity is in the favorable range of values the asymptotic
SH rate in these flows can be quite substantial.
Title: Coronal MHD Waves and Theoretical Constraints of Wave Heating
Authors: Poedts, S.; de Groof, A.
Bibcode: 2004ESASP.575...62P
Altcode: 2004soho...15...62P
No abstract at ADS
Title: The effect of curvature on quasi-modes in coronal loops
Authors: Van Doorsselaere, T.; Debosscher, A.; Andries, J.; Poedts, S.
Bibcode: 2004A&A...424.1065V
Altcode:
This paper studies quasi-mode oscillations in models of coronal loops
that include longitudinal curvature. Using a toroidal coordinate system
to incorporate curvature in a basic coronal loop model, the linearized
ideal MHD equations are solved for the plasma-β=0. As a result of
the curvature, quasi-modes with different poloidal wave numbers are
coupled resulting in modifications of the frequencies. However, for
small curvature, only the coupling of quasi-modes with a neighbouring
poloidal wave number remains in first order. In addition, the quasi-mode
frequencies are unchanged up to first order in the curvature. The
imaginary part of the frequency, however, does change in first order,
and quasi-modes are slightly more damped in realistically curved coronal
loop configurations. Appendix A is only available in electronic
form at http://www.edpsciences.org
Title: Principles of Magnetohydrodynamics
Authors: Goedbloed, J. P. Hans; Poedts, Stefaan
Bibcode: 2004prma.book.....G
Altcode:
Part I. Plasma Physics Preliminaries: 1. Introduction; 2. Elements
of plasma physics; 3. 'Derivation' of the macroscopic equations;
Part II. Basic Magnetohydrodynamics: 4. The MHD model; 5. Waves and
characteristics; 6. Spectral theory; 7. Waves and instabilities
on inhomogeneous plasmas; 8. Magnetic structures and dynamics;
9. Cylindrical plasmas; 10. Initial value problem and wave damping;
11. Resonant absorption and wave heating; Appendices; References; Index.
Title: CMEs and CME Shock Evolution on Different Background Winds
Authors: Van der Holst, B.; Poedts, S.; Jacobs, C.; Chane, E.;
Chattopadhyay, I.; Shapakidze, D.; Banerjee, D.
Bibcode: 2004AAS...204.6709V
Altcode: 2004BAAS...36..784V
Coronal Mass Ejections (CMEs) play a key role in many Space Weather
phenomena and are important for prediction models as well. A short
overview is given of the different types of CME models and different
triggering mechanisms currently under study. The shocks in the solar
corona and interplanetary (IP) space caused by fast Coronal Mass
Ejections (CMEs) are simulated numerically and their complex structure
and evolution is studied in the framework of magnetohydrodynamics
(MHD). The complexity of these shocks is caused by the presence of
three characteristic velocities and the anisotropy induced by the
magnetic field. As a result, the CME shocks generated in the lower
corona can have a complex topology including secondary shock fronts,
over-compressive and compound shocks, etc. The evolution of these CME
shocks is followed during their propagation through the solar wind
and, in particular, though the critical points in the wind. Particular
attention is given to the effect of the background wind. Different,
`frequently used' wind models are reconstructed with the same numerical
code and the same resolution. Also different, 'popular' CME models
are reconstructed. Then, the different CME models are combined with
the different wind models. The results are sometimes surprising.
Title: Damping of Coronal Loop Oscillations: Calculation of Resonantly
Damped Kink Oscillations of One-dimensional Nonuniform Loops
Authors: Van Doorsselaere, T.; Andries, J.; Poedts, S.; Goossens, M.
Bibcode: 2004ApJ...606.1223V
Altcode:
The analytic study of coronal loop oscillations in equilibrium states
with thin nonuniform boundary layers is extended by a numerical
investigation for one-dimensional nonuniform equilibrium states. The
frequency and the damping time of the ideal kink quasi mode are
calculated in fully resistive MHD. In this numerical investigation there
is no need to adopt the assumption of a thin nonuniform boundary layer,
which is essential for analytic theory. An important realization is
that analytical expressions for the damping rate that are equivalent
for thin nonuniform layers give results differing by a factor of 2
when they are used for thick nonuniform layers. Analytical theory for
thin nonuniform layers does not allow us to discriminate between these
analytical expressions. The dependence of the complex frequency of the
kink mode on the width of the nonuniform layer, on the length of the
loop, and on the density contrast between the internal and the external
region is studied and is compared with analytical theory, which is valid
only for thin boundaries. Our numerical results enable us to show that
there exists an analytical expression for thin nonuniform layers that
might be used as a qualitative tool for extrapolation into the regime
of thick nonuniform layers. However, when the width of the nonuniform
layer is varied, the differences between our numerical results and the
results obtained with the version of the analytical approximation that
can be extended into the regime of thick nonuniform layers are still
as large as 25%.
Title: Waves in bounded dusty plasma
Authors: Vranješ, J.; Poedts, S.
Bibcode: 2004AIPC..703...92V
Altcode:
Perturbations propagating obliquely to the magnetic field lines are
studied in a cylindric magnetized dusty plasma configuration. A set
of two coupled equations describing the perturbed electrostatic and
gravity potentials in a radially nonuniform plasma is derived. The
equations are discussed and solved in two limits, without and with the
self-gravity effects included. Without the gravity the corresponding
equation for the electrostatic potential is solved analytically for a
Gaussian-type equilibrium density profile. The general solution, which
can be applied to various plasma situations, is expressed in terms of
the Kummer confluent hypergeometric functions. In the self-gravitating
case the equations are solved analytically for a homogeneous plasma
and the general solutions are written in terms of the Bessel functions,
describing well-behaving radially localized wave amplitudes.
Title: The effects of image charge on waves in dusty plasma
Authors: Vranješ, J.; Poedts, S.
Bibcode: 2004AIPC..703...96V
Altcode:
A quantitative analysis of the image charge effects in dusty plasmas
is presented. It is emphasized that the electrostatic interaction
caused by the induced charge on grains can play an important role in
dusty plasmas even in the case when in the equilibrium dust grains
are not charged. As an example, the behavior of the ion electrostatic
perturbations propagating in a plasma containing static and neutral
(uncharged) dust grains is examined. A dispersion equation describing
a dispersive and always unstable ion wave is obtained. Both the wave
dispersion and the instability are a direct consequence of the image
charge effect.
Title: Transient shear instability of differentially rotating and
self-gravitating dusty plasma
Authors: Rogava, Andria D.; Poedts, Stefaan; Osmanov, Zaza
Bibcode: 2004PhPl...11.1655R
Altcode:
Recently it was found [Poedts et al., Phys. Plasmas 7, 3204 (2000)]
that dusty plasma flows host nonperiodic modes-shear-dust-acoustic
(SDA) vortices. These modes, interlaced with dust-acoustic (DA) waves,
are able to exchange energy with the ambient flow. In this paper it
is studied how these processes evolve in differentially rotating and
self-gravitating flows of dusty plasmas. It is found that the presence
of the self-gravity and of Coriolis forces makes both SDA vortices
and DA waves transiently unstable. It is argued that the transient
shear instability could be important for the formation of the fine
structure of planetary rings, for the dynamics of charged dust masses
and transition to dust-acoustic turbulence in galactic gaseous disks.
Title: Intensity variations in EIT shutterless mode: Waves or flows?
Authors: De Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.;
Poedts, S.
Bibcode: 2004A&A...415.1141D
Altcode:
On 11 July 2001 an EIT shutterless campaign was conducted which provided
120 high-cadence (68 s) 304 Å images of the north eastern quarter of
the Sun. The most interesting feature seen in the data is an off-limb
half loop structure along which systematic intensity variations are
seen which appear to propagate from the top of the loop towards its
footpoint. We investigate the underlying cause of these propagating
disturbances, i.e. whether they are caused by waves or by plasma
flows. First we identify 7 blobs with the highest intensities and
follow them along the loop. By means of a location-time plot, bulk
velocities can be measured at several locations along the loop. The
velocity curve found this way is then compared with characteristic
wave speeds and with the free-fall speed in order to deduce the nature
of the intensity variations. Additional information on density and
temperature is derived by measuring the relative intensity enhancements
and comparing the EIT 304 Å sequence with Big Bear data and 171 Å
data (TRACE/EIT). The combination of all these constraints gives us an
insight on the nature and origin of these intensity variations. The
idea of slow magneto-acoustic waves is rejected, and we find several
arguments supporting that these intensity variations are due to
flowing/falling plasma blobs.
Title: Active Region Oscillations as Observed by CDS, EIT and TRACE
Authors: Banerjee, D.; O'Shea, E.; de Groof, A.; Poedts, S.
Bibcode: 2004ESASP.547...39B
Altcode: 2004soho...13...39B
No abstract at ADS
Title: Modeling CMEs
Authors: van der Holst, B.; Poedts, S.; Jacobs, C.; Chattopadhyay,
I.; Banerjee, D.; Shapakidze, D.; Chane, E.
Bibcode: 2004cosp...35.4394V
Altcode: 2004cosp.meet.4394V
Coronal Mass Ejections (CMEs) play a key role in many Space Weather
phenomena and are important for prediction models as well. A short
overview is given of the different types of CME models and different
triggering mechanisms currently under study. The shocks in the solar
corona and interplanetary (IP) space caused by fast Coronal Mass
Ejections (CMEs) are simulated numerically and their complex structure
and evolution is studied in the framework of magnetohydrodynamics
(MHD). The complexity of these shocks is caused by the presence of
three characteristic velocities and the anisotropy induced by the
magnetic field. As a result, the CME shocks generated in the lower
corona can have a complex topology including secondary shock fronts,
over-compressive and compound shocks, etc. The evolution of these CME
shocks is followed during their propagation through the solar wind
and, in particular, though the critical points in the wind. Particular
attention is given to the effect of the background wind. Different,
'frequently used' wind models are reconstructed with the same numerical
code and the same resolution. Also different, 'popular' CME models
are reconstructed. Then, the different CME models are combined with
the different wind models. The results are sometimes surprising.
Title: On the Effect of Non-Uniform Subsurface Flows on High Degree
p-Modes
Authors: Shergelashvili, B. M.; Poedts, S.
Bibcode: 2004ESASP.547...87S
Altcode: 2004soho...13...87S
The observed power spectrum of high-degree solar pmodes ( >
200) shows discrepancies with the power spectrum predicted by the
stochastic excitation and damping theory. In an attempt to explain these
discrepancies, the present paper is concerned with the influence of the
observed subsurface flows on the trapped acoustic modes (p-modes). The
effect of these inhomogeneous background flows is investigated by
means of a nonmodal analysis and a multi-layer model. It is shown that
the rotational and meridional components of the velocity field change
the wavelengths of the oscillation modes which, in turn, results in
modifications of the corresponding modal frequencies. The magnitudes of
the frequency residuals depend on the spatial scales of the modes and on
the gradients of the different components of the flow velocity. Together
with other mechanisms (e.g. the scattering of modes by the convective
motions [1]), the nonmodal effect of the variation of the frequencies
in time contributes: 1) to the observed widening of the corresponding
peaks in the observed power spectrum with increasing angular degree;
2) to the partial dissipation of spectral power, and, as a result,
3) to the discrepancies between the predicted and the observed power
spectrum of solar p-modes.
Title: Intensity Variations in EIT Shutterless Mode: Waves or Flows?
Authors: de Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.;
Poedts, S.
Bibcode: 2004ESASP.547..245D
Altcode: 2004soho...13..245D
On 11 July 2001 an EIT shutterless campaign was conducted which provided
120 high-cadence (68s) 304 Å images of the north eastern quarter of the
Sun. The most interesting feature seen in the data is an off-limb half
loop structure along which systematic intensity variations appear to
propagate from the top of the loop towards its footpoint. We investigate
the underlying cause of these propagating disturbances, i.e. whether
they are caused by waves or by plasma flows. First we identify 7 blobs
with the highest intensities and follow them along the loop. By means
of a location-time plot, bulk velocities can be measured at several
locations along the loop. The velocity curve found this way is then
compared with characteristic wave speeds and with the free-fall speed
in order to deduce the nature of the intensity variations. Additional
information is derived by measuring the relative intensity enhancements
and comparing the EIT 304 Å sequence with Big Bear and 171 Å data. The
idea of slow magneto-acoustic waves is rejected, and we find several
arguments supporting that these intensity variations are due to
flowing/falling plasma blobs.
Title: Quasi-Modes on Curved Solar Coronal Loops
Authors: van Doorsselaere, T.; Debosscher, A.; Poedts, S.
Bibcode: 2004ESASP.547..525V
Altcode: 2004soho...13..525V
Toroidal coordinates are the natural coordinates to describe
semi-toroidal structures. We use this coordinate system to solve the
linearized ideal MHD-equations to find the frequencies and damping rates
of the ideal quasimodes in solar coronal loops taking into account the
curvature along the loop. When we take a simple radial density variation
that is discontinuous at the edge of the loop, the eigenfunctions are
found in terms of hypergeometric functions. The curvature results in
coupling between the modes with different poloidal wave numbers. When
we take the `nocurvature', `thin-loop' limit (straight cylinder) of
the solution, we recover the straight thin flux tube solution. When
we include a smooth density profile in the region connecting the two
homogeneous zones, we get a system of weakly coupled differential
equations. Solving this system of differential equations will yield
an expression for the damping of the quasi-mode oscillations.
Title: Simulation of shock waves in the interplanetary medium
Authors: Poedts, S.; van der Holst, B.; Chattopadhyay, I.; Banerjee,
D.; van Lier, T.; Keppens, R.
Bibcode: 2003ESASP.535..603P
Altcode: 2003iscs.symp..603P
The shocks in the solar corona and interplanetary (IP) space caused
by fast Coronal Mass Ejections (CMEs) are simulated numerically
and their structure and evolution is studied in the framework of
magnetohydrodynamics (MHD). Due to the presence of three characteristic
velocities and the anisotropy induced by the magnetic field, CME
shocks generated in the lower corona can have a complex structure
including secondary shock fronts, over-compressive and compound
shocks, etc. The evolution of these CME shocks is followed during
their propagation through the solar wind and, in particular, through
the critical points in the wind. Particular attention is given to
complex IP events involving two CME shocks colliding to each other,
as often observed. The CME shocks are important for "space weather"
because they can easily be observed in radio wavelengths. This makes
it possible to track the position of the CMEs/magnetic clouds and,
hence, to follow their propagation through the corona.
Title: Computer simulations of solar plasmas
Authors: Goedbloed, J. P.; Keppens, R.; Poedts, S.
Bibcode: 2003SSRv..107...63G
Altcode:
Plasma dynamics has been investigated intensively for toroidal
magnetic confinement in tokamaks with the aim to develop a controlled
thermonuclear energy source. On the other hand, it is known that
more than 90% of visible matter in the universe consists of plasma,
so that the discipline of plasma-astrophysics has an enormous
scope. Magnetohydrodynamics (MHD) provides a common theoretical
description of these two research areas where the hugely different
scales do not play a role. It describes the interaction of electrically
conducting fluids with magnetic fields that are, in turn, produced by
the dynamics of the plasma itself. Since this theory is scale invariant
with respect to lengths, times, and magnetic field strengths, for
the nonlinear dynamics it makes no difference whether tokamaks, solar
coronal magnetic loops, magnetospheres of neutron stars, or galactic
plasmas are described. Important is the magnetic geometry determined
by the magnetic field lines lying on magnetic surfaces where also the
flows are concentrated. Yet, transfer of methods and results obtained
in tokamak research to solar coronal plasma dynamics immediately
runs into severe problems with trans‘sonic’ (surpassing any one
of the three critical MHD speeds) stationary flows. For those flows,
the standard paradigm for the analysis of waves and instabilities,
viz. a split of the dynamics in equilibrium and perturbations, appears
to break down. This problem is resolved by a detailed analysis of the
singularities and discontinuities that appear in the trans‘sonic’
transitions, resulting in a unique characterization of the permissible
flow regimes. It then becomes possible to initiate MHD spectroscopy of
axi-symmetric transonic astrophysical plasmas, like accretion disks or
solar magnetic loops, by computing the complete wave and instability
spectra by means of the same methods (with unprecedented accuracy)
exploited for tokamak plasmas. These large-scale linear programs are
executed in tandem with the non-linear (shock-capturing, massively
parallel) Versatile Advection Code to describe both the linear and
the nonlinear phases of the instabilities.
Title: Variation of coronal line widths on and off the disk
Authors: O'Shea, E.; Banerjee, D.; Poedts, S.
Bibcode: 2003A&A...400.1065O
Altcode:
We present observations of a Mg X 625 Å coronal line, obtained
with the CDS instrument on SoHO, extending from the disk part
of the coronal hole to ~ 90 000 km above the limb in the north
polar coronal hole. Observations were performed in polar plumes and
inter-plume lanes. To obtain a sufficiently high signal-to-noise ratio
the observations were made over long periods of time and subsequent
time frames were summed up. For the off-limb observations we notice a
turnover point, around 65 000 km above the limb, where the line widths
seem to suddenly decrease or level-off. The initial linear increase
of line width with altitude supports previous observations and is
consistent with an interpretation of linear undamped Alfvèn waves
propagating outwards in open field regions. The turnover point seems to
indicate the location where a change of physics takes place. We find
that this turnover occurs at approximately the same line width value
for each of the datasets examined, suggesting that the turnover occurs
whenever the non-thermal velocity reaches a certain key velocity. For
the on-disk data we find larger widths in the deep coronal hole as
compared to the adjacent quiet Sun regions, suggesting the presence
of additional waves and/or turbulence in the coronal hole.
Title: CME shock warps coronal streamer - observation and MHD
simulation
Authors: van der Holst, B.; van Driel-Gesztelyi, L.; Poedts, S.
Bibcode: 2002ESASP.506...71V
Altcode: 2002svco.conf...71V; 2002ESPM...10...71V
A fast (v ≥ 1000 km s-1) CME was observed on 14 January
2002, which was linked to an M4.4 long-duration flare event and
a post-eruption loop system visible on, but partially occulted by,
the SW limb. The fast expanding CME collided with a North-hemispheric
helmet streamer, which was located above NOAA AR 9773 and was in 60°
distance from the CME source region. An interaction with the CME (I)
pushed the streamer aside and (II) created a deflection, setting off an
outward propagating wavelike deformation along it. At the same time,
a decametric-hectometric type-II radio burst was observed with the
WAVES RAD2 instrument onboard the WIND spacecraft. Type-II bursts
are indicative of shock waves. At about the time of the CME-streamer
interaction a splitting was seen in the type-II emission, which
indicated a shock continuing to propagate away from the Sun (thus
getting into lower and lower density domains) and another branch,
which indicated a shock propagating into denser plasma domain. We
interpret this fine-structure of the type-II bursts as a result of the
CME-streamer interaction. We suggest that the shock wave, which was
associated with this fast CME, penetrated into the helmet streamer
and then died away in the denser plasma (the splitting lasted for
about 30 minutes). With our 2-D MHD code we simulate this CME-streamer
interaction, using the observed configuration and magnetic topology. The
simulation results confirm our hypothesis.
Title: On the nature of umbral oscillations: theory and observation
by CDS/SoHO
Authors: Banerjee, D.; O'Shea, E.; Goossens, M.; Poedts, S.; Doyle,
J. G.
Bibcode: 2002ESASP.506..427B
Altcode: 2002ESPM...10..427B; 2002svco.conf..427B
We will present solutions for magneto-acoustic-gravity (or MAG)
waves. The possible wave modes in the 3-5 min range will be
discussed. We will then present observations of sunspots performed
in the EUV wavelength range with the Coronal Diagnostic Spectrometer
(CDS) on SoHO. We examine the time series for the line intensities
and relative velocities and calculate their power spectrum using
wavelet transforms. We find oscillations in the chromosphere and
transition region above the sunspots in the temperature range logT =
4.6 -5.4. Most of the spectral power above the umbra is contained in
the 5-7 mHz frequency range. When the CDS slit crosses the sunspot
plume a clear 3 min oscillation is observed. The observations are
interpreted in terms of slow magnetoacoustic waves propagating upwards.
Title: Axisymmetric magnetized winds and stellar spin-down
Authors: van der Holst, B.; Banerjee, D.; Keppens, R.; Poedts, S.
Bibcode: 2002ESASP.506...75V
Altcode: 2002svco.conf...75V; 2002ESPM...10...75V
We present 2.5D stationary solar/stellar wind numerical simulation
results obtained within the magnetohydrodynamic (MHD) model. This is
an extension of earlier work by Keppens & Goedbloed (1999, 2000),
where spherically symmetric, isothermal, unmagnetized, non-rotating
Parker winds were generalized to axisymmetric, polytropic, magnetized,
rotating models containing both a 'wind' and a 'dead' zone. We study
the influence of stellar rotation and coronal magnetic field strength
on the wind acceleration. Since dynamos in cool stars are thought to
operate more efficiently and to produce a stronger coronal magnetic
field with increasing stellar rotation rate, we assume this increase is
linear. We quantify the stellar angular momentum loss via the magnetized
wind with an equatorial dead zone. The obtained spin-down rates are much
smaller than values obtained from Weber-Davis wind estimates. The need
to invoke a dynamo with magnetic field saturation to lower the spin-down
rates for fast rotators is re-evaluated in view of these results.
Title: On the theory of MAG waves and a comparison with sunspot
observations from CDS/SoHO
Authors: Banerjee, D.; O'Shea, E.; Goossens, M.; Doyle, J. G.;
Poedts, S.
Bibcode: 2002A&A...395..263B
Altcode:
We examine the influence of non-adiabatic effects on the modes of an
isothermal stratified magnetic atmosphere. We present new solutions for
magneto-acoustic-gravity (or MAG) waves in the presence of a radiative
heat exchange based on Newton's law of cooling. An analytic expression
for the dispersion relation is derived, which allows the effect of a
weak magnetic field on the modes to be studied. The insight so gained
proves useful in extending the computations to the moderate-high field
case. In the second part we present observations of two sunspots
obtained in the EUV wavelength range with the Coronal Diagnostic
Spectrometer (CDS) on SoHO. We examine the time series for the line
intensities and relative velocities and calculate their power spectra
using wavelet transforms. We find oscillations in the chromosphere
and transition region above the sunspots in the temperature range
log T = 4.6-5.4 K. Most of the spectral power above the umbra is
contained in the 5-7 mHz frequency range. When the CDS slit crosses
the sunspot umbra a clear 3 min oscillation is observed. The observed
oscillation frequencies are compared with the computed frequencies and
the observations are interpreted in terms of the slow magneto-acoustic
waves.
Title: Slow MAG waves in the sunspot umbra as observed by CDS/SOHO
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.;
Poedts, S.
Bibcode: 2002ESASP.505..187B
Altcode: 2002solm.conf..187B; 2002IAUCo.188..187B
We present observations, in the EUV wavelength range, of two
sunspots, carried out by the Coronal Diagostic Spectrometer (CDS)
on SoHO. We examine the time series for the line intensities and
relative velocities and calculate their power spectrum using wavelet
transforms. We find oscillations in the chromosphere and transition
region above the sunspots in the temperature range logT = 4.6 -
5.4. Most of the spectral power above the umbra are contained in the
5 - 7 mHz frequency range. When the CDS slit croses the sunspot plume
a clear 3 in oscillation is observed. We also present new solutions
for magnetic-acoustic-gravity (or MAG) waves in the presence of
radiative heat exchange based on Newton's law of cooling. The observed
oscillation frequencies are compared with the computed frequencies. The
observations are interpreted in terms of slow magnetoacoustic waves
propagating upwards.
Title: Three-Wave Interaction in a Self-Gravitating Fluid
Authors: Vranješ, J.; Poedts, S.
Bibcode: 2002PhRvL..89m1102V
Altcode:
Nonlinear three-wave interaction is investigated in rotating
self-gravitating astrophysical fluids. Both direct and inverse cascades
are found. The latter should be of importance for the formation of
structures in rotating astrophysical objects like protogalaxies and
galaxies. Linear gravitational instability is shown to be a process
that develops on much longer time scales, compared to the nonlinear
wave interaction, and the nonlinear precipitation of energy from the
linearly unstable, slowly contracting mode towards smaller spatial
and time scales is shown to be possible.
Title: Electron acoustic wave in a dusty plasma
Authors: Vranješ, J.; Saleem, H.; Poedts, S.
Bibcode: 2002P&SS...50..807V
Altcode:
Electromagnetic and mechanical effects, typical for a dusty plasma,
and the interplay between them, are discussed. More precisely,
the effects of charge fluctuations on dust grains, caused by the
collision with electrons and ions from the ambient plasma, on the
electron acoustic mode, are studied. The conditions for instability,
driven by the charge fluctuation, are derived in several limits,
regarding the ratio of the ion and electron attachment frequencies,
as well as the wavelength of the perturbations.
Title: Does spiral galaxy IC 342 exhibit shear induced wave
transformations!?
Authors: Poedts, S.; Rogava, A. D.
Bibcode: 2002A&A...385...32P
Altcode:
In this paper we argue that the peculiar magnetic spiral structure of
the giant, face-on spiral galaxy IC 342 may be evidence for velocity
shear induced magnetohydrodynamic (MHD) density wave transformations.
Title: Numerical modeling of CME initiation and propagation
Authors: Poedts, S.; van der Holst, B.; de Sterck, H.; van
Driel-Gesztelyi, L.; Csík, A.; Milesi, A.; Deconinck, H.
Bibcode: 2002ESASP.477..263P
Altcode: 2002scsw.conf..263P
The shocks in the solar corona caused by fast Coronal Mass Ejections
(CMEs) and the shock at the Earth's magnetosphere caused by the
corresponding magnetic clouds (superposed on the solar wind) are studied
in the framework of computational magnetohydrodynamics (MHD). Due to the
presence of three characteristic velocities and the anisotropy induced
by the magnetic field, MHD shocks can have a complicated structure
including secondary shock fronts, overcompressive and compound shocks,
etc. Numerical simulations show that CME shocks (in the lower corona)
and the shock at the Earth's magnetosphere (at times of the impact of
a magnetic cloud) have such a complex structure. The CME shocks are
important for 'space weather' because they can easily be observed in
radio wavelengths. This makes it possible to track the position of the
CMEs/magnetic clouds and, hence, to follow their propagation through
the corona. The collision of two such shocks is discussed. Also,
the possibility of locating the magnetic cloud from the passage of
a satellite through the leading shock front is discussed. Moreover,
the topology of the shock at the Earth's magnetosphere at the impact
of a magnetic cloud is important for the 'geo-effectiveness' of the
magnetic storms. Hence, a detailed study of the MHD shocks generated
by CMEs may reveal some of the key properties space weather.
Title: Magnetic build-up and precursors of CMEs
Authors: van Driel-Gesztelyi, Lidia; Schmieder, Brigitte; Poedts,
Stefaan
Bibcode: 2002ESASP.477...47V
Altcode: 2002scsw.conf...47V
CMEs are fundamentally magnetic phenomena, thus to improve CME forecast
we have to find out more about the characteristics of the small and
large-scale magnetic field in and around their source region prior
to CME occurrence. In this paper we show examples of the magnetic
evolution of CME-prolific active regions using SOHO/MDI data. It
appears that CMEs are preceded by magnetic evolution during which
the helicity of the source region is increasing due to twisted flux
emergence, shearing motions between opposite polarity footpoints
of subsequently emerging bipoles and, in a smaller extend, by the
differential rotation acting on the emerged flux. Furthermore, we find
short-term magnetic precursors of CME events, typically a combination of
major flux emergence, cancellation and fast shearing motions in active
regions with strong concentrated magnetic fields prior to flare-related
CMEs and small-scale cancellation events along the magnetic inversion
line in decayed active regions with low magnetic flux density prior to
filament eruption-related CMEs. We make an overview of recent studies
on magnetic helicity and suggest that such analyses will be able to
provide a key to unlock the secrets of CME buildup and initiation.
Title: Helicity Loading and Dissipation: The Helicity Budget of AR
7978 from the Cradle to the Grave
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
Plunkett, S.; Thompson, B.; Kövári, Zs.; Aulanier, G.; Young, A.;
López Fuentes, M.; Poedts, S.
Bibcode: 2002mwoc.conf..143V
Altcode:
An isolated active region was observed on the Sun during seven
rotations, starting in July 1996. I will present a study of its magnetic
field, concentrating on its helicity budget. The photospheric field
is extrapolated into the corona in a linear force-free approach,
using SOHO/MDI magnetograms and Yohkoh/SXT images, allowing us to
compute, in a crude way, the relative coronal magnetic helicity of
the active region. Using the observed magnetic field distribution
(SOHO/MDI magnetograms) we also calculate the helicity injected by
the differential rotation during seven solar rotations. Finally, using
SOHO/LASCO and EIT as well as Yohkoh/SXT observations, we identify all
the 26 CMEs which originated from this active region during its lifetime
and using average values of the field and radius of magnetic clouds,
we estimate the helicity which should be shed via CMEs. We compare
these three values to evaluate the importance of the differential
rotation relative to twisted flux emergence as a source of magnetic
helicity. We find that the differential rotation can neither provide
enough helicity to account for the diagnosed coronal heicity values,
nor for the helicity carried away by CMEs. We suggest that the main
source of the magnetic helicity must be the inherent twist of the
magnetic flux tube forming the active region. This magnetic helicity is
transferred to the corona either by a slow continuous emergence of the
flux tube or by torsional Alfven waves, during several solar rotations.
Title: Disintegration and reformation of intermediate-shock segments
in three-dimensional MHD bow shock flows
Authors: De Sterck, H.; Poedts, S.
Bibcode: 2001JGR...10630023D
Altcode:
Recently, it has been shown that for strong upstream magnetic field,
stationary three-dimensional magnetohydrodynamic (MHD) bow shock
flows exhibit a complex double-front shock topology with particular
segments of the shock fronts being of the intermediate MHD shock
type. The large-scale stability of this new bow shock topology is
investigated. Two types of numerical experiments are described in which
the upstream flow is perturbed in a time-dependent manner. It is found
that large-amplitude noncyclic localized perturbations may cause the
disintegration of the intermediate shocks, which are indeed known to
be unstable against perturbations with integrated amplitudes above
critical values, but that in the driven bow shock problem there are
always shock front segments where intermediate shocks are reformed
dynamically, resulting in the reappearance of the new double-front
topology with intermediate-shock segments after the perturbation has
passed. These MHD results indicate a theoretical mechanism for the
possible intermittent formation of shock segments of intermediate
type in unsteady space physics bow shock flows when upstream magnetic
fields are strong, for example, in the terrestrial bow shock during
periods of strong interplanetary magnetic field, which are more common
under solar maximum conditions, or in leading shock fronts induced
by fast coronal mass ejections in the solar corona. It remains to
be confirmed if intermediate-shock segments would be formed when
kinetic effects and realistic dissipation in real space plasmas are
taken into account. The detailed interaction of realistic, wave-like
cyclic perturbations with the intermediate-shock segments in bow shock
flows may lead to unsteady structures composed of (time-dependent)
intermediate shocks, rotational discontinuities, and nonlinear wave
trains, as in the scenarios proposed by Markovskii and Skorokhodov
[2000]. The possible relevance of the new bow shock topology with
intermediate shocks for space weather phenomena is discussed.
Title: Spatial aspect of wave transformations in astrophysical flows
Authors: Bodo, G.; Poedts, S.; Rogava, A.; Rossi, P.
Bibcode: 2001A&A...374..337B
Altcode:
The phenomenon of Shear Induced wave Transformations (SITs)
(Chagelishvili et al. 1996), is a common feature of flows, sustaining
n>1 mode of wave motion. Until now this ``nonmodal'' phenomenon was
described only in terms of the time evolution of individual Fourier
harmonics of perturbations in the space of wave numbers (k-space). In
this paper we present the results of the first, direct numerical
simulations of SITs, giving compelling evidence in favor of the robust
and recognizable character of SITs. The importance of these results for
an understanding of physical processes in astrophysical shear flows is
pointed out. Namely, concrete astrophysical situations (solar plasma
flows, galactic gaseous disks, accretion disks and accretion-ejection
flows), where this approach may help to shed some light on observational
appearances of related objects, are indicated and discussed.
Title: Shear Induced Phenomena in Dusty Plasma Flows
Authors: Khujadze, George R.; Poedts, Stefaan; Rogava, Andria D.
Bibcode: 2001Ap&SS.277..135K
Altcode:
It is found that velocity shear enables the extraction of kinetic
energy from the background flow by Dust-Acoustic waves. It is also
shown that the velocity shear leads to the appearance of a new mode
of the dust particles collective behaviour, called shear dust vortices.
Title: A Survey of Field-Aligned Mach Number and Plasma Beta in the
Solar Wind
Authors: De Keyser, Johan; Roth, Michel; De Sterck, Hans; Poedts,
Stefaan
Bibcode: 2001SSRv...97..201D
Altcode:
We have surveyed solar wind plasma beta and field-aligned Alfvénic
Mach number using Ulysses and Wind data. We show the characteristic
timescale and occurrence frequency of `magnetically dominated' solar
wind, whose interaction with a planetary magnetosphere may produce a
bow shock with multiple shock fronts. We discuss radial, latitudinal,
and solar cycle effects.
Title: Slow magnetoacoustic waves in coronal loops: EIT and TRACE
Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.;
Poedts, S.; Nakariakov, V. M.
Bibcode: 2001A&A...370..591R
Altcode:
On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board
of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition
Region And Coronal Explorer) instruments produced simultaneous high
cadence image sequences of the same active region (AR 8218). TRACE
achieved a 25 s cadence in the Fe Ix (171 Å) bandpass while EIT
achieved a 15 s cadence (operating in ``shutterless mode'', SoHO JOP
80) in the Fe Xii (195 Å) bandpass. These high cadence observations
in two complementary wavelengths have revealed the existence of weak
transient disturbances in an extended coronal loop system. These
propagating disturbances (PDs) seem to be a common phenomenon in
this part of the active region. The disturbances originate from small
scale brightenings at the footpoints of the loops and propagate along
the loops. The projected propagation speeds roughly vary between 65
and 150 km s-1 for both instruments which is close to and
below the expected sound speed in the coronal loops. The measured slow
magnetoacoustic propagation speeds seem to suggest that the transients
are sound (or slow) wave disturbances. This work differs from previous
studies in the sense that it is based on a multi-wavelength observation
of an entire loop bundle at high cadence by two EUV imagers. The
observation of sound waves along the same path shows that they propagate
along the same loop, suggesting that loops contain sharp temperature
gradients and consist of either concentric shells or thin loop threads,
at different temperatures.
Title: 3D MHD shocks caused by CMEs/magnetic clouds
Authors: Poedts, S.; de Sterck, H.; van der Holst, B.; Pandey, B. P.;
Csík, Á.; Deconinck, H.
Bibcode: 2001sps..proc..324P
Altcode:
The shocks in the solar corona caused by fast CMEs and the shock
at the Earth's magnetosphere caused by the corresponding magnetic
clouds (superposed on the solar wind) are studied in the framework of
computational magnetohydrodynamics (MHD). Due to the presence of three
characteristic velocities and the anisotropy induced by the magnetic
field, MHD shocks can have a complicated structure including secondary
shock fronts, overcompressive and compound shocks, etc. The CME shocks
are important for `space weather' because they can easily be observed in
radio wavelengths. This makes it possible to track the position of the
CMEs/magnetic clouds and, hence, to follow their propagation through
the corona. The topology of the shock at the Earth's magnetosphere at
the impact of a magnetic cloud is important for the `geo-effectiveness'
of the magnetic storms.
Title: The effect of shear flows on the Rayleigh-Taylor unstable
magnetopause
Authors: van der Holst, B.; Pandey, B. P.; Poedts, S.
Bibcode: 2001sps..proc..384V
Altcode:
At times, the Earth's magnetopause boundary may become Rayleigh-Taylor
(RT) unstable. In the present work, we study the effect of the flow
velocity and magnetic shear on the growth rate of instability. It
is found that for a normalized wave vector k > 1, for the
hydrodynamic (HD) case, the RT mode overlaps with Kelvin-Helmholtz
(KH) mode. Whereas, the growth rate of RT instability decreases with
increasing shear, the KH mode starts growing with increasing shear. The
overlap window disappears for k < 1 and the KH mode only appears
after the complete suppression of the RT mode. In the presence of
magnetic shear, the maximum growth rate of RT mode is reduced in
comparison to the HD case. The secondary hydrodynamic mode in the
presence of magnetic shear overtakes the primary KH mode indicating
that the magnetic shear can play both a stabilizing as well as a
destabilizing role in the magnetopause.
Title: Slow magnetoacoustic waves in coronal loops: EIT vs TRACE
Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.;
Poedts, S.
Bibcode: 2000AIPC..537..271R
Altcode: 2000wdss.conf..271R
On May 13, 1998 the EIT (Extreme-Ultraviolet Imaging Telescope) and
TRACE (Transition Region And Coronal Explorer) instruments produced
simultaneous high cadence image sequences of the same active region
(AR 8218). TRACE achieved a 25 sec cadence in the Fe IX/X (171 Å)
bandpass while EIT achieved a 15 sec cadence (operating in `shutterless
mode,' SOHO JOP 80) in the Fe XII (195 Å) bandpass. These high
cadence observations in two complementary wavelengths have revealed
the existence of weak transient disturbances in an extended coronal
loop system. These propagating disturbances (PDs) seem to be a
common phenomenon in this part of the active region. The disturbances
originate from small scale brightenings at the footpoints of the loops
and propagate along the loops. The apparent propagation speeds roughly
vary between 65 and 150 km s-1 which is close to the expected
sound speed of the coronal loops. The measured propagation speeds seem
to suggest that the transients are sound (or slow) wave disturbances. .
Title: Disintegration and reformation of intermediate shock segments
in 3D MHD bow shock flows
Authors: de Sterck, H.; Poedts, S.
Bibcode: 2000AIPC..537..232D
Altcode: 2000wdss.conf..232D
Recently it has been shown that for strong upstream magnetic field
stationary three-dimensional (3D) magnetohydrodynamic (MHD) bow shock
flows exhibit a complex double-front shock topology with particular
segments of the shock fronts being of the intermediate MHD shock
type. The large-scale stability of this new bow shock topology is
investigated. It is found that large-amplitude perturbations may cause
the disintegration of the intermediate shocks-which are indeed known
to be unstable against perturbations with integrated amplitudes above
critical values- but that in the driven bow shock problem there are
always shock front segments where intermediate shocks are reformed
dynamically, resulting in the reappearance of the new double-front
topology. This shows that the new bow shock topology, and shock segments
of intermediate type in general, may be found in MHD plasma flows even
when there are large-amplitude perturbations. .
Title: Nonmodal phenomena in differentially rotating dusty plasmas
Authors: Poedts, Stefaan; Rogava, Andria D.
Bibcode: 2000AIPC..537...76P
Altcode: 2000wdss.conf...76P
In this paper the foundation is layed for the nonmodal investigation
of velocity shear induced phenomena in a differentially rotating
flow of a dusty plasma. The simplest case of nonmagnetized flow is
considered. It is shown that, together with the innate properties
of the dusty plasma, the presence of differential rotation, Coriolis
forces, and self-gravity casts a considerable richness on the nonmodal
dynamics of linear perturbations in the flow. In particular: (i)
dust-acoustic waves acquire the ability to extract energy from the mean
flow and (ii) shear-induced, nonperiodic modes of collective plasma
behavior-shear-dust-acoustic vortices-are generated. The presence of
self-gravity and the nonzero Coriolis parameter (``epicyclic shaking'')
makes these collective modes transiently unstable. .
Title: Intermediate Shocks in Three-Dimensional Magnetohydrodynamic
Bow-Shock Flows with Multiple Interacting Shock Fronts
Authors: de Sterck, H.; Poedts, S.
Bibcode: 2000PhRvL..84.5524D
Altcode:
Simulation results of three-dimensional (3D) stationary
magnetohydrodynamic (MHD) bow-shock flows around perfectly conducting
spheres are presented. For strong upstream magnetic field a new
complex bow-shock flow topology arises consisting of two consecutive
interacting shock fronts. It is shown that the leading shock front
contains a segment of intermediate 1-3 shock type. This is the first
confirmation in 3D that intermediate shocks, which were believed
to be unphysical for a long time, can be formed and can persist for
small-dissipation MHD in a realistic flow configuration.
Title: Shear-driven wave oscillations in astrophysical flux tubes
Authors: Rogava, A. D.; Poedts, S.; Mahajan, S. M.
Bibcode: 2000A&A...354..749R
Altcode:
In plane-parallel flows velocity shear couples magnetohydrodynamic
(MHD) wave modes and induces their mutual transformations. Since the
majority of astrophysical flows are not plane-parallel it is important
to clarify whether this nonmodal phenomenon also takes place in flows
with a more complicated spatial geometry and kinematics. The recently
devised local method for studying linear perturbation dynamics in
flows with arbitrary kinematic complexity is tailor-made for this
actual problem. In this paper we apply this new method to the study
of velocity shear induced wave transformations in a cylindrical flux
tube. We found that the MHD modes sustained by the flux tube flow--the
Alfvén (AW), the slow magnetosonic (SMW), and the fast magnetosonic
(FMW) waves -- are efficiently coupled through the agency of the
velocity shear. Based on this issue we argue that the individual wave
transformation events, happenning perpetually and irregularly in the
whole space occupied by the flux tube flow, establish the regime of
shear induced wave oscillations throughout the flow. We claim that
this previously overlooked linear phenomenon may be important for the
generation of solar hydromagnetic waves, for the transmission of the
waves through the transition region, for coronal heating and for the
acceleration of the solar wind.
Title: Complex Interacting Shock Fronts Induced by Fast CMEs
Authors: de Sterck, H.; Poedts, S.
Bibcode: 1999ESASP.448..935D
Altcode: 1999mfsp.conf..935D; 1999ESPM....9..935D
No abstract at ADS
Title: What May Spring Up in Solar Tornadoes?
Authors: Rogava, A.; Poedts, S.
Bibcode: 1999ESASP.448..355R
Altcode: 1999ESPM....9..355R; 1999mfsp.conf..355R
No abstract at ADS
Title: Waves in the Transition Region and Corona: a Theorist's View
Authors: Poedts, S.
Bibcode: 1999ESASP.448..167P
Altcode: 1999ESPM....9..167P; 1999mfsp.conf..167P
No abstract at ADS
Title: Slow Magnetoacoustic Waves in Coronal Loops?
Authors: Robbrecht, E.; Berghmans, D.; Nakariakov, V.; Poedts, S.
Bibcode: 1999ESASP.446..575R
Altcode: 1999soho....8..575R
On May 13, 1998 the EIT and TRACE instruments produced simultaneous
high cadence image sequences of the same active region (AR 8218). TRACE
achieved a 25 sec cadence in the 171 deg passband while EIT achieved
a 15 sec cadence (operating in 'shutterless mode', SOHO JOP 80) in the
195 deg passband. These high cadence observations in two complementary
wavelengths have revealed the existence of weak disturbances in an
extended coronal loop system. The disturbances originate from small
scale brightenings at the footpoints of the loops and propagate along
the loops at an apparant speed of the order of 150 km/s which is close
to the expected sound speed. To conclude whether these propagating
disturbances should be interpreted as slow magnetoacoustic waves or as
mass motions ('microflows'), we compare our observational findings with
theoretical models. Our results suggest that the recent discovery of
DeForest and Gurman (1998) of slow MHD waves in polar plumes, are in
fact not typical of polar plumes but occur also in extended coronal
structures elsewhere.
Title: Stationary slow shocks in the magnetosheath for solar wind
conditions with β<2/γ: Three-dimensional MHD simulations
Authors: De Sterck, H.; Poedts, S.
Bibcode: 1999JGR...10422401D
Altcode:
Magnetohydrodynamic simulation results are presented of
three-dimensional bow shock flows around a conducting paraboloid
surface. For upstream parameter values for which switch-on shocks occur,
a stationary secondary shock of slow type is formed which follows
the leading shock front and is attached to it. These results may
have direct implications for the structure of the flow in the Earth's
magnetosheath. They offer a physically attractive explanation for the
possible observation of stationary slow shocks in the magnetosheath
and in the distant magnetotail region.
Title: Are galactic magnetohydrodynamic waves coupled?
Authors: Rogava, Andria D.; Poedts, Stefaan; Heirman, Stijn
Bibcode: 1999MNRAS.307L..31R
Altcode:
Recently, Fan & Lou considered the excitation and time evolution of
hydromagnetic density waves in a differentially rotating thin gaseous
disc embedded in an azimuthal magnetic field. The authors found that
both fast and slow hydromagnetic density waves are amplified while
they `swing' from leading to trailing configurations, and gave a
detailed description of the phenomenon. Fan & Lou noticed that
the results of their numerical study indicate the existence of a
`coupling' between slow and fast waves. In this Letter we prove, in
a simple and exact analytic way, that the coupling between slow and
fast waves, presumed by Fan & Lou on the basis of their numerical
study, indeed exists. We show that the coupling is induced exclusively
by the presence of the velocity shear in the gaseous disc, and that
it leads to the mutual transformations of the different density wave
modes. We argue that the shear-induced wave transformations may play a
significant role in the overall dynamics of galactic MHD density waves.
Title: Field-aligned magnetohydrodynamic bow shock flows in the
switch-on regime. Parameter study of the flow around a cylinder and
results for the axi-symmetrical flow over a sphere
Authors: de Sterck, H.; Poedts, S.
Bibcode: 1999A&A...343..641D
Altcode:
A parameter study is undertaken for steady symmetrical planar
field-aligned MHD bow shock flows around a perfectly conducting
cylinder. For sets of values of the inflow plasma beta and Alfvénic
Mach number (MA) which allow for switch-on shocks, a
numerical solution is obtained which exhibits a complex bow shock
shape and topology with multiple shock fronts and a dimpled leading
front. For parameter values outside the switch-on domain, a classical
single-front bow shock flow is obtained. These results show that the
beta and MA parameter regime for which the complex bow
shock topology occurs, corresponds closely to the parameter regime for
which switch-on shocks are possible. The axi-symmetrical field-aligned
bow shock flow over a perfectly conducting sphere is then calculated
for one set of values for beta and MA in the switch-on
domain, resulting in a complex bow shock topology similar to the
topology of the flow around a cylinder. These complex shock shapes
and topologies may be encountered in low-beta space plasmas. Fast
coronal mass ejections moving away from the sun in the low-beta inner
corona may induce preceding shock fronts with upstream parameters
in the switch-on domain. Planetary and cometary bow shocks may have
upstream parameters in the switch-on domain when the impinging solar
wind occasionally becomes low-beta . The simulation results may be
important for phenomena in the Earth's magnetosheath.
Title: Velocity Shear Induced Phenomena in Solar Atmosphere
Authors: Poedts, S.; Rogava, A. D.; Mahajan, S. M.
Bibcode: 1999SSRv...87..295P
Altcode:
We present a brief overview of the probable velocity-shear induced
phenomena in solar plasma flows. Shear-driven MHD wave oscillations
may be the needed mechanism for the generation of solar Alfvén waves,
for the transmission of fast waves through the transition region,
and for the acceleration of the solar wind.
Title: 3D Nonlinear MHD Wave Heating of Coronal LoopsCD
Authors: Poedts, S.; Keppens, R.; Beliën, A. J. C.
Bibcode: 1999ASSL..240..319P
Altcode: 1999numa.conf..319P
No abstract at ADS
Title: Complex magnetohydrodynamic bow shock topology in field-aligned
low-β flow around a perfectly conducting cylinder
Authors: de Sterck, H.; Low, B. C.; Poedts, S.
Bibcode: 1998PhPl....5.4015D
Altcode:
Two-dimensional ideal magnetohydrodynamic (MHD) simulations are
presented that demonstrate several novel phenomena in MHD shock
formation. The stationary symmetrical flow of a uniform, planar,
field-aligned, low-β and superfast magnetized plasma around a
perfectly conducting cylinder is calculated. The velocity of the
incoming flow is chosen such that the formation of fast switch-on
shocks is possible. Using a time marching procedure, a stationary
bow shock is obtained, composed of two consecutive interacting shock
fronts. The leading shock front has a dimpled shape and is composed
of fast, intermediate and hydrodynamic shock parts. A second shock
front follows the leading front. Additional intermediate shocks and
tangential discontinuities are present in the downstream part of the
flow. The intermediate shocks are of the 1-3, 1-4, 2-4 and 1=2-3=4
types. This is a confirmation in two dimensions of recent results
on the admissibility of these types of shocks. Recently it has also
been shown that the 1=2-3=4 shock, embedded in a double compound wave,
is present in the analytical solution of some planar one-dimensional
MHD Riemann problems. This MHD flow with interacting shocks may have
applications for some observed features of fast solar Coronal Mass
Ejections and other phenomena in low-β space plasmas.
Title: Shear-flow-induced Wave Couplings In The Solar Wind
Authors: Poedts, Stefaan; Rogava, Andria D.; Mahajan, Swadesh M.
Bibcode: 1998ApJ...505..369P
Altcode:
A sheared background flow in a plasma induces coupling between different
MHD wave modes, which results in their mutual transformation with
corresponding energy redistribution between the modes. In this way,
the energy can be transferred from one wave mode to the other, but
energy can also be added to or extracted from the background flow. In
the present paper we investigate whether the wave coupling and energy
transfer mechanisms can operate under solar wind conditions. It is shown
that this is indeed the case. Hence, the long-period waves observed
in the solar wind at r > 0.3 AU might be generated by much faster
periodic oscillations in the photosphere of the Sun. Other possible
consequences for the observable peculiar beat phenomena in the wind
and acceleration of the wind particles are also discussed.
Title: Wave heating of coronal arcades driven by toroidally polarised
footpoint motions. Stationary behaviour in dissipative MHD
Authors: Tirry, W. J.; Poedts, S.
Bibcode: 1998A&A...329..754T
Altcode:
We study the heating of 2-D coronal arcades by linear resonant Alfven
waves that are excited by photospheric footpoint motions of the magnetic
field lines. The analysis is restricted to toroidally polarised
footpoint motions so that Alfven waves are excited directly. At the
magnetic surfaces where Alfven waves, travelling back and forth along
the loop-like magnetic field lines, are in phase with the footpoint
motions, the oscillations grow unbounded in ideal linear MHD. Inclusion
of dissipation prevents singular growth and we can look at the steady
state in which the energy input at the photospheric base of the arcade
is balanced by the energy dissipated at the resonance layer. In the
present study we take the toroidal wave number to be non-zero which
means that also fast waves, including quasi-modes, can be excited by the
purely toroidally polarised footpoint motions. In this case resonant
Alfven waves are not only excited directly by the footpoint motions
but also indirectly through coupling to the fast waves. Our results
confirm the phenomena previous found by Berghmans & Tirry (1997)
for a coronal loop model : for some footpoint motions the direct and
indirect contributions to the resonance counteract each other leading to
virtually no heating (anti-resonance) while, for values of the driving
frequency and the toroidal wave number corresponding to a quasi-mode,
the two contributions act in concert leading to enhanced heating.
Title: Two-dimensional equilibrium in coronal magnetostatic flux
tubes: an accurate equilibrium solver
Authors: Beliën, A. J. C.; Poedts, S.; Goedbloed, J. P.
Bibcode: 1997CoPhC.106...21B
Altcode:
To study linearized magnetohydrodynamic (MHD) waves, continuous spectra,
and instabilities in coronal magnetic flux tubes that are anchored
in dense chromospheric and photospheric regions, a two-dimensional
numerical code, called PARIS, has been developed. PARIS solves the
pertinent nonlinear Grad-Shafranov type, partial differential equation
for the magnetic flux on a flux coordinate grid. Both a straight field
line coordinate system and an orthogonal flux coordinate system are
exploited. Isoparametric bicubic Hermite finite elements have been
adopted to solve the Grad-Shafranov-like equation. These elements
allow for a continuous representation of the flux and the gradient
of the flux throughout the tube and can be aligned conveniently along
the boundary of the tube. These properties are important to obtain an
accurate representation of the solution on flux coordinate grids. An
analytical test case is used to show that accurate solutions have
been obtained, even for a small number of grid points. The equilibria
calculated by PARIS are used to study the continuous spectra of
two-dimensional magnetic flux tubes. One illustrative example is
given here; extensive results are presented elsewhere (A.J.C. Beliën,
S. Poedts and J.P. Goedbloed, Astron. Astrophys. 322 (1997) 995). The
equilibria obtained by PARIS are also well suited to calculate the
stability and the normal mode MHD spectrum.
Title: Continuous magnetohydrodynamic spectra of two-dimensional
coronal magnetostatic flux tubes.
Authors: Belieen, A. J. C.; Poedts, S.; Goedbloed, J. P.
Bibcode: 1997A&A...322..995B
Altcode:
In this paper we derive the equations for the continuous ideal
magnetohydrodynamic (MHD) spectrum of two-dimensional coronal
loops, including gravity and expansion, in general curvilinear
coordinates. The equations clearly show the coupling between Alfven
and slow magnetosonic continuum waves when both pressure and geodesic
curvature of the magnetic field lines are present. Gravity always
gives rise to Alfven-slow mode coupling when the magnetic field is
twisted. Numerical calculations show that the coupling of Alfven
and slow magnetosonic continuum waves can be strong, especially for
Alfven-like continuum waves, when the magnetic flux concentration
near the bases of flux tubes is taken into account. Amplitude ratios
of the parallel and perpendicular displacement components of 0.4 were
obtained for concentration of the flux with a factor of 4. Gravity has
less effect on the coupling of Alfven and slow magnetosonic continuum
waves than the concentration of flux but it has a large influence on
the low frequency slow magnetosonic-like continuum branches.
Title: Nonlinear MHD Simulations of Wave Dissipation in Flux Tubes
Authors: Poedts, S.; Tóth, G.; Beliën, A. J. C.; Goedbloed, J. P.
Bibcode: 1997SoPh..172...45P
Altcode: 1997ESPM....8...45P
The phase mixing and resonant dissipation of Alfvén waves is studied in
both the 'closed' magnetic loops and the 'open' coronal holes observed
in the hot solar corona. The resulting energy transfer from large
to small length scales contributes to the heating of these magnetic
structures. The nonlinear simulations show that the periodically varying
shear flows that occur in the resonant layers are unstable. In coronal
holes, the phase mixing of running Alfvén waves is speeded up by the
'flaring out' of the magnetic field lines in the lower chromosphere.
Title: Nonlinear wave heating of solar coronal loops.
Authors: Poedts, S.; Goedbloed, J. P.
Bibcode: 1997A&A...321..935P
Altcode:
The heating of magnetically closed structures (loops) in the solar
corona by the resonant absorption of incident waves is studied
by means of numerical simulations in the framework of nonlinear
resistive magnetohydrodynamics (MHD). It is shown that the dynamics
in the resonant layer is indeed very nonlinear for typical coronal
parameters. The effect of the nonlinearity on the efficiency of the
resonant heating mechanism is investigated. It turns out that this
heating mechanism may be less efficient than concluded from the linear
MHD studies. As a matter of fact, the modification of the background
magnetic field results in a shift of the resonance positions in time
which in turn yields broader dissipation layers.
Title: Direct excitation of resonant torsional Alfven waves by
footpoint motions.
Authors: Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.
Bibcode: 1997A&A...320..305R
Altcode:
The present paper studies the heating of coronal loops by linear
resonant Alfven waves that are excited by the motions of the
photospheric footpoints of the magnetic field lines. The analysis
is restricted to torsionally polarised footpoint motions in an
axially symmetric system so that only torsional Alfven waves are
excited. For this subclass of footpoint motions, the Alfven and cusp
singularities are absent from the analysis which means that resonant
coupling between global modes of the loop and localised oscillations
is avoided. Instead, the focus is on the resonances due to the finite
extent of the loop in the longitudinal direction: at the radii where
Alfven waves travelling back and forth along the length of the loop are
in phase with the footpoint motions, the oscillations grow unbounded
in ideal MHD. Inclusion of electrical resistivity and viscosity as
dissipation mechanisms prevents singular growth and we can look at the
steady state in which the energy injected at the photospheric part
of the loop is balanced by the energy dissipated at the dissipative
layer around the resonance. In this sense, we show that the direct
excitation of Alfven waves by torsionally polarised footpoint motions
leads to a very efficient heating mechanism for coronal loops, even
without resonant coupling to global modes.
Title: MHD wave heating of coronal loops
Authors: Poedts, S.; Tirry, W.; Berghmans, D.; Goossens, M.
Bibcode: 1997jena.confE..54P
Altcode:
The possibility of heating coronal loops by phase-mixing and resonant
absorption of MHD waves is discussed. The focus is on the efficiency and
time scales of the conversion of the wave energy to heat for typical
coronal loop parameter values. Both the sideways excitation of loops
by incident waves and the footpoint driving by convective motions are
discussed. First, the mechanisms of phase-mixing and resonant absorption
are explained in a simple set-up. Next, linear MHD results on solar
coronal loop applications are reviewed. In sideways excited loops
(by incident waves), `quasi-modes' (or `collective modes') play the
crucial role of energy carrier from the external region {through the
flux surfaces} to the resonant layers. The quasi-modes are required
to obtain a reasonable efficiency unless the resonances are located
in the outer region of the loop. In footpoint driven loops, on the
other hand, resonant Alfven can be excited directly and the efficiency
depends of the polarization of the driving source. Recent results take
the variation of plasma density and magnetic field strength {along the
loop} into account. For typical coronal loop parameters, the MHD wave
heating mechanism turns out to be very efficient, i.e. the coupling
of the loop plasma to the external driver is very good and the time
scales for dissipation are much smaller than the typical life time of
a loop. However, the dynamics in the resonant layers is very nonlinear
in the hot (very well conducting) coronal plasma. Computer simulations
show that the shear flow in these layers can become unstable. It will
be shown that the Kelvin-Helmholtz-like instabilities may destroy
the resonant layers and lead to a turbulent state. Finally, some
observational results and consequences are discussed. This brings
us to the problems of the discrepancy between the observed and the
required power spectrum of MHD waves and the distinction between
different candidate heating mechanisms. Scientific visualization of
the observational consequences of the computer simulated results
may lead to different observable features for different candidate
heating mechanisms and, hence, to the identification of the mechanism
responsible for the heating of the coronal loops.
Title: Slow Magnetosonic Waves and Instabilities in Expanded Flux
Tubes Anchored in Chromospheric/Photospheric Regions
Authors: Beliën, A. J. C.; Poedts, S.; Goedbloed, J. P.
Bibcode: 1997ESASP.404..193B
Altcode: 1997cswn.conf..193B
No abstract at ADS
Title: Visualization of resonant absorption in solar coronal loops
by simulation of soft X-ray images.
Authors: Belien, A. J. C.; Poedts, S.; Spoelder, H. J. W.; Leenders,
R.; Goedbloed, J. P.
Bibcode: 1996ComPh..10..573B
Altcode: 1996CoPhy..10..573B
One of the proposed mechanisms to explain the heating of the solar
corona is resonant absorption of magnetic Alfven waves. Numerical
studies of this mechanism often involve large scale computations
and produce large amounts of data that need to be visualized. In
this article the authors present a method to visualize numerically
calculated density and temperature evolutions of heating calculations
by simulating the soft X-ray observations of the soft X-ray telescope
aboard the Yohkoh satellite. The visualization method is applied to
two different model calculations of the heating of coronal magnetic
loops by the resonant absorption of Alfven waves. For these two
cases, information on the variations of temperature and density can be
extracted conveniently from the generated images. The resulting images
reveal features that are characteristic of the resonant absorption
process. This suggests that signatures of resonant absorption can be
extracted from real soft X-ray observations of coronal loops.
Title: Book reviews
Authors: Humphreys, R. M.; Kemp, S.; Savonije, G.; van der Hucht,
K. A.; van der Kruit, P. C.; Miley, G.; Bumba, V.; van Nieuwkoop,
J.; van Hoolst, T.; Cox, A.; Rutten, R. J.; Kleczek, J.; de Jager,
Cornelis; Jerzykiewicz, M.; Zwaan, C.; Poedts, S.; Sakai, Jun-Ichi;
Pecker, J. -C.; Heikkila, W.; de Jong, T.; Wilson, P. R.; Müller,
E. A.; Hoyng, P.; Icke, V.; Shore, S. N.; Achterberg, A.; Lucchin, F.;
Butcher, H.; Ne'Eman, Y.; Heidmann, J.; Belton, M. J. S.; de Graauw,
Th.; Waters, L. B. F. M.; Pacini, F.; Hultqvist, B.; Akasofu, S. -I.;
Vial, J. -C.; Schatzman, E.; van der Laan, H.; Cole, K. D.; Vanbeveren,
D.; Southwood, D.; van der Klis, M.; Katgert, Peter
Bibcode: 1996SSRv...76..339H
Altcode:
No abstract at ADS
Title: Nonlinear magnetohydrodynamics of footpoint-driven coronal
loops.
Authors: Poedts, S.; Boynton, G. C.
Bibcode: 1996A&A...306..610P
Altcode:
Results are presented from magnetohydrodynamic (MHD) simulations of the
phase-mixing and resonant absorption of standing torsional Alfven waves
generated by motion at the footpoint of a line-tied coronal loop with
axial symmetry. The high wave amplitudes that develop in the resonant
layer cause nonlinear effects and the driven coronal loop does not
evolve to a stationary state in contrast to linear MHD results. The
energetics of a monochromatically driven coronal loop show that resonant
heating can be very efficient even in the absence of global modes.
Title: Calculation of Soft X-ray Images from MHD Simulations of
Heating of Coronal Loops
Authors: Belien, A. J. C.; Poedts, S.; Goedbloed, J. P.
Bibcode: 1996mpsa.conf..423B
Altcode: 1996IAUCo.153..423B
No abstract at ADS
Title: Magnetohydrodynamic Continua and Stratification Induced
Alfvén Eigenmodes in Coronal Magnetic Loops
Authors: Beliën, A. J. C.; Poedts, S.; Goedbloed, J. P.
Bibcode: 1996PhRvL..76..567B
Altcode:
The continuous spectra of a 2D inhomogeneous, cylindrical magnetic flux
tube are studied and applied to solar coronal loops. The density is
stratified radially as well as longitudinally, while other equilibrium
quantities only vary in the radial direction. Stratification causes
gaps to appear in the continuous spectrum, and it is shown that
discrete global, stratification-induced Alfvén eigenmodes occur in
these gaps. These global modes may be important for the heating of
coronal loops.
Title: 2D and 3D Nonlinear MHD Simulations of Coronal Loop Heating
by Alfven Waves
Authors: Poedts, S.; Goedbloed, J. P.
Bibcode: 1996mpsa.conf..425P
Altcode: 1996IAUCo.153..425P
No abstract at ADS
Title: On the Quality of Resonant Absorption as a Coronal Loop
Heating Mechanism
Authors: Poedts, S.; Belien, A. J. C.; Goedbloed, J. P.
Bibcode: 1994SoPh..151..271P
Altcode:
The qualityQ of a resonance is defined as the ratio of the total energy
contained in the system to the dissipation per driving cycle. Hence,
a `good quality' resonance is one with little losses, i.e., little
dissipation per driving cycle. However, for heating coronal plasmas by
means of resonant absorption of waves, `bad' quality resonances are
required. Here, the quality of the MHD resonances that occur when an
inhomogeneous coronal loop is excited by incident waves is investigated
for typical coronal loop parameter values in the frame work of linear,
resistive MHD. It is shown that the resonances in coronal loops have
bad quality and, hence, yield a lot of Ohmic heating per driving cycle
compared to the total energy stored in the loop. As a consequence, the
time scales of the heating process are relatively short and resonant
absorption turns out to be a viable candidate for the heating of the
magnetic loops observed in the solar corona.
Title: 3D nonlinear wave heating of coronal loops
Authors: Poedts, S.; Goedbloed, J. P.
Bibcode: 1994SSRv...68..103P
Altcode:
The heating of solar coronal loops by the resonant absorption or
phase-mixing of incident wave energy is investigated in the framework
of 3D nonlinear magnetohydrodynamics (MHD) by means of numerical
simulations.
Title: Linear Visco-Resistive Computations of Magnetohydrodynamics
Waves I. The Code and Test Cases
Authors: Erdelyi, R.; Goossens, M.; Poedts, S.
Bibcode: 1994scs..conf..503E
Altcode: 1994IAUCo.144..503E
The stationary state of resonant absorption of linear, MHD waves in
cylindrical magnetic flux tubes is studied in viscous, compressible
MHD with a numerical code using finite element discretization. The
full viscosity tensor with the five viscosity coefficients as given by
Braginskii is included in the analysis. The computations reproduce the
absorption rates obtained by Lou in scalar viscous MHD and Goossens
and Poedts in resistive MHD, which guarantee the numerical accuracy
of the tensorial viscous MHD code.
Title: Nonlinear wave heating of the solar corona
Authors: Poedts, S.; Goedbloed, J. P.
Bibcode: 1994smf..conf..396P
Altcode:
No abstract at ADS
Title: Total Resonant Absorption of Acoustic Oscillations in Sunspots
Authors: Stenuit, Hilde; Poedts, Stefaan; Goossens, Marcel
Bibcode: 1993SoPh..147...13S
Altcode:
The question of total resonant absorption of acoustic oscillations in
sunspots is studied for cylindrical 1-D flux tubes that are stratified
only in the radial direction and surrounded by a uniform, non-magnetic
plasma. The numerical investigation of Goossens and Poedts (1992)
in linear resistive MHD is taken further by increasing the strength
of the azimuthal magnetic field in the equilibrium flux tubes. For
relatively strong azimuthal magnetic fields, total absorption is found
over a relatively wide range of spot radii.
Title: Coronal heating: the role of resonant absorption.
Authors: Poedts, Stefaan; Goedbloed, J. P.
Bibcode: 1992ESASP.348..253P
Altcode: 1992cscl.work..253P
The efficiency and time scales of Alfvén wave heating of solar coronal
loops is investigated by means of numerical simulations in the framework
of both linear and nonlinear dissipative magnetohydrodynamics. The
coronal loops are modeled by cylindrical plasma columns that are
excited by waves that are incident on them. Parameter studies are
presented of the efficiency of the coupling of the external source to
the coronal loop plasma, the fraction of the power supplied by the
external source that is actually absorbed and converted into heat,
the quality of the resonances that occur, the basic time scales of
the resonant absorption mechanism, and the temporal evolution of the
energetics of the driven dissipative system. The results of these
investigations indicate that resonant absorption is a viable heating
mechanism for solar coronal loops.
Title: Time scales and efficiency of resonant absorption in
periodically driven resistive plasmas
Authors: Poedts, Stefaan; Kerner, Wolfgang
Bibcode: 1992JPlPh..47..139P
Altcode:
The time scales and efficiency of plasma heating by resonant absorption
of Alfvén waves are studied in the framework of linearized compressible
and resistive magnetohydrodynamics. The configuration considered
consists of a straight cylindrical axisymmetric plasma column surrounded
by a vacuum region and a perfectly conducting shell. The plasma is
excited periodically by an external source, located in the vacuum
region. The temporal evolution of this driven system is simulated
numerically. It is shown that the so-called ‘ideal quasi-modes’
(or ‘collective modes’) play a fundamental role in resonant
absorption, and affect both the temporal evolution of the driven
system and the efficiency of this heating mechanism considerably. The
variation of the energetics in periodically driven resistive systems
is analysed in detail for three different choices of the driving
frequency, viz an arbitrary continuum frequency, the frequency of an
ideal ‘quasi-mode’, and a discrete Alfvén wave frequency. The
consequences for Alfvén wave heating of both laboratory plasmas and
solar coronal loops are discussed.
Title: Linear Resistive Magnetohydrodynamic Computations of Resonant
Absorption of Acoustic Oscillations in Sunspots
Authors: Goossens, Marcel; Poedts, Stefaan
Bibcode: 1992ApJ...384..348G
Altcode:
A numerical study of the resonant absorption of p-modes by sunspots is
performed in linear resistive MHD. A parametric evaluation shows that
the efficiency of the absorption mechanism depends significantly on both
the equilibrium model and the characteristics of the p-modes. Results
from this numerical study of the relevant parameter domain indicate
that the resonant absorption of p-modes is more efficient in larger
sun spots with twisted magnetic fields. This is particularly true for
p-modes with higher azimuthal wave numbers.
Title: On Poloidal Mode Coupling in the Continuous Spectrum of
2d Equilibria
Authors: Poedts, Stefaan; Goossens, Marcel
Bibcode: 1991SoPh..133..281P
Altcode:
The continuous spectrum of linear ideal MHD is determined analytically
in 2D magnetostatic models for coronal loops and arcades by means
of a perturbation expansion. Poloidal mode coupling, induced by
non-circularity of the cross-sections of the magnetic surfaces and/or
variation of the plasma density along the magnetic field lines, is
shown to occur in first order. The coupling is most pronounced on
and near rational surfaces for particular poloidal and toroidal mode
numbers and produces gaps in the continuous spectrum of ideal MHD.
Title: Ideal quasimodes reviewed in resistive magnetohydrodynamics
Authors: Poedts, Stefaan; Kerner, Wolfgang
Bibcode: 1991PhRvL..66.2871P
Altcode:
The characteristics of so-called ideal ``quasimodes'' or ``collective
modes'' are investigated in the framework of linearized, compressible
and resistive magnetohydrodynamics. It is shown that ideal quasimodes
correspond to weakly damped eigenmodes of the resistive-MHD differential
operator. The damping of these modes becomes independent of the plasma
resistivity in the limit of vanishing η. Hence, for the first time
in the range of the Alfvén continuum, resistive eigenmodes have been
found that converge to their ideal-MHD transforms as η-->0.
Title: Analytical study of plasma heating by resonant absorption of
the modified external kink mode
Authors: van Eester, D.; Goossens, M.; Poedts, S.
Bibcode: 1991JPlPh..45....3V
Altcode:
A simplified analytic description is used to understand recent
results of large-scale numerical simulations of resonant absorption
and to disentangle the basic physics. It is shown that very efficient
absorption takes place at frequencies where a discrete external kink
and an Alfvén continuum mode merge into a modified external kink
mode. The relation between this ‘hybrid’ mode and ‘pure’
continuum or discrete spectrum modes is discussed.
Title: On the Time Scales and the Efficiency of Solar Coronal Loop
Heating by Resonant Absorption (With 1 Figure)
Authors: Poedts, S. M.
Bibcode: 1991mcch.conf..486P
Altcode:
No abstract at ADS
Title: Line-Tying Effects on Stability and Heating of Solar Coronal
Loops (With 2 Figures)
Authors: Halberstadt, G.; Goedbloed, J. P.; Poedts, S. M.; van der
Linden, R. A. M.
Bibcode: 1991mcch.conf..489H
Altcode:
No abstract at ADS
Title: On the Efficiency of Coronal Loop Heating by Resonant
Absorption
Authors: Poedts, Stefaan; Goossens, Marcel; Kerner, Wolfgang
Bibcode: 1990ApJ...360..279P
Altcode:
The heating of solar coronal loops by resonant absorption of Alfven
waves is investigated in the framework of linearized compressible
resistive MHD. The resonant absorption of the waves incident on
the coronal loops is numerically simulated in straight cylindrical,
axisymmetric loop models externally excited by a periodic source. The
stationary state of this driven system and the ohmic dissipation rate in
this state are determined by a very accurate code based on the finite
element technique. The efficiency of the heating mechanism and the
energy deposition profile in this stationary state strongly depend on
the characteristics of both the external driver and the equilibrium. It
is shown that resonant absorption is very efficient for typical coronal
loops as a considerable part of the energy supplied by the external
source is actually dissipated ohmically and converted into heat. The
heating rate is proportional to the square of the magnitude of the
background magnetic field.
Title: Main-Sequence Broadening in the Double Cluster H-Persei
and Chi-Persei
Authors: Denoyelle, J.; Waelkens, C.; Cuypers, J.; Degryse, K.;
Heynderickx, D.; Lampens, P.; Poedts, S.; Polfliet, R.; Rufener, F.;
Smeyers, P.; van den Abeele, K.
Bibcode: 1990Ap&SS.169..109D
Altcode:
Precise photometric observations of stars in the double cluster h and
Ξ Persei reveal a large spread in the colours and magnitudes of the
upper Main-Sequence; half of the stars are variables that are Be stars
or related stars. The reported age difference between both clusters is
found to be spurious. Rotation apparently affects both the intrinsic and
the observed colours of the early-type stars in h and Ξ Persei. This
result questions the validity of photometric calibrations that heavily
rely on h and Ξ Persei or similar clusters.
Title: Temporal evolution of resonant absorption in solar coronal
loops
Authors: Poedts, Stefaan; Goossens, Marcel; Kerner, Wolfgang
Bibcode: 1990CoPhC..59...95P
Altcode:
A numerical code is presented for the computation of the
temporal evolution of an externally driven cylindrical plasma
column in the framework of linearized compressible and resistive
magnetohydrodynamics. The partial differential equations are solved with
a semi-discretization method using cubic and quadratic finite elements
for the spatial discretization and a fully implicit time advance. This
numerical technique yields very accurate results even for small values
of the resistivity. With this code it is, amongst others, possible to
simulate the heating of solar coronal loops by the resonant absorption
of waves that inpitch on them in order to determine the role of this
dissipation mechanism in coronal heating. In particular, it is necessary
to find out how the time scales of this heating mechanism compare to the
life of the coronal loops. Present address: JET Joint Undertaking,
Theory Division, Abingdon, Oxfordshire OX14 3EA, England.
Title: Numerical simulation of the stationary state of periodically
driven coronal loops
Authors: Poedts, Stefaan; Goossens, Marcel; Kerner, Wolfgang
Bibcode: 1990CoPhC..59...75P
Altcode:
The heating of solar coronal loops by resonant absorption of Alfvén
waves is studied in the framework of linearized, compressible,
resistive MHD by means of numerical simulations in which the loops
are approximated by straight cylindrical, axisymmetric plasma columns
with equilibrium quantities varying only in the radial direction. The
incident waves that excite the loops are modelled by a periodic external
source. The stationary state of this driven system is determined
numerically with a finite element code. The finite element technique is
extremely suitable to compute the nearly-singular solutions and yields
very accurate results. The efficiency of the heating mechanism and the
energy deposition profile in this stationary state strongly depend on
the characteristics of both the external driver and the equilibrium. A
numerical survey of the relevant parameter space shows that resonant
absorption is very efficient for typical coronal parameter values and
appears to be a viable candidate heating mechanism for solar loops. Present address: JET Joint Undertaking, Theory Division, Abingdon,
Oxfordshire OX14 3EA, England.
Title: Geneva photometry of stars in the double cluster H and
KHI Persei.
Authors: Waelkens, C.; Lampens, P.; Heynderickx, D.; Cuypers, J.;
Degryse, K.; Poedts, S.; Polfliet, R.; Denoyelle, J.; van den Abeele,
K.; Rufener, F.; Smeyers, P.
Bibcode: 1990A&AS...83...11W
Altcode:
Results are presented of a campaign of photometric observations of stars
in the double cluster h and Chi Persei that spanned eight years. The
long-time scale of the data has made it possible to discover that
at least half of the brighter stars in h and Chi Persei are variable
stars. It appears that most of these variables are Be stars or related
objects. Accurate color-magnitude diagrams for the brightest stars of
the double cluster show that the reddening is not as uniform as was
assumed so far; that the observed parameters of many stars are very much
affected by the high rotational velocities, and thus cannot be easily
interpreted in terms of physical quantities; and that the reported age
and distance differences of both clusters are probably spurious. It is
noted that the large intrinsic scatter of the colors and magnitudes of
the h and Chi Persei stars casts doubt on the validity of photometric
calibrations that rely heavily on observations of the double cluster.
Title: Coronal loop heating by resonant absorption
Authors: Poedts, Stefaan; Gooseens, Marcel; Kerner, Wolfgang
Bibcode: 1990GMS....58..257P
Altcode:
The heating of coronal loops by resonant absorption of Alfven waves
is studied in compressible, resistive magnetohydrodynamics by means of
numerical simulations in which the loops are approximated by straight
cylindrical, axisymmetric plasma columns. The incident waves, which
excite the coronal loops, are modeled by a periodic external driver. The
efficiency of the heating mechanism and the localization of the heating
strongly depend on the characteristics of both the external source and
the equilibrium. The numerical results show that resonant absorption
is very efficient for typical coronal loop parameter values. A
considerable part of the energy supplied by the external driver,
is actually dissipated ohmically and converted into heat.
Title: Alfvén-wave heating in resistive MHD
Authors: Poedts, Stefaan; Kerner, Wolfgang; Goossens, Marcel
Bibcode: 1989JPlPh..42...27P
Altcode:
Resonant absorption of Alfvén waves in tokamak plasmas is
studied numerically using the linearized equations of resistive
magnetohydrodynamics. A numerical code based on a finite-element
discretization is used for determining the stationary state of a
cylindrical plasma column that is excited by an external periodic
driver. The energy dissipation rate in the stationary state is
calculated and the dependence of the plasma heating on electrical
resistivity, the equilibrium profiles, and the wavenumbers and frequency
of the external driver is investigated. Resonant absorption is extremely
efficient when the plasma is excited with a frequency near that of a
so-called ‘collective mode’. The heating of a plasma by driving
it at the frequencies of discrete Alfvén waves is also investigated.
Title: Numerical simulation of coronal heating by resonant absorption
of Alfvén waves
Authors: Poedts, Stefaan; Goossens, Marcel; Kerner, Wolfgang
Bibcode: 1989SoPh..123...83P
Altcode:
The heating of coronal loops by resonant absorption of Alfvén waves
is studied in compressible, resistive magnetohydrodynamics. The
loops are approximated by straight cylindrical, axisymmetric plasma
columns and the incident waves which excite the coronal loops are
modelled by a periodic external driver. The stationary state of
this system is determined with a numerical code based on the finite
element method. Since the power spectrum of the incident waves is
not well known, the intrinsic dissipation is computed. The intrinsic
dissipation spectrum is independent of the external driver and reflects
the intrinsic ability of the coronal loops to extract energy from
incident waves by the mechanism of resonant absorption.
Title: Kink modes in coronal loops.
Authors: Goedbloed, J. P.; Goossens, M.; Poedts, S.
Bibcode: 1989plap.work..103G
Altcode:
Spectral theory of magnetohydrodynamic waves and instabilities has been
extensively developed. With proper modifications results obtained for
tokamaks can be transferred to the study of stability of coronal flux
loops and heating of the corona by means of Alfvén waves. In tokamaks
external kink modes are stabilized by the geometric constraint that
the modes should fit into the torus. In current-carrying coronal
loops the opposite problem arises, viz. the apparent absence of
external kink modes, as evidenced by their long life-time, spanning
many orders of magnitude of the characteristic growth-time of these
instabilities. Anchoring of the foot points of the field lines in the
photosphere is generally considered to be the responsible agent for
stabilization. Given the overall MHD stability of a coronal magnetic
loop structure, the subtle analysis of Alfvén wave heating by means
of the continuous spectrum may be undertaken. Here, an additional
complication is encountered which turns out to be quite beneficial
though from the point of view of heating efficiency. This gives rise to
improper modes which have both a global character and a non-integrable
part which admits quasi-dissipation.
Title: Coronal heating by resonant absorption in resistive MHD.
Authors: Poedts, S.; Goossens, M.; Kerner, W.
Bibcode: 1989plap.work..107P
Altcode:
The heating of coronal loops by the process of resonant
absorption of Alfvén waves is studied in compressible, resistive
magnetohydrodynamics. The authors consider a one-dimensional,
cylindrical-symmetric plasma column which is excited periodically by
means of an external driver. They determine the intrinsic dissipation
spectrum which is independent of the external driver (whose power
spectrum is not known) and yet reveals some interesting features of
heating by resonant absorption. Resonant absorption is very efficient
for typical coronal loop parameter values. A considerable part of
the energy supplied by the external driver, is actually dissipated
Ohmically and converted into heat. The energy dissipation rate is
almost independent of the resistivity for the relevant values of this
parameter. The efficiency of the heating mechanism strongly depends
on the equilibrium profiles, the wave numbers and the frequency of
the external driver.
Title: The continuous spectrum of MHD waves in 2-D solar loops and
arcades - Parametric study of poloidal mode coupling for poloidal
magnetic fields
Authors: Poedts, S.; Goossens, M.
Bibcode: 1988A&A...198..331P
Altcode:
This parametric study investigates how poloidal mode coupling of ideal
MHD continuum modes of two-dimensional models for coronal loops and
arcades depends on equilibrium quantities. The two physical causes
for poloidal mode coupling considered are non-circularity of the
cross-sections of the flux surfaces and variation of the equilibrium
density along the magnetic field lines. This phenomenon of wave number
coupling is typical for the continuous spectrum of MHD waves of 2D
plasmas. It has two important consequences: the eigenfrequencies
are modified, and the eigenfunctions tend to localize. The present
parametric study is concerned with the dependence of poloidal mode
coupling on the value of the plasma beta (i.e. the ratio of the
plasma pressure to the magnetic pressure), the ellipticity of the
cross-sections, and the variation of the equilibrium density normal to
the magnetic surfaces and along the magnetic field lines. For realistic
values of the parameters, it is found that the continuous spectrum is
modified, the ranges of the continuum frequencies are considerably
enlarged, and the derivatives of the continuum frequencies normal
to the magnetic surfaces are considerably increased. Consequently,
the phasemixing time is reduced, and the efficiency of phase-mixing
as a heating mechanism of solar loops and arcades is increased. The
dissipation of wave energy depends on two spatial coordinates and is
found to be larger at the tops of the coronal loops.
Title: The Continuous Spectrum of Magnetohydrodynamic Waves in 2d
Solar Loops and Arcades - First Results on Poloidal Mode Coupling
for Poloidal Magnetic Fields
Authors: Poedts, S.; Goossens, M.
Bibcode: 1987SoPh..109..265P
Altcode:
A first attempt is made to study the continuous spectrum of linear
ideal MHD for 2D solar loops and to understand how 2D effects change
the continuum eigenfrequencies and continuum eigenfunctions. The
continuous spectrum is computed for 2D solar loops with purely poloidal
magnetic fields and it is investigated how non-circularity of the
cross-sections of the poloidal magnetic surfaces and variations
of density along the poloidal magnetic field lines change the
continuous spectrum and induce poloidal wave number coupling in the
eigenfunctions. Approximate analytical results and numerical results
are obtained for the eigenfrequencies and the eigenfunctions and the
poloidal wave number coupling is clearly illustrated. It is found
that the continuum frequencies are substantially increased, that the
ranges of the continuum frequencies are considerably enlarged and that
the derivatives of the continuum frequencies normal to the magnetic
surfaces are substantially increased. The eigenfunctions are strongly
influenced by poloidal wave number coupling. Implications of these
findings for the heating mechanisms of resonant absorption and phase
mixing are briefly considered.
Title: Poloidal Mode Coupling of Alfvén Continuum Modes in 2D
Coronal Loops
Authors: Poedts, S.; Goossens, M.
Bibcode: 1987rfsm.conf..272P
Altcode:
No abstract at ADS
Title: Poloidal mode coupling of Alfvén continuum modes in 2D
coronal loops.
Authors: Poedts, S.; Goossens, M.
Bibcode: 1987rfsm.conf..277P
Altcode:
Study of the continuous spectrum of two-dimensional (2D) solar loops is
obviously required to see how 2D effects change the continuous spectrum
and influence resonant absorption and phase mixing. The results show
that the Alfvén continuum of static 2D solar loops can be changed
substantially compared with the 1D plasma case. This can have important
consequences for resonant absorption and phase mixing. In particular
the present results indicate that density variation along magnetic
field lines increases the efficiency of phase mixing of Alfvén
continuum waves.
Title: Viscous Normal Modes on Coronal Inhomogeneities and Their
Role as a Heating Mechanism
Authors: Steinolfson, R. S.; Priest, E. R.; Poedts, S.; Nocera, L.;
Goossens, M.
Bibcode: 1986ApJ...304..526S
Altcode:
Viscous damping of Alfven surface waves is examined both analytically
and numerically using incompressible MHD. Normal modes are shown to
exist on discontinuous as well as continuously varying interfaces in
Alfven speed. The waves experience negligible decay below the transition
zone. High-frequency waves damp just above the transition region,
while those of lower frequency lose energy further out. A comparison of
dissipative decay rates shows that wave damping by viscosity proceeds
approximately two orders of magnitude faster than by resistivity.
Title: On the existence of the continuous spectrum of ideal MHD in
a 2D magnetostatic equilibrium.
Authors: Goossens, M.; Poedts, S.; Hermans, D.
Bibcode: 1985SoPh..102...51G
Altcode:
The continuous spectrum of a 2D magnetostatic equilibrium with
y-invariance is derived. It is shown that the continuous spectrum is
given by an eigenvalue problem on each magnetic surface and is related
to the different behaviour of the equilibrium quantities in different
magnetic surfaces. The special case of a uniform poloidal magnetic field
in a 1D equilibrium that is stratified with height, has been considered
in detail and it is found that there is no continuous spectrum. It is
shown that this result relies completely on the artificial property
that the behaviour of the equilibrium quantities along a magnetic field
line is independent of the field line considered. As a consequence
the non-existence of a continuous spectrum in a 1D equilibrium with
a uniform magnetic field cannot be used to argue that the continuous
spectrum has no physical relevance.
Title: The continuous spectrum of an axisymmetric self-gravitating and
static equilibrium with a mixed poloidal and toroidal magnetic field
Authors: Poedts, S.; Hermans, D.; Goossens, M.
Bibcode: 1985A&A...151...16P
Altcode:
The continuous spectrum of the linearized equations of ideal MHD
is investigated for an axisymmetric, self-gravitating equilibrium
with a mixed poloidal and toroidal magnetic field. The continuous
spectrum for a purely poloidal magnetic field is treated as a special
case. The continuous spectrum of a purely poloidal magnetic field
is given by an eigenvalue problem of two uncoupled ordinary second
order differential equations along the magnetic field lines, so
that there are two uncoupled continuous parts of the spectrum: an
Alfvén continuum and a cusp continuum. Variational expressions for
the continuum frequencies are derived for each of the two continua,
and it is found that the Alfvén continuum is always on the stable side
of the spectrum but the cusp continuum can be unstable. The continuous
spectrum in the presence of a mixed poloidal and toroidal magnetic field
is given by an eigenvalue problem of a fourth order system of coupled
ordinary differential equations. A variational expression is derived
for the continuum frequencies and it is found that the equilibrium
gravitational field can lead to an unstable continuous spectrum.
Title: The Continuous Spectrum of AN Axisymmetric, Self-Gravitating
Equilibrium in the Presence of a Poloidal Magnetic Field
Authors: Hermans, D.; Goossens, M.; Poedts, S.
Bibcode: 1984ESASP.207..297H
Altcode:
The continuous spectrum of oscillation frequencies is examined for an
axisymmetric, self-gravitating equilibrium in the presence of a purely
poloidal magnetic field. It is shown that the continuous spectrum is
given by an eigenvalue problem of two uncoupled ordinary second orders
differential equations along the magnetic field lines. The two decoupled
continuous spectra have modes that are polarized either perpendicular or
parallel to the magnetic field lines and may be called Alfven continuum
and cusp continuum in analogy to the linear diffuse pinch. Curvature
and toroidicity influence the two continua, but only the cusp continuum
is affected by gravity and compressibility. Variational expressions
for the continuum frequencies are derived and it is found that only
the cusp continuum can attain negative values. The stability depends
on the distribution of density, pressure, gravity, and magnetic field
along the magnetic field lines.
Title: The continuous spectrum of an axisymmetric equilibrium with a
mixed poloidal and toroidal magnetic field and with gravity included.
Authors: Poedts, S.; Goossens, M.; Hermans, D.
Bibcode: 1984ESASP.220..201P
Altcode: 1984ESPM....4..201P
The continuous spectrum of a static, axisymmetric self-gravitating
equilibrium with a mixed poloidal and toroidal magnetic field is
given by an eigenvalue problem of two coupled ordinary second-order
differential equations. The solutions have motions in the magnetic
surfaces that are not polarized purely perpendicular and purely parallel
to the magnetic field lines and show mixed properties. This coupling of
the classical Alfven and cusp continuum is due to the toroidal magnetic
field component and even persists in the incompressible limit. A
variational expression was derived for the continuum frequencies
and it is shown that the continuum frequencies can be negative. The
stability depends on the distributions of density and pressure in the
magnetic surfaces.
Title: Continuous Spectra of Oscillation Frequencies of an
Axisymmetric Incompressible Equilibrium with a Poloidal Magnetic field
Authors: Goossens, M.; Hermans, D.; Poedts, S.
Bibcode: 1984LIACo..25..382G
Altcode: 1984trss.conf..382G; 1984tpss.conf..382G
No abstract at ADS