Author name code: erdelyi
ADS astronomy entries on 2022-09-14
author:"Erdelyi, Robertus" OR "Von Fay-Siebenburgen" OR "Erdélyi, Robertus" OR "Erdélyi, Robert" OR "Erdelyi, Robert"
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Title: Coronal loop kink oscillation periods derived from the
information of density, magnetic field, and loop geometry
Authors: Chen, G. Y.; Chen, L. Y.; Guo, Y.; Ding, M. D.; Chen, P. F.;
Erdélyi, R.
Bibcode: 2022A&A...664A..48C
Altcode:
Context. Coronal loop oscillations can be triggered by solar eruptions,
for example, and are observed frequently by the Atmospheric Imaging
Assembly (AIA) on board Solar Dynamics Observatory (SDO). The
Helioseismic and Magnetic Imager (HMI) on board SDO offers us the
opportunity to measure the photospheric vector magnetic field and
carry out solar magneto-seismology (SMS).
Aims: By applying SMS,
we aim to verify the consistency between the observed period and the
one derived from the information of coronal density, magnetic field,
and loop geometry, that is, the shape of the loop axis.
Methods:
We analysed the data of three coronal loop oscillation events detected
by SDO/AIA and SDO/HMI. First, we obtained oscillation parameters
by fitting the observational data. Second, we used a differential
emission measure (DEM) analysis to diagnose the temperature and
density distribution along the coronal loop. Subsequently, we applied
magnetic field extrapolation to reconstruct the three-dimensional
magnetic field and then, finally, used the shooting method to compute
the oscillation periods from the governing equation.
Results:
The average magnetic field determined by magnetic field extrapolation
is consistent with that derived by SMS. A new analytical solution is
found under the assumption of exponential density profile and uniform
magnetic field. The periods estimated by combining the coronal density
and magnetic field distribution and the associated loop geometry are
closest to the observed ones, and are more realistic than when the
loop geometry is regarded as being semi-circular or having a linear
shape.
Conclusions: The period of a coronal loop is sensitive
to not only the density and magnetic field distribution but also the
loop geometry.
Title: Solar Magneto-seismology of a Magnetic Slab in an Asymmetric
Magnetic Environment
Authors: Zsámberger, Noémi Kinga; Erdélyi, Róbert
Bibcode: 2022ApJ...934..155Z
Altcode:
Diagnosing the solar atmospheric plasma remains one of the major
challenges in solar physics. In recent years, new methods have been
developed to apply the powerful concept of solar magneto-seismology
(SMS) to obtain information about plasma parameters in solar structures
guiding magnetohydrodynamic (MHD) waves that would otherwise be
difficult to measure. This paper uses the Cartesian model of a magnetic
slab placed in an asymmetric magnetic environment to generalize recently
discovered SMS techniques. Utilizing the fact that the asymmetric
environment changes the character of the classical kink and sausage
eigenmodes, we describe two spatial seismology methods built upon
this mixed character of quasi-sausage and quasi-kink modes. First, we
present the amplitude ratio technique, which compares the oscillation
amplitudes measured at the two boundaries of the slab, and we provide
expressions to estimate the internal Alfvén speed in the thin slab and
in the incompressible plasma approximations. The second main technique
relies on the changed distribution of wave power throughout the slab
under the effect of waveguide asymmetry. This minimum perturbation
shift technique is then also utilized to provide Alfvén speed estimates
that depend on the plasma and magnetic parameters of the environment,
as well as the measured slab width and oscillation frequency. Finally,
we perform a brief investigation of how the amplitude ratio and the
minimum perturbation shift depend on the different sources of waveguide
asymmetry, and illustrate our findings with numerical results.
Title: MHD Wave Propagation and the Kelvin-Helmholtz Instability in
an Asymmetric Magnetic Slab System
Authors: Zsámberger, Noémi Kinga; Tong, Yihui; Asztalos, Balázs;
Erdélyi, Róbert
Bibcode: 2022ApJ...935...41Z
Altcode:
Magnetohydrodynamic waves are ubiquitously detected in the finely
structured solar atmosphere. At the same time, our Sun is a highly
dynamic plasma environment, giving rise to flows of various magnitudes,
which can lead to the instability of waveguides. Recent studies have
employed the method of introducing waveguide asymmetry to generalize
"classical" symmetric descriptions of the fine structuring within
the solar atmosphere, with some of them introducing steady flows
as well. Building on these recent studies, here we investigate the
magnetoacoustic waves guided by a magnetic slab within an asymmetric
magnetic environment, in which the slab is under the effect of a steady
flow. We provide an analytical investigation of how the phase speeds
of the guided waves are changed, and where possible, determine the
limiting flow speeds required for the onset of the Kelvin-Helmholtz
instability. Furthermore, we complement the study with initial
numerical results, which allows us to demonstrate the validity of
our approximations and extend the investigation to a wider parameter
regime. This configuration is part of a series of studies aimed to
generalize, step-by-step, well-known symmetric waveguide models and
understand the additional physics stemming from introducing further
sources of asymmetry.
Title: Magnetic Helicity Flux Oscillations in the Atmospheres of
Flaring and Nonflaring Active Regions
Authors: Korsós, M. B.; Erdélyi, R.; Huang, X.; Morgan, H.
Bibcode: 2022ApJ...933...66K
Altcode:
Analyzing the evolution of magnetic helicity flux at different
atmospheric heights is key for identifying its role in the dynamics
of active regions (ARs). The three-dimensional (3D) magnetic field of
both flaring and nonflaring ARs is constructed using potential field
extrapolations, enabling the derivation of emergence, shearing, and
total magnetic helicity components at a range of atmospheric heights. An
analysis of temporal oscillations of the derived components shows that
the largest significant period of the three helicity fluxes are common
(within ±2 hr) from the photosphere up to at least 1 Mm for flaring
ARs-being consistent with the presence of a coupled oscillatory behavior
that is absent in the nonflaring ARs. We suggest that large, energetic
solar eruptions may have been produced in ARs when the vertical and
horizontal helicity flux components became a coupled oscillatory system
in the low solar atmosphere.
Title: The Solar Activity Monitor Network - SAMNet
Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang,
Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.;
Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša,
Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez,
Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.;
Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu,
Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer,
James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen,
Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz,
Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili,
Teimuraz; Zuccarello, Francesca
Bibcode: 2022JSWSC..12....2E
Altcode:
The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a
future UK-led international network of ground-based solar telescope
stations. SAMNet, at its full capacity, will continuously monitor
the Sun's intensity, magnetic, and Doppler velocity fields at
multiple heights in the solar atmosphere (from photosphere to upper
chromosphere). Each SAMM sentinel will be equipped with a cluster of
identical telescopes each with a different magneto-optical filter (MOFs)
to take observations in K I, Na D, and Ca I spectral bands. A subset
of SAMM stations will have white-light coronagraphs and emission line
coronal spectropolarimeters. The objectives of SAMNet are to provide
observational data for space weather research and forecast. The goal
is to achieve an operationally sufficient lead time of e.g., flare
warning of 2-8 h and provide many sought-after continuous synoptic
maps (e.g., LoS magnetic and velocity fields, intensity) of the lower
solar atmosphere with a spatial resolution limited only by seeing or
diffraction limit, and with a cadence of 10 min. The individual SAMM
sentinels will be connected to their master HQ hub where data received
from all the slave stations will be automatically processed and flare
warning issued up to 26 h in advance.
Title: Magnetohydrodynamic Simulations of Spicular Jet Propagation
Applied to Lower Solar Atmosphere Model. II. Case Studies with
Tilted Jets
Authors: Mackenzie Dover, Fionnlagh; Sharma, Rahul; Erdélyi, Robertus
Bibcode: 2022ApJ...929...88M
Altcode:
We report on numerical simulations of a propagating momentum pulse,
representing an inclined jet structure in a stratified lower solar
atmosphere model. Here, the numerical jets were generated via injection
of a momentum pulse misaligned with the radial magnetic field, which
resulted in a collimated structure that mimicked the observed inclined
jet features in the chromosphere. The influence of inclination angle
was examined for a variety of initial driver conditions (amplitude,
period) and magnetic field magnitudes to identify their potential
role in determining the morphological and dynamical characteristics
of chromospheric jets. The numerical jets in our computational
domain were consistent with the observed magnitudes of apex height
and cross-sectional width for average inclination of chromospheric
features. Furthermore, with an increasing misalignment between the
momentum pulse and ambient magnetic field, the simulated structures
showed a drop in the maximum apex height and length, while an increase
in cross-sectional width magnitudes. Our numerical experiments
also revealed the development of a pulse-like transverse motions
in jets along with high density edges/nodes in the direction of jet
displacement. It is postulated that dynamic kink instability might be
responsible for the observed kinematic behavior of the inclined jet
structures in the solar chromosphere.
Title: Twin Extreme Ultraviolet Waves in the Solar Corona
Authors: Zheng, Ruisheng; Wang, Bing; Zhang, Liang; Chen, Yao;
Erdélyi, Robertus
Bibcode: 2022ApJ...929L...4Z
Altcode: 2022arXiv220315513Z
Solar extreme ultraviolet (EUV) waves are spectacular propagating
disturbances with EUV enhancements in annular shapes in the solar
corona. These EUV waves carry critical information about the coronal
magnetized plasma that can shed light on the elusive physical
parameters (e.g., the magnetic field strength) by global solar
coronal magnetoseismology. EUV waves are closely associated with a
wide range of solar atmospheric eruptions, from violent flares and
coronal mass ejections to less energetic plasma jets or mini-filament
eruptions. However, the physical nature and driving mechanism of EUV
waves are still controversial. Here, we report the unique discovery
of twin EUV waves (TEWs) that were formed in a single eruption with
observations from two different perspectives. In all earlier studies,
a single eruption was associated at most with a single EUV wave. The
newly found TEWs urge us to revisit our theoretical understanding of
the underlying formation mechanism(s) of coronal EUV waves. Two distinct
scenarios of TEWs were found. In the first scenario, the two waves were
separately associated with a filament eruption and a precursor jet,
while in another scenario, the two waves were successively associated
with a filament eruption. Hence, we label these distinguished scenarios
as "fraternal TEWs" and "identical TEWs," respectively. Further,
we also suggest that impulsive lateral expansions of two distinct
groups of coronal loops are critical to the formation of TEWs in a
single eruption.
Title: Polymeric jets throw light on the origin and nature of the
forest of solar spicules
Authors: Dey, Sahel; Chatterjee, Piyali; Murthy, O. V. S. N.; Korsós,
Marianna B.; Liu, Jiajia; Nelson, Christopher J.; Erdélyi, Robertus
Bibcode: 2022NatPh..18..595D
Altcode:
Spicules are plasma jets that are observed in the dynamic interface
region between the visible solar surface and the hot corona. At any
given time, it is estimated that about 3 million spicules are present
on the Sun. We find an intriguing parallel between the simulated
spicular forest in a solar-like atmosphere and the numerous jets of
polymeric fluids when both are subjected to harmonic forcing. In a
radiative magnetohydrodynamic numerical simulation with sub-surface
convection, solar global surface oscillations are excited similarly to
those harmonic vibrations. The jets thus produced match remarkably well
with the forests of spicules detected in observations of the Sun. Taken
together, the numerical simulations of the Sun and the laboratory fluid
dynamics experiments provide insights into the mechanism underlying
the ubiquity of jets. The non-linear focusing of quasi-periodic waves
in anisotropic media of magnetized plasma as well as polymeric fluids
under gravity is sufficient to generate a forest of jets.
Title: HiRISE - High-Resolution Imaging and Spectroscopy Explorer
- Ultrahigh resolution, interferometric and external occulting
coronagraphic science
Authors: Erdélyi, Robertus; Damé, Luc; Fludra, Andrzej; Mathioudakis,
Mihalis; Amari, T.; Belucz, B.; Berrilli, F.; Bogachev, S.; Bolsée,
D.; Bothmer, V.; Brun, S.; Dewitte, S.; de Wit, T. Dudok; Faurobert,
M.; Gizon, L.; Gyenge, N.; Korsós, M. B.; Labrosse, N.; Matthews,
S.; Meftah, M.; Morgan, H.; Pallé, P.; Rochus, P.; Rozanov, E.;
Schmieder, B.; Tsinganos, K.; Verwichte, E.; Zharkov, S.; Zuccarello,
F.; Wimmer-Schweingruber, R.
Bibcode: 2022ExA...tmp...21E
Altcode:
Recent solar physics missions have shown the definite role of waves and
magnetic fields deep in the inner corona, at the chromosphere-corona
interface, where dramatic and physically dominant changes occur. HiRISE
(High Resolution Imaging and Spectroscopy Explorer), the ambitious new
generation ultra-high resolution, interferometric, and coronagraphic,
solar physics mission, proposed in response to the ESA Voyage 2050
Call, would address these issues and provide the best-ever and most
complete solar observatory, capable of ultra-high spatial, spectral,
and temporal resolution observations of the solar atmosphere, from the
photosphere to the corona, and of new insights of the solar interior
from the core to the photosphere. HiRISE, at the L1 Lagrangian
point, would provide meter class FUV imaging and spectro-imaging,
EUV and XUV imaging and spectroscopy, magnetic fields measurements,
and ambitious and comprehensive coronagraphy by a remote external
occulter (two satellites formation flying 375 m apart, with a
coronagraph on a chaser satellite). This major and state-of-the-art
payload would allow us to characterize temperatures, densities, and
velocities in the solar upper chromosphere, transition zone, and inner
corona with, in particular, 2D very high resolution multi-spectral
imaging-spectroscopy, and, direct coronal magnetic field measurement,
thus providing a unique set of tools to understand the structure and
onset of coronal heating. HiRISE's objectives are natural complements
to the Parker Solar Probe and Solar Orbiter-type missions. We present
the science case for HiRISE which will address: i) the fine structure
of the chromosphere-corona interface by 2D spectroscopy in FUV at
very high resolution; ii) coronal heating roots in the inner corona by
ambitious externally-occulted coronagraphy; iii) resolved and global
helioseismology thanks to continuity and stability of observing at the
L1 Lagrange point; and iv) solar variability and space climate with,
in addition, a global comprehensive view of UV variability.
Title: On the Differences in the Periodic Behavior of Magnetic
Helicity Flux in Flaring Active Regions with and without X-class
Events
Authors: Soós, Sz.; Korsós, M. B.; Morgan, H.; Erdélyi, R.
Bibcode: 2022ApJ...925..129S
Altcode: 2021arXiv211205933S
Observational precursors of large solar flares provide a basis
for future operational systems for forecasting. Here, we study the
evolution of the normalized emergence (EM), shearing (SH), and total
(T) magnetic helicity flux components for 14 flaring (with at least one
X-class flare) and 14 nonflaring (<M5-class flares) active regions
(ARs) using the Space-weather Helioseismic Magnetic Imager Active Region
Patches vector magnetic field data. Each of the selected ARs contain a
δ-type spot. The three helicity components of these ARs were analyzed
using wavelet analysis. Localized peaks of the wavelet power spectrum
(WPS) were identified and statistically investigated. We find that (i)
the probability density function of the identified WPS peaks for all
the EM/SH/T profiles can be fitted with a set of Gaussian functions
centered at distinct periods between ~3 and 20 hr. (ii) There is a
noticeable difference in the distribution of periods found in the EM
profiles between the flaring and nonflaring ARs, while no significant
difference is found in the SH and T profiles. (iii) In flaring ARs,
the distributions of the shorter EM/SH/T periods (<10 hr) split up
into two groups after flares, while the longer periods (>10 hr) do
not change. (iv) When the EM periodicity does not contain harmonics,
the ARs do not host a large energetic flare. (v) Finally, significant
power at long periods (~20 hr) in the T and EM components may serve
as a precursor for large energetic flares.
Title: Blobs in a Solar EUV Jet
Authors: Chen, Jie; Erdélyi, Robertus; Liu, Jiajia; Deng, Yuanyong;
Dover, Fionnlagh Mackenzie; Zhang, Qingmin; Zhang, Mei; Li, Leping;
Su, Jiangtao
Bibcode: 2022FrASS...8..238C
Altcode:
An Extreme Ultraviolet (EUV) jet that occurred around 22:30 on July 2,
2012 was observed by the Atmospheric Imaging Assembly (AIA) on-board the
Solar Dynamics Observatory (SDO). There were two phases of the jet. In
Phase 1, two blobs were observed. In Phase 2, the intensity of the jet
was almost coherent initially. One minute later, three blobs were formed
at the same time in the jet, and the width of the jet changed after
the formation of these blobs. The formation and evolution processes of
the blobs in these two phases are analyzed in this paper. The physical
parameters of the blobs are determined. The measured width of the
blobs is $0.8 - 2.3$ Mm, and the apparent velocities of the blobs are
from 59 km s$^{-1}$ to 185 km s$^{-1}$. The formation mechanism of
the blobs is likely to be tear-mode instability..
Title: Interactions Among Magnetic Bands in Extended Solar Cycles
Authors: Belucz, Bernadett; Dikpati, Mausumi; McIntosh, Scott; Erdelyi,
Robertus; Leamon, Robert
Bibcode: 2021AGUFMSH55D1875B
Altcode:
The extended solar cycle, observationally revealed from the evolutions
of ephemeral regions, X-ray and EUV brightpoints, plages, filaments and
faculae, indicates the existence of oppositely-directed double magnetic
bands at the bottom dynamo-layer in each hemisphere. The band-pairs
in the North and South hemispheres migrate towards the equator and
plausibly evolve in amplitude as the cycle progresses. By studying
the MHD interactions of these band-pairs among themselves in each
hemisphere, as well as with their opposite-hemisphere's counterparts,
we show that the cross-equatorial interactions between the low-latitude
bands (which are essentially the active cycle's bands) in the North and
South effectively start when the band-separation across the equator is
less than 30 degrees (the bands are at 15-degree latitude or lower in
the North and South). Analyzing the properties of this interaction we
show how certain changes in the energy extractions by various stresses
from the magnetic fields can lead to the start of the declining phase
of the solar cycle.
Title: Impact of Time-varying High-latitude Meridional Circulation
Cell in Polar Fields
Authors: Elek, Anett; Belucz, Bernadett; Dikpati, Mausumi; Erdelyi,
Robertus; Gyenge, Norbert; Korsos, Marianna
Bibcode: 2021AGUFMSH35A2033E
Altcode:
Solar differential rotation, undergoing (magneto)hydrodynamics in the
presence of magnetic fields, can produce cyclones and anticyclones,
i.e. anticlockwise and clockwise flows, respectively associated
with high and low pressure regions. These swirls at high-latitudes
may or may not be very tightly confined to the poles, or exactly
circumpolar either. Instead they can be obliquely rotating about the
polar axis. Nonetheless, these nonaxisymmetric swirling plasma near the
poles will appear as time-varying modulations in the mean meridional
circulation. By incorporating several plausible time-varying reverse,
high-latitude flow cells extending from pole down to about 60-degree
latitudes, we perform a number of numerical experiments to simulate
polar fields in a flux-transport dynamo model and estimate the
short-term variability in polar faculae evolutionary patterns. Our
simulations indicate that a much faster appearance and disappearance
of a strong reverse flow cell approximately with a time-scale of about
two weeks can successfully reproduce the short time-scale (~monthly
?) criss-cross type evolutions of polar faculae. Speed, profile and
time-variation of meridional flow poleward of 60-degrees latitude are
not known from observations yet. Long-awaited SOLARIS mission's data
for polar regions' flow can validate (or unvalidate) our model-results.
Title: Periodic behaviors of white-light faculae
Authors: Korsos, Marianna; Erdelyi, Robertus; Belucz, Bernadett;
Dikpati, Mausumi; Gyenge, Norbert; Elek, Anett
Bibcode: 2021AGUFMSH55D1873K
Altcode:
The solar faculae may be considered as markers of the global magnetism
of the Sun. Properties of faculae do show a correlation with the
solar activity cycle. Similar to sunspots, they possess an 1112 years
periodicity. The presenting work reports further global oscillations
of the white-light faculae with very long periods, from a couple of
months and few years. These oscillatory patterns were measured by
analyzing 18 years of observations from the Solar and Heliospheric
Observatory (SOHO) and Solar Dynamics Observatory (SDO). Using the
Debrecen facular data constructed from the two satellites measurements,
we show that the newly discovered oscillations manifest themselves at
the solar surface as swirling motions.
Title: Periodicities in X-ray solar flare occurrences and coherency
with daily mean magnetic field
Authors: Joshi, C.; Sobha, B.; Erdélyi, R.
Bibcode: 2021MNRAS.508.3604J
Altcode: 2021MNRAS.tmp.2612J
We present here the study of periodic behaviour of occurrence of
solar X-ray flares over a wide range of time-scales during four solar
cycles. We have also investigated the coherency between the value of
daily mean magnetic field of the Sun and solar flare occurrences. Data
of daily X-ray flare counts from the GOES network and daily mean
magnetic field values from Wilcox Observatory are used to carry
out the investigations reported here. Wavelet analysis method was
employed to search for and identify the periodicities and to test the
coherency between these two values parameters. Oscillatory periods
of squared daily mean magnetic field (SMF) and weighted flare count
(WFC) were found in the data. The results are consistent with and
support the conjecture of the existence of wave guide concept of the
solar upper atmosphere. For SMF, we found a common shortest period of
29 d in solar cycles 21-24 while the longer periods are different in
different cycles. The longest period found is 890 d during SC 22. In
WFC, the shortest period of 25.5 d is identified in SC 22, while the
longest one of 950 d is in SC 24.
Title: Reflection and Evolution of Torsional Alfvén Pulses in
Zero-beta Flux Tubes
Authors: Scalisi, Joseph; Ruderman, Michael S.; Erdélyi, Robertus
Bibcode: 2021ApJ...922..118S
Altcode:
We model the behavior of a torsional Alfvén pulse, assumed to
propagate through the chromosphere. Building on our existing model,
we utilize the zero-beta approximation appropriate for plasma in an
intense magnetic flux tube, e.g., a magnetic bright point. The model
is adapted to investigate the connection between these features
and chromospheric spicules. A pulse is introduced at the lower,
photospheric boundary of the tube as a magnetic shear perturbation,
and the resulting propagating Alfvén waves are reflected from an upper
boundary, representing the change in density found at the transition
region. The induced upward mass flux is followed by the reversal of
the flux that may be identified with the rising and falling behavior of
certain lower solar atmospheric jets. The ratio of the transmitted and
reflected mass flux is estimated and compared with the relative total
mass of spicules and the solar wind. An example is used to study the
properties of the pulse. We also find that the interaction between the
initial and reflected waves may create a localized flow that persists
independently from the pulse itself.
Title: Comparative case study of two methods to assess the eruptive
potential of selected active regions
Authors: Zuccarello, Francesca; Ermolli, Ilaria; Korsós, Marianna
B.; Giorgi, Fabrizio; Guglielmino, Salvo L.; Erdélyi, Robertus;
Romano, Paolo
Bibcode: 2021RAA....21..313Z
Altcode: 2022RAA....21..313Z; 2021arXiv211001272Z
Solar eruptive events, like flares and coronal mass ejections, are
characterized by the rapid release of energy that can give rise to
emission of radiation across the entire electromagnetic spectrum and to
an abrupt significant increase in the kinetic energy of particles. These
energetic phenomena can have important effects on the space weather
conditions and therefore it is necessary to understand their origin, in
particular, what is the eruptive potential of an active region (AR). In
these case studies, we compare two distinct methods that were used in
previous works to investigate the variations of some characteristic
physical parameters during the pre-flare states of flaring ARs. These
methods consider: i) the magnetic flux evolution and magnetic helicity
accumulation, and ii) the fractal and multi-fractal properties of
flux concentrations in ARs. Our comparative analysisis based on time
series of photospheric data obtained bythe Solar Dynamics Observatory
between March 2011 and June 2013. We selected two distinct samples
of ARs: one is distinguished by the occurrence of more energetic M-
and X-class flare events, that may have a rapid effect on not just the
near-Earth space, but also on the terrestrial environment; the second
is characterized by no-flares or having just a few C- and B-class
flares. We foundthat the two tested methods complement each other
in their ability to assess the eruptive potentials of ARs and could
be employed to identify ARs prone to flaring activity. Based on the
presented case study, we suggest that using a combination of different
methods may aid to identify more reliably the eruptive potentials of
ARs and help to better understand the pre-flare states.
Title: The high-energy Sun - probing the origins of particle
acceleration on our nearest star
Authors: Matthews, S. A.; Reid, H. A. S.; Baker, D.; Bloomfield, D. S.;
Browning, P. K.; Calcines, A.; Del Zanna, G.; Erdelyi, R.; Fletcher,
L.; Hannah, I. G.; Jeffrey, N.; Klein, L.; Krucker, S.; Kontar, E.;
Long, D. M.; MacKinnon, A.; Mann, G.; Mathioudakis, M.; Milligan,
R.; Nakariakov, V. M.; Pesce-Rollins, M.; Shih, A. Y.; Smith, D.;
Veronig, A.; Vilmer, N.
Bibcode: 2021ExA...tmp..135M
Altcode:
As a frequent and energetic particle accelerator, our Sun provides
us with an excellent astrophysical laboratory for understanding
the fundamental process of particle acceleration. The exploitation
of radiative diagnostics from electrons has shown that acceleration
operates on sub-second time scales in a complex magnetic environment,
where direct electric fields, wave turbulence, and shock waves all
must contribute, although precise details are severely lacking. Ions
were assumed to be accelerated in a similar manner to electrons, but
γ-ray imaging confirmed that emission sources are spatially separated
from X-ray sources, suggesting distinctly different acceleration
mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic
understanding of accelerated particle spectra and the total energy
budgets are therefore poorly constrained. Additionally, the recent
detection of relativistic ion signatures lasting many hours, without
an electron counterpart, is an enigma. We propose a single platform
to directly measure the physical conditions present in the energy
release sites and the environment in which the particles propagate and
deposit their energy. To address this fundamental issue, we set out
a suite of dedicated instruments that will probe both electrons and
ions simultaneously to observe; high (seconds) temporal resolution
photon spectra (4 keV - 150 MeV) with simultaneous imaging (1 keV -
30 MeV), polarization measurements (5-1000 keV) and high spatial and
temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray)
regimes. These instruments will observe the broad range of radiative
signatures produced in the solar atmosphere by accelerated particles.
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: Could Switchbacks Originate in the Lower Solar
Atmosphere? II. Propagation of Switchbacks in the Solar Corona
Authors: Magyar, Norbert; Utz, Dominik; Erdélyi, Robertus; Nakariakov,
Valery M.
Bibcode: 2021ApJ...914....8M
Altcode: 2021arXiv210410126M
The magnetic switchbacks observed recently by the Parker Solar Probe
have raised the question about their nature and origin. One of the
competing theories of their origin is the interchange reconnection
in the solar corona. In this scenario, switchbacks are generated at
the reconnection site between open and closed magnetic fields, and
are either advected by an upflow or propagate as waves into the solar
wind. In this paper we test the wave hypothesis, numerically modeling
the propagation of a switchback, modeled as an embedded Alfvén wave
packet of constant magnetic field magnitude, through the gravitationally
stratified solar corona with different degrees of background magnetic
field expansion. While switchbacks propagating in a uniform medium with
no gravity are relatively stable, as reported previously, we find that
gravitational stratification together with the expansion of the magnetic
field act in multiple ways to deform the switchbacks. These include WKB
effects, which depend on the degree of magnetic field expansion, and
also finite-amplitude effects, such as the symmetry breaking between
nonlinear advection and the Lorentz force. In a straight or radially
expanding magnetic field the propagating switchbacks unfold into waves
that cause minimal magnetic field deflections, while a super-radially
expanding magnetic field aids in maintaining strong deflections. Other
important effects are the mass uplift the propagating switchbacks
induce and the reconnection and drainage of plasmoids contained within
the switchbacks. In the Appendix, we examine a series of setups with
different switchback configurations and parameters, which broaden the
scope of our study.
Title: Magnetohydrodynamic Simulations of Spicular Jet Propagation
Applied to Lower Solar Atmosphere Model
Authors: Mackenzie Dover, Fionnlagh; Sharma, Rahul; Erdélyi, Robertus
Bibcode: 2021ApJ...913...19M
Altcode:
We report a series of numerical experiments for the propagation of
a momentum pulse representing a chromospheric jet, simulated using an
idealized magnetohydrodynamic model. The jet in a stratified lower solar
atmosphere is subjected to a varied initial driver (amplitude, period)
and magnetic field conditions to examine the parameter influence over
jet morphology and kinematics. The simulated jet captured key observed
spicule characteristics including maximum heights, field-aligned mass
motions/trajectories, and cross-sectional width deformations. Next, the
jet features also show a prominent bright, bulb-like apex, similar to
reported observed chromospheric jets, formed due to the higher density
of plasma and/or waves. Furthermore, the simulations highlight the
presence of not yet observed internal crisscross/knots substructures
generated by shock waves reflected within the jet structure. Therefore
we suggest verifying these predicted fine-scale structures in highly
localized lower solar atmospheric jets, e.g., in spicules or fibrils
by high-resolution observations, offered by the Daniel K. Inoyue Solar
Telescope or otherwise.
Title: Flute oscillations of cooling coronal loops with variable
cross-section
Authors: Shukhobodskaia, Daria; Shukhobodskiy, Alexander A.; Erdélyi,
Robert
Bibcode: 2021A&A...649A..36S
Altcode:
We consider fluting oscillations in a thin straight expanding magnetic
flux tube in the presence of a background flow. The tube is divided
into a core region that is wrapped in a thin transitional region,
where the damping takes place. The method of multiple scales is
used for the derivation of the system of governing equations. This
system is applicable to study both standing and propagating
waves. Furthermore, the system of equations is obtained for magnetic
tubes with a sharp boundary. An adiabatic invariant is derived using
the Wentzel-Kramer-Brillouin method for a magnetic flux tube with
slowly varying density, and the theoretical results are then used to
investigate the effect of cooling on flute oscillations of a curved
flux tube semi-circlular in shape. We have analysed numerically the
dependencies of the dimensionless amplitude for a range of values
of the expansion factor and the ratio of internal to external plasma
densities at an initial time. We find that the amplitude increases due
to cooling and is higher for a higher expansion factor. Higher values
of the wave number lead to localisation of the oscillation closer to
the boundary. Finally, we show that the higher the value of the ratio
of internal to external plasma densities, the higher the amplification
of oscillation due to cooling. Therefore, we conclude that the wave
number, density ratio, and the variation of tube expansion are all
relevant parameters in the cooling process of an oscillating flux tube.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: The Plasma Universe: A Coherent Science Theme for Voyage 2050
Authors: Verscharen, Daniel; Wicks, Robert T.; Branduardi-Raymont,
Graziella; Erdélyi, Robertus; Frontera, Filippo; Götz,
Charlotte; Guidorzi, Cristiano; Lebouteiller, Vianney; Matthews,
Sarah A.; Nicastro, Fabrizio; Rae, Iain Jonathan; Retinò,
Alessandro; Simionescu, Aurora; Soffitta, Paolo; Uttley, Phil;
Wimmer-Schweingruber, Robert F.
Bibcode: 2021FrASS...8...30V
Altcode: 2021arXiv210407983V
In review of the White Papers from the Voyage 2050 process and after
the public presentation of a number of these papers in October 2019
in Madrid, we as White Paper lead authors have identified a coherent
science theme that transcends the divisions around which the Topical
Teams are structured. This note aims to highlight this synergistic
science theme and to make the Topical Teams and the Voyage 2050 Senior
Committee aware of the wide importance of these topics and the broad
support that they have across the worldwide science community.
Title: Could Switchbacks Originate in the Lower Solar
Atmosphere? I. Formation Mechanisms of Switchbacks
Authors: Magyar, Norbert; Utz, Dominik; Erdélyi, Robertus; Nakariakov,
Valery M.
Bibcode: 2021ApJ...911...75M
Altcode: 2021arXiv210303726M
The recent rediscovery of magnetic field switchbacks or deflections
embedded in the solar wind flow by the Parker Solar Probe mission lead
to a huge interest in the modeling of the formation mechanisms and
origin of these switchbacks. Several scenarios for their generation were
put forth, ranging from lower solar atmospheric origins by reconnection,
to being a manifestation of turbulence in the solar wind, and so
on. Here we study some potential formation mechanisms of magnetic
switchbacks in the lower solar atmosphere, using three-dimensional
magnetohydrodynamic (MHD) numerical simulations. The model is that of an
intense flux tube in an open magnetic field region, aiming to represent
a magnetic bright point opening up to an open coronal magnetic field
structure, e.g., a coronal hole. The model is driven with different
plasma flows in the photosphere, such as a fast up-shooting jet,
as well as shearing flows generated by vortex motions or torsional
oscillations. In all scenarios considered, we witness the formation
of magnetic switchbacks in regions corresponding to chromospheric
heights. Therefore, photospheric plasma flows around the foot-points
of intense flux tubes appear to be suitable drivers for the formation
of magnetic switchbacks in the lower solar atmosphere. Nevertheless,
these switchbacks do not appear to be able to enter the coronal heights
of the simulation in the present model. In conclusion, based on the
presented simulations, switchbacks measured in the solar wind are
unlikely to originate from photospheric or chromospheric dynamics.
Title: Propagation of Torsional Alfvén Pulses in Zero-beta Flux Tubes
Authors: Scalisi, Joseph; Oxley, William; Ruderman, Michael S.;
Erdélyi, Robertus
Bibcode: 2021ApJ...911...39S
Altcode:
In this study, we investigate analytically the generation of
mass flux due to a torsional Alfvén pulse. We derive that the
presence of torsional Alfvén waves, which have been observed in,
e.g., photospheric magnetic bright points (MBPs), can result in
vertical plasma motions. The formation of this mass flux may even
be a viable contribution to the generation of chromospheric mass
transport, playing potential roles in the form of localized lower
solar atmospheric jets. This relationship is studied using a flux
tube model, with the waves introduced at the lower boundary of the
tube as a magnetic shear perturbation. Due to the nature of MBPs
we simplify the model by using the zero-beta approximation for the
plasma inside the tube. The analytical results are demonstrated by
an example of the type of Alfvén wave perturbation that one might
expect to observe, and comparison is made with properties of spicules
known from observations. We find that field-aligned plasma flux is
formed nonlinearly as a result of the Lorentz force generated by the
perturbations, and could be consistent with jet formation, although the
current model is not intended to determine the entire evolution of a
jet. Critical discussion of the model follows, including suggestions
for improvements and for high-resolution proposed observations in
order to constrain the driving magnetic and velocity shear.
Title: On the partial eruption of a bifurcated solar filament
structure
Authors: Monga, Aabha; Sharma, Rahul; Liu, Jiajia; Cid, Consuelo;
Uddin, Wahab; Chandra, Ramesh; Erdélyi, Robertus
Bibcode: 2021MNRAS.500..684M
Altcode: 2020MNRAS.500..684M; 2020arXiv200908619M
The partial eruption of a filament channel with bifurcated substructures
is investigated using data sets obtained from both ground-based and
space-borne facilities. Small-scale flux reconnection/cancellation
events in the region triggered the pile-up of ambient magnetic field,
observed as bright extreme ultraviolet (EUV) loops in close proximity
to the filament channel. This led to the formation of a V-shaped
cusp structure at the site of interaction between the coalesced
EUV loops and the filament channel, with the presence of distinct
plasmoid structures and associated bidirectional flows. Analysis
of imaging data from SDO/AIA further suggests vertical splitting of
the filament structure into two substructures. The perturbed upper
branch of the filament structure rose up and erupted with the onset
of an energetic GOES M1.4 flare at 04:30 UT on 2015 January 28. The
estimated twist number and squashing factor obtained from non-linear
force free-field extrapolation of the magnetic field data support the
vertical split in the filament structure with high twist in the upper
substructure. The loss in equilibrium of the upper branch due to torus
instability implies that this is a potential triggering mechanism for
the observed partial eruption.
Title: Testing and Validating Two Morphological Flare Predictors by
Logistic Regression Machine Learning
Authors: Korsós, M. B.; Erdélyi, R.; Liu, J.; Morgan, H.
Bibcode: 2021FrASS...7..113K
Altcode: 2020arXiv201208164K
Whilst the most dynamic solar active regions (ARs) are known to flare
frequently, predicting the occurrence of individual flares and their
magnitude, is very much a developing field with strong potentials for
machine learning applications. The present work is based on a method
which is developed to define numerical measures of the mixed states of
ARs with opposite polarities. The method yields compelling evidence for
the assumed connection between the level of mixed states of a given AR
and the level of the solar eruptive probability of this AR by employing
two morphological parameters: (i) the separation parameter $S_{l-f}$ and
(ii) the sum of the horizontal magnetic gradient $G_{S}$. In this work,
we study the efficiency of $S_{l-f}$ and $G_{S}$ as flare predictors
on a representative sample of ARs, based on the SOHO/MDI-Debrecen Data
(SDD) and the SDO/HMI - Debrecen Data (HMIDD) sunspot catalogues. In
particular, we investigate about 1000 ARs in order to test and validate
the joint prediction capabilities of the two morphological parameters
by applying the logistic regression machine learning method. Here,
we confirm that the two parameters with their threshold values are,
when applied together, good complementary predictors. Furthermore,
the prediction probability of these predictor parameters is given at
least 70\% a day before.
Title: Magnetoacoustic Waves in a Magnetic Slab Embedded in an
Asymmetric Magnetic Environment. III. Applications to the Solar
Atmosphere
Authors: Zsámberger, Noémi Kinga; Erdélyi, Róbert
Bibcode: 2021ApJ...906..122Z
Altcode:
Analytical and numerical modeling of the behavior of magnetohydrodynamic
waves in various magnetic geometries can offer a valuable
contribution to the field of solar magnetoseismology. Based on
analytical results from our previous studies, here we illustrate a few
solar applications of these findings concerning the propagation of
magnetoacoustic waves in a magnetic slab embedded in an asymmetric
environment. Bearing in mind the simplifying assumptions made,
this asymmetric model incorporating external magnetic fields can
be used to describe a wide variety of multilayered solar features,
some of which are observable and have already been studied in solar
structures. Specific potential applications are: prominences,
polar plumes and their environment, magnetic bright points, and
light bridges, as well as adjacent large-scale layers in the solar
atmosphere (e.g., the photosphere—interface region—corona triad,
or the chromosphere—transition region—corona group). In these
individual cases, the appropriate dispersion relations are derived
and solved. The obtained wave propagation solutions may serve (i) not
just as impetus to be confirmed by high-resolution observations but
(ii) also to be exploited for further diagnostic purposes by solar
magnetoseismology of these frequently studied magnetic structures.
Title: Significance of Cooling Effect On Comprehension of Kink
Oscillations of Coronal Loops
Authors: Shukhobodskaia, Daria; Shukhobodskiy, Alexander A.; Nelson,
Chris J.; Ruderman, Michael S.; Erdélyi, Robert
Bibcode: 2021FrASS...7..106S
Altcode:
Kink oscillations of coronal loops have been widely studied, both
observationally and theoretically, over the past few decades. It
has been shown that the majority of observed driven coronal loop
oscillations appear to damp with either exponential or Gaussian
profiles and a range of mechanisms have been proposed to account for
this. However, some driven oscillations seem to evolve in manners which
cannot be modelled with purely Gaussian or exponential profiles, with
amplification of oscillations even being observed on occasions. Recent
research has shown that incorporating the combined effects of coronal
loop expansion, resonant absorption, and cooling can cause significant
deviations from Gaussian and exponential profiles in damping profiles,
potentially explaining increases in oscillation amplitude through time
in some cases. In this article, we analyse 10 driven kink oscillations
in coronal loops to further investigate the ability of expansion and
cooling to explain complex damping profiles. Our results do not rely
on fitting a periodicity to the oscillations meaning complexities in
both temporal (period changes) and spatial (amplitude changes) can be
accounted for in an elegant and simple way. Furthermore, this approach
could also allow us to infer some important diagnostic information
(such as, for example, the density ratio at the loop foot-points)
from the oscillation profile alone, without detailed measurements
of the loop and without complex numerical methods. Our results imply
the existence of correlations between the density ratio at the loop
foot-points and the amplitudes and periods of the oscillations. Finally,
we compare our results to previous models, namely purely Gaussian and
purely exponential damping profiles, through the calculation of chi^2
values, finding the inclusion of cooling can produce better fits in
some cases. The current study indicates that thermal evolution should
be included in kink-mode oscillation models in the future to help
us to better understand oscillations that are not purely Gaussian
or exponential.
Title: Reliability of AI-generated magnetograms from only EUV images
Authors: Liu, Jiajia; Wang, Yimin; Huang, Xin; Korsós, Marianna B.;
Jiang, Ye; Wang, Yuming; Erdélyi, Robert
Bibcode: 2021NatAs...5..108L
Altcode:
No abstract at ADS
Title: Torsional oscillations within a magnetic pore in the solar
photosphere
Authors: Stangalini, Marco; Erdélyi, Robertus; Boocock, Callum;
Tsiklauri, David; Nelson, Christopher J.; Del Moro, Dario; Berrilli,
Francesco; Korsós, Marianna B.
Bibcode: 2021NatAs...5..691S
Altcode: 2021NatAs.tmp...82S
Alfvén waves have proven to be important in a range of physical
systems due to their ability to transport non-thermal energy over long
distances in a magnetized plasma. This property is of specific interest
in solar physics, where the extreme heating of the atmosphere of the
Sun remains unexplained. In an inhomogeneous plasma such as a flux
tube in the solar atmosphere, they manifest as incompressible torsional
perturbations. However, despite evidence in the upper atmosphere, they
have not been directly observed in the photosphere. Here, we report the
detection of antiphase incompressible torsional oscillations observed in
a magnetic pore in the photosphere by the Interferometric Bidimensional
Spectropolarimeter. State-of-the-art numerical simulations suggest that
a kink mode is a possible excitation mechanism of these waves. The
excitation of torsional waves in photospheric magnetic structures
can substantially contribute to the energy transport in the solar
atmosphere and the acceleration of the solar wind, especially if such
signatures will be ubiquitously detected in even smaller structures
with the forthcoming next generation of solar telescopes.
Title: Formation of Chromospheric Spicules in Magnetic Bright Points:
An Analytical Approach Using Cartesian Slab Geometry
Authors: Oxley, William; Scalisi, Joseph; Ruderman, Michael S.;
Erdélyi, Róbert
Bibcode: 2020ApJ...905..168O
Altcode:
We aim to provide insight into chromospheric spicules by suggesting
a new formation mechanism. A magnetic field boundary condition is
imposed, generating an Alfvén wave that shears a magnetic slab and
propagates up the slab. The resulting Lorentz force accelerates material
vertically, potentially nonlinearly driving a jet-like feature. This
formation mechanism is applied to take place in a magnetic bright
point embedded in the photosphere, providing motivation to use the
simplifying assumption of a zero-β plasma. After deriving an analytical
expression describing the vertical mass flux that constitutes the
spicular jet, further understanding is gained by examining a model
example of a magnetic field boundary condition in terms of standard
functions. By visualizing the vertical mass flux through 3D plots,
we demonstrate that the jet properties capture the observed properties
of chromospheric spicules during their formation. This vindicates the
model and simplifying assumptions used. Although we do not provide
insight into the full evolution of a spicule, we show that the role of
Alfvén waves triggered by shear in fact could be a viable formation
mechanism for at least some chromospheric spicules. Consequently,
we provide a starting point for further studies of this formation
mechanism, which will lead to a greater understanding of the vast
variety of chromospheric jets.
Title: Signatures of Cross-sectional Width Modulation in Solar
Spicules due to Field-aligned Flows
Authors: Dover, Fionnlagh Mackenzie; Sharma, Rahul; Korsós, Marianna
B.; Erdélyi, Robertus
Bibcode: 2020ApJ...905...72D
Altcode: 2020ApJ...905...72M
We report the first observational detection of frequency modulation in
the cross-sectional width of spicule structures due to field-aligned
plasma flows. Cross-sectional width variations were estimated for
the least superimposed off-limb spicules observed in high-resolution
Hα imaging spectroscopy data. Analysis of estimated cross-sectional
widths suggest periodic oscillations, concurrent with 2D numerical
modeling for a jet structure in a stratified solar atmosphere. Spectral
analysis for both observed and simulated cross-sectional widths indicate
frequency modulation as noticeable shifts in estimated periodicities
during rise and fall phases of field-aligned plasma flows in the
jet structure. Furthermore, the presence of the first overtone in a
dynamic/spicular waveguide is also evident in both the observed and
the simulated jet structures. These harmonics can be an important
tool for future chromospheric magnetoseismology investigations and
applications to dynamic waveguides (like spicules).
Title: MHD of double-bands representing extended solar cycle
Authors: Belucz, B.; Dikpati, M.; McIntosh, S. W.; Erdelyi, R.
Bibcode: 2020AGUFMSH0020020B
Altcode:
Along with the "butterfly diagram" of sunspots, combined observational
studies of ephemeral active regions, X-ray and EUV brightpoints, plage,
filaments, facule and prominences demonstrate a pattern, which is known
as the Extended Solar Cycle (ESC). This pattern indicates the wings of
the sunspot butterfly could be extended to much higher latitudes (about
60 degrees) and to earlier time than the start of a sunspot cycle,
hence creating a strong overlap between cycles, meaning that, during the
ongoing cycle's activity near 30-degrees latitude in each hemisphere,
the next cycle is starting at around 60-degrees. By representing these
epochs by oppositely-directed double magnetic bands in each hemisphere,
we compute the eigen modes for MHD Rossby waves at the base of the
convection zone and study how the properties of unstable MHD Rossby
waves change as these band-pairs migrate equatorward. We find that
the low-latitude band itself drives the major dynamics as the solar
activity progresses from 35 to 20 degrees. When the activity proceeds
further equatorward of 20 degrees, the next cycle's band from higher
latitudes starts taking over to drive the majority of the activity
features by interacting with the low-latitude band.
Title: Standing MHD Waves in a Magnetic Slab Embedded in an Asymmetric
Magnetic Plasma Environment: Surface Waves
Authors: Oxley, William; Zsámberger, Noémi Kinga; Erdélyi, Róbert
Bibcode: 2020ApJ...898...19O
Altcode: 2020arXiv200605425O
Building on a previous study that analyzed standing surface waves in
magnetic slabs embedded in a non-magnetic external environment, in
this study the model is generalized and external magnetic fields
are added. The slab is assumed to be thin, with weak magnetic
asymmetry. The frequencies of the standing harmonic modes are derived
to leading order in the small quantities representing the thin slab
width and the weak asymmetry. It is found that the frequencies are
more sensitive to changes to the width of the slab than changes in
the magnetic asymmetry. The frequency ratio of the first harmonic to
the fundamental mode is derived, along with the amplitude difference
between the two sides of the slab, as these may be observable quantities
that can be compared with observational results and applied to carry
out solar magnetoseismology.
Title: Differences in Periodic Magnetic Helicity Injection Behavior
between Flaring and Non-flaring Active Regions: Case Study
Authors: Korsós, M. B.; Romano, P.; Morgan, H.; Ye, Y.; Erdélyi,
R.; Zuccarello, F.
Bibcode: 2020ApJ...897L..23K
Altcode: 2020arXiv200607659K
The evolution of magnetic helicity has a close relationship with solar
eruptions and is of interest as a predictive diagnostic. In this case
study, we analyze the evolution of the normalized emergence, shearing,
and total magnetic helicity components in the case of three flaring and
three non-flaring active regions (ARs) using Spaceweather Helioseismic
Magnetic Imager Active Region Patches vector magnetic field data. The
evolution of the three magnetic helicity components is analyzed with
wavelet transforms, revealing significant common periodicities of
the normalized emergence, shearing, and total helicity fluxes before
flares in the flaring ARs. The three non-flaring ARs do not show such
common periodic behavior. This case study suggests that the presence
of significant periodicities in the power spectrum of magnetic helicity
components could serve as a valuable precursor for flares.
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: Wave amplitude modulation in fan loops as observed by AIA/SDO
Authors: Sharma, Aishawnnya; Tripathi, Durgesh; Erdélyi, Robertus;
Gupta, Girjesh R.; Ahmed, Gazi A.
Bibcode: 2020A&A...638A...6S
Altcode: 2020arXiv200405797S
Aims: We perform a detailed analysis to understand the evolution
and dynamics of propagating intensity disturbances observed in a fan
loop system.
Methods: We performed multiwavelength time-distance
analysis of a fan loop system anchored in an isolated sunspot region
(AR 12553). The active region was observed by the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory. We measured
the phase speeds of the propagating intensity disturbances by
employing cross-correlation analysis, and by obtaining the slopes
in xt-plots. We obtained original and detrended light curves at
different heights of the time-distance maps and characterised them
by performing Fourier and wavelet analysis, respectively.
Results: The time-distance maps reveal clear propagation of intensity
oscillations in all the coronal extreme ultraviolet (EUV) channels
except AIA 94 and 335 Å. We determine the nature of the intensity
disturbances as slow magneto-acoustic waves by measuring their phase
speeds. The time-distance maps, as well as the detrended light curves,
show an increase and decrease in the amplitude of propagating 3 min
oscillations over time. The amplitude variations appear most prominently
in AIA 171 Å, though other EUV channels also show such signatures. The
Fourier power spectrum yields the presence of significant powers with
several nearby frequencies in the range of 2-3 min (5-8 mHz), along
with many other smaller peaks between 2-4 min. Wavelet analysis shows
an increase and decrease of oscillating power around 3 min simultaneous
to the amplitude variations. We obtain the modulation period to be in
the range of 20-30 min.
Conclusions: Our results provide the
viability of occurrence of phenomenon like "Beat" among the nearby
frequencies giving rise to the observed amplitude modulation. However,
we cannot at this stage rule out the possibility that the modulation
may be driven by variability in an underlying unknown source.
Title: Magnetoacoustic Waves in a Magnetic Slab Embedded in an
Asymmetric Magnetic Environment. II. Thin and Wide Slabs, Hot and
Cold Plasmas
Authors: Zsámberger, Noémi Kinga; Erdélyi, Róbert
Bibcode: 2020ApJ...894..123Z
Altcode:
Wave propagation in magnetically structured atmospheres is a thoroughly
studied, yet practically inexhaustible, well of investigations in
the field of solar magneto-seismology. A simple but powerful example
is the examination of wave behavior in a magnetic slab. Our previous
study used an analytical approach to derive the general dispersion
relation for magnetoacoustic waves in a magnetic slab of homogeneous
plasma, which was enclosed in an asymmetric magnetic environment. In
the present study, we focus on the analysis of wave propagation in
various limiting cases applicable to solar and space plasma physics or
astrophysics. The thin- and wide-slab approximations, as well as the
limits of low and high plasma β values, are considered. Utilizing
the fact that in a weakly asymmetric slab the dispersion relation
can be decoupled, the behavior of quasi-sausage and quasi-kink modes
is studied in further analytical and numerical detail, and their
avoided crossings are described. The results highlight how asymmetry
influences the wave properties, e.g., the phase speed of eigenmodes,
depending on the ratios of external to internal densities and magnetic
fields on the two sides. Notably, the phase speeds of surface modes
will converge to different values for the quasi-sausage and quasi-kink
modes in the wide-slab limit, and cutoff frequencies are introduced with
respect to both surface and body modes, in thin as well as wide slabs,
beyond which the solutions become leaky. These obtained properties
of MHD wave behavior could be measured with suitable high-resolution
instruments in the future.
Title: Formation of Two Homologous Transequatorial Loops
Authors: Chen, Jie; Pevtsov, Alexei A.; Su, Jiangtao; Erdélyi,
Robertus; Deng, Yuanyong; Yang, Shangbin; Song, Yongliang
Bibcode: 2020SoPh..295...59C
Altcode:
The formation mechanism of two homologous transequatorial loops (TLs)
of July 7-8, 1999 (SOL1999-07-07) is studied. The TLs connected active
region AR 8614 from the northern hemisphere to AR 8626 in the southern
hemisphere. The first TL appeared as a distinct structure at 12:49 UT
on July 7, the second TL appeared at 06:21 UT, on July 8. Important
results are obtained in this analysis: (i) The configuration of the
two TLs is similar in X-rays. (ii) The sizes of the two active regions
related to the TLs increased before and during the formation of the
two TLs, this induced the expansion of their coronal loops. (iii)
Both TLs formed globally on a time scale shorter than 110 min (time
resolution of observations). (iv) An X-shaped coronal structure was
observed. This observational evidence suggests that the two TLs formed
by the same physical mechanism, magnetic reconnection, between the
two expanding magnetic configurations of the two ARs.
Title: Magneto-acoustic waves in a magnetic slab embedded in an
asymmetric magnetic environment II: Thin and wide slabs, hot and
cold plasmas
Authors: Kinga Zsámberger, Noémi; Erdélyi, Róbert
Bibcode: 2020arXiv200405584K
Altcode:
Wave propagation in magnetically structured atmospheres is a thoroughly
studied, yet practically inexhaustible well of investigations in the
field of solar magneto-seismology. A simple but powerful example is the
examination of wave behaviour in a magnetic slab. Our previous study
(Zsámberger, Allcock and Erdélyi, Astrophys. J., 853, p. 136, 2018)
used an analytical approach to derive the general dispersion relation
for magneto-acoustic waves in a magnetic slab of homogeneous plasma,
which was enclosed in an asymmetric magnetic environment. In the present
study, we focus on the analysis of wave propagation in various limiting
cases applicable to solar and space plasma or astrophysics. The thin-
and wide-slab approximations, as well as the limits of low and high
plasma-beta values are considered. Utilising the fact that in a
weakly asymmetric slab, the dispersion relation can be decoupled,
the behaviour of quasi-sausage and quasi-kink modes is studied in
further analytical and numerical detail, and their avoided crossings
are described. The results highlight how the asymmetry influences the
wave properties, e.g. the phase speed of eigenmodes, depending on the
ratios of external-to-internal densities and magnetic fields on the
two sides. Notably, the phase speeds of surface modes will converge
to different values for quasi-sausage and quasi-kink modes in the
wide-slab limit, and cut-off frequencies are introduced with respect
to both surface and body modes, in thin as well as wide slabs, beyond
which the solutions become leaky. These obtained properties of MHD wave
behaviour could be measured with suitable high-resolution instruments
in the future.
Title: Standing MHD Waves in a Magnetic Slab Embedded in an Asymmetric
Plasma Environment: Slow Surface Waves
Authors: Oxley, William; Zsámberger, Noémi Kinga; Erdélyi, Róbert
Bibcode: 2020ApJ...890..109O
Altcode:
The field of solar magnetoseismology (SMS) is heavily reliant upon our
understanding of magnetohydrodynamic (MHD) waves that occur in many
solar features. Building on previous studies of propagating MHD waves
in a magnetic slab embedded in a nonmagnetic asymmetric environment, in
this study we assume a line-tying boundary condition and use analytical
techniques to derive the dispersion relation for linear standing MHD
oscillations. The slab is first assumed thin, with arbitrary asymmetry,
in order to derive the frequencies of the standing harmonic modes for
both slow quasi-sausage and slow quasi-kink waves. Besides this, the
asymmetry is assumed to be weak in order to determine the frequency
dependence on the width of the slab and the asymmetry of the system,
to leading order. For both the quasi-sausage and quasi-kink modes,
the derived eigenfrequencies show that the dependence on the asymmetry
in the system is much weaker than the dependence on the width of the
slab. Using the eigenfrequencies, other observable quantities are
derived (such as, e.g., the frequency ratio) providing an opportunity
to use SMS to infer background diagnostics of the system.
Title: Magnetic Rayleigh-Taylor instability at a contact discontinuity
with an oblique magnetic field
Authors: Vickers, E.; Ballai, I.; Erdélyi, R.
Bibcode: 2020A&A...634A..96V
Altcode: 2019arXiv191112734V
Aims: We investigate the nature of the magnetic Rayleigh-Taylor
instability at a density interface that is permeated by an oblique
homogeneous magnetic field in an incompressible limit.
Methods:
Using the system of linearised ideal incompressible magnetohydrodynamics
equations, we derive the dispersion relation for perturbations of the
contact discontinuity by imposing the necessary continuity conditions
at the interface. The imaginary part of the frequency describes the
growth rate of waves due to instability. The growth rate of waves
is studied by numerically solving the dispersion relation.
Results: The critical wavenumber at which waves become unstable,
which is present for a parallel magnetic field, disappears because the
magnetic field is inclined. Instead, waves are shown to be unstable
for all wavenumbers. Theoretical results are applied to diagnose the
structure of the magnetic field in prominence threads. When we apply our
theoretical results to observed waves in prominence plumes, we obtain
a wide range of field inclination angles, from 0.5° up to 30°. These
results highlight the diagnostic possibilities that our study offers.
Title: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
Bibcode: 2019arXiv191208650S
Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
Title: Co-spatial velocity and magnetic swirls in the simulated
solar photosphere
Authors: Liu, Jiajia; Carlsson, Mats; Nelson, Chris J.; Erdélyi,
Robert
Bibcode: 2019A&A...632A..97L
Altcode: 2019arXiv191110923L
Context. Velocity or intensity swirls have now been shown to be
widely present throughout the photosphere and chromosphere. It has
been suggested that these events could contribute to the heating
of the upper solar atmosphere, via exciting Alfvén pulses, which
could carry significant amounts of energy. However, the conjectured
necessary physical conditions for their excitation, that the magnetic
field rotates co-spatially and co-temporally with the velocity field,
has not been verified.
Aims: We aim to understand whether
photospheric velocity swirls exist co-spatially and co-temporally with
photospheric magnetic swirls, in order to demonstrate the link between
swirls and pulses.
Methods: The automated swirl detection
algorithm (ASDA) is applied to the photospheric horizontal velocity
and vertical magnetic fields obtained from a series of realistic
numerical simulations using the radiative magnetohydrodynamics (RMHD)
code Bifrost. The spatial relationship between the detected velocity
and magnetic swirls is further investigated via a well-defined
correlation index (CI) study.
Results: On average, there are
∼63 short-lived photospheric velocity swirls (with lifetimes mostly
less than 20 s, and average radius of ∼37 km and rotating speeds of
∼2.5 km s-1) detected in a field of view (FOV) of 6 ×
6 Mm-2, implying a total population of velocity swirls of
∼1.06 × 107 in the solar photosphere. More than 80% of the
detected velocity swirls are found to be accompanied by local magnetic
concentrations in intergranular lanes. On average, ∼71% of the
detected velocity swirls have been found to co-exist with photospheric
magnetic swirls with the same rotating direction.
Conclusions:
The co-temporal and co-spatial rotation in the photospheric velocity
and magnetic fields provide evidence that the conjectured condition for
the excitation of Alfvén pulses by photospheric swirls is fulfilled.
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi;
Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu;
Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie
Bibcode: 2019Sci...366..890S
Altcode: 2020arXiv200602571S
Spicules are rapidly evolving fine-scale jets of magnetized plasma in
the solar chromosphere. It remains unclear how these prevalent jets
originate from the solar surface and what role they play in heating
the solar atmosphere. Using the Goode Solar Telescope at the Big Bear
Solar Observatory, we observed spicules emerging within minutes of the
appearance of opposite-polarity magnetic flux around dominant-polarity
magnetic field concentrations. Data from the Solar Dynamics Observatory
showed subsequent heating of the adjacent corona. The dynamic
interaction of magnetic fields (likely due to magnetic reconnection)
in the partially ionized lower solar atmosphere appears to generate
these spicules and heat the upper solar atmosphere.
Title: Spatially Resolved Signatures of Bidirectional Flows Observed
in Inverted-Y Shaped Jets
Authors: Nelson, C. J.; Freij, N.; Bennett, S.; Erdélyi, R.;
Mathioudakis, M.
Bibcode: 2019ApJ...883..115N
Altcode: 2019arXiv190805132N
Numerous apparent signatures of magnetic reconnection have been
reported in the solar photosphere, including inverted-Y shaped jets. The
reconnection at these sites is expected to cause localized bidirectional
flows and extended shock waves; however, these signatures are rarely
observed as extremely high spatial-resolution data are required. Here,
we use Hα imaging data sampled by the Swedish Solar Telescope’s CRisp
Imaging SpectroPolarimeter to investigate whether bidirectional flows
can be detected within inverted-Y shaped jets near the solar limb. These
jets are apparent in the Hα line wings, while no signature of either
jet is observed in the Hα line core, implying reconnection took place
below the chromospheric canopy. Asymmetries in the Hα line profiles
along the legs of the jets indicate the presence of bidirectional flows,
consistent with cartoon models of reconnection in chromospheric anemone
jets. These asymmetries are present for over two minutes, longer than
the lifetimes of Rapid Blue Excursions, and beyond ±1 Å into the wings
of the line indicating that flows within the inverted-Y shaped jets
are responsible for the imbalance in the profiles, rather than motions
in the foreground. Additionally, surges form following the occurrence
of the inverted-Y shaped jets. This surge formation is consistent with
models, which suggests such events could be caused by the propagation
of shock waves from reconnection sites in the photosphere to the
upper atmosphere. Overall, our results provide evidence that magnetic
reconnection in the photosphere can cause bidirectional flows within
inverted-Y shaped jets and could be the driver of surges.
Title: Modelling 3D magnetic networks in a realistic solar atmosphere
Authors: Gent, Frederick A.; Snow, Ben; Fedun, Viktor; Erdélyi,
Robertus
Bibcode: 2019MNRAS.489...28G
Altcode: 2019arXiv190411421G
The magnetic network extending from the photosphere (solar radius ≃
R⊙) to the lower corona ( R_⊙ +10 Mm) plays an important
role in the heating mechanisms of the solar atmosphere. Here we develop
further the models of the authors with realistic open magnetic flux
tubes, in order to model more complicated configurations. Closed
magnetic loops and combinations of closed and open magnetic flux
tubes are modelled. These are embedded within a stratified atmosphere,
derived from observationally motivated semi-empirical and data-driven
models subject to solar gravity and capable of spanning from the
photosphere up into the chromosphere and lower corona. Constructing
a magnetic field comprising self-similar magnetic flux tubes, an
analytic solution for the kinetic pressure and plasma density is
derived. Combining flux tubes of opposite polarity, it is possible to
create a steady background magnetic field configuration, modelling
a solar atmosphere exhibiting realistic stratification. The result
can be applied to the Solar and Heliospheric Observatory Michelson
Doppler Imager (SOHO/MDI), Solar Dynamics Observatory Helioseismic
and Magnetic Imager (SDO/HMI) and other magnetograms from the solar
surface, for which photospheric motions can be simulated to explore
the mechanism of energy transport. We demonstrate this powerful and
versatile method with an application to HMI data.
Title: Evidence of ubiquitous Alfvén pulses transporting energy
from the photosphere to the upper chromosphere
Authors: Liu, Jiajia; Nelson, Chris J.; Snow, Ben; Wang, Yuming;
Erdélyi, Robert
Bibcode: 2019NatCo..10.3504L
Altcode:
The multi-million degree temperature increase from the middle to
the upper solar atmosphere is one of the most fascinating puzzles
in plasma-astrophysics. Although magnetic waves might transport
enough energy from the photosphere to heat up the local chromosphere
and corona, observationally validating their ubiquity has proved
challenging. Here, we show observational evidence that ubiquitous
Alfvén pulses are excited by prevalent intensity swirls in the
solar photosphere. Correlation analysis between swirls detected at
different heights in the solar atmosphere, together with realistic
numerical simulations, show that these Alfvén pulses propagate upwards
and reach chromospheric layers. We found that Alfvén pulses carry
sufficient energy flux (1.9 to 7.7 kW m-2) to balance the
local upper chromospheric energy losses ( 0.1 kW m-2) in
quiet regions. Whether this wave energy flux is actually dissipated
in the chromosphere and can lead to heating that balances the losses
is still an open question.
Title: CME Arrival Time Prediction Using Convolutional Neural Network
Authors: Wang, Yimin; Liu, Jiajia; Jiang, Ye; Erdélyi, Robert
Bibcode: 2019ApJ...881...15W
Altcode:
Fast and accurate prediction of the arrival time of coronal mass
ejections (CMEs) at Earth is vital to minimize hazards caused
by CMEs. In this paper, we use a deep-learning framework, i.e., a
convolutional neural network (CNN) regression model, to analyze transit
times from the Sun to Earth of 223 geoeffective CME events observed in
the past 30 yr. 90% of them were used to build the prediction model,
and the rest 10% have been used for test purpose. Unlike previous
studies on this topic, our proposed CNN regression model does not
require manually selected features for model training, it does not
need time spent on feature collection, and it can deliver predictions
without deeper expert knowledge. The only input to our CNN regression
model is the instances of the white-light observations of CMEs. The
mean absolute error of the constructed CNN regression model is about
12.4 hr, which is comparable to the average performance of the previous
studies on this subject. As more CME data become available, we expect
the CNN regression model will reveal better results.
Title: Magnetohydrodynamic waves in multi-layered asymmetric
waveguides: solar magneto-seismology theory and application
Authors: Allcock, Matthew; Shukhobodskaia, Daria; Zsámberger, Noémi
Kinga; Erdélyi, Robert
Bibcode: 2019FrASS...6...48A
Altcode:
Diagnosing the solar atmospheric plasma is one of the major challenges
in solar physics. Magnetohydrodynamic (MHD) waves, by means of applying
the powerful concept of solar magneto-seismology (SMS), provide a tool
to obtain diagnostic insight into the magnetised solar plasma in MHD
waveguides. This paper provides a road-map of simple but applicable
models of solar atmospheric waveguides in the framework of Cartesian
geometry. We focus on exploiting the diagnostic potential of waveguide
asymmetry and consider the effects of steady flow. In particular,
the dispersion relation describing linear MHD wave propagation
along a multi-layered MHD waveguide is derived. Aiming at lower
solar atmospheric applications of SMS, the special case of a single
magnetic slab embedded in an asymmetric magnetised plasma environment
is revisited. As a proof of concept, the Amplitude Ratio Method is used
to make a seismological estimate of the local Alfvén speed in several
chromospheric fibrils that exhibit asymmetric oscillations. Absolute
ratios of boundary oscillations between 1.29 and 3.42 are detected
and, despite the significant errors expected, the local Alfvén speed
estimates agree with previously derived estimates from magnetic field
extrapolations. Finally, the effects of asymmetric shear flows present
in these slab MHD waveguides are considered as a suitable model of
Kelvin-Helmholtz instability initiation that is applicable, for example,
to coronal mass ejection flanks.
Title: The Effect Of Cooling On Driven Kink Oscillations Of Coronal
Loops
Authors: Nelson, Chris J.; Shukhobodskiy, Alexander A.; Erdélyi,
Robertus; Mathioudakis, Mihalis
Bibcode: 2019FrASS...6...45N
Altcode: 2019arXiv190513137N
Ever since their detection two decades ago, standing kink oscillations
in coronal loops have been extensively studied both observationally
and theoretically. Almost all driven coronal loop oscillations
(e.g., by flares) are observed to damp through time often with
Gaussian or exponential profiles. Intriguingly, however, it has
been shown theoretically that the amplitudes of some oscillations
could be modified from Gaussian or exponential profiles if cooling
is present in the coronal loop systems. Indeed, in some cases the
oscillation amplitude can even increase through time. In this article,
we analyse a flare-driven coronal loop oscillation observed by the
Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA)
in order to investigate whether models of cooling can explain the
amplitude profile of the oscillation and whether hints of cooling can
be found in the intensity evolution of several SDO/AIA filters. During
the oscillation of this loop system, the kink mode amplitude appears to
differ from a typical Gaussian or exponential profile with some hints
being present that the amplitude increases. The application of cooling
coronal loop modelling allowed us to estimate the density ratio between
the loop and the background plasma, with a ratio of between 2.05-2.35
being returned. Overall, our results indicate that consideration of
the thermal evolution of coronal loop systems can allow us to better
describe oscillations in these structures and return more accurate
estimates of the physical properties of the loops (e.g., density,
scale height, magnetic field strength).
Title: How Many Twists Do Solar Coronal Jets Release?
Authors: Liu, Jiajia; Wang, Yuming; Erdélyi, Robert
Bibcode: 2019FrASS...6...44L
Altcode: 2019arXiv190509576L
Highly twisted magnetic flux ropes, with finite length, are subject to
kink instabilities, and could lead to a number of eruptive phenomena in
the solar atmosphere, including flares, coronal mass ejections (CMEs)
and coronal jets. The kink instability threshold, which is the maximum
twist a kink-stable magnetic flux rope could contain, has been widely
studied in analytical models and numerical simulations, but still needs
to be examined by observations. In this article, we will study twists
released by 30 off-limb rotational solar coronal jets, and compare the
observational findings with theoretical kink instability thresholds. We
have found that: 1) the number of events with more twist release becomes
less; 2) each of the studied jets has released a twist number of at
least 1.3 turns (a twist angle of 2.6π); and 3) the size of a jet is
highly related to its twist pitch instead of twist number. Our results
suggest that the kink instability threshold in the solar atmosphere
should not be a constant. The found lower limit of twist number of 1.3
turns should be merely a necessary but not a sufficient condition for
a finite solar magnetic flux rope to become kink unstable.
Title: Automated Swirl Detection Algorithm (ASDA) and Its Application
to Simulation and Observational Data
Authors: Liu, Jiajia; Nelson, Chris J.; Erdélyi, Robertus
Bibcode: 2019ApJ...872...22L
Altcode: 2018arXiv180402931L
Swirling motions in the solar atmosphere have been widely observed in
recent years and suggested to play a key role in channeling energy
from the photosphere into the corona. Here, we present a newly
developed Automated Swirl Detection Algorithm (ASDA) and discuss
its applications. ASDA is found to be very proficient at detecting
swirls in a variety of synthetic data with various levels of noise,
implying our subsequent scientific results are astute. Applying ASDA
to photospheric observations with a pixel size of 39.2 km sampled by
the Solar Optical Telescope on board Hinode suggests a total number
of 1.62 × 105 swirls in the photosphere, with an average
radius and rotating speed of ∼290 km and <1.0 km s-1,
respectively. Comparisons between swirls detected in Bifrost numerical
MHD simulations and both ground-based and space-borne observations
suggest that (1) the spatial resolution of data plays a vital role in
the total number and radii of swirls detected, and (2) noise introduced
by seeing effects could decrease the detection rate of swirls, but has
no significant influences in determining their inferred properties. All
results have shown that there is no significant difference in the
analyzed properties between counterclockwise or clockwise rotating
swirls. About 70% of swirls are located in intergranular lanes. Most
of the swirls have lifetimes of less than twice the cadences, meaning
future research should aim to use data with much higher cadences than
6 s. In the conclusions, we propose some promising future research
applications where ASDA may provide useful insight.
Title: Investigation of pre-flare dynamics using the weighted
horizontal magnetic gradient method: From small to major flare classes
Authors: Korsós, Marianna B.; Yang, Shuhong; Erdélyi, Robertus
Bibcode: 2019JSWSC...9A...6K
Altcode: 2019arXiv190105984K
There is a wide range of eruptions in the solar atmosphere which
contribute to space weather, including the major explosions of radiation
known as flares. To examine pre-event behavior in δ-spot regions, we
use here a method based on the weighted horizontal gradient of magnetic
field (WGM), defined between opposite polarity umbrae at
the polarity inversion line of active regions (ARs) as measured using
from the Debrecen Heliophysical Observatory catalogues. In this work,
we extend the previous analysis of high-energy flares to include
both medium (M) and low-energy (C and B) flares. First, we found a
logarithmic relationship between the log value of highest flare class
intensity (from B- to X-class) in a δ-spot AR and the maximum value
of WGM of the 127 ARs investigated. We confirm a trend
in the convergence-divergence phase of the barycenters of opposite
polarities in the vicinity of the polarity inversion line. The extended
sample, (i) affirms the linear connection between the durations of the
convergence-divergence phases of barycenters of opposite polarities in
δ-spot regions up to flare occurrence and (ii) provides a geometric
constraint for the location of flare emission around the polarity
inversion line. The method provides a tool to possibly estimate the
likelihood of a subsequent flare of the same or larger energy.
Title: An Analytical Model of the Kelvin-Helmholtz Instability of
Transverse Coronal Loop Oscillations
Authors: Barbulescu, Mihai; Ruderman, Michael S.; Van Doorsselaere,
Tom; Erdélyi, Robert
Bibcode: 2019ApJ...870..108B
Altcode: 2019arXiv190106132B
Recent numerical simulations have demonstrated that transverse
coronal loop oscillations are susceptible to the Kelvin-Helmholtz (KH)
instability due to the counterstreaming motions at the loop boundary. We
present the first analytical model of this phenomenon. The region at the
loop boundary where the shearing motions are greatest is treated as a
straight interface separating time-periodic counterstreaming flows. In
order to consider a twisted tube, the magnetic field at one side of the
interface is inclined. We show that the evolution of the displacement
at the interface is governed by Mathieu’s equation, and we use this
equation to study the stability of the interface. We prove that the
interface is always unstable and that, under certain conditions, the
magnetic shear may reduce the instability growth rate. The result,
that the magnetic shear cannot stabilize the interface, explains the
numerically found fact that the magnetic twist does not prevent the
onset of the KH instability at the boundary of an oscillating magnetic
tube. We also introduce the notion of the loop σ-stability. We say
that a transversally oscillating loop is σ-stable if the KH instability
growth time is larger than the damping time of the kink oscillation. We
show that even relatively weakly twisted loops are σ-stable.
Title: Propagating Spectropolarimetric Disturbances in a Large Sunspot
Authors: Stangalini, M.; Jafarzadeh, S.; Ermolli, I.; Erdélyi, R.;
Jess, D. B.; Keys, P. H.; Giorgi, F.; Murabito, M.; Berrilli, F.;
Del Moro, D.
Bibcode: 2018ApJ...869..110S
Altcode: 2018arXiv181012595S
We present results derived from the analysis of spectropolarimetric
measurements of active region AR12546, which represents one of the
largest sunspots to have emerged onto the solar surface over the last
20 years. The region was observed with full-Stokes scans of the Fe I
617.3 nm and Ca II 854.2 nm lines with the Interferometric BIdimensional
Spectrometer instrument at the Dunn Solar Telescope over an uncommon,
extremely long time interval exceeding three hours. Clear circular
polarization (CP) oscillations localized at the umbra-penumbra boundary
of the observed region were detected. Furthermore, the multi-height
data allowed us to detect the downward propagation of both CP and
intensity disturbances at 2.5-3 mHz, which was identified by a phase
delay between these two quantities. These results are interpreted as
a propagating magnetohydrodynamic surface mode in the observed sunspot.
Title: Propagation of Surface Magnetohydrodynamic Waves in Asymmetric
Multilayered Plasma
Authors: Shukhobodskaia, Daria; Erdélyi, Róbert
Bibcode: 2018ApJ...868..128S
Altcode:
Investigation of magnetohydrodynamic wave propagation in different
equilibrium configurations is important for the development of
solar magnetoseismology. In the present work, a magnetized plasma
slab sandwiched between an arbitrary number of nonmagnetic layers is
considered and an analytical approach is used for the derivation of
its dispersion relation. This work is a natural generalization of the
symmetric slab model studied by Roberts and the asymmetric magnetic
slab model, considered by Allcock & Erdélyi. Similar to the
dispersion relation for an asymmetric slab, and unlike a symmetric
slab, the dispersion relation for an asymmetric multilayered plasma
cannot be decoupled into sausage and kink eigenmodes. The waves that
permitted us to propagate in multilayered slabs have mixed characters;
therefore, the notion of quasi-sausage and quasi-kink waves is
more appropriate. Here, we focus on how a multilayered structuring
affects the eigenmodes. The amplitudes of the eigenmodes depend on
the equilibrium structuring and the model parameters; this motivates
an application as a solar magnetoseismology tool. Finally, specific
cases of two- and three-layered slabs are studied in detail and their
potential applicability to magnetic bright points is discussed.
Title: Resonant damping of kink oscillations of thin cooling and
expanding coronal magnetic loops
Authors: Shukhobodskiy, A. A.; Ruderman, M. S.; Erdélyi, R.
Bibcode: 2018A&A...619A.173S
Altcode:
We have considered resonant damping of kink oscillations of cooling and
expanding coronal magnetic loops. We derived an evolutionary equation
describing the dependence of the oscillation amplitude on time. When
there is no resonant damping, this equation reduces to the condition of
conservation of a previously derived adiabatic invariant. We used the
evolutionary equation describing the amplitude to study the competition
between damping due to resonant absorption and amplification due to
cooling. Our main aim is to investigate the effect of loop expansion
on this process. We show that the loop expansion acts in favour of
amplification. We found that, when there is no resonant damping,
the larger the loop expansion the faster the amplitude growths. When
the oscillation amplitude decays due to resonant damping, the loop
expansion reduces the damping rate. For some values of parameters the
loop expansion can fully counterbalance the amplitude decay and turn
the amplitude evolution into amplification.
Title: Varying driver velocity fields in photospheric MHD wave
simulations
Authors: Leonard, A. J.; Mumford, S. J.; Fedun, V.; Erdélyi, R.
Bibcode: 2018MNRAS.480.2839L
Altcode: 2018arXiv180710049L; 2018MNRAS.tmp.1899L
Torsional motions are ubiquitous in the solar atmosphere. In this work,
we perform three-dimensional (3D) numerical simulations that mimic a
vortex-type photospheric driver with a Gaussian spatial profile. This
driver is implemented to excite magnetohydrodynamic waves in an
axially symmetric, 3D magnetic flux tube embedded in a realistic
solar atmosphere. The Gaussian width of the driver is varied, and the
resulting perturbations are compared. Velocity vectors were decomposed
into parallel, perpendicular, and azimuthal components with respect
to pre-defined magnetic flux surfaces. These components correspond
broadly to the fast, slow, and Alfvén modes, respectively. From
these velocities, the corresponding wave energy fluxes are calculated,
allowing us to estimate the contribution of each mode to the energy
flux. For the narrowest driver (0.15 Mm), the parallel component
accounts for ∼ 55-65 per cent of the flux. This contribution increases
smoothly with driver width up to nearly 90 per cent for the widest
driver (0.35 Mm). The relative importance of the perpendicular and
azimuthal components decreases at similar rates. The azimuthal energy
flux varied between ∼35 per cent for the narrowest driver and <
10 per cent for the widest one. Similarly, the perpendicular flux was
∼ 25-10 per cent. We also demonstrate that the fast mode corresponds
to the sausage wave in our simulations. Our results, therefore, show
that the fast sausage wave is easily excited by this driver and that it
carries the majority of the energy transported. For this vortex-type
driver, the Alfvén wave does not contribute a significant amount
of energy.
Title: Propagation of Leaky MHD Waves at Discontinuities with Tilted
Magnetic Field
Authors: Vickers, E.; Ballai, I.; Erdélyi, R.
Bibcode: 2018SoPh..293..139V
Altcode: 2018arXiv180903907V
We investigate the characteristics of magneto-acoustic surface waves
propagating at a single density interface, in the presence of an
inclined magnetic field. For linear wave propagation, the dispersion
relation is obtained and analytical solutions are derived for small
inclination angle. The inclination of the field renders the frequency of
the waves complex, where the imaginary part describes wave attenuation,
due to lateral energy leakage.
Title: Buoyancy-driven Magnetohydrodynamic Waves in a Partially
Ionized Plasma
Authors: Hague, A.; Erdélyi, R.
Bibcode: 2018ApJ...866..114H
Altcode:
A magnetohydrodynamic (MHD) fluid description is typically employed
to study the magnetized plasma comprising the solar atmosphere. This
approach has had many successes in modeling and explaining solar
phenomena. Most often, the plasma is assumed to be fully ionized. While
this approach is justified in the higher atmosphere, i.e., the solar
corona; the temperature in the lower solar atmosphere is such that a
large proportion of the fluid may be electrically neutral. This begs
the question: to what degree are the results derived from a fully
ionized MHD description valid? In this article, we investigate the
effect of partial ionization on buoyancy-driven MHD waves (the MHD
analog of internal gravity waves) by applying a simplified two-fluid
description. We show that previously derived results may be applied,
when the fluid is weakly ionized, if the ion-neutral collision frequency
is high. We derive dispersion relations for buoyancy-driven MHD waves,
which include correction factors and damping rates due to ion-neutral
collisions.
Title: Spatial Inhomogeneity in Solar Faculae
Authors: Elek, A.; Gyenge, N.; Korsós, M. B.; Erdélyi, R.
Bibcode: 2018IAUS..335...17E
Altcode: 2018arXiv180101716E
In this paper, we investigate the inhomogeneous spatial distribution
of solar faculae. The focus is on the latitudinal and longitudinal
distributions of these highly localised features covering ubiquitously
the solar surface. The statistical analysis is based on white light
observations of the Solar and Heliospheric Observatory (SOHO) and Solar
Dynamics Observatory (SDO) between 1996 and 2014. We found that the
fine structure of the latitudinal distribution of faculae displays
a quasi-biennial oscillatory pattern. Furthermore, the longitudinal
distribution of photospheric solar faculae does not show homogeneous
behaviour either. In particular, the non-axisymmetric behaviour of
these events show similar properties as that of the active longitude
(AL) found in the distribution of sunspots. Our results, preliminary
though, may provide a valuable observational constrain for developing
the next-generation solar dynamo model.
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: Predicting the Loci of Solar Eruptions
Authors: Gyenge, N.; Erdélyi, R.
Bibcode: 2018IAUS..335..201G
Altcode: 2017arXiv171006196G
The longitudinal distribution of solar active regions shows
non-homogeneous spatial behaviour, which is often referred to as Active
Longitude (AL). Evidence for a significant statistical relationships
between the AL and the longitudinal distribution of flare and coronal
mass ejections (CME) occurrences is found in Gyenge et al. 2017 (ApJ,
838, 18). The present work forecasts the spatial position of AL, hence
the most flare/CME capable active regions are also predictable. Our
forecast method applies Autoregressive Integrated Moving Average
model for the next 2 years time period. We estimated the dates when
the solar flare/CME-capable longitudinal belts face towards Earth.
Title: Magnetoacoustic Waves and the Kelvin-Helmholtz Instability
in a Steady Asymmetric Slab. I: The Effects of Varying Density Ratios
Authors: Barbulescu, M.; Erdélyi, R.
Bibcode: 2018SoPh..293...86B
Altcode:
Recent observations have shown that bulk flow motions in structured
solar plasmas, most evidently in coronal mass ejections (CMEs), may lead
to the formation of Kelvin-Helmholtz instabilities (KHIs). Analytical
models are thus essential in understanding both how the flows affect
the propagation of magnetohydrodynamic (MHD) waves, and what the
critical flow speed is for the formation of the KHI. We investigate
both these aspects in a novel way: in a steady magnetic slab embedded
in an asymmetric environment. The exterior of the slab is defined as
having different equilibrium values of the background density, pressure,
and temperature on either side. A steady flow and constant magnetic
field are present in the slab interior. Approximate solutions to the
dispersion relation are obtained analytically and classified with
respect to mode and speed. General solutions and the KHI thresholds
are obtained numerically. It is shown that, generally, both the KHI
critical value and the cut-off speeds for magnetoacoustic waves are
lowered by the external asymmetry.
Title: Periodic Recurrence Patterns In X-Ray Solar Flare Appearances
Authors: Gyenge, N.; Erdélyi, R.
Bibcode: 2018ApJ...859..169G
Altcode: 2018arXiv180411229G
The temporal recurrence of micro-flare events is studied for a time
interval before and after of major solar flares. Our sample is based
on the X-ray flare observations by the Geostationary Operational
Environmental Satellite (GOES) and Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). The analyzed data contain 1330/301
M-class and X-class GOES/RHESSI energetic solar flares and 4062/4119
GOES/RHESSI micro-flares covering the period elapse since 2002. The
temporal analysis of recurrence, by Fast Fourier Transform, of the
micro-flares, shows multiple significant periods. Based on the GOES
and RHESSI data, the temporal analysis also demonstrates that multiple
periods manifest simultaneously in both statistical samples without
any significant shift over time. In the GOES sample, the detected
significant periods are: 11.33, 5.61, 3.75, 2.80, and 2.24 minutes. The
RHESSI data show similar significant periods at 8.54, 5.28, 3.66,
2.88, and 2.19 minutes. The periods are interpreted as signatures of
standing oscillations, with the longest period (P 1) being
the fundamental and others being higher harmonic modes. The period
ratio of the fundamental and higher harmonics (P 1/P
N ) is also analyzed. The standing modes may be signatures
of global oscillations of the entire solar atmosphere encompassing
magnetized plasma from the photosphere to the corona in active regions.
Title: Observing Kelvin-Helmholtz instability in solar blowout jet
Authors: Li, Xiaohong; Zhang, Jun; Yang, Shuhong; Hou, Yijun;
Erdélyi, Robert
Bibcode: 2018NatSR...8.8136L
Altcode: 2018arXiv180605867L
Kelvin-Helmholtz instability (KHI) is a basic physical process in
fluids and magnetized plasmas, with applications successfully modelling
e.g. exponentially growing instabilities observed at magnetospheric
and heliospheric boundaries, in the solar or Earth's atmosphere and
within astrophysical jets. Here, we report the discovery of the KHI
in solar blowout jets and analyse the detailed evolution by employing
high-resolution data from the Interface Region Imaging Spectrograph
(IRIS) satellite launched in 2013. The particular jet we focus on
is rooted in the surrounding penumbra of the main negative polarity
sunspot of Active Region 12365, where the main body of the jet is a
super-penumbral structure. At its maximum, the jet has a length of 90
Mm, a width of 19.7 Mm, and its density is about 40 times higher than
its surroundings. During the evolution of the jet, a cavity appears
near the base of the jet, and bi-directional flows originated from the
top and bottom of the cavity start to develop, indicating that magnetic
reconnection takes place around the cavity. Two upward flows pass along
the left boundary of the jet successively. Next, KHI develops due to
a strong velocity shear (∼204 km s-1) between these two
flows, and subsequently the smooth left boundary exhibits a sawtooth
pattern, evidencing the onset of the instability.
Title: PROGRESS: Fusion of forecasts from the Sun to the Earth
Authors: Erdelyi, Robertus; Boynton, Richard; Walker, Simon; Arber,
Tony; Bennett, Keith; Ganushkina, Natalia; Dubyagin, Stepan; Wintoft,
Peter; Wik, Magnus; Liemohn, Michael; van der Holst, Bart; Shprits,
Yuri; Tibocha, Angelica; Krasnoselskikh, Volodya
Bibcode: 2018EGUGA..2011374E
Altcode:
PROGRESS, PRediction Of Geospace Radiation Environment and Solar wind
parameterS, is an Horizon 2020 funded project that aims to provide
accurate and reliable forecasts of the geospace environment and its
response to space weather events. PROGRESS focuses on three broad
topics, 1) the forecast of the state of the solar wind at L1 based on
GONG magnetograms, 2) the evolution of geomagnetic activity as expressed
by the geomagnetic indices Kp, Dst, and AE, and 3) the characterisation
of the electron environment of the radiation belts. This presentation
provides an overview of the tools and models developed and shows
examples for the forecasts generated.
Title: CAT-PUMA: CME Arrival Time Prediction Using Machine learning
Algorithms
Authors: Liu, Jiajia; Ye, Yudong; Shen, Chenglong; Wang, Yuming;
Erdélyi, Robert
Bibcode: 2018ascl.soft04013L
Altcode:
CAT-PUMA (CME Arrival Time Prediction Using Machine learning Algorithms)
quickly and accurately predicts the arrival of Coronal Mass Ejections
(CMEs) of CME arrival time. The software was trained via detailed
analysis of CME features and solar wind parameters using 182 previously
observed geo-effective partial-/full-halo CMEs and uses algorithms of
the Support Vector Machine (SVM) to make its predictions, which can
be made within minutes of providing the necessary input parameters of
a CME.
Title: On Quasi-biennial Oscillations in Chromospheric Macrospicules
and Their Potential Relation to the Global Solar Magnetic Field
Authors: Kiss, T. S.; Erdélyi, R.
Bibcode: 2018ApJ...857..113K
Altcode: 2018arXiv180401513K
This study aims to provide further evidence for the potential influence
of the global solar magnetic field on localized chromospheric jets, the
macrospicules (MS). To find a connection between the long-term variation
of properties of MS and other solar activity proxies, including,
e.g., the temporal variation of the frequency shift of solar global
oscillations, sunspot area, etc., a database overarching seven years
of observations was compiled. This database contains 362 MS, based on
observations at the 30.4 nm of the Atmospheric Imaging Assembly on board
the Solar Dynamics Observatory. Three of the five investigated physical
properties of MS show a clear long-term temporal variation after
smoothing the raw data. Wavelet analysis of the temporal variation of
maximum length, maximum area, and average velocity is carried out. The
results reveal a strong pattern of periodicities at around 2 years
(also referred to as quasi-biennial oscillations—QBOs). A comparison
with solar activity proxies that also possess the properties of QBOs
provides some interesting features: the minima and maxima of QBOs of
MS properties occur at around the same epoch as the minima and maxima
of these activity proxies. For most of the time span investigated,
the oscillations are out of phase. This out-of-phase behavior was also
corroborated by a cross-correlation analysis. These results suggest
that the physical processes that generate and drive the long-term
evolution of the global solar activity proxies may be coupled to the
short-term local physical processes driving the macrospicules, and,
therefore modulate the properties of local dynamics.
Title: Photospheric Observations of Surface and Body Modes in Solar
Magnetic Pores
Authors: Keys, Peter H.; Morton, Richard J.; Jess, David B.; Verth,
Gary; Grant, Samuel D. T.; Mathioudakis, Mihalis; Mackay, Duncan H.;
Doyle, John G.; Christian, Damian J.; Keenan, Francis P.; Erdélyi,
Robertus
Bibcode: 2018ApJ...857...28K
Altcode: 2018arXiv180301859K
Over the past number of years, great strides have been made in
identifying the various low-order magnetohydrodynamic wave modes
observable in a number of magnetic structures found within the solar
atmosphere. However, one aspect of these modes that has remained
elusive, until now, is their designation as either surface or body
modes. This property has significant implications for how these modes
transfer energy from the waveguide to the surrounding plasma. Here, for
the first time to our knowledge, we present conclusive, direct evidence
of these wave characteristics in numerous pores that were observed to
support sausage modes. As well as outlining methods to detect these
modes in observations, we make estimates of the energies associated
with each mode. We find surface modes more frequently in the data,
as well as that surface modes appear to carry more energy than those
displaying signatures of body modes. We find frequencies in the range
of ∼2-12 mHz, with body modes as high as 11 mHz, but we do not find
surface modes above 10 mHz. It is expected that the techniques we have
applied will help researchers search for surface and body signatures
in other modes and in differing structures from those presented here.
Title: Magnetic Shocks and Substructures Excited by Torsional Alfvén
Wave Interactions in Merging Expanding Flux Tubes
Authors: Snow, B.; Fedun, V.; Gent, F. A.; Verth, G.; Erdélyi, R.
Bibcode: 2018ApJ...857..125S
Altcode: 2018arXiv180306112S
Vortex motions are frequently observed on the solar photosphere. These
motions may play a key role in the transport of energy and momentum from
the lower atmosphere into the upper solar atmosphere, contributing to
coronal heating. The lower solar atmosphere also consists of complex
networks of flux tubes that expand and merge throughout the chromosphere
and upper atmosphere. We perform numerical simulations to investigate
the behavior of vortex-driven waves propagating in a pair of such flux
tubes in a non-force-free equilibrium with a realistically modeled
solar atmosphere. The two flux tubes are independently perturbed
at their footpoints by counter-rotating vortex motions. When the
flux tubes merge, the vortex motions interact both linearly and
nonlinearly. The linear interactions generate many small-scale transient
magnetic substructures due to the magnetic stress imposed by the vortex
motions. Thus, an initially monolithic tube is separated into a complex
multithreaded tube due to the photospheric vortex motions. The wave
interactions also drive a superposition that increases in amplitude
until it exceeds the local Mach number and produces shocks that
propagate upward with speeds of approximately 50 km s-1. The
shocks act as conduits transporting momentum and energy upward, and
heating the local plasma by more than an order of magnitude, with a
peak temperature of approximately 60,000 K. Therefore, we present a
new mechanism for the generation of magnetic waveguides from the lower
solar atmosphere to the solar corona. This wave guide appears as the
result of interacting perturbations in neighboring flux tubes. Thus, the
interactions of photospheric vortex motions is a potentially significant
mechanism for energy transfer from the lower to upper solar atmosphere.
Title: Applying the Weighted Horizontal Magnetic Gradient Method to
a Simulated Flaring Active Region
Authors: Korsós, M. B.; Chatterjee, P.; Erdélyi, R.
Bibcode: 2018ApJ...857..103K
Altcode: 2018arXiv180410351K
Here, we test the weighted horizontal magnetic gradient (WG
M ) as a flare precursor, introduced by Korsós et al., by
applying it to a magnetohydrodynamic (MHD) simulation of solar-like
flares. The preflare evolution of the WG M and the behavior
of the distance parameter between the area-weighted barycenters of
opposite-polarity sunspots at various heights is investigated in the
simulated δ-type sunspot. Four flares emanated from this sunspot. We
found the optimum heights above the photosphere where the flare
precursors of the WG M method are identifiable prior
to each flare. These optimum heights agree reasonably well with the
heights of the occurrence of flares identified from the analysis of
their thermal and ohmic heating signatures in the simulation. We also
estimated the expected time of the flare onsets from the duration of the
approaching-receding motion of the barycenters of opposite polarities
before each single flare. The estimated onset time and the actual time
of occurrence of each flare are in good agreement at the corresponding
optimum heights. This numerical experiment further supports the use
of flare precursors based on the WG M method.
Title: Studies of Isolated and Non-isolated Photospheric Bright
Points in an Active Region Observed by the New Vacuum Solar Telescope
Authors: Liu, Yanxiao; Xiang, Yongyuan; Erdélyi, Robertus; Liu,
Zhong; Li, Dong; Ning, Zongjun; Bi, Yi; Wu, Ning; Lin, Jun
Bibcode: 2018ApJ...856...17L
Altcode:
Properties of photospheric bright points (BPs) near an active region
have been studied in TiO λ 7058 Å images observed by the New Vacuum
Solar Telescope of the Yunnan Observatories. We developed a novel
recognition method that was used to identify and track 2010 BPs. The
observed evolving BPs are classified into isolated (individual) and
non-isolated (where multiple BPs are observed to display splitting
and merging behaviors) sets. About 35.1% of BPs are non-isolated. For
both isolated and non-isolated BPs, the brightness varies from 0.8
to 1.3 times the average background intensity and follows a Gaussian
distribution. The lifetimes of BPs follow a log-normal distribution,
with characteristic lifetimes of (267 ± 140) s and (421 ± 255) s,
respectively. Their size also follows log-normal distribution, with an
average size of about (2.15 ± 0.74) × 104 km2
and (3.00 ± 1.31) × 104 km2 for area, and
(163 ± 27) km and (191 ± 40) km for diameter, respectively. Our
results indicate that regions with strong background magnetic field
have higher BP number density and higher BP area coverage than regions
with weak background field. Apparently, the brightness/size of BPs
does not depend on the background field. Lifetimes in regions with
strong background magnetic field are shorter than those in regions
with weak background field, on average.
Title: A New Tool for CME Arrival Time Prediction using Machine
Learning Algorithms: CAT-PUMA
Authors: Liu, Jiajia; Ye, Yudong; Shen, Chenglong; Wang, Yuming;
Erdélyi, Robert
Bibcode: 2018ApJ...855..109L
Altcode: 2018arXiv180202803L
Coronal mass ejections (CMEs) are arguably the most violent eruptions in
the solar system. CMEs can cause severe disturbances in interplanetary
space and can even affect human activities in many aspects, causing
damage to infrastructure and loss of revenue. Fast and accurate
prediction of CME arrival time is vital to minimize the disruption
that CMEs may cause when interacting with geospace. In this paper,
we propose a new approach for partial-/full halo CME Arrival Time
Prediction Using Machine learning Algorithms (CAT-PUMA). Via detailed
analysis of the CME features and solar-wind parameters, we build
a prediction engine taking advantage of 182 previously observed
geo-effective partial-/full halo CMEs and using algorithms of the
Support Vector Machine. We demonstrate that CAT-PUMA is accurate and
fast. In particular, predictions made after applying CAT-PUMA to a
test set unknown to the engine show a mean absolute prediction error
of ∼5.9 hr within the CME arrival time, with 54% of the predictions
having absolute errors less than 5.9 hr. Comparisons with other
models reveal that CAT-PUMA has a more accurate prediction for 77%
of the events investigated that can be carried out very quickly, i.e.,
within minutes of providing the necessary input parameters of a CME. A
practical guide containing the CAT-PUMA engine and the source code of
two examples are available in the Appendix, allowing the community to
perform their own applications for prediction using CAT-PUMA.
Title: Solar Magnetoseismology with Magnetoacoustic Surface Waves
in Asymmetric Magnetic Slab Waveguides
Authors: Allcock, Matthew; Erdélyi, Robert
Bibcode: 2018ApJ...855...90A
Altcode:
Solar magnetoseismology is an indirect method to approximate plasma
parameters that are traditionally difficult to measure in the solar
atmosphere using observations of magnetohydrodynamic waves. A magnetic
slab can act as waveguide for magnetoacoustic waves that approximates
magnetic structures in the solar atmosphere. The asymmetry of the
slab caused by different plasma parameters in each external region
affects both the eigenfrequencies and eigenfunctions differently at
each side of the slab, that is, both the temporal and spatial profiles
of the eigenmodes of propagation along the slab are influenced by the
equilibrium asymmetry. We present two novel diagnostic tools for solar
magnetoseismology that use this distortion to estimate the slab magnetic
field strength using the spatial distribution of magnetoacoustic
surface waves: the amplitude ratio and the minimum perturbation shift
techniques. They have the potential to estimate background equilibrium
parameters in inhomogeneous solar structures such as elongated magnetic
bright points, prominences, and the clusters of magnetic brightenings
rooted in sunspot light bridges known as light bridge surges or light
walls, which may be locally approximated as slabs.
Title: Period Increase and Amplitude Distribution of Kink Oscillation
of Coronal Loop
Authors: Su, W.; Guo, Y.; Erdélyi, R.; Ning, Z. J.; Ding, M. D.;
Cheng, X.; Tan, B. L.
Bibcode: 2018NatSR...8.4471S
Altcode: 2018arXiv180306848S
Coronal loops exist ubiquitously in the solar atmosphere. These loops
puzzle astronomers over half a century. Solar magneto-seismology (SMS)
provides a unique way to constrain the physical parameters of coronal
loops. Here, we study the evolution of oscillations of a coronal loop
observed by the Atmospheric Imaging Assembly (AIA). We measure geometric
and physical parameters of the loop oscillations. In particular, we
find that the mean period of the oscillations increased from 1048 to
1264 s during three oscillatory cycles. We employ the differential
emission measure method and apply the tools of SMS. The evolution
of densities inside and outside the loop is analyzed. We found that
an increase of density inside the loop and decrease of the magnetic
field strength along the loop are the main reasons for the increase
in the period during the oscillations. Besides, we also found that
the amplitude profile of the loop is different from a profile would
it be a homogeneous loop. It is proposed that the distribution of
magnetic strength along the loop rather than density stratification is
responsible for this deviation. The variation in period and distribution
of amplitude provide, in terms of SMS, a new and unprecedented insight
into coronal loop diagnostics.
Title: Magneto-acoustic Waves in a Magnetic Slab Embedded in an
Asymmetric Magnetic Environment: The Effects of Asymmetry
Authors: Zsámberger, Noémi Kinga; Allcock, Matthew; Erdélyi, Róbert
Bibcode: 2018ApJ...853..136K
Altcode: 2018ApJ...853..136Z
Modeling the behavior of magnetohydrodynamic waves in a range of
magnetic geometries mimicking solar atmospheric waveguides, from
photospheric flux tubes to coronal loops, can offer a valuable
contribution to the field of solar magneto-seismology. The present
study uses an analytical approach to derive the dispersion relation for
magneto-acoustic waves in a magnetic slab of homogeneous plasma enclosed
on its two sides by semi-infinite plasma of different densities,
temperatures, and magnetic field strengths, providing an asymmetric
plasma environment. This is a step further in the generalization of
the classic magnetic slab model, which is symmetric about the slab,
was developed by Roberts, and is an extension of the work by Allcock
& Erdélyi where a magnetic slab is sandwiched in an asymmetric
nonmagnetic plasma environment. In contrast to the symmetric case,
the dispersion relation governing the asymmetric slab cannot be
factorized into separate sausage and kink eigenmodes. The solutions
obtained resemble these well-known modes; however, their properties
are now mixed. Therefore we call these modes quasi-sausage and
quasi-kink modes. If conditions on the two sides of the slab do not
differ strongly, then a factorization of the dispersion relation can
be achieved for the further analytic study of various limiting cases
representing a solar environment. In the current paper, we examine the
incompressible limit in detail and demonstrate its possible application
to photospheric magnetic bright points. After the introduction of a
mechanical analogy, we reveal a relationship between the external
plasma and magnetic parameters, which allows for the existence of
quasi-symmetric modes.
Title: Dissipative instabilities in a partially ionised prominence
plasma slab. II. The effect of compressibility
Authors: Mather, J. F.; Ballai, I.; Erdélyi, R.
Bibcode: 2018A&A...610A..56M
Altcode: 2017arXiv171109855M
This study deals with the dissipative instability that appears
in a compressible partially ionised plasma slab embedded in a
uniform magnetic field, modelling the state of the plasma in solar
prominences. In the partially ionised plasma, the dominant dissipative
effect is the Cowling resistivity. The regions outside the slab
(modelling the solar corona) are fully ionised, and the dominant
mechanism of dissipation is viscosity. Analytical solutions to the
extended magnetohydrodynamic (MHD) equations are found inside and
outside of the slab and solutions are matched at the boundaries of
the slab. The dispersion relation is derived and solutions are found
analytically in the slender slab limit, while the conditions necessary
for the appearance of the instability is investigated numerically for
the entire parameter space. Our study is focussed on the effect of the
compressibility on the generation and evolution of instabilities. We
find that compressibility reduces the threshold of the equilibrium
flow, where waves can be unstable, to a level that is comparable to
the internal cusp speed, which is of the same order of flow speeds
that are currently observed in solar prominences. Our study addresses
only the slow waves, as these are the most likely perturbations to
become unstable, however the time-scales of the instability are found
to be rather large ranging from 105-107 s. It
is determined that the instability threshold is further influenced
by the concentration of neutrals and the strength of the viscosity
of the corona. Interestingly, these two latter aspects have opposite
effects. Our numerical analysis shows that the interplay between the
equilibrium flow, neutrals and dispersion can change considerably the
nature of waves. Despite employing a simple model, our study confirms
the necessity of consideration of neutrals when discussing the stability
of prominences under solar conditions.
Title: Erratum: “On the Magnetic and Energy
Characteristics of Homologous Jets From an Emerging Flux” (2016, ApJ, 833,
150)
Authors: Liu, Jiajia; Wang, Yuming; Erdélyi, Robertus; Liu, Rui;
McIntosh, Scott W.; Gou, Tingyu; Chen, Jun; Liu, Kai; Liu, Lijuan;
Pan, Zonghao
Bibcode: 2018ApJ...853..201L
Altcode:
No abstract at ADS
Title: Where do running penumbral waves emerge in chromosphere?
Authors: Priya, T. G.; Su, Jiangtao; Erdelyi, Robertus
Bibcode: 2018IAUS..340..155P
Altcode:
The earlier work on the oscillatory phenomena in sunspot structures
have supported in validating the detection of long-period oscillations,
which are generated by the photospheric umbral response to the five
minute p-mode global oscillations. We report here on the events of 3-
min umbral oscillations which are detected within a duration of one hour
from a single-polarity sunspot of active region NOAA 12132. The umbral
oscillations that appear first around umbral boundaries is speculated
to be excited by the wavefronts at the umbral-penumbral boundaries due
to sub-photospheric or photospheric granular buffetings. The appearance
of the wavefronts in spiral structures suggests that the wave guides
are twisted. In addition, the newly formed running penumbral waves
(RPWs) appears to be connected with the preceding RPWs.
Title: Solar atmosphere wave dynamics generated by solar global
oscillating eigenmodes
Authors: Griffiths, M. K.; Fedun, V.; Erdélyi, R.; Zheng, R.
Bibcode: 2018AdSpR..61..720G
Altcode:
The solar atmosphere exhibits a diverse range of wave phenomena,
where one of the earliest discovered was the five-minute global
acoustic oscillation, also referred to as the p-mode. The analysis of
wave propagation in the solar atmosphere may be used as a diagnostic
tool to estimate accurately the physical characteristics of the Sun's
atmospheric layers. In this paper, we investigate the dynamics and
upward propagation of waves which are generated by the solar global
eigenmodes. We report on a series of hydrodynamic simulations of a
realistically stratified model of the solar atmosphere representing its
lower region from the photosphere to low corona. With the objective of
modelling atmospheric perturbations, propagating from the photosphere
into the chromosphere, transition region and low corona, generated by
the photospheric global oscillations the simulations use photospheric
drivers mimicking the solar p-modes. The drivers are spatially
structured harmonics across the computational box parallel to the solar
surface. The drivers perturb the atmosphere at 0.5 Mm above the bottom
boundary of the model and are placed coincident with the location of
the temperature minimum. A combination of the VALIIIC and McWhirter
solar atmospheres are used as the background equilibrium model. We report how synthetic photospheric oscillations may manifest
in a magnetic field free model of the quiet Sun. To carry out the
simulations, we employed the magnetohydrodynamics code, SMAUG (Sheffield
MHD Accelerated Using GPUs). Our results show that the amount
of energy propagating into the solar atmosphere is consistent with a
model of solar global oscillations described by Taroyan and Erdélyi
(2008) using the Klein-Gordon equation. The computed results indicate
a power law which is compared to observations reported by Ireland et
al. (2015) using data from the Solar Dynamics Observatory/Atmospheric
Imaging Assembly.
Title: Untwisting Jets Related to Magnetic Flux Cancellation
Authors: Liu, Jiajia; Erdélyi, Robert; Wang, Yuming; Liu, Rui
Bibcode: 2018ApJ...852...10L
Altcode: 2017arXiv171106066L
The rotational motion of solar jets is believed to be a signature of
the untwisting process resulting from magnetic reconnection, which
takes place between twisted closed magnetic loops (i.e., magnetic
flux ropes) and open magnetic field lines. The identification of
the pre-existing flux rope, and the relationship between the twist
contained in the rope and the number of turns the jet experiences,
are then vital in understanding the jet-triggering mechanism. In
this paper, we will perform a detailed analysis of imaging, spectral,
and magnetic field observations of four homologous jets, among which
the fourth one releases a twist angle of 2.6π. Nonlinear force-free
field extrapolation of the photospheric vector magnetic field before
the jet eruption presents a magnetic configuration with a null point
between twisted and open fields—a configuration highly in favor
of the eruption of solar jets. The fact that the jet rotates in the
opposite sense of handness to the twist contained in the pre-eruption
photospheric magnetic field confirms the unwinding of the twist by the
jet’s rotational motion. The temporal relationship between jets’
occurrence and the total negative flux at their source region, together
with the enhanced magnetic submergence term of the photospheric Poynting
flux, shows that these jets are highly associated with local magnetic
flux cancellation.
Title: An application of the weighted horizontal magnetic gradient
to solar compact and eruptive events
Authors: Korsós, M. B.; Ruderman, Michael S.; Erdélyi, R.
Bibcode: 2018AdSpR..61..595K
Altcode: 2018arXiv180100281K
We propose to apply the weighted horizontal magnetic gradient
(WGM), introduced in Korsós et al., 2015, for analysing
the pre-flare and pre-CME behaviour and evolution of Active Regions
(ARs) using the SDO/HMI-Debrecen Data catalogue. To demonstrate the
power of investigative capabilities of the WGM method, in
terms of flare and CME eruptions, we studied two typical ARs, namely,
AR 12158 and AR 12192. The choice of ARs represent canonical cases. AR
12158 produced an X1.6 flare with fast "halo" CME (vlinear
= 1267 kms-1) while in AR 12192 there occurred a range
of powerful X-class eruptions, i.e. X1.1, X1.6, X3.1, X1.0, X2.0 and
X2.0-class energetic flares, interestingly, none with an accompanying
CME. The value itself and temporal variation of WGM is
found to possess potentially important diagnostic information about
the intensity of the expected flare class. Furthermore, we have also
estimated the flare onset time from the relationship of duration of
converging and diverging motions of the area-weighted barycenters of
two subgroups of opposite magnetic polarities. This test turns out
not only to provide information about the intensity of the expected
flare-class and the flare onset time but may also indicate whether a
flare will occur with/without fast CME. We have also found that, in the
case when the negative polarity barycenter has moved around and the
positive one "remained" at the same coordinates preceding eruption,
the flare occurred with fast "halo" CME. Otherwise, when both the
negative and the positive polarity barycenters have moved around,
the AR produced flares without CME. If these properties found for the
movement of the barycenters are generic pre-cursors of CME eruption (or
lack of it), identifying them may serve as an excellent pre-condition
for refining the forecast of the lift-off of CMEs.
Title: Detailed analysis of dynamic evolution of three Active Regions
before flare and CME occurrence at the photospheric level
Authors: Ye, Yudong; Korsos, M. B.; Erdelyi, R.
Bibcode: 2018arXiv180100430Y
Altcode:
We present a combined analysis of the applications of the weighted
horizontal magnetic gradient (denoted as WG_M in Korsos et al., ApJ,
802, L21, 2015) method and the magnetic helicity tool (Berger &
Field, JFM, 147, 133, 1984) employed for three active regions (ARs),
namely NOAA AR11261, AR11283 and AR11429. All three active regions
produced series flares and CMEs. We followed the evolution of the
components of the WG_M and the magnetic helicity before the flare and
CME occurrences. We found an unique and mutually shared behavior,
called the U-shaped pattern, of the weighted distance component of
WG_M and of the shearing component of the helicity flux before the
flare and CME eruptions. This common pattern is associated with the
decreasing-receding phase yet reported only known to be a necessary
feature prior to solar flare eruption(s), but found now at the same time
in the evolution of the shearing helicity parameter. This result leads
to the conclusion that (i) the shearing motion of photospheric magnetic
field may be a key driver for the solar eruption in addition to the
flux emerging process, and that (ii) the found decreasing-approaching
pattern in the evolution of shearing helicity may be another precursor
indicator for improving the forecasting of solar eruptions.
Title: Quasi-biennial oscillations in the cross-correlation of
properties of macrospicules
Authors: Kiss, T. S.; Gyenge, N.; Erdélyi, R.
Bibcode: 2018AdSpR..61..611K
Altcode: 2017arXiv170600275K
Jets, whatever small (e.g. spicules) or large (e.g. macrospicules)
their size, may play a key role in momentum and energy transport from
photosphere to chromosphere and at least to the low corona. Here,
we investigate the properties of abundant, large-scale dynamic jets
observable in the solar atmosphere: the macrospicules (MS). These
jets are observationally more distinct phenomena than their little,
and perhaps more ubiquitous, cousins, the spicules. Investigation of
long-term variation of the properties of macrospicules may help to a
better understanding of their underlying physics of generation and
role in coronal heating. Taking advantage of the high temporal and
spatial resolution of the Solar Dynamics Observatory, a new dataset,
with several hundreds of macrospicules, was constructed encompassing a
period of observations over six years. Here, we analyse the measured
properties and relations between these properties of macrospicules
as function of time during the observed time interval. We found that
cross-correlations of several of these macrospicule properties display
a strong oscillatory pattern. Next, wavelet analysis is used to provide
more detailed information about the temporal behaviour of the various
properties of MS. For coronal hole macrospicules, a significant peak
is found at around 2-year period. This peak also exists partially or is
shifted to longer period, in the case of quiet Sun macrospicules. These
observed findings may be rooted in the underlying mechanism generating
the solar magnetic field, i.e. the global solar dynamo.
Title: MHD code using multi graphical processing units: SMAUG+
Authors: Gyenge, N.; Griffiths, M. K.; Erdélyi, R.
Bibcode: 2018AdSpR..61..683G
Altcode: 2017arXiv171006423G
This paper introduces the Sheffield Magnetohydrodynamics
Algorithm Using GPUs (SMAUG+), an advanced numerical code for
solving magnetohydrodynamic (MHD) problems, using multi-GPU
systems. Multi-GPU systems facilitate the development of accelerated
codes and enable us to investigate larger model sizes and/or more
detailed computational domain resolutions. This is a significant
advancement over the parent single-GPU MHD code, SMAUG (Griffiths et
al., 2015). Here, we demonstrate the validity of the SMAUG + code,
describe the parallelisation techniques and investigate performance
benchmarks. The initial configuration of the Orszag-Tang vortex
simulations are distributed among 4, 16, 64 and 100 GPUs. Furthermore,
different simulation box resolutions are applied: 1000 × 1000, 2044 ×
2044, 4000 × 4000 and 8000 × 8000 . We also tested the code with the
Brio-Wu shock tube simulations with model size of 800 employing up to 10
GPUs. Based on the test results, we observed speed ups and slow downs,
depending on the granularity and the communication overhead of certain
parallel tasks. The main aim of the code development is to provide
massively parallel code without the memory limitation of a single
GPU. By using our code, the applied model size could be significantly
increased. We demonstrate that we are able to successfully compute
numerically valid and large 2D MHD problems.
Title: Evolution of Complex 3D Motions in Spicules
Authors: Sharma, Rahul; Verth, Gary; Erdélyi, Robertus
Bibcode: 2018ApJ...853...61S
Altcode:
Ubiquitous transverse oscillations observed in spicular waveguides,
identified as the kink wave-mode had previously been reported along
with periodic structural distortions of the flux tubes, observed as
cross-sectional width and associated photometric variations. Previous
studies identified these perturbations as the observed signatures
of concurrent kink and sausage wave-modes. High-resolution Hα
imaging-spectroscopy data from the CRisp Imaging SpectroPolarimeter at
the Swedish Solar Telescope are used to analyze the off-limb spicular
structures. For the first time, the evolution of the resultant
transverse displacement of the flux-tube structure, estimated from
the perpendicular velocity components, is analyzed along with
longitudinal, cross-sectional width, photometric, and azimuthal
shear/torsion variations. The pulse-like nonlinear kink wave-mode
shows strong coupling with these observables, with a period-doubling,
-tripling aspect, supported by mutual phase relations concentrated
around 0° and +/- 180^\circ . The three-dimensional ensemble of the
observed dynamical components revealed complexities pertinent to the
accurate identification and interpretation of, e.g., linear/nonlinear,
coupled/uncoupled magnetohydrodynamical wave-modes in spicules.
Title: Fundamental (f) oscillations in a magnetically coupled solar
interior-atmosphere system - An analytical approach
Authors: Pintér, Balázs; Erdélyi, R.
Bibcode: 2018AdSpR..61..759P
Altcode:
Solar fundamental (f) acoustic mode oscillations are investigated
analytically in a magnetohydrodynamic (MHD) model. The model consists
of three layers in planar geometry, representing the solar interior,
the magnetic atmosphere, and a transitional layer sandwiched between
them. Since we focus on the fundamental mode here, we assume the
plasma is incompressible. A horizontal, canopy-like, magnetic field
is introduced to the atmosphere, in which degenerated slow MHD waves
can exist. The global (f-mode) oscillations can couple to local
atmospheric Alfvén waves, resulting, e.g., in a frequency shift of
the oscillations. The dispersion relation of the global oscillation
mode is derived, and is solved analytically for the thin-transitional
layer approximation and for the weak-field approximation. Analytical
formulae are also provided for the frequency shifts due to the
presence of a thin transitional layer and a weak atmospheric magnetic
field. The analytical results generally indicate that, compared to the
fundamental value (ω =√{ gk }), the mode frequency is reduced by the
presence of an atmosphere by a few per cent. A thin transitional layer
reduces the eigen-frequencies further by about an additional hundred
microhertz. Finally, a weak atmospheric magnetic field can slightly,
by a few percent, increase the frequency of the eigen-mode. Stronger
magnetic fields, however, can increase the f-mode frequency by even up
to ten per cent, which cannot be seen in observed data. The presence
of a magnetic atmosphere in the three-layer model also introduces
non-permitted propagation windows in the frequency spectrum; here,
f-mode oscillations cannot exist with certain values of the harmonic
degree. The eigen-frequencies can be sensitive to the background
physical parameters, such as an atmospheric density scale-height or the
rate of the plasma density drop at the photosphere. Such information,
if ever observed with high-resolution instrumentation and inverted,
could help to gain further insight into solar magnetic structures by
means of solar magneto-seismology, and could provide further insight
into the role of magnetism in solar oscillations.
Title: Detailed analysis of dynamic evolution of three Active Regions
at the photospheric level before flare and CME occurrence
Authors: Ye, Yudong; Korsós, M. B.; Erdélyi, R.
Bibcode: 2018AdSpR..61..673Y
Altcode:
We present a combined analysis of the applications of the weighted
horizontal magnetic gradient (denoted as WGM in Korsós et
al. (2015)) method and the magnetic helicity tool (Berger and Field,
1984) employed for three active regions (ARs), namely NOAA AR 11261,
AR 11283 and AR 11429. We analysed the time series of photospheric data
from the Solar Dynamics Observatory taken between August 2011 and March
2012. During this period the three ARs produced a series of flares
(eight M- and six X-class) and coronal mass ejections (CMEs). AR
11261 had four M-class flares and one of them was accompanied by
a fast CME. AR 11283 had similar activities with two M- and two
X-class flares, but only with a slow CME. Finally, AR 11429 was the
most powerful of the three ARs as it hosted five compact and large
solar flare and CME eruptions. For applying the WGM method
we employed the Debrecen sunspot data catalogue, and, for estimating
the magnetic helicity at photospheric level we used the Space-weather
HMI Active Region Patches (SHARP's) vector magnetograms from SDO/HMI
(Solar Dynamics Observatory/Helioseismic and Magnetic Imager). We
followed the evolution of the components of the WGM and
the magnetic helicity before the flare and CME occurrences. We found
a unique and mutually shared behaviour, called the U-shaped pattern,
of the weighted distance component of WGM and of the shearing
component of the helicity flux before the flare and CME eruptions. This
common pattern is associated with the decreasing-receding phases yet
reported only known to be a necessary feature prior to solar flare
eruption(s) but found now at the same time in the evolution of the
shearing helicity flux. This result leads to the conclusions that (i)
the shearing motion of photospheric magnetic field may be a key driver
for solar eruption in addition to the flux emerging process, and that
(ii) the found decreasing-approaching pattern in the evolution of
shearing helicity flux may be another precursor indicator for improving
the forecasting of solar eruptions.
Title: The Frequency-dependent Damping of Slow Magnetoacoustic Waves
in a Sunspot Umbral Atmosphere
Authors: Krishna Prasad, S.; Jess, D. B.; Van Doorsselaere, T.; Verth,
G.; Morton, R. J.; Fedun, V.; Erdélyi, R.; Christian, D. J.
Bibcode: 2017ApJ...847....5K
Altcode: 2017ApJ...847....5P; 2017arXiv170804835K
High spatial and temporal resolution images of a sunspot,
obtained simultaneously in multiple optical and UV wavelengths, are
employed to study the propagation and damping characteristics of slow
magnetoacoustic waves up to transition region heights. Power spectra are
generated from intensity oscillations in sunspot umbra, across multiple
atmospheric heights, for frequencies up to a few hundred mHz. It is
observed that the power spectra display a power-law dependence over
the entire frequency range, with a significant enhancement around 5.5
mHz found for the chromospheric channels. The phase difference spectra
reveal a cutoff frequency near 3 mHz, up to which the oscillations
are evanescent, while those with higher frequencies propagate
upward. The power-law index appears to increase with atmospheric
height. Also, shorter damping lengths are observed for oscillations
with higher frequencies suggesting frequency-dependent damping. Using
the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we
estimate the energy flux at different heights, which seems to decay
gradually from the photosphere, in agreement with recent numerical
simulations. Furthermore, a comparison of power spectra across the
umbral radius highlights an enhancement of high-frequency waves near
the umbral center, which does not seem to be related to magnetic field
inclination angle effects.
Title: IRIS Burst Spectra Co-spatial to a Quiet-Sun Ellerman-like
Brightening
Authors: Nelson, C. J.; Freij, N.; Reid, A.; Oliver, R.; Mathioudakis,
M.; Erdélyi, R.
Bibcode: 2017ApJ...845...16N
Altcode: 2017arXiv170705080N
Ellerman bombs (EBs) have been widely studied over the past two
decades; however, only recently have the counterparts of these events
been observed in the quiet-Sun. The aim of this article is to further
understand small-scale quiet-Sun Ellerman-like brightenings (QSEBs)
through research into their spectral signatures, including investigating
whether the hot signatures associated with some EBs are also visible
co-spatial to any QSEBs. We combine Hα and Ca II 8542 Å line scans at
the solar limb with spectral and imaging data sampled by the Interface
Region Imaging Spectrograph (IRIS). Twenty-one QSEBs were identified
with average lifetimes, lengths, and widths measured to be around 120 s,
0.″63, and 0.″35, respectively. Three of these QSEBs displayed clear
repetitive flaring through their lifetimes, comparable to the behavior
of EBs in active regions. Two QSEBs in this sample occurred co-spatial
to increased emission in SDO/AIA 1600 Å and IRIS slit-jaw imager 1400
Å data; however, these intensity increases were smaller than those
reported co-spatially with EBs. One QSEB was also sampled by the IRIS
slit during its lifetime, displaying increases in intensity in the
Si IV 1393 Å and Si IV 1403 Å cores, as well as the C II and Mg II
line wings, analogous to IRIS bursts (IBs). Using RADYN simulations,
we are unable to reproduce the observed QSEB Hα and Ca II 8542 Å
line profiles, leaving the question of the temperature stratification
of QSEBs open. Our results imply that some QSEBs could be heated to
transition region temperatures, suggesting that IB profiles should be
observed throughout the quiet-Sun.
Title: Sunspot Light Walls Suppressed by Nearby Brightenings
Authors: Yang, Shuhong; Zhang, Jun; Erdélyi, Robertus; Hou, Yijun;
Li, Xiaohong; Yan, Limei
Bibcode: 2017ApJ...843L..15Y
Altcode: 2017arXiv170607158Y
Light walls, as ensembles of oscillating bright structures rooted in
sunspot light bridges, have not been well studied, although they are
important for understanding sunspot properties. Using the Interface
Region Imaging Spectrograph and Solar Dynamics Observatory observations,
here we study the evolution of two oscillating light walls each
within its own active region (AR). The emission of each light wall
decays greatly after the appearance of adjacent brightenings. For
the first light wall, rooted within AR 12565, the average height,
amplitude, and oscillation period significantly decrease from 3.5
Mm, 1.7 Mm, and 8.5 minutes to 1.6 Mm, 0.4 Mm, and 3.0 minutes,
respectively. For the second light wall, rooted within AR 12597,
the mean height, amplitude, and oscillation period of the light wall
decrease from 2.1 Mm, 0.5 Mm, and 3.0 minutes to 1.5 Mm, 0.2 Mm,
and 2.1 minutes, respectively. Particularly, a part of the second
light wall even becomes invisible after the influence of a nearby
brightening. These results reveal that the light walls are suppressed
by nearby brightenings. Considering the complex magnetic topology in
light bridges, we conjecture that the fading of light walls may be
caused by a drop in the magnetic pressure, where the flux is canceled
by magnetic reconnection at the site of the nearby brightening. Another
hypothesis is that the wall fading is due to the suppression of driver
source (p-mode oscillation), resulting from the nearby avalanche of
downward particles along reconnected brightening loops.
Title: An Inside Look at Sunspot Oscillations with Higher Azimuthal
Wavenumbers
Authors: Jess, David B.; Van Doorsselaere, Tom; Verth, Gary; Fedun,
Viktor; Krishna Prasad, S.; Erdélyi, Robert; Keys, Peter H.; Grant,
Samuel D. T.; Uitenbroek, Han; Christian, Damian J.
Bibcode: 2017ApJ...842...59J
Altcode: 2017arXiv170506282J
Solar chromospheric observations of sunspot umbrae offer an exceptional
view of magnetohydrodynamic wave phenomena. In recent years, a
wealth of wave signatures related to propagating magneto-acoustic
modes have been presented, which demonstrate complex spatial and
temporal structuring of the wave components. Theoretical modeling has
demonstrated how these ubiquitous waves are consistent with an m = 0
slow magneto-acoustic mode, which is excited by trapped sub-photospheric
acoustic (p-mode) waves. However, the spectrum of umbral waves is broad,
suggesting that the observed signatures represent the superposition
of numerous frequencies and/or modes. We apply Fourier filtering,
in both spatial and temporal domains, to extract chromospheric umbral
wave characteristics consistent with an m = 1 slow magneto-acoustic
mode. This identification has not been described before. Angular
frequencies of 0.037+/- 0.007 {rad} {{{s}}}-1 (2.1+/-
0.4 \deg {{{s}}}-1, corresponding to a period ≈170 s)
for the m = 1 mode are uncovered for spatial wavenumbers in the range
of 0.45< k< 0.90 arcsec-1 (5000-9000 km). Theoretical
dispersion relations are solved, with corresponding eigenfunctions
computed, which allows the density perturbations to be investigated
and compared with our observations. Such magnetohydrodynamic modeling
confirms our interpretation that the identified wave signatures are
the first direct observations of an m = 1 slow magneto-acoustic mode
in the chromospheric umbra of a sunspot.
Title: Kink oscillations of cooling coronal loops with variable
cross-section
Authors: Ruderman, M. S.; Shukhobodskiy, A. A.; Erdélyi, R.
Bibcode: 2017A&A...602A..50R
Altcode:
We study kink waves and oscillations in a thin expanding magnetic tube
in the presence of flow. The tube consists of a core region and a thin
transitional region at the tube boundary. In this region the plasma
density monotonically decreases from its value in the core region to
the value outside the tube. Both the plasma density and velocity of
background flow vary along the tube and in time. Using the multiscale
expansions we derive the system of two equations describing the kink
oscillations. When there is no transitional layer the oscillations are
described by the first of these two equations. We use this equation
to study the effect of plasma density variation with time on kink
oscillations of an expanding tube with a sharp boundary. We assume
that the characteristic time of the density variation is much greater
than the characteristic time of kink oscillations. Then we use the
Wentzel-Kramer-Brillouin (WKB) method to derive the expression for the
adiabatic invariant, which is the quantity that is conserved when the
plasma density varies. The general theoretical results are applied
to the kink oscillations of coronal magnetic loops. We consider an
expanding loop with the half-circle shape and assume that the plasma
temperature inside a loop decays exponentially with time. We numerically
calculated the dependences of the fundamental mode frequency, the
ratio of frequencies of the first overtone and fundamental mode, and
the oscillation amplitude on time. We obtained that the oscillation
frequency and amplitude increase and the frequency ratio decreases
due to cooling. The amplitude increase is stronger for loops with
a greater expansion factor. This effect is also more pronounced for
higher loops. However, it is fairly moderate even for loops that are
quite high.
Title: Dynamic Behavior of Spicules Inferred from Perpendicular
Velocity Components
Authors: Sharma, Rahul; Verth, Gary; Erdélyi, Robertus
Bibcode: 2017ApJ...840...96S
Altcode:
Understanding the dynamic behavior of spicules, e.g., in terms of
magnetohydrodynamic (MHD) wave mode(s), is key to unveiling their
role in energy and mass transfer from the photosphere to corona. The
transverse, torsional, and field-aligned motions of spicules have
previously been observed in imaging spectroscopy and analyzed separately
for embedded wave-mode identification. Similarities in the Doppler
signatures of spicular structures for both kink and torsional Alfvén
wave modes have led to the misinterpretation of the dominant wave mode
in these structures and is a subject of debate. Here, we aim to combine
line- of-sight (LOS) and plane-of-sky (POS) velocity components using
the high spatial/temporal resolution Hα imaging-spectroscopy data
from the CRisp Imaging SpectroPolarimeter based at the Swedish Solar
Telescope to achieve better insight into the underlying nature of these
motions as a whole. The resultant three-dimensional velocity vectors
and the other derived quantities (e.g., magnetic pressure perturbations)
are used to identify the MHD wave mode(s) responsible for the observed
spicule motion. We find a number of independent examples where the
bulk transverse motion of the spicule is dominant either in the POS
or along the LOS. It is shown that the counterstreaming action of the
displaced external plasma due to spicular bulk transverse motion has a
similar Doppler profile to that of the m = 0 torsional Alfvén wave when
this motion is predominantly perpendicular to the LOS. Furthermore,
the inferred magnetic pressure perturbations support the kink wave
interpretation of observed spicular bulk transverse motion rather than
any purely incompressible MHD wave mode, e.g., the m = 0 torsional
Alfvén wave.
Title: Polarized Kink Waves in Magnetic Elements: Evidence for
Chromospheric Helical Waves
Authors: Stangalini, M.; Giannattasio, F.; Erdélyi, R.; Jafarzadeh,
S.; Consolini, G.; Criscuoli, S.; Ermolli, I.; Guglielmino, S. L.;
Zuccarello, F.
Bibcode: 2017ApJ...840...19S
Altcode: 2017arXiv170402155S
In recent years, new high spatial resolution observations of the Sun's
atmosphere have revealed the presence of a plethora of small-scale
magnetic elements down to the resolution limit of the current cohort
of solar telescopes (∼100-120 km on the solar photosphere). These
small magnetic field concentrations, due to the granular buffeting,
can support and guide several magnetohydrodynamic wave modes that
would eventually contribute to the energy budget of the upper layers
of the atmosphere. In this work, exploiting the high spatial and
temporal resolution chromospheric data acquired with the Swedish
1 m Solar Telescope, and applying the empirical mode decomposition
technique to the tracking of the solar magnetic features, we analyze
the perturbations of the horizontal velocity vector of a set of
chromospheric magnetic elements. We find observational evidence that
suggests a phase relation between the two components of the velocity
vector itself, resulting in its helical motion.
Title: Active Longitude and Coronal Mass Ejection Occurrences
Authors: Gyenge, N.; Singh, T.; Kiss, T. S.; Srivastava, A. K.;
Erdélyi, R.
Bibcode: 2017ApJ...838...18G
Altcode: 2017arXiv170206664G
The spatial inhomogeneity of the distribution of coronal mass ejection
(CME) occurrences in the solar atmosphere could provide a tool to
estimate the longitudinal position of the most probable CME-capable
active regions in the Sun. The anomaly in the longitudinal distribution
of active regions themselves is often referred to as active longitude
(AL). In order to reveal the connection between the AL and CME spatial
occurrences, here we investigate the morphological properties of active
regions. The first morphological property studied is the separateness
parameter, which is able to characterize the probability of the
occurrence of an energetic event, such as a solar flare or CME. The
second morphological property is the sunspot tilt angle. The tilt
angle of sunspot groups allows us to estimate the helicity of active
regions. The increased helicity leads to a more complex buildup of
the magnetic structure and also can cause CME eruption. We found that
the most complex active regions appear near the AL and that the AL
itself is associated with the most tilted active regions. Therefore,
the number of CME occurrences is higher within the AL. The origin of the
fast CMEs is also found to be associated with this region. We concluded
that the source of the most probably CME-capable active regions is at
the AL. By applying this method, we can potentially forecast a flare
and/or CME source several Carrington rotations in advance. This finding
also provides new information for solar dynamo modeling.
Title: Effects of Steady Flow on Magnetoacoustic-Gravity Surface
Waves: I. The Weak Field Case
Authors: Erdélyi, R.; Mather, J. F.
Bibcode: 2017SoPh..292...26E
Altcode:
Magnetoacoustic gravity (MAG) waves have been studied for some
time. In this article, we investigate the effect that a shear flow at
a tangential discontinuity embedded in a gravitationally stratified
and magnetised plasma has on MAG surface waves. The dispersion
relation found is algebraically analogous to the relation of the
non-flow cases obtained by Miles and Roberts (Solar Phys.141, 205,
1992), except for the introduction of a Doppler-shifted frequency
for the eigenvalue. This feature, however, introduces rather
interesting physics, including the asymmetric presence of forward-
and backward-propagating surface waves. We find that increasing the
equilibrium flow speed leads to a shift in the permitted regions of
propagation for surface waves. For most wave number combinations
this leads to the fast mode being completely removed, as well as
more limited phase speed regimes for slow-mode propagation. We also
find that upon increasing the flow, the phase speeds of the backward
propagating waves are increased. Eventually, at high enough flow speeds,
the wave's direction of propagation is reversed and is in the positive
direction. However, the phase speed of the forward-propagating wave
remains mainly the same. For strong enough flows we find that the
Kelvin-Helmholtz instability can also occur when the forward- and
backward-propagating modes couple.
Title: Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab
Authors: Allcock, Matthew; Erdélyi, Robert
Bibcode: 2017SoPh..292...35A
Altcode:
Analytical models of solar atmospheric magnetic structures
have been crucial for our understanding of magnetohydrodynamic
(MHD) wave behaviour and in the development of the field of solar
magneto-seismology. Here, an analytical approach is used to derive the
dispersion relation for MHD waves in a magnetic slab of homogeneous
plasma enclosed on its two sides by non-magnetic, semi-infinite plasma
with different densities and temperatures. This generalises the classic
magnetic slab model, which is symmetric about the slab. The dispersion
relation, unlike that governing a symmetric slab, cannot be decoupled
into the well-known sausage and kink modes, i.e. the modes have mixed
properties. The eigenmodes of an asymmetric magnetic slab are better
labelled as quasi-sausage and quasi-kink modes. Given that the solar
atmosphere is highly inhomogeneous, this has implications for MHD
mode identification in a range of solar structures. A parametric
analysis of how the mode properties (in particular the phase speed,
eigenfrequencies, and amplitudes) vary in terms of the introduced
asymmetry is conducted. In particular, avoided crossings occur between
quasi-sausage and quasi-kink surface modes, allowing modes to adopt
different properties for different parameters in the external region.
Title: Systematic Variations of Macrospicule Properties Observed by
SDO/AIA over Half a Decade
Authors: Kiss, T. S.; Gyenge, N.; Erdélyi, R.
Bibcode: 2017ApJ...835...47K
Altcode: 2016arXiv161202224K
Macrospicules (MSs) are localized small-scale jet-like phenomena in the
solar atmosphere, which have the potential to transport a considerable
amount of momentum and energy from the lower solar atmospheric regions
to the transition region and the low corona. A detailed statistical
analysis of their temporal behavior and spatial properties is carried
out in this work. Using state-of-the-art spatial and temporal resolution
observations, yielded by the Atmospheric Imaging Assembly of Solar
Dynamics Observatory, we constructed a database covering a 5.5 year long
period, containing 301 macrospicules that occurred between 2010 June
and 2015 December, detected at 30.4 nm wavelength. Here, we report
the long-term variation of the height, length, average speed, and
width of MS in coronal holes and Quiet Sun areas both in the northern
and southern hemisphere of the Sun. This new database helps to refine
our knowledge about the physical properties of MSs. Cross-correlation
of these properties shows a relatively strong correlation, but not
always a dominant one. However, a more detailed analysis indicates
a wave-like signature in the behavior of MS properties in time. The
periods of these long-term oscillatory behaviors are just under two
years. Also, in terms of solar north/south hemispheres, a strong
asymmetry was found in the spatial distribution of MS properties,
which may be accounted for by the solar dynamo. This latter feature
may then indicate a strong and rather intrinsic link between global
internal and local atmospheric phenomena in the Sun.
Title: Magnetic and Energy Characteristics of Recurrent Homologous
Jets from an Emerging Flux
Authors: Liu, J.; Wang, Y.; Erdelyi, R.; Liu, R.; Mcintosh, S. W.;
Gou, T.; Chen, J.; Liu, K.; Liu, L.; Pan, Z.
Bibcode: 2016AGUFMSH12B..02L
Altcode:
We present the detailed analysis of recurrent homologous jets
originating from an emerging negative magnetic flux at the edge of an
Active Region. Detailed investigation of the related Poynting flux
across the photosphere employing the HMI vector magnetic field data
confirms the vital role of the emerging flux in accumulating the
necessary free magnetic energy for the associated reconnection to
initiate jets. The observed jets show multi-thermal features. Their
evolution shows high consistence with the characteristic parameters
of the emerging flux, suggesting that with more free magnetic energy,
the eruptions tend to be more violent, frequent and blowout-like. The
average temperature, average electron number density and axial speed
are found to be similar for different jets, indicating that they
should have been formed by plasmas from similar origins. Statistical
analysis of the jets and their footpoint region conditions reveals a
strong positive relationship between the footpoint region total 131 Å
intensity enhancement and jets' length/width. Stronger linearly positive
relationships also exist between the total intensity enhancement/thermal
energy of the footpoint regions and jets' mass/kinetic/thermal energy,
with higher cross-correlation coefficients. All the above results,
together, confirm the direct relationship between the magnetic
reconnection and the jets, and validate the important role of magnetic
reconnection in transporting large amount of free magnetic energy
into jets. It is also suggested that there should be more free energy
released during the magnetic reconnection of blowout than of standard
jet events.
Title: On the Magnetic and Energy Characteristics of Recurrent
Homologous Jets from An Emerging Flux
Authors: Liu, Jiajia; Wang, Yuming; Erdélyi, Robertus; Liu, Rui;
McIntosh, Scott W.; Gou, Tingyu; Chen, Jun; Liu, Kai; Liu, Lijuan;
Pan, Zonghao
Bibcode: 2016ApJ...833..150L
Altcode: 2016arXiv160807705L
In this paper, we present the detailed analysis of recurrent homologous
jets originating from an emerging negative magnetic flux at the edge of
an active region. The observed jets show multithermal features. Their
evolution shows high consistence with the characteristic parameters
of the emerging flux, suggesting that with more free magnetic energy,
the eruptions tend to be more violent, frequent, and blowout-like. The
average temperature, average electron number density, and axial speed
are found to be similar for different jets, indicating that they
should have been formed by plasmas from similar origins. Statistical
analysis of the jets and their footpoint region conditions reveals
a strong positive relationship between the footpoint region total
131 Å intensity enhancement and jets’ length/width. Stronger
linearly positive relationships also exist between the total
intensity enhancement/thermal energy of the footpoint regions and
jets’ mass/kinetic/thermal energy, with higher cross-correlation
coefficients. All the above results together confirm the direct
relationship between the magnetic reconnection and the jets and
validate the important role of magnetic reconnection in transporting
large amounts of free magnetic energy into jets. It is also suggested
that there should be more free energy released during the magnetic
reconnection of blowout than of standard jet events.
Title: On the relationship between magnetic cancellation and UV
burst formation
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.
Bibcode: 2016MNRAS.463.2190N
Altcode: 2016arXiv160806505N; 2016MNRAS.tmp.1156N
Burst-like events with signatures in the UV are often observed
co-spatial to strong line-of-sight photospheric magnetic fields. Several
authors, for example, have noted the spatial relationship between
Ellerman bombs (EBs) and moving magnetic features (MMFs), regions of
flux which disconnect from a sunspot or pore before propagating away
in the moat flow and often displaying evidence of cancellation. In
this article, data collected by the Solar Dynamics Observatory's
Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly
are analysed in an attempt to understand the potential links between
such cancellation and UV burst formation. Two MMFs from AR 11579,
three bi-poles from AR 11765, and six bi-poles (four of which were
co-spatial to Interface Region Imaging Spectrograph bursts) in AR 11850
were identified for analysis. All of these cancellation features were
found to have lifetimes of the order hours and cancellation rates of
the order 1014-1015 Mx s-1. Hα line
wing data from the Dunn Solar Telescope's Interferometric BIdimensional
Spectrometer were also available for AR 11579 facilitating a discussion
of links between MMFs and EBs. Using an algebraic model of photospheric
magnetic reconnection, the measured cancellation rates are then used
to ascertain estimates of certain quantities (such as upflow speeds,
jet extents, and potential energy releases), which compared reasonably
to the properties of EBs reported within the literature. Our results
suggest that cancellation rates of the order measured here are capable
of supplying enough energy to drive certain UV bursts (including EBs),
however, they are not a guaranteeing condition for burst formation.
Title: Enhancement of a Sunspot Light Wall with External Disturbances
Authors: Yang, Shuhong; Zhang, Jun; Erdélyi, Robert
Bibcode: 2016ApJ...833L..18Y
Altcode: 2016arXiv161110032Y
Based on the Interface Region Imaging Spectrograph observations,
we study the response of a solar sunspot light wall to external
disturbances. A flare occurrence near the light wall caused material to
erupt from the lower solar atmosphere into the corona. Some material
falls back to the solar surface and hits the light bridge (I.e., the
base of the light wall), then sudden brightenings appear at the wall
base followed by the rise of wall top, leading to an increase of the
wall height. Once the brightness of the wall base fades, the height
of the light wall begins to decrease. Five hours later, another nearby
flare takes place, and a bright channel is formed that extends from the
flare toward the light bridge. Although no obvious material flow along
the bright channel is found, some ejected material is conjectured to
reach the light bridge. Subsequently, the wall base brightens and the
wall height begins to increase again. Once more, when the brightness
of the wall base decays, the wall top fluctuates to lower heights. We
suggest, based on the observed cases, that the interaction of falling
material and ejected flare material with the light wall results in
the brightenings of wall base and causes the height of the light wall
to increase. Our results reveal that the light wall can be not only
powered by the linkage of p-mode from below the photosphere, but may
also be enhanced by external disturbances, such as falling material.
Title: Buoyancy-driven Magnetohydrodynamic Waves
Authors: Hague, A.; Erdélyi, R.
Bibcode: 2016ApJ...828...88H
Altcode:
Turbulent motions close to the visible solar surface may generate
low-frequency internal gravity waves (IGWs) that propagate through the
lower solar atmosphere. Magnetic activity is ubiquitous throughout
the solar atmosphere, so it is expected that the behavior of IGWs
is to be affected. In this article we investigate the role of an
equilibrium magnetic field on propagating and standing buoyancy
oscillations in a gravitationally stratified medium. We assume that this
background magnetic field is parallel to the direction of gravitational
stratification. It is known that when the equilibrium magnetic field
is weak and the background is isothermal, the frequencies of standing
IGWs are sensitive to the presence of magnetism. Here, we generalize
this result to the case of a slowly varying temperature. To do this,
we make use of the Boussinesq approximation. A comparison between the
hydrodynamic and magnetohydrodynamic cases allows us to deduce the
effects due to a magnetic field. It is shown that the frequency of
IGWs may depart significantly from the Brunt-Väisälä frequency,
even for a weak magnetic field. The mathematical techniques applied
here give a clearer picture of the wave mode identification, which
has previously been misinterpreted. An observational test is urged to
validate the theoretical findings.
Title: The European Solar Telescope (EST)
Authors: Matthews, Sarah A.; Collados, Manuel; Mathioudakis, Mihalis;
Erdelyi, Robertus
Bibcode: 2016SPIE.9908E..09M
Altcode:
The European Solar Telescope (EST) is being designed to optimize
studies of the magnetic coupling between the lower layers of the solar
atmosphere (the photosphere and chromosphere) in order to investigate
the origins and evolution of the solar magnetic field and its role
in driving solar activity. In order to achieve this, the thermal,
dynamic and magnetic properties of the solar plasma must be probed
over many scale heights and at intrinsic scales, requiring the use of
multi wavelength spectroscopy and spectropolarimetry at high spatial,
spectral and temporal resolution. In this paper we describe some of
the over-arching science questions that EST will address and briefly
outline the main features of the proposed telescope design and the
associated instrumentation package.
Title: On the State of a Solar Active Region Before Flares and CMEs
Authors: Korsós, M. B.; Erdélyi, R.
Bibcode: 2016ApJ...823..153K
Altcode:
Several attempts have been made to find reliable diagnostic tools
to determine the state prior to flares and related coronal mass
ejections (CMEs) in solar active regions (ARs). Characterization of
the level of mixed states is carried out using the Debrecen sunspot
Data for 116 flaring ARs. Conditional flare probabilities (CFPs)
are calculated for different flaring classes. The association with
slow/fast CMEs is examined. Two precursor parameters are introduced:
(I) the sum of the (daily averaged) horizontal magnetic gradient G
S (G DS ) and (II) the separation parameter
{S}l-f. We found that if {S}l-f≤slant 1 for a
flaring AR then the CFP of the expected highest-intensity flare being
X-class is more than 70%. If 1≤slant {S}l-f≤slant 3 the
CFP is more than 45% for the highest-intensity flare(s) to be M-class,
and if 3≤slant {S}l-f≤slant 13 there is larger than 60%
CFP that C-class flare(s) may have the strongest intensity within 48
hr. Next, from analyzing G S for determining CFP we found:
if 5.5≤slant {log}({G}S) ≤slant 6.5, then it is very
likely that C-class flare(s) may be the most intense; if 6.5≤slant
{log}({G}S)≤slant 7.5 then there is ∼45% CFP that
M-class could have the highest intensity; finally, if 7.5≤slant
{log}({G}S) then there is at least 70% chance that the
strongest energy release will be X-class in the next 48 hr. ARs are
unlikely to produce X-class flare(s) if 13≤slant {S}l-f
and log(G S ) ≤slant 5.5. Finally, in terms of
providing an estimate of an associated slow/fast CME, we found that,
if {log}({S}l-f) ≥slant 0.4 or {log}({G}{DS})
≤slant 6.5, there is no accompanying fast CME in the following 24 hr.
Title: Propagation of Long-Wavelength Nonlinear Slow Sausage Waves
in Stratified Magnetic Flux Tubes
Authors: Barbulescu, M.; Erdélyi, R.
Bibcode: 2016SoPh..291.1369B
Altcode: 2016SoPh..tmp...74B
The propagation of nonlinear, long-wavelength, slow sausage waves in
an expanding magnetic flux tube, embedded in a non-magnetic stratified
environment, is discussed. The governing equation for surface waves,
which is akin to the Leibovich-Roberts equation, is derived using the
method of multiple scales. The solitary wave solution of the equation
is obtained numerically. The results obtained are illustrative of
a solitary wave whose properties are highly dependent on the degree
of stratification.
Title: Magneto-Acoustic Waves in a Gravitationally Stratified
Magnetized Plasma: Eigen-Solutions and their Applications to the
Solar Atmosphere
Authors: Mather, J. F.; Erdélyi, R.
Bibcode: 2016ApJ...822..116M
Altcode:
Magneto-acoustic gravity (MAG) waves have been studied intensively in
the context of astrophysical plasmas. There are three popular choices
of analytic modeling using a Cartesian coordinate system: a magnetic
field parallel, perpendicular, or at an angle to the gravitational
field. Here, we study a gravitationally stratified plasma embedded in
a parallel, so called vertical, magnetic field. We find a governing
equation for the auxiliary quantity Θ = p 1/ρ 0,
and find solutions in terms of hypergeometric functions. With the
convenient relationship between Θ and the vertical velocity component,
v z , we derive the solution for v z . We
show that the four linearly independent functions for v z
can also be cast as single hypergeometric functions, rather than the
Frobenius series derived by Leroy & Schwartz. We are then able to
analyze a case of approximation for a one-layer solution, taking the
small wavelength limit. Motivated by solar atmospheric applications,
we finally commence study of the eigenmodes of perturbations for a
two-layer model using our solutions, solving the dispersion relation
numerically. We show that, for a transition between a photospheric
and chromospheric plasma embedded in a vertical magnetic field,
modes exist that are between the observationally widely investigated
three and five minute oscillation periods, interpreted as solar
global oscillations in the lower solar atmosphere. It is also shown
that, when the density contrast between the layers is large (e.g.,
applied to photosphere/chromosphere-corona), the global eigenmodes
are practically a superposition of the same as in each of the separate
one-layer systems.
Title: On The Role of MHD Waves in Heating Localised Magnetic
Structures
Authors: Erdélyi, R.; Nelson, C. J.
Bibcode: 2016ASPC..504..153E
Altcode:
Satellite and ground-based observations from e.g. SOHO, TRACE, STEREO,
Hinode, SDO and IRIS to DST/ROSA, IBIS, CoMP, STT/CRISP have provided
a wealth of evidence of waves and oscillations present in a wide range
of spatial scales of the magnetised solar atmosphere. Our understanding
about localised solar structures has been considerably changed in light
of these high spatial and time resolution observations. However, MHD
waves not only enable us to perform sub-resolution magneto-seismology of
magnetic waveguides but are also potential candidates to carry and damp
the necessary non-thermal energy in these localised waveguides. First,
we will briefly outline the basic recent developments in MHD wave
theory focussing on linear waves. Next, we discuss the role of
the most frequently studied wave classes, including the Alfven, and
magneto-acoustic kink and sausage waves. The current theoretical (and
often difficult) interpretations of the detected solar atmospheric
wave and oscillatory phenomena within the framework of MHD will be
shown. Last, the latest reported observational findings of potential MHD
wave flux, in terms of localised plasma heating, in the solar atmosphere
is discussed, bringing us closer to solve the coronal heating problem.
Title: On the Properties of Slow MHD Sausage Waves within Small-scale
Photospheric Magnetic Structures
Authors: Freij, N.; Dorotovič, I.; Morton, R. J.; Ruderman, M. S.;
Karlovský, V.; Erdélyi, R.
Bibcode: 2016ApJ...817...44F
Altcode: 2015arXiv150908680F
The presence of magnetoacoustic waves in magnetic structures in the
solar atmosphere is well-documented. Applying the technique of solar
magneto-seismology (SMS) allows us to infer the background properties of
these structures. Here, we aim to identify properties of the observed
magnetoacoustic waves and study the background properties of magnetic
structures within the lower solar atmosphere. Using the Dutch Open
Telescope and Rapid Oscillations in the Solar Atmosphere instruments,
we captured two series of high-resolution intensity images with short
cadences of two isolated magnetic pores. Combining wavelet analysis
and empirical mode decomposition (EMD), we determined characteristic
periods within the cross-sectional (I.e., area) and intensity time
series. Then, by applying the theory of linear magnetohydrodynamics
(MHD), we identified the mode of these oscillations within the MHD
framework. Several oscillations have been detected within these two
magnetic pores. Their periods range from 3 to 20 minutes. Combining
wavelet analysis and EMD enables us to confidently find the phase
difference between the area and intensity oscillations. From these
observed features, we concluded that the detected oscillations can
be classified as slow sausage MHD waves. Furthermore, we determined
several key properties of these oscillations such as the radial
velocity perturbation, the magnetic field perturbation, and the
vertical wavenumber using SMS. The estimated range of the related
wavenumbers reveals that these oscillations are trapped within these
magnetic structures. Our results suggest that the detected oscillations
are standing harmonics, and this allows us to estimate the expansion
factor of the waveguides by employing SMS. The calculated expansion
factor ranges from 4 to 12.
Title: Linear MHD Wave Propagation in Time-Dependent Flux
Tube. III. Leaky Waves in Zero-Beta Plasma
Authors: Williamson, A.; Erdélyi, R.
Bibcode: 2016SoPh..291..175W
Altcode: 2015SoPh..tmp..157W
In this article, we evaluate the time-dependent wave properties and
the damping rate of propagating fast magneto-hydrodynamic (MHD) waves
when energy leakage into a magnetised atmosphere is considered. By
considering a cold plasma, initial investigations into the evolution
of MHD wave damping through this energy leakage will take place. The
time-dependent governing equations have been derived previously in
Williamson and Erdélyi (2014a, Solar Phys.289, 899 - 909) and are
now solved when the assumption of evanescent wave propagation in the
outside of the waveguide is relaxed. The dispersion relation for leaky
waves applicable to a straight magnetic field is determined in both an
arbitrary tube and a thin-tube approximation. By analytically solving
the dispersion relation in the thin-tube approximation, the explicit
expressions for the temporal evolution of the dynamic frequency and
wavenumber are determined. The damping rate is, then, obtained from
the dispersion relation and is shown to decrease as the density ratio
increases. By comparing the decrease in damping rate to the increase
in damping for a stationary system, as shown, we aim to point out
that energy leakage may not be as efficient a damping mechanism as
previously thought.
Title: Axisymmetric Modes in Magnetic Flux Tubes with Internal and
External Magnetic Twist
Authors: Giagkiozis, I.; Fedun, V.; Erdélyi, R.; Verth, G.
Bibcode: 2015ApJ...810...53G
Altcode: 2017arXiv170609669G
Observations suggest that twisted magnetic flux tubes are ubiquitous
in the Sun's atmosphere. The main aim of this work is to advance the
study of axisymmetric modes of magnetic flux tubes by modeling both
twisted internal and external magnetic fields, when the magnetic
twist is weak. In this work, we solve the derived wave equations
numerically assuming that the twist outside the tube is inversely
proportional to the distance from its boundary. We also study the case
of a constant magnetic twist outside the tube and solve these equations
analytically. We show that the solution for a constant twist outside
the tube is a good approximation for the case where the magnetic
twist is proportional to 1/r, namely, the error is in all cases less
than 5.4%. The solution is in excellent agreement with solutions
to simpler models of twisted magnetic flux tubes, i.e., without
external magnetic twist. It is shown that axisymmetric Alfvén waves
are naturally coupled with magnetic twist as the azimuthal component
of the velocity perturbation is nonzero. We compared our theoretical
results with observations and comment on what the Doppler signature
of these modes is expected to be. Lastly, we argue that the character
of axisymmetric waves in twisted magnetic flux tubes can lead to false
positives in identifying observations with axisymmetric Alfvén waves.
Title: Semicircular-like Secondary Flare Ribbons Associated with a
Failed Eruption
Authors: Zheng, R.; Korsós, M. B.; Erdélyi, R.
Bibcode: 2015ApJ...809...45Z
Altcode:
Flare ribbons (FRs) are one of the most apparent signatures of
solar flares and have been treated as an indicator of magnetic
reconnection. Drawing upon the observations from the Solar Dynamics
Observatory, we present semicircular-like secondary FRs (SFRs) of a
C2.3 flare on 2013 June 19. Before the flare eruption, two bipoles in
this core region subsequently emerged. Due to the interaction between
the two bipoles, a tether-cutting eruption took place in the core
region. The SFRs, surrounding the core region nearly simultaneously
with the flare onset, were much weaker than the two normal FRs. Two
ends of the SFRs experienced a separation and extension movement, but
the middle part of the SFRs hardly expanded outward. We find SFRs are
closely associated with the footpoint brightenings of some small loops
around the core region. The eruption was confined by transequatorial
loops (TLs), which resulted in the plasma material falling in the
north end of the TLs and remote brightenings showing up in the south
end of the TLs. The disappearance of the faint (filament) material
during the emergence of the SFRs could indicate another eruption. We
conclude that two or more magnetic reconnections are involved in this
event and propose that SFRs consisting of a small part of true FRs
resulted from the second magnetic reconnection and bright footpoints
of loop clusters likely heated by the main flare.
Title: On the Statistics of Macrospicules
Authors: Bennett, S. M.; Erdélyi, R.
Bibcode: 2015ApJ...808..135B
Altcode:
A new generation of solar telescopes has led to an increase in
the resolution of localized features seen on the Sun spatially,
temporally, and spectrally, enabling a detailed study of
macrospicules. Macrospicules are members of a wide variety of solar
ejecta and ascertaining where they belong in this family is vitally
important, particularly given that they are chromospheric events
which penetrate the transition region and lower corona. We examine the
overall properties of macrospicules, both temporal and spatial. We also
investigate possible relationships between the macrospicule properties
and the sample time period itself, which is selected as a proxy for
the ramp from solar minimum to solar maximum. Measurements are taken
using the Solar Dynamic Observatory to provide the necessary temporal
resolution and coverage. At each point in time, the length of the
macrospicule is measured from base to tip and the width is recorded
at half the length at each step. The measurements were then applied to
determine the statistical properties and relationships between them. It
is evident that the properties of maximum velocity, maximum length,
and lifetime are all related in specific, established terms. We provide
appropriate scaling in terms of the physical properties, which would
be a useful test bed for modeling. Also, we note that the maximum
lengths and lifetimes of the features show some correlation with the
sample epoch and, therefore, by proxy the solar minimum to maximum ramp.
Title: Observations and mode identification of sausage waves in a
magnetic pore
Authors: Moreels, M. G.; Freij, N.; Erdélyi, R.; Van Doorsselaere,
T.; Verth, G.
Bibcode: 2015A&A...579A..73M
Altcode:
Aims: We aim to determine the phase speed of an oscillation
in a magnetic pore using only intensity images at one height. The
observations were obtained using the CRisp Imaging SpectroPolarimeter
at the Swedisch 1-m Solar Telescope and show variations in both
cross-sectional area and intensity in a magnetic pore.
Methods: We have designed and tested an observational method to
extract the wave parameters that are important for seismology. We
modelled the magnetic pore as a straight cylinder with a uniform
plasma both inside and outside the flux tube and identify different
wave modes. Using analytic expressions, we are able to distinguish
between fast and slow modes and obtain the phase speed of the
oscillations.
Results: We found that the observed oscillations
are slow modes with a phase speed around 5 km s-1. We
also have strong evidence that the oscillations are standing
harmonics. Appendix A is available in electronic form at http://www.aanda.org
Title: Wave Damping Observed in Upwardly Propagating Sausage-mode
Oscillations Contained within a Magnetic Pore
Authors: Grant, S. D. T.; Jess, D. B.; Moreels, M. G.; Morton, R. J.;
Christian, D. J.; Giagkiozis, I.; Verth, G.; Fedun, V.; Keys, P. H.;
Van Doorsselaere, T.; Erdélyi, R.
Bibcode: 2015ApJ...806..132G
Altcode: 2015arXiv150501484G
We present observational evidence of compressible MHD wave modes
propagating from the solar photosphere through to the base of the
transition region in a solar magnetic pore. High cadence images were
obtained simultaneously across four wavelength bands using the Dunn
Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode
oscillations displaying significant power were detected in both
intensity and area fluctuations. The intensity and area fluctuations
exhibit a range of periods from 181 to 412 s, with an average period
∼290 s, consistent with the global p-mode spectrum. Intensity and
area oscillations present in adjacent bandpasses were found to be
out of phase with one another, displaying phase angles of 6.°12,
5.°82, and 15.°97 between the 4170 Å continuum-G-band, G-band-Na i
D1, and Na i D1-Ca ii K heights, respectively,
reiterating the presence of upwardly propagating sausage-mode waves. A
phase relationship of ∼0° between same-bandpass emission and area
perturbations of the pore best categorizes the waves as belonging to
the “slow” regime of a dispersion diagram. Theoretical calculations
reveal that the waves are surface modes, with initial photospheric
energies in excess of 35,000 W m-2. The wave energetics
indicate a substantial decrease in energy with atmospheric height,
confirming that magnetic pores are able to transport waves that exhibit
appreciable energy damping, which may release considerable energy into
the local chromospheric plasma.
Title: Photospheric logarithmic velocity spirals as MHD wave
generation mechanisms
Authors: Mumford, S. J.; Erdélyi, R.
Bibcode: 2015MNRAS.449.1679M
Altcode: 2015arXiv150101871M
High-resolution observations of the solar photosphere have identified
a wide variety of spiralling motions in the solar plasma. These
spirals vary in properties, but are observed to be abundant at the
solar surface. In this work, these spirals are studied for their
potential as magnetohydrodynamic (MHD) wave generation mechanisms. The
inter-granular lanes, where these spirals are commonly observed,
are also regions where the magnetic field strength is higher than
average. This combination of magnetic field and spiralling plasma is
a recipe for the generation of Alfvén waves and other MHD waves. This
work employs numerical simulations of a self-similar magnetic flux tube
embedded in a realistic, gravitationally stratified, solar atmosphere
to study the effects of a single magnetic flux tube perturbed by
a logarithmic velocity spiral driver. The expansion factor of the
logarithmic spiral driver is varied and multiple simulations are
run for a range of values of the expansion factor centred around
observational constraints. The simulations are analysed using `flux
surfaces' constructed from the magnetic field lines so that the vectors
perpendicular, parallel and azimuthal to the local magnetic field vector
can be calculated. The results of this analysis show that the Alfvén
wave is the dominant wave for lower values of the expansion factor,
whereas for the higher values the parallel component is dominant. This
transition occurs within the range of the observational constraints,
meaning that spiral drivers, as observed in the solar photosphere,
have the potential to generate a variety of MHD wave modes.
Title: On Flare Predictability Based on Sunspot Group Evolution
Authors: Korsós, M. B.; Ludmány, A.; Erdélyi, R.; Baranyi, T.
Bibcode: 2015ApJ...802L..21K
Altcode: 2015arXiv150304634K
The forecast method introduced by Korsós et al. is generalized from
the horizontal magnetic gradient (GM), defined between
two opposite polarity spots, to all spots within an appropriately
defined region close to the magnetic neutral line of an active
region. This novel approach is not limited to searching for the largest
GM of two single spots as in previous methods. Instead,
the pre-flare conditions of the evolution of spot groups is captured
by the introduction of the weighted horizontal magnetic gradient, or
W{{G}M}. This new proxy enables the potential to forecast
flares stronger than M5. The improved capability includes (i) the
prediction of flare onset time and (ii) an assessment of whether a
flare is followed by another event within about 18 hr. The prediction
of onset time is found to be more accurate here. A linear relationship
is established between the duration of converging motion and the time
elapsed from the moment of closest position to that of the flare onset
of opposite polarity spot groups. The other promising relationship is
between the maximum of the W{{G}M} prior to flaring and the
value of W{{G}M} at the moment of the initial flare onset in
the case of multiple flaring. We found that when the W{{G}M}
decreases by about 54%, then there is no second flare. If, however,
when the W{{G}M} decreases less than 42%, then there likely
will be a follow-up flare stronger than M5. This new capability may
be useful for an automated flare prediction tool.
Title: Editorial
Authors: Fedun, V.; Srivastava, A. K.; Erdelyi, R.; Pandey, J. C.
Bibcode: 2015JApA...36....1F
Altcode: 2015JApA..tmp...28.; 2015JApA...36....1.
Special Issue: Dynamical Plasma Processes in the Sun and Sun-like Stars
Title: A Fast MHD Code for Gravitationally Stratified Media using
Graphical Processing Units: SMAUG
Authors: Griffiths, M. K.; Fedun, V.; Erdélyi, R.
Bibcode: 2015JApA...36..197G
Altcode: 2015JApA..tmp...23G
Parallelization techniques have been exploited most successfully by
the gaming/graphics industry with the adoption of graphical processing
units (GPUs), possessing hundreds of processor cores. The opportunity
has been recognized by the computational sciences and engineering
communities, who have recently harnessed successfully the numerical
performance of GPUs. For example, parallel magnetohydrodynamic (MHD)
algorithms are important for numerical modelling of highly inhomogeneous
solar, astrophysical and geophysical plasmas. Here, we describe the
implementation of SMAUG, the Sheffield Magnetohydrodynamics Algorithm
Using GPUs. SMAUG is a 1-3D MHD code capable of modelling magnetized
and gravitationally stratified plasma. The objective of this paper is to
present the numerical methods and techniques used for porting the code
to this novel and highly parallel compute architecture. The methods
employed are justified by the performance benchmarks and validation
results demonstrating that the code successfully simulates the physics
for a range of test scenarios including a full 3D realistic model of
wave propagation in the solar atmosphere.
Title: Non-homogeneous Behaviour of the Spatial Distribution of
Macrospicules
Authors: Gyenge, N.; Bennett, S.; Erdélyi, R.
Bibcode: 2015JApA...36..103G
Altcode: 2015arXiv151208216G; 2015JApA..tmp...16G
In this paper the longitudinal and latitudinal spatial distribution of
macrospicules is examined. We found a statistical relationship between
the active longitude (determined by sunspot groups) and the longitudinal
distribution of macrospicules. This distribution of macrospicules shows
an inhomogeneity and non-axisymmetrical behaviour in the time interval
between June 2010 and December 2012, covered by observations of the
Solar Dynamic Observatory (SDO) satellite. The enhanced positions
of the activity and its time variation have been calculated. The
migration of the longitudinal distribution of macrospicules shows a
similar behaviour to that of the sunspot groups.
Title: The Dynamics of Rapid Redshifted and Blueshifted Excursions
in the Solar Hα Line
Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Erdélyi, R.;
Zaqarashvili, T. V.; Shelyag, S.; Keys, P. H.; Keenan, F. P.
Bibcode: 2015ApJ...802...26K
Altcode: 2015arXiv150106205K
We analyze high temporal and spatial resolution time-series of spectral
scans of the Hα line obtained with the CRisp Imaging SpectroPolarimeter
instrument mounted on the Swedish Solar Telescope. The data reveal
highly dynamic, dark, short-lived structures known as Rapid Redshifted
and Blueshifted Excursions (RREs, RBEs) that are on-disk absorption
features observed in the red and blue wings of spectral lines formed
in the chromosphere. We study the dynamics of RREs and RBEs by tracking
their evolution in space and time, measuring the speed of the apparent
motion, line of sight (LOS) Doppler velocity, and transverse velocity
of individual structures. A statistical study of their measured
properties shows that RREs and RBEs have similar occurrence rates,
lifetimes, lengths, and widths. They also display non-periodic,
nonlinear transverse motions perpendicular to their axes at speeds of
4-31 km s-1. Furthermore, both types of structures either
appear as high speed jets and blobs that are directed outwardly from
a magnetic bright point with speeds of 50-150 km s-1,
or emerge within a few seconds. A study of the different velocity
components suggests that the transverse motions along the LOS of
the chromospheric flux tubes are responsible for the formation and
appearance of these redshifted/blueshifted structures. The short
lifetime and fast disappearance of the RREs/RBEs suggests that, similar
to type II spicules, they are rapidly heated to transition region
or even coronal temperatures. We speculate that the Kelvin-Helmholtz
instability triggered by observed transverse motions of these structures
may be a viable mechanism for their heating.
Title: Magnetohydrodynamic Seismology of a Coronal Loop System by
the First Two Modes of Standing Kink Waves
Authors: Guo, Y.; Erdélyi, R.; Srivastava, A. K.; Hao, Q.; Cheng,
X.; Chen, P. F.; Ding, M. D.; Dwivedi, B. N.
Bibcode: 2015ApJ...799..151G
Altcode: 2014arXiv1411.7095G
We report the observation of the first two harmonics of the horizontally
polarized kink waves excited in a coronal loop system lying southeast of
AR 11719 on 2013 April 11. The detected periods of the fundamental mode
(P 1), its first overtone (P 2) in the northern
half, and that in the southern one are 530.2 ± 13.3, 300.4 ± 27.7, and
334.7 ± 22.1 s, respectively. The periods of the first overtone in the
two halves are the same considering uncertainties in the measurement. We
estimate the average electron density, temperature, and length of
the loop system as (5.1 ± 0.8) × 108 cm-3,
0.65 ± 0.06 MK, and 203.8 ± 13.8 Mm, respectively. As a zeroth-order
estimation, the magnetic field strength, B = 8.2 ± 1.0 G, derived by
the coronal seismology using the fundamental kink mode matches with
that derived by a potential field model. The extrapolation model also
shows the asymmetric and nonuniform distribution of the magnetic field
along the coronal loop. Using the amplitude profile distributions of
both the fundamental mode and its first overtone, we observe that the
antinode positions of both the fundamental mode and its first overtone
shift toward the weak field region along the coronal loop. The results
indicate that the density stratification and the temperature difference
effects are larger than the magnetic field variation effect on the
period ratio. On the other hand, the magnetic field variation has a
greater effect on the eigenfunction of the first overtone than the
density stratification does for this case.
Title: Generation of Magnetohydrodynamic Waves in Low Solar
Atmospheric Flux Tubes by Photospheric Motions
Authors: Mumford, S. J.; Fedun, V.; Erdélyi, R.
Bibcode: 2015ApJ...799....6M
Altcode: 2013arXiv1305.7415M
Recent ground- and space-based observations reveal the presence
of small-scale motions between convection cells in the solar
photosphere. In these regions, small-scale magnetic flux tubes are
generated via the interaction of granulation motion and the background
magnetic field. This paper studies the effects of these motions on
magnetohydrodynamic (MHD) wave excitation from broadband photospheric
drivers. Numerical experiments of linear MHD wave propagation in a
magnetic flux tube embedded in a realistic gravitationally stratified
solar atmosphere between the photosphere and the low choromosphere
(above β = 1) are performed. Horizontal and vertical velocity field
drivers mimic granular buffeting and solar global oscillations. A
uniform torsional driver as well as Archimedean and logarithmic spiral
drivers mimic observed torsional motions in the solar photosphere. The
results are analyzed using a novel method for extracting the parallel,
perpendicular, and azimuthal components of the perturbations, which
caters to both the linear and non-linear cases. Employing this method
yields the identification of the wave modes excited in the numerical
simulations and enables a comparison of excited modes via velocity
perturbations and wave energy flux. The wave energy flux distribution
is calculated to enable the quantification of the relative strengths
of excited modes. The torsional drivers primarily excite Alfvén modes
(≈60% of the total flux) with small contributions from the slow kink
mode, and, for the logarithmic spiral driver, small amounts of slow
sausage mode. The horizontal and vertical drivers primarily excite
slow kink or fast sausage modes, respectively, with small variations
dependent upon flux surface radius.
Title: Small-scale Structuring of Ellerman Bombs at the Solar Limb
Authors: Nelson, C. J.; Scullion, E. M.; Doyle, J. G.; Freij, N.;
Erdélyi, R.
Bibcode: 2015ApJ...798...19N
Altcode: 2014arXiv1410.5715N
Ellerman bombs (EBs) have been widely studied in recent years due to
their dynamic, explosive nature and apparent links to the underlying
photospheric magnetic field implying that they may be formed by
magnetic reconnection in the photosphere. Despite a plethora of
researches discussing the morphologies of EBs, there has been a limited
investigation of how these events appear at the limb, specifically,
whether they manifest as vertical extensions away from the disk. In
this article, we make use of high-resolution, high-cadence observations
of an Active Region at the solar limb, collected by the CRisp Imaging
SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their
physical properties. The upper atmosphere is also probed using the
Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). We
analyze 22 EB events evident within these data, finding that 20 appear
to follow a parabolic path away from the solar surface at an average
speed of 9 km s-1, extending away from their source by 580
km, before retreating back at a similar speed. These results show strong
evidence of vertical motions associated with EBs, possibly explaining
the dynamical "flaring" (changing in area and intensity) observed
in on-disk events. Two in-depth case studies are also presented that
highlight the unique dynamical nature of EBs within the lower solar
atmosphere. The viewing angle of these observations allows for a direct
linkage between these EBs and other small-scale events in the Hα line
wings, including a potential flux emergence scenario. The findings
presented here suggest that EBs could have a wider-reaching influence
on the solar atmosphere than previously thought, as we reveal a direct
linkage between EBs and an emerging small-scale loop, and other near-by
small-scale explosive events. However, as previous research found,
these extensions do not appear to impact upon the Hα line core,
and are not observed by the SDO/AIA EUV filters.
Title: Novel Approach to Construction Realistic Magnetic Field
Configuration in the Lower Solar Atmosphere
Authors: Fedun, V.; Gent, F.; Erdelyi, R.
Bibcode: 2014AGUFMSH13A4075F
Altcode:
Models of realistic magnetic field configurations, typical of the lower
solar atmosphere, in magneto-hydrostatic equilibrium are analytically
constructed. Systems incorporating open single and multiple flux tubes
and closed magnetic loops can be combined to form magnetic structures
that could even represent complex solar active regions.The developed
model successfully spans the Interface Region of the solar atmosphere,
from the photosphere up to the solar corona across the challenging
transition region, while retaining physically valid plasma pressure,
density and magnetic flux. Modelling magnetic structures can depict the
main characteristics of solar intergranular lanes or active regions. HMI
data can be used, as an initial magnetic field distribution,to construct
a realistic magnetic field distribution. The model includes a number
of free parameters, which makes the solution applicable to a variety
of other physical problems, and it may therefore be of more general
interest.
Title: Resonant Damping of Propagating Kink Waves in Time-Dependent
Magnetic Flux Tube. I. Zero Plasma-pmb{\upbeta}
Authors: Williamson, A.; Erdélyi, R.
Bibcode: 2014SoPh..289.4105W
Altcode: 2014SoPh..tmp..109W
We explore the notion of resonant absorption in a dynamic time-dependent
magnetised plasma background. Very many works have investigated
resonance in the Alfvén and slow MHD continua under both ideal and
dissipative MHD regimes. Jump conditions in static and steady systems
have been found in previous works, connecting solutions at both sides of
the resonant layer. Here, we derive the jump conditions in a temporally
dependent, magnetised, inhomogeneous plasma background to leading
order in the Wentzel-Kramers-Billouin (WKB) approximation. Next, we
exploit the results found in Williamson and Erdélyi (Solar Phys.289,
899, 2014) to describe the evolution of the jump condition in the
dynamic model considered. The jump across the resonant point is shown
to increase exponentially in time. We determined the damping as a
result of the resonance over the same time period and investigated the
temporal evolution of the damping itself. We found that the damping
coefficient, as a result of the evolution of the resonance, decreases
as the density gradient across the transitional layer decreases. This
has the consequence that in such time-dependent systems resonant
absorption may not be as efficient as time progresses.
Title: Coronal wave associated with a non-radial filament eruption
observed by the Solar Dynamics Observatory
Authors: Zheng, R.; Jiang, Y.; Yang, J.; Erdélyi, R.
Bibcode: 2014MNRAS.444.1119Z
Altcode:
We analyse a coronal wave that occurred during a non-radial filament
eruption observed by the Solar Dynamics Observatory on 2011 August
10. The filament underwent an extended time activation phase
followed by an abrupt ejection, and during its evolution it rotated
towards the south. The eruption was accompanied by fast-wave and
slow-perturbation phenomena. The slow perturbation occurred before
the eruption and impulsively accelerated almost simultaneously
with the eruption; its final propagation velocity was about 300 km
s-1, approximately equal tothat of the associated coronal
mass ejection. The slow perturbation is possibly an indicator of an
expanding loop overlying the filament. The fast wave was probably caused
by the rapid inflation of the overlying loop. Because of the eruption
location close to the limb and the effect of the complex environment,
the fast coronal wave showed different characteristics in different
directions: the kick-off speed was about 430-480 km s-1,
showing deceleration in some directions, and a high speed of up to 782
± 21 km s-1 in another direction. All the results indicate
that the coronal wave was a fast-mode magnetohydrodynamic wave, and the
wavelet analysis confirms the periodic wave nature of the coronal wave.
Title: The Detection of Upwardly Propagating Waves Channeling Energy
from the Chromosphere to the Low Corona
Authors: Freij, N.; Scullion, E. M.; Nelson, C. J.; Mumford, S.;
Wedemeyer, S.; Erdélyi, R.
Bibcode: 2014ApJ...791...61F
Altcode: 2014arXiv1408.4621F
There have been ubiquitous observations of wave-like motions in
the solar atmosphere for decades. Recent improvements to space- and
ground-based observatories have allowed the focus to shift to smaller
magnetic structures on the solar surface. In this paper, high-resolution
ground-based data taken using the Swedish 1 m Solar Telescope is
combined with co-spatial and co-temporal data from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory
(SDO) satellite to analyze running penumbral waves (RPWs). RPWs
have always been thought to be radial wave propagation that occurs
within sunspots. Recent research has suggested that they are in fact
upwardly propagating field-aligned waves (UPWs). Here, RPWs within a
solar pore are observed for the first time and are interpreted as UPWs
due to the lack of a penumbra that is required to support RPWs. These
UPWs are also observed co-spatially and co-temporally within several
SDO/AIA elemental lines that sample the transition region and low
corona. The observed UPWs are traveling at a horizontal velocity of
around 17 ± 0.5 km s-1 and a minimum vertical velocity
of 42 ± 21 km s-1. The estimated energy of the waves is
around 150 W m-2, which is on the lower bound required to
heat the quiet-Sun corona. This is a new, yet unconsidered source of
wave energy within the solar chromosphere and low corona.
Title: Magnetohydrostatic Equilibrium. II. Three-dimensional Multiple
Open Magnetic Flux Tubes in the Stratified Solar Atmosphere
Authors: Gent, F. A.; Fedun, V.; Erdélyi, R.
Bibcode: 2014ApJ...789...42G
Altcode: 2014arXiv1405.0613G
A system of multiple open magnetic flux tubes spanning the solar
photosphere and lower corona is modeled analytically, within a realistic
stratified atmosphere subject to solar gravity. This extends results
for a single magnetic flux tube in magnetohydrostatic equilibrium,
described in Gent et al. Self-similar magnetic flux tubes are combined
to form magnetic structures, which are consistent with high-resolution
observations. The observational evidence supports the existence
of strands of open flux tubes and loops persisting in a relatively
steady state. Self-similar magnetic flux tubes, for which an analytic
solution to the plasma density and pressure distribution is possible,
are combined. We calculate the appropriate balancing forces, applying
to the equations of momentum and energy conservation to preserve
equilibrium. Multiplex flux tube configurations are observed to remain
relatively stable for up to a day or more, and it is our aim to apply
our model as the background condition for numerical studies of energy
transport mechanisms from the solar surface to the corona. We apply
magnetic field strength, plasma density, pressure, and temperature
distributions consistent with observational and theoretical estimates
for the lower solar atmosphere. Although each flux tube is identical in
construction apart from the location of the radial axis, combinations
can be applied to generate a non-axisymmetric magnetic field with
multiple non-uniform flux tubes. This is a considerable step forward
in modeling the realistic magnetized three-dimensional equilibria of
the solar atmosphere.
Title: Longitudinal Magnetohydrodynamics Oscillations in Dissipative,
Cooling Coronal Loops
Authors: Al-Ghafri, K. S.; Ruderman, M. S.; Williamson, A.; Erdélyi,
R.
Bibcode: 2014ApJ...786...36A
Altcode:
This paper investigates the effect of cooling on standing slow
magnetosonic waves in coronal magnetic loops. The damping mechanism
taken into account is thermal conduction that is a viable candidate for
dissipation of slow magnetosonic waves in coronal loops. In contrast
to earlier studies, here we assume that the characteristic damping
time due to thermal conduction is not small, but arbitrary, and can
be of the order of the oscillation period, i.e., a temporally varying
plasma is considered. The approximation of low-beta plasma enables us
to neglect the magnetic field perturbation when studying longitudinal
waves and consider, instead, a one-dimensional motion that allows
a reliable first insight into the problem. The background plasma
temperature is assumed to be decaying exponentially with time, with
the characteristic cooling timescale much larger than the oscillation
period. This assumption enables us to use the WKB method to study
the evolution of the oscillation amplitude analytically. Using this
method we obtain the equation governing the oscillation amplitude. The
analytical expressions determining the wave properties are evaluated
numerically to investigate the evolution of the oscillation frequency
and amplitude with time. The results show that the oscillation period
increases with time due to the effect of plasma cooling. The plasma
cooling also amplifies the amplitude of oscillations in relatively
cool coronal loops, whereas, for very hot coronal loop oscillations
the damping rate is enhanced by the cooling. We find that the critical
point for which the amplification becomes dominant over the damping is
in the region of 4 MK. These theoretical results may serve as impetus
for developing the tools of solar magneto-seismology in dynamic plasmas.
Title: Linear MHD Wave Propagation in Time-Dependent Flux
Tube. II. Finite Plasma Beta
Authors: Williamson, A.; Erdélyi, R.
Bibcode: 2014SoPh..289.1193W
Altcode:
The propagation of magnetohydrodynamic (MHD) waves is an area that
has been thoroughly studied for idealised static and steady state
magnetised plasma systems applied to numerous solar structures. By
applying the generalisation of a temporally varying background density
to an open magnetic flux tube, mimicking the observed slow evolution of
such waveguides in the solar atmosphere, further investigations into
the propagation of both fast and slow MHD waves can take place. The
assumption of a zero-beta plasma (no gas pressure) was applied in
Williamson and Erdélyi (Solar Phys.2013, doi:10.1007/s11207-013-0366-9,
Paper I) is now relaxed for further analysis here. Firstly, the
introduction of a finite thermal pressure to the magnetic flux
tube equilibrium modifies the existence of fast MHD waves which are
directly comparable to their counterparts found in Paper I. Further,
as a direct consequence of the non-zero kinetic plasma pressure,
a slow MHD wave now exists, and is investigated. Analysis of the
slow wave shows that, similar to the fast MHD wave, wave amplitude
amplification takes place in time and height. The evolution of the
wave amplitude is determined here analytically. We conclude that for
a temporally slowly decreasing background density both propagating
magnetosonic wave modes are amplified for over-dense magnetic flux
tubes. This information can be very practical and useful for future
solar magneto-seismology applications in the study of the amplitude and
frequency properties of MHD waveguides, e.g. for diagnostic purposes,
present in the solar atmosphere.
Title: Linear MHD Wave Propagation in Time-Dependent Flux
Tube. I. Zero Plasma-β
Authors: Williamson, A.; Erdélyi, R.
Bibcode: 2014SoPh..289..899W
Altcode:
MHD waves and oscillations in sharply structured magnetic plasmas
have been studied for static and steady systems in the thin tube
approximation over many years. This work will generalize these studies
by introducing a slowly varying background density in time, in order
to determine the changes to the wave parameters introduced by this
temporally varying equilibrium, i.e. to investigate the amplitude,
frequency, and wavenumber for the kink and higher order propagating fast
magnetohydrodynamic wave in the leading order approximation to the WKB
approach in a zero-β plasma representing the upper solar atmosphere. To
progress, the thin tube and over-dense loop approximations are used,
restricting the results found here to the duration of a number of
multiples of the characteristic density change timescale. Using such
approximations it is shown that the amplitude of the kink wave is
enhanced in a manner proportional to the square of the Alfvén speed,
. The frequency of the wave solution tends to the driving frequency of
the system as time progresses; however, the wavenumber approaches zero
after a large multiple of the characteristic density change timescale,
indicating an ever increasing wavelength. For the higher order fluting
modes the changes in amplitude are dependent upon the wave mode; for
the m=2 mode the wave is amplified to a constant level; however, for
all m≥3 the fast MHD wave is damped within a relatively small multiple
of the characteristic density change timescale. Understanding MHD wave
behavior in time-dependent plasmas is an important step towards a more
complete model of the solar atmosphere and has a key role to play in
solar magneto-seismological applications.
Title: Standing sausage waves in photospheric magnetic waveguides
Authors: Dorotovič, I.; Erdélyi, R.; Freij, N.; Karlovský, V.;
Márquez, I.
Bibcode: 2014A&A...563A..12D
Altcode: 2012arXiv1210.6476D
Aims: By focussing on the oscillations of the cross-sectional
area and the total intensity of magnetic waveguides located in the lower
solar atmosphere, we aim to detect and identify magnetohydrodynamic
(MHD) sausage waves.
Methods: Capturing several high-resolution
time series of magnetic waveguides and employing a wavelet analysis,
in conjunction with empirical mode decomposition (EMD), makes the MHD
wave analysis possible. For this paper, two sunspots and one pore
(with a light bridge) were chosen as examples of MHD waveguides in
the lower solar atmosphere.
Results: The waveguides display a
range of periods from 4 to 65 min. These structures display in-phase
behaviour between the area and intensity, presenting mounting evidence
for sausage modes within these waveguides. The detected periods point
towards standing oscillations.
Conclusions: The presence of fast
and slow MHD sausage waves has been detected in three different magnetic
waveguides in the solar photosphere. Furthermore, these oscillations
are potentially standing harmonics supported in the waveguides that
are sandwiched vertically between the temperature minimum in the lower
solar atmosphere and the transition region. The relevance of standing
harmonic oscillations is that their exploitation by means of solar
magneto-seismology may allow insight into the sub-pixel resolution
structure of photospheric MHD waveguides.
Title: The Generation and Damping of Propagating MHD Kink Waves in
the Solar Atmosphere
Authors: Morton, R. J.; Verth, G.; Hillier, A.; Erdélyi, R.
Bibcode: 2014ApJ...784...29M
Altcode: 2013arXiv1310.4650M
The source of the non-thermal energy required for the heating of the
upper solar atmosphere to temperatures in excess of a million degrees
and the acceleration of the solar wind to hundreds of kilometers
per second is still unclear. One such mechanism for providing the
required energy flux is incompressible torsional Alfvén and kink
magnetohydrodynamic (MHD) waves, which are magnetically dominated
waves supported by the Sun's pervasive and complex magnetic field. In
particular, propagating MHD kink waves have recently been observed
to be ubiquitous throughout the solar atmosphere, but, until now,
critical details of the transport of the kink wave energy throughout
the Sun's atmosphere were lacking. Here, the ubiquity of the
waves is exploited for statistical studies in the highly dynamic
solar chromosphere. This large-scale investigation allows for the
determination of the chromospheric kink wave velocity power spectra, a
missing link necessary for determining the energy transport between the
photosphere and corona. Crucially, the power spectra contain evidence
for horizontal photospheric motions being an important mechanism for
kink wave generation in the quiescent Sun. In addition, a comparison
with measured coronal power spectra is provided for the first time,
revealing frequency-dependent transmission profiles, suggesting that
there is enhanced damping of kink waves in the lower corona.
Title: NEOCE: a new external occulting coronagraph experiment for
ultimate observations of the chromosphere, corona and interface
Authors: Damé, Luc; Fineschi, Silvano; Kuzin, Sergey; Von
Fay-Siebenburgen, Erdélyi Robert
Bibcode: 2014cosp...40E.617D
Altcode:
Several ground facilities and space missions are currently dedicated
to the study of the Sun at high resolution and of the solar corona
in particular. However, and despite significant progress with the
advent of space missions and UV, EUV and XUV direct observations
of the hot chromosphere and million-degrees coronal plasma, much is
yet to be achieved in the understanding of these high temperatures,
fine dynamic dissipative structures and of the coronal heating in
general. Recent missions have shown the definite role of a wide
range of waves and of the magnetic field deep in the inner corona,
at the chromosphere-corona interface, where dramatic and physically
fundamental changes occur. The dynamics of the chromosphere and corona
is controlled and governed by the emerging magnetic field. Accordingly,
the direct measurement of the chromospheric and coronal magnetic fields
is of prime importance. The solar corona consists of many localised
loop-like structures or threads with the plasmas brightening and
fading independently. The plasma evolution in each thread is believed
to be related to the formation of filaments, each one being dynamic,
in a non-equilibrium state. The mechanism sustaining this dynamics,
oscillations or waves (Alfvén or other magneto-plasma waves),
requires both very high-cadence, multi-spectral observations, and high
resolution and coronal magnetometry. This is foreseen in the future
Space Mission NEOCE (New External Occulting Coronagraph Experiment),
the ultimate new generation high-resolution coronagraphic heliospheric
mission, to be proposed for ESA M4. NEOCE, an evolution of the HiRISE
mission, is ideally placed at the L5 Lagrangian point (for a better
follow-up of CMEs), and provides FUV imaging and spectro-imaging,
EUV and XUV imaging and spectroscopy, and ultimate coronagraphy by
a remote external occulter (two satellites in formation flying 375 m
apart minimizing scattered light) allowing to characterize temperature,
densities and velocities up to the solar upper chromosphere, transition
zone and inner corona with, in particular, 2D very high resolution
multi-spectral imaging-spectroscopy and direct coronal magnetic field
measurement: a unique set of tools to understand the structuration and
onset of coronal heating. We give a detailed account of the proposed
mission profile, and its major scientific objectives and model payload
(in particular of the SuperASPIICS package of visible, NIR and UV,
Lyman-Alpha and OVI, coronagraphs).
Title: Effects of Stratification and Flows on P 1/ P
2 Ratios and Anti-node Shifts Within Closed Loop Structures
Authors: Erdélyi, R.; Hague, A.; Nelson, C. J.
Bibcode: 2014SoPh..289..167E
Altcode: 2013arXiv1306.1051E
The solar atmosphere is a dynamic environment, constantly evolving
to form a wide range of magnetically dominated structures (coronal
loops, spicules, prominences, etc.) which cover a significant
percentage of the surface at any one time. Oscillations and waves
in many of these structures are now widely observed and have led
to the new analytic technique of solar magneto-seismology, where
inferences of the background conditions of the plasma can be deduced
by studying magneto-hydrodynamic (MHD) waves. Here, we generalise
a novel magneto-seismological method designed to infer the density
distribution of a bounded plasma structure from the relationship of
its fundamental and subsequent harmonics. Observations of the solar
atmosphere have emphatically shown that stratification, leading to
complex density profiles within plasma structures, is common thereby
rendering this work instantly accessible to solar physics. We show,
in a dynamic waveguide, how the period ratio differs from the idealised
harmonic ratios prevalent in homogeneous structures. These ratios show
strong agreement with recent observational work. Next, anti-node shifts
are also analysed. Using typical scaling parameters for bulk flows
within atmospheric waveguides, e.g., coronal loops, it is found that
significant anti-node shifts can be predicted, even to the order of 10
Mm. It would be highly encouraged to design specific observations to
confirm the predicted anti-node shifts and apply the developed theory
of solar magneto-seismology to gain more accurate waveguide diagnostics
of the solar atmosphere.
Title: Novel approach to construction realistic magnetic field
configuration in the lower solar atmosphere
Authors: Fedun, Viktor; Von Fay-Siebenburgen, Erdélyi Robert; Gent,
Frederick
Bibcode: 2014cosp...40E.846F
Altcode:
Models of realistic magnetic field configurations, typical of the lower
solar atmosphere, in magneto-hydrostatic equilibrium are analytically
constructed. Systems incorporating open single and multiple flux tubes
and closed magnetic loops can be combined to form magnetic structures
that could even represent complex solar active regions. The developed
model successfully spans the Interface Region of the solar atmosphere,
from the photosphere up to the solar corona across the challenging
transition region, while retaining physically valid plasma pressure,
density and magnetic flux. Modelling magnetic structures can depict the
main characteristics of solar intergranular lanes or active regions. HMI
data can be used, as an initial magnetic field distribution, to
construct a realistic magnetic field distribution. The model includes
a number of free parameters, which makes the solution applicable to
a variety of other physical problems, and it may therefore be of more
general interest.
Title: The energy flux of MHD wave modes excited by realistic
photospheric drivers
Authors: Fedun, Viktor; Von Fay-Siebenburgen, Erdélyi Robert;
Mumford, Stuart
Bibcode: 2014cosp...40E.847F
Altcode:
The mechanism(s) responsible for solar coronal heating are still an
unresolved and challenging task. In the framework of 3D numerical
modelling of MHD wave excitation and propagation in the strongly
stratified solar atmosphere we analyse the mode coupling and estimate
the wave energy partition which can be supplied to the upper layers
of the solar atmosphere by locally decomposed slow, fast and Alfven
modes. These waves are excited by a number of realistic photospheric
drivers which are mimicking the random granular buffeting, the coherent
global solar oscillations and swirly motion observed in e.g. magnetic
bright points. Based on a self-similar approach, a realistic magnetic
flux tubes configuration is constructed and implemented in the VALIIIC
model of the solar atmosphere. A novel method for decomposing the
velocity perturbations into parallel, perpendicular and azimuthal
components in 3D geometry is developed using field lines to trace
a volume of constant energy flux. This method is used to identify
the excited wave modes propagating upwards from the photosphere and
to compute the percentage energy contribution of each mode. We have
found, that for all cases where torsional motion is present, the main
contribution to the flux (60%) is by Alfven wave. In the case of the
vertical driver it is found to mainly excite the fast- and slow-sausage
modes and a horizontal driver primarily excites the slow kink mode.
Title: Characteristics of Transverse Waves in Chromospheric Mottles
Authors: Kuridze, D.; Verth, G.; Mathioudakis, M.; Erdélyi, R.;
Jess, D. B.; Morton, R. J.; Christian, D. J.; Keenan, F. P.
Bibcode: 2013ApJ...779...82K
Altcode: 2013arXiv1310.3628K
Using data obtained by the high temporal and spatial resolution
Rapid Oscillations in the Solar Atmosphere instrument on the Dunn
Solar Telescope, we investigate at an unprecedented level of detail
transverse oscillations in chromospheric fine structures near the solar
disk center. The oscillations are interpreted in terms of propagating
and standing magnetohydrodynamic kink waves. Wave characteristics
including the maximum transverse velocity amplitude and the phase
speed are measured as a function of distance along the structure's
length. Solar magnetoseismology is applied to these measured parameters
to obtain diagnostic information on key plasma parameters (e.g.,
magnetic field, density, temperature, flow speed) of these localized
waveguides. The magnetic field strength of the mottle along the ~2 Mm
length is found to decrease by a factor of 12, while the local plasma
density scale height is ~280 ± 80 km.
Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the
Lower Solar Atmosphere
Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.;
Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R.
Bibcode: 2013ApJ...779..125N
Altcode: 2013arXiv1310.7756N
The presence of photospheric magnetic reconnection has long been thought
to give rise to short and impulsive events, such as Ellerman bombs (EBs)
and Type II spicules. In this article, we combine high-resolution,
high-cadence observations from the Interferometric BIdimensional
Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments
at the Dunn Solar Telescope, National Solar Observatory, New Mexico,
with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly
and Hinode Solar Optical Telescope (SOT) data to observe small-scale
events situated within an active region. These data are then compared
with state-of-the-art numerical simulations of the lower atmosphere
made using the MURaM code. It is found that brightenings, in both the
observations and the simulations, of the wings of the Hα line profile,
interpreted as EBs, are often spatially correlated with increases in
the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred
from Hinode/SOT magnetic field data show evidence of flux cancellation
associated, co-spatially, with these EBs, suggesting that magnetic
reconnection could be a driver of these high-energy events. Through
the analysis of similar events in the simulated lower atmosphere,
we are able to infer that line profiles analogous to the observations
occur co-spatially with regions of strong opposite-polarity magnetic
flux. These observed events and their simulated counterparts are
interpreted as evidence of photospheric magnetic reconnection at scales
observable using current observational instrumentation.
Title: A Statistical Study of Transverse Oscillations in a Quiescent
Prominence
Authors: Hillier, A.; Morton, R. J.; Erdélyi, R.
Bibcode: 2013ApJ...779L..16H
Altcode: 2013arXiv1310.8009H
The launch of the Hinode satellite has allowed for seeing-free
observations at high-resolution and high-cadence making it well suited
to study the dynamics of quiescent prominences. In recent years it
has become clear that quiescent prominences support small-amplitude
transverse oscillations, however, sample sizes are usually too small
for general conclusions to be drawn. We remedy this by providing a
statistical study of transverse oscillations in vertical prominence
threads. Over a 4 hr period of observations it was possible to
measure the properties of 3436 waves, finding periods from 50 to
6000 s with typical velocity amplitudes ranging between 0.2 and 23
km s-1. The large number of observed waves allows the
determination of the frequency dependence of the wave properties and
derivation of the velocity power spectrum for the transverse waves. For
frequencies less than 7 mHz, the frequency dependence of the velocity
power is consistent with the velocity power spectra generated from
observations of the horizontal motions of magnetic elements in the
photosphere, suggesting that the prominence transverse waves are
driven by photospheric motions. However, at higher frequencies the two
distributions significantly diverge, with relatively more power found
at higher frequencies in the prominence oscillations. These results
highlight that waves over a large frequency range are ubiquitous in
prominences, and that a significant amount of the wave energy is found
at higher frequency.
Title: Effect of stratification on the frequency of bounded Rossby
modes over a non-flat bottom
Authors: Colantuono, Giuseppe; Erdélyi, Robert; Ruderman, Michael S.
Bibcode: 2013GApFD.107..541C
Altcode:
This work attempts to express and analyze the challenges, induced by
stratification, affecting the Rossby-topographic eigenmodes of a closed
domain with a general uneven bottom of arbitrary shape filled with a
uniform fluid in the unperturbed configuration. The modified eigenmodes
have been computed analytically: stratification is introduced in the
mathematical form of a perturbation of a homogeneous fluid over a
non-flat bottom. The eigenmodes lose their barotropic character and
differences appear in the dynamical fields (velocity and pressure)
from upper to lower layer, as expected. Expressions for the baroclinic
and ageostrophic velocity components due to the perturbation are
given. The analysis is carried out in the frame of linear shallow
water approximation. All terms have been retained apart from nonlinear
advection in the governing equations. We find that the frequencies
of the eigenmodes change; an analytical expression of frequency
correction as a function of layer density difference and interface
depth is found. Initial results for some elementary geometrical
settings with a waveguide bottom are determined and expressed in
a concise, easily readable closed form. The results obtained in the
shallow water approximation are expanded in series with respect to the
Rossby number. Next, they are compared with the frequency correction
obtained in an alternative framework in which the quasi-geostrophic
approximation is used, and a purely baroclinic perturbation is imposed
from the outset as the result of the introduction of stratification
in the otherwise homogeneous fluid. In this scenario, reduced gravity
and the ratio of upper to lower layer depth are, in turn, used as the
expansion parameters in lieu of the Rossby number.
Title: Magnetohydrostatic equilibrium - I. Three-dimensional open
magnetic flux tube in the stratified solar atmosphere
Authors: Gent, F. A.; Fedun, V.; Mumford, S. J.; Erdélyi, R.
Bibcode: 2013MNRAS.435..689G
Altcode: 2013arXiv1305.4788A; 2013MNRAS.tmp.1974G
A single open magnetic flux tube spanning the solar photosphere (solar
radius ≃ R⊙) and the lower corona (R⊙
+ 10 Mm) is modelled in magnetohydrostatic equilibrium within a
realistic stratified atmosphere subject to solar gravity. Such flux
tubes are observed to remain relatively stable for up to a day or more,
and it is our aim to apply the model as the background condition for
numerical studies of energy transport mechanisms from the surface to
the corona. We solve analytically an axially symmetric 3D structure
for the model, with magnetic field strength, plasma density, pressure
and temperature all consistent with observational and theoretical
estimates. The self-similar construction ensures the magnetic field is
divergence free. The equation of pressure balance for this particular
set of flux tubes can be integrated analytically to find the pressure
and density corrections required to preserve the magnetohydrostatic
equilibrium. The model includes a number of free parameters, which
makes the solution applicable to a variety of other physical problems
and it may therefore be of more general interest.
Title: PREFACE: Eclipse on the Coral Sea: Cycle 24 Ascending
Authors: Cally, Paul; Erdélyi, Robert; Norton
Bibcode: 2013JPhCS.440a1001C
Altcode:
A total solar eclipse is the most spectacular and awe-inspiring
astronomical phenomenon most people will ever see in their
lifetimes. Even hardened solar scientists draw inspiration from it. The
eclipse with 2 minutes totality in the early morning of 14 November 2012
(local time) drew over 120 solar researchers (and untold thousands of
the general public) to the small and picturesque resort town of Palm
Cove just north of Cairns in tropical north Queensland, Australia,
and they were rewarded when the clouds parted just before totality
to reveal a stunning solar display. Eclipse photograph The
eclipse was also the catalyst for an unusually broad and exciting
conference held in Palm Cove over the week 12--16 November. Eclipse on
the Coral Sea: Cycle 24 Ascending served as GONG 2012, LWS/SDO-5, and
SOHO 27, indicating how widely it drew on the various sub-communities
within solar physics. Indeed, as we neared the end of the ascending
phase of the peculiar Solar Cycle 24, it was the perfect time to
bring the whole community together to discuss our Sun's errant recent
behaviour, especially as Cycle 24 is the first to be fully observed by
the Solar Dynamics Observatory (SDO). The whole-Sun perspective was a
driving theme of the conference, with the cycle probed from interior
(helioseismology), to atmosphere (the various lines observed by the
Atmospheric Imaging Assemble (AIA) aboard SDO, the several instruments
on Hinode, and other modern observatories), and beyond (CMEs etc). The
quality of the presentations was exceptional, and the many speakers
are to be commended for pitching their talks to the broad community
present. These proceedings draw from the invited and contributed
oral presentations and the posters exhibited in Palm Cove. They give an
(incomplete) snapshot of the meeting, illustrating its broad vistas. The
published contributions are organized along the lines of the conference
sessions, as set out in the Contents, leading off with a provocative
view of Cycle 24 thus far from Sarbani Basu. Other invited papers
presented here include an appreciation of Hinode's view of solar
activity as the cycle rises by Toshifumi Shimizu; a first taxonomy of
magnetic tornadoes and chromospheric swirls by Sven Wedemeyer {\it et
al}; an analysis of Hinode/EIS observations of transient heating events;
a timely re-examination of solar dynamo theory by Paul Charbonneau;
an exciting teaser for the solar potential of the Murchison Widefield
Array now operating in Western Australia by Steven Tingay {\it et al};
an overview and critique of the state of nonlinear force-free magnetic
field extrapolation theory and practice by Mike Wheatland and Stuart
Gilchrist; and a masterful review of atmospheric MHD wave coupling to
the Sun's internal p-mode oscillations by Elena Khomenko and Irantzu
Calvo Santamaria. The many contributed papers published here are no less
exciting. All papers have been refereed to a high standard. The
editors thank all the referees, drawn both from conference attendees
and the wider community, who have taken their tasks very seriously and
provided very detailed and helpful reports. Nearly all contributions
have been substantially improved by the process. We must also thank
our financial sponsors. Both the Global Oscillations Network Group
(GONG) and LWS/SDO were generous in their support, as were the School
of Mathematical Sciences and the Monash Centre for Astrophysics (MoCA)
at Monash University, Melbourne, and the Centre for Astronomy at James
Cook University, Townsville. The Local Organizing Committee and the
many students who assisted before and during the conference also deserve
high praise for facilitating such a memorable meeting. Paul Cally,
Robert Erdélyi and Aimee Norton Conference photograph
Title: Alfvén Waves in the Solar Atmosphere. From Theory to
Observations
Authors: Mathioudakis, M.; Jess, D. B.; Erdélyi, R.
Bibcode: 2013SSRv..175....1M
Altcode: 2012SSRv..tmp...94M; 2012arXiv1210.3625M
Alfvén waves are considered to be viable transporters of the
non-thermal energy required to heat the Sun's quiescent atmosphere. An
abundance of recent observations, from state-of-the-art facilities, have
reported the existence of Alfvén waves in a range of chromospheric
and coronal structures. Here, we review the progress made in
disentangling the characteristics of transverse kink and torsional
linear magnetohydrodynamic (MHD) waves. We outline the simple, yet
powerful theory describing their basic properties in (non-)uniform
magnetic structures, which closely resemble the building blocks of
the real solar atmosphere.
Title: Evidence for the Photospheric Excitation of Incompressible
Chromospheric Waves
Authors: Morton, R. J.; Verth, G.; Fedun, V.; Shelyag, S.; Erdélyi, R.
Bibcode: 2013ApJ...768...17M
Altcode: 2013arXiv1303.2356M
Observing the excitation mechanisms of incompressible transverse
waves is vital for determining how energy propagates through the lower
solar atmosphere. We aim to show the connection between convectively
driven photospheric flows and incompressible chromospheric waves. The
observations presented here show the propagation of incompressible
motion through the quiet lower solar atmosphere, from the photosphere
to the chromosphere. We determine photospheric flow vectors to search
for signatures of vortex motion and compare results to photospheric
flows present in convective simulations. Further, we search for the
chromospheric response to vortex motions. Evidence is presented that
suggests incompressible waves can be excited by the vortex motions of a
strong magnetic flux concentration in the photosphere. A chromospheric
counterpart to the photospheric vortex motion is also observed,
presenting itself as a quasi-periodic torsional motion. Fine-scale,
fibril structures that emanate from the chromospheric counterpart
support transverse waves that are driven by the observed torsional
motion. A new technique for obtaining details of transverse waves from
time-distance diagrams is presented and the properties of transverse
waves (e.g., amplitudes and periods) excited by the chromospheric
torsional motion are measured.
Title: SDO/AIA observations of periodic and quasi-periodic phenomenon
associated with an EUV jet
Authors: Morton, Richard; Verth, Gary; Erdelyi, Robertus; Srivastava,
Abhi
Bibcode: 2013EGUGA..15...52M
Altcode:
It has long been advocated that explosive magnetic activity is
responsible for the mass-balance in the solar atmosphere, supplying
the corona and the solar wind with heated plasma. The explosive
events are thought to be the result of emerging bi-polar (EB) regions
reconnecting with pre-existing, open fields, with the size of the EB's
(i.e., granular, super-granular) being related to size of the resulting
feature (i.e., spicules, EUV/X-ray jets). Recent evidence has suggested
a deeper relationship between spicules and EUV jets (Sterling et al.,
2010). We present here observations of a EUV jet observed with SDO/AIA
close to a southern coronal hole. The jet can be considered as a
'Blowout jet' (using the terminology of Moore et al., 2010), launching
vast amounts of chromospheric plasma into the atmosphere along with
hotter material. The hotter part of the jet appears to be composed
of multiple, (quasi-)periodic ejections that individually resemble
fast moving (>100 km/s) spicules. The multiple ejections appear
crucial for distributing the hotter material high into the corona,
possibly suggesting that larger EUV/X-ray are composed of many smaller
spicule-like events. Although the event is close to the limb, evidence
for reconnection at the chromospheric level is provided. Further,
evidence for helicity (or torsional motion) and the presence of slow and
fast Magnetohydrodynamic waves is given, with the wave mode excitation
likely due to the reconnection process. Exploiting the observed wave
motion, we also use magneto-seismological techniques to determine local
plasma parameters with sub-resolution accuracy along one of the jets
unique features.
Title: Statistical Analysis of Small Ellerman Bomb Events
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.;
Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K.
Bibcode: 2013SoPh..283..307N
Altcode: 2013arXiv1301.1351N
The properties of Ellerman bombs (EBs), small-scale brightenings in
the Hα line wings, have proved difficult to establish because their
size is close to the spatial resolution of even the most advanced
telescopes. Here, we aim to infer the size and lifetime of EBs using
high-resolution data of an emerging active region collected using
the Interferometric BIdimensional Spectrometer (IBIS) and Rapid
Oscillations of the Solar Atmosphere (ROSA) instruments as well as
the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We develop an algorithm to track EBs through their
evolution, finding that EBs can often be much smaller (around 0.3″)
and shorter-lived (less than one minute) than previous estimates. A
correlation between G-band magnetic bright points and EBs is also
found. Combining SDO/HMI and G-band data gives a good proxy of the
polarity for the vertical magnetic field. It is found that EBs often
occur both over regions of opposite polarity flux and strong unipolar
fields, possibly hinting at magnetic reconnection as a driver of these
events.The energetics of EB events is found to follow a power-law
distribution in the range of a nanoflare (1022−25 ergs).
Title: Effect of Variable Background on an Oscillating Hot Coronal
Loop
Authors: Al-Ghafri, K. S.; Erdélyi, R.
Bibcode: 2013SoPh..283..413A
Altcode:
We investigate the effect of a variable, i.e. time-dependent, background
on the standing acoustic (i.e. longitudinal) modes generated in a
hot coronal loop. A theoretical model of 1D geometry describing the
coronal loop is applied. The background temperature is allowed to
change as a function of time and undergoes an exponential decay with
characteristic cooling times typical for coronal loops. The magnetic
field is assumed to be uniform. Thermal conduction is assumed to
be the dominant mechanism for damping hot coronal oscillations in
the presence of a physically unspecified thermodynamic source that
maintains the initial equilibrium. The influence of the rapidly
cooling background plasma on the behaviour of standing acoustic
(longitudinal) waves is investigated analytically. The temporally
evolving dispersion relation and wave amplitude are derived by using
the Wenzel-Kramers-Brillouin theory. An analytic solution for the
time-dependent amplitude that describes the influence of thermal
conduction on the standing longitudinal (acoustic) wave is obtained by
exploiting the properties of Sturm-Liouville problems. Next, numerical
evaluations further illustrate the behaviour of the standing acoustic
waves in a system with a variable, time-dependent background. The
results are applied to a number of detected loop oscillations. We
find a remarkable agreement between the theoretical predictions and
the observations. Despite the emergence of the cooling background
plasma in the medium, thermal conduction is found to cause a strong
damping for the slow standing magneto-acoustic waves in hot coronal
loops in general. In addition to this, the increase in the value of
thermal conductivity leads to a strong decay in the amplitude of the
longitudinal standing slow MHD waves.
Title: Observational Evidence of Sausage-pinch Instability in Solar
Corona by SDO/AIA
Authors: Srivastava, A. K.; Erdélyi, R.; Tripathi, Durgesh; Fedun,
V.; Joshi, N. C.; Kayshap, P.
Bibcode: 2013ApJ...765L..42S
Altcode: 2013arXiv1302.1286S
We present the first observational evidence of the evolution of
sausage-pinch instability in active region 11295 during a prominence
eruption using data recorded on 2011 September 12 by the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We
have identified a magnetic flux tube visible in AIA 304 Å that shows
curvatures on its surface with variable cross-sections as well as
enhanced brightness. These curvatures evolved and thereafter smoothed
out within a timescale of a minute. The curved locations on the flux
tube exhibit a radial outward enhancement of the surface of about 1-2 Mm
(a factor of two larger than the original thickness of the flux tube)
from the equilibrium position. AIA 193 Å snapshots also show the
formation of bright knots and narrow regions in-between at the four
locations as that of 304 Å along the flux tube where plasma emission
is larger compared to the background. The formation of bright knots
over an entire flux tube as well as the narrow regions in <60 s
may be the morphological signature of the sausage instability. We
also find the flows of confined plasma (propagation of brightness)
in these bright knots along the field lines, which indicates the
dynamicity of the flux tube that probably causes the dominance of the
longitudinal field component over short temporal scales. The observed
longitudinal motion of the plasma frozen in the magnetic field lines
further vanishes the formed curvatures and plasma confinements as well
as growth of instability to stabilize the flux tube.
Title: Ellerman bombs: small-scale brightenings in the photosphere
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Madjarska, M.;
Mumford, S. J.
Bibcode: 2013MmSAI..84..436N
Altcode:
Observations of small-scale events in the solar atmosphere are
limited by the spatial and temporal resolutions of the current crop
of observational instruments. Both high-cadence and high-resolution
observations of the photosphere have shown the continued dynamics to
extremely small-scales. Ellerman bombs, brightening events in the
wings of the Halpha line profile, are one example of small-scale,
short-lived events which have been widely studied due to their fast
dynamics in recent years. By combining the Interferometric BIdimensional
Spectrometer (IBIS) instrument with the Helioseismic and Magnetic Imager
(HMI/SDO), we show the small-scale nature of these events, as well as
their link to the background magnetic field. It is found that EBs can
be much smaller and shorter-lived than previous estimates have stated,
implying the continued dynamics of the solar atmosphere below current
observational limits.
Title: Observations of ubiquitous compressive waves in the Sun's
chromosphere
Authors: Morton, Richard J.; Verth, Gary; Jess, David B.; Kuridze,
David; Ruderman, Michael S.; Mathioudakis, Mihalis; Erdélyi, Robertus
Bibcode: 2012NatCo...3.1315M
Altcode: 2012NatCo...3E1315M; 2013arXiv1306.4124M
The details of the mechanism(s) responsible for the observed
heating and dynamics of the solar atmosphere still remain a
mystery. Magnetohydrodynamic waves are thought to have a vital role
in this process. Although it has been shown that incompressible
waves are ubiquitous in off-limb solar atmospheric observations,
their energy cannot be readily dissipated. Here we provide, for the
first time, on-disk observation and identification of concurrent
magnetohydrodynamic wave modes, both compressible and incompressible,
in the solar chromosphere. The observed ubiquity and estimated energy
flux associated with the detected magnetohydrodynamic waves suggest
the chromosphere is a vast reservoir of wave energy with the potential
to meet chromospheric and coronal heating requirements. We are also
able to propose an upper bound on the flux of the observed wave energy
that is able to reach the corona based on observational constraints,
which has important implications for the suggested mechanism(s) for
quiescent coronal heating.
Title: Multiwavelength Observations of Supersonic Plasma Blob
Triggered by Reconnection-Generated Velocity Pulse in AR10808
Authors: Srivastava, A. K.; Erdélyi, R.; Murawski, K.; Kumar, Pankaj
Bibcode: 2012SoPh..281..729S
Altcode: 2012arXiv1203.6209S; 2012SoPh..tmp..166S
Using multi-wavelength observations of Solar and Heliospheric
Observatory (SoHO)/Michelson Doppler Imager (MDI), Transition Region
and Coronal Explorer (TRACE, 171 Å), and Hα from Culgoora Solar
Observatory at Narrabri, Australia, we present a unique observational
signature of a propagating supersonic plasma blob before an M6.2-class
solar flare in active region 10808 on 9 September 2005. The blob was
observed between 05:27 UT and 05:32 UT with almost a constant shape
for the first 2 - 3 min, and thereafter it quickly vanished in the
corona. The observed lower-bound speed of the blob is estimated as ≈
215 km s−1 in its dynamical phase. The evidence of the
blob with almost similar shape and velocity concurrent in Hα and TRACE
171 Å images supports its formation by a multi-temperature plasma. The
energy release by a recurrent three-dimensional reconnection process via
the separator dome below the magnetic null point, between the emerging
flux and pre-existing field lines in the lower solar atmosphere,
is found to be the driver of a radial velocity pulse outwards that
accelerates this plasma blob in the solar atmosphere. In support
of identification of the possible driver of the observed eruption,
we solve the two-dimensional ideal magnetohydrodynamic equations
numerically to simulate the observed supersonic plasma blob. The
numerical modelling closely match the observed velocity, evolution
of multi-temperature plasma, and quick vanishing of the blob found
in the observations. Under typical coronal conditions, such blobs may
also carry an energy flux of 7.0×106 erg cm−2
s−1 to balance the coronal losses above active regions.
Title: Vortices in the Solar Photosphere
Authors: Shelyag, S.; Fedun, V.; Erdélyi, R.; Keenan, F. P.;
Mathioudakis, M.
Bibcode: 2012ASPC..463..107S
Altcode: 2012arXiv1202.1966S
Using numerical simulations of the magnetized solar photosphere
and radiative diagnostics of the simulated photospheric models,
we further analyse the physical nature of magnetic photospheric
intergranular vortices. We confirm the magnetic nature of the vortices
and find that most MHD Umov-Poynting flux is produced by horizontal
vortex motions in the magnetised intergranular lanes. In addition,
we consider possible ways to directly observe photospheric magnetic
vortices using spectropolarimetry. Although horizontal plasma motions
cannot be detected in the spectropolarimetric observations of solar disk
center, we find an observational signature of photospheric vortices in
simulated observations of Stokes-V amplitude asymmetry close to the
solar limb. Potential ways to find the vortices in the observations
are discussed.
Title: Three-dimensional Simulations of Magnetohydrodynamic Waves
in Magnetized Solar Atmosphere
Authors: Vigeesh, G.; Fedun, V.; Hasan, S. S.; Erdélyi, R.
Bibcode: 2012ApJ...755...18V
Altcode: 2011arXiv1109.6471V
We present results of three-dimensional numerical simulations of
magnetohydrodynamic (MHD) wave propagation in a solar magnetic flux
tube. Our study aims at understanding the properties of a range of MHD
wave modes generated by different photospheric motions. We consider two
scenarios observed in the lower solar photosphere, namely, granular
buffeting and vortex-like motion, among the simplest mechanism for
the generation of waves within a strong, localized magnetic flux
concentration. We show that granular buffeting is likely to generate
stronger slow and fast magnetoacoustic waves as compared to swirly
motions. Correspondingly, the energy flux transported differs as a
result of the driving motions. We also demonstrate that the waves
generated by granular buffeting are likely to manifest in stronger
emission in the chromospheric network. We argue that different
mechanisms of wave generation are active during the evolution of a
magnetic element in the intergranular lane, resulting in temporally
varying emission at chromospheric heights.
Title: Magneto-seismology of solar atmospheric loops by means of
longitudinal oscillations
Authors: Luna-Cardozo, M.; Verth, G.; Erdélyi, R.
Bibcode: 2012IAUS..286..437L
Altcode: 2012arXiv1204.4197L
There is increasingly strong observational evidence that slow
magnetoacoustic modes arise in the solar atmosphere. Solar
magneto-seismology is a novel tool to derive otherwise
directly un-measurable properties of the solar atmosphere
when magnetohydrodynamic (MHD) wave theory is compared to wave
observations. Here, MHD wave theory is further developed illustrating
how information about the magnetic and density structure along coronal
loops can be determined by measuring the frequencies of the slow MHD
oscillations. The application to observations of slow magnetoacoustic
waves in coronal loops is discussed.
Title: Observations of quasi-periodic phenomena associated with a
large blowout solar jet
Authors: Morton, R. J.; Srivastava, A. K.; Erdélyi, R.
Bibcode: 2012A&A...542A..70M
Altcode: 2012arXiv1204.5033M
Aims: A variety of periodic phenomena have been observed in
conjunction with large solar jets. We aim to find further evidence for
(quasi-)periodic behaviour in solar jets and determine what the periodic
behaviour can tell us about the excitation mechanism and formation
process of the large solar jet.
Methods: Using the 304 Å
(He-II), 171 Å (Fe IX), 193 Å (Fe XII/XXIV) and 131 Å (Fe VIII/XXI)
filters onboard the Solar Dynamic Observatory (SDO) Atmospheric
Imaging Assembly (AIA), we investigate the intensity oscillations
associated with a solar jet.
Results: Evidence is provided for
multiple magnetic reconnection events occurring between a pre-twisted,
closed field and open field lines. Components of the jet are seen
in multiple SDO/AIA filters covering a wide range of temperatures,
suggesting the jet can be classified as a blowout jet. Two bright,
elongated features are observed to be co-spatial with the large jet,
appearing at the jet's footpoints. Investigation of these features
reveal they are defined by multiple plasma ejections. The ejecta
display (quasi-)periodic behaviour on timescales of 50 s and have
rise velocities of 40-150 km s-1 along the open field
lines. Due to the suggestion that the large jet is reconnection-driven
and the observed properties of the ejecta, we further propose that these
ejecta events are similar to type-II spicules. The bright features also
display (quasi)-periodic intensity perturbations on the timescale of
300 s. Possible explanations for the existence of the (quasi-)periodic
perturbations in terms of jet dynamics and the response of the
transition region are discussed. Movies are available in electronic
form at http://www.aanda.org
Title: Magnetic tornadoes as energy channels into the solar corona
Authors: Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, Oskar;
Rouppe van der Voort, Luc; de La Cruz Rodriguez, Jaime; Fedun, Viktor;
Erdélyi, Robert
Bibcode: 2012Natur.486..505W
Altcode:
Heating the outer layers of the magnetically quiet solar atmosphere to
more than one million kelvin and accelerating the solar wind requires
an energy flux of approximately 100 to 300 watts per square metre,
but how this energy is transferred and dissipated there is a puzzle and
several alternative solutions have been proposed. Braiding and twisting
of magnetic field structures, which is caused by the convective flows
at the solar surface, was suggested as an efficient mechanism for
atmospheric heating. Convectively driven vortex flows that harbour
magnetic fields are observed to be abundant in the photosphere
(the visible surface of the Sun). Recently, corresponding swirling
motions have been discovered in the chromosphere, the atmospheric
layer sandwiched between the photosphere and the corona. Here we
report the imprints of these chromospheric swirls in the transition
region and low corona, and identify them as observational signatures
of rapidly rotating magnetic structures. These ubiquitous structures,
which resemble super-tornadoes under solar conditions, reach from
the convection zone into the upper solar atmosphere and provide an
alternative mechanism for channelling energy from the lower into the
upper solar atmosphere.
Title: Transverse Oscillations in Chromospheric Mottles
Authors: Kuridze, D.; Morton, R. J.; Erdélyi, R.; Dorrian, G. D.;
Mathioudakis, M.; Jess, D. B.; Keenan, F. P.
Bibcode: 2012ApJ...750...51K
Altcode: 2012arXiv1202.5697K
A number of recent investigations have revealed that transverse
waves are ubiquitous in the solar chromosphere. The vast majority
of these have been reported in limb spicules and active region
fibrils. We investigate long-lived, quiet-Sun, on-disk features such as
chromospheric mottles (jet-like features located at the boundaries of
supergranular cells) and their transverse motions. The observations
were obtained with the Rapid Oscillations in the Solar Atmosphere
instrument at the Dunn Solar Telescope. The data set is comprised
of simultaneous imaging in the Hα core, Ca II K, and G band of an
on-disk quiet-Sun region. Time-distance techniques are used to study
the characteristics of the transverse oscillations. We detect over
40 transverse oscillations in both bright and dark mottles, with
periods ranging from 70 to 280 s, with the most frequent occurrence
at ~165 s. The velocity amplitudes and transverse displacements
exhibit characteristics similar to limb spicules. Neighboring mottles
oscillating in-phase are also observed. The transverse oscillations
of individual mottles are interpreted in terms of magnetohydrodynamic
kink waves. Their estimated periods and damping times are consistent
with phase mixing and resonant mode conversion.
Title: Generation of Quasi-periodic Waves and Flows in the Solar
Atmosphere by Oscillatory Reconnection
Authors: McLaughlin, J. A.; Verth, G.; Fedun, V.; Erdélyi, R.
Bibcode: 2012ApJ...749...30M
Altcode: 2012arXiv1203.6846M
We investigate the long-term evolution of an initially buoyant magnetic
flux tube emerging into a gravitationally stratified coronal hole
environment and report on the resulting oscillations and outflows. We
perform 2.5-dimensional nonlinear numerical simulations, generalizing
the models of McLaughlin et al. and Murray et al. We find that the
physical mechanism of oscillatory reconnection naturally generates
quasi-periodic vertical outflows, with a transverse/swaying aspect. The
vertical outflows consist of both a periodic aspect and evidence
of a positively directed flow. The speed of the vertical outflow
(20-60 km s-1) is comparable to those reported in the
observational literature. We also perform a parametric study varying
the magnetic strength of the buoyant flux tube and find a range of
associated periodicities: 1.75-3.5 minutes. Thus, the mechanism of
oscillatory reconnection may provide a physical explanation to some
of the high-speed, quasi-periodic, transverse outflows/jets recently
reported by a multitude of authors and instruments.
Title: Longitudinal Oscillations in Density Stratified and Expanding
Solar Waveguides
Authors: Luna-Cardozo, M.; Verth, G.; Erdélyi, R.
Bibcode: 2012ApJ...748..110L
Altcode: 2012arXiv1204.4201L
Waves and oscillations can provide vital information about the internal
structure of waveguides in which they propagate. Here, we analytically
investigate the effects of density and magnetic stratification on linear
longitudinal magnetohydrodynamic (MHD) waves. The focus of this paper is
to study the eigenmodes of these oscillations. It is our specific aim
to understand what happens to these MHD waves generated in flux tubes
with non-constant (e.g., expanding or magnetic bottle) cross-sectional
area and density variations. The governing equation of the longitudinal
mode is derived and solved analytically and numerically. In particular,
the limit of the thin flux tube approximation is examined. The general
solution describing the slow longitudinal MHD waves in an expanding
magnetic flux tube with constant density is found. Longitudinal MHD
waves in density stratified loops with constant magnetic field are
also analyzed. From analytical solutions, the frequency ratio of the
first overtone and fundamental mode is investigated in stratified
waveguides. For small expansion, a linear dependence between the
frequency ratio and the expansion factor is found. From numerical
calculations it was found that the frequency ratio strongly depends
on the density profile chosen and, in general, the numerical results
are in agreement with the analytical results. The relevance of these
results for solar magneto-seismology is discussed.
Title: Small-scale rotating magnetic flux structures as alternative
energy channels into the low corona
Authors: Wedemeyer-Böhm; , Sven; Scullion; , Eamon; Steiner; , Oskar;
Rouppe van der Voort, Luc; de la Cruz Rodriguez, Jaime; Erdelyi,
Robertus; Fedun, Viktor
Bibcode: 2012decs.confE..67W
Altcode:
Vortex flows are frequently observed in the downflow areas in the lanes
between granules. The magnetic field is advected and trapped by these
flows in the low photosphere. Consequently, the rotation of a vortex
flow is transferred to the atmospheric layers above by means of the
magnetic flux structure. This effect results in so-called swirls, which
are observed in the chromosphere. New simultaneous observations with
the Swedish Solar Telescope and the Solar Dynamics Observatory reveal
that chromospheric swirls can have a coronal counterpart. This finding
implies that the rotating flux structure couples the layers of the solar
atmosphere from the photosphere to the (low) corona. Three-dimensional
numerical simulations confirm this picture and reproduce the swirl
signature. A combined analysis of the simulations and observations
implies that such small-scale rotating flux structures could provide
an alternative mechanism for channeling substantial energy from the
photosphere into the upper solar atmosphere.
Title: The Effect of Variable Background on Oscillating Hot Coronal
Loop due to Thermal Conduction
Authors: Al-Ghafri, K. S.; Erdélyi, R.
Bibcode: 2012arXiv1203.6765A
Altcode:
We investigate the effect of a variable, i.e. time-dependent, background
on the standing acoustic (i.e. longitudinal) modes generated in
a hot coronal loop. A theoretical model of 1D geometry describing
the coronal loop is applied. The background temperature is allowed
to change as a function of time and undergoes an exponential decay
with characteristic cooling times typical for coronal loops. The
magnetic field is assumed to be uniform. Thermal conduction is
the dominant mechanism of cooling the hot background plasma in the
presence of an unspecified thermodynamic source that maintains the
initial equilibrium. The influence of the rapidly cooling background
plasma on the behaviour of standing acoustic (longitudinal) waves is
investigated analytically. The temporally evolving dispersion relation
and wave amplitude are derived by using the WKB theory. An analytic
solution for the time-dependent amplitude that describes the influence
of thermal conduction on the standing longitudinal (acoustic) wave is
obtained by exploiting the properties of Sturm-Liouville problems. Next,
numerical evaluations further illustrate the behaviour of the standing
acoustic waves in a system with variable, time dependent background. The
results are applied to a number of detected loop oscillations. We
find a remarkable agreement between the theoretical predictions and
the observations. The cooling of the background plasma due to thermal
conduction is found to cause a strong damping for the slow standing
magneto-acoustic waves in hot coronal loops in general. Further to this,
the increase in the value of thermal conductivity leads to a strong
decay in the amplitude of the longitudinal standing slow MHD waves.
Title: Determination of Sub-resolution Structure of a Jet by Solar
Magnetoseismology
Authors: Morton, R. J.; Verth, G.; McLaughlin, J. A.; Erdélyi, R.
Bibcode: 2012ApJ...744....5M
Altcode: 2011arXiv1109.4851M
A thin dark thread is observed in a UV/EUV solar jet in the 171 Å,
193 Å, and 211 Å, and partially in 304 Å. The dark thread appears
to originate in the chromosphere but its temperature does not appear
to lie within the passbands of the Atmospheric Imaging Assembly
onboard the Solar Dynamics Observatory. We therefore implement solar
magnetoseismology to estimate the plasma parameters of the dark
thread. A propagating kink (transverse) wave is observed to travel
along the dark thread. The wave is tracked over a range of ~7000 km
by placing multiple slits along the axis of the dark thread. The phase
speed and amplitude of the wave are estimated and magnetoseismological
theory is employed to determine the plasma parameters. We are able
to estimate the plasma temperature, density gradient, magnetic field
gradient, and sub-resolution expansion of the dark thread. The dark
thread is found to be cool, T <~ 3 × 104, with both
strong density and magnetic field gradients. The expansion of the flux
tube along its length is ~300-400 km.
Title: The Response of A Three-dimensional Solar Atmosphere to
Wave-driven Jets
Authors: Scullion, E.; Erdélyi, R.; Fedun, V.; Doyle, J. G.
Bibcode: 2011ApJ...743...14S
Altcode:
Global oscillations from the solar interior are, mainly, pressure-driven
(p-modes) oscillations with a peak power of a five-minute period. These
oscillations are considered to manifest in many phenomena in the lower
solar atmosphere, most notably, in spicules. These small-scale jets
may provide the key to understanding the powering mechanisms of the
transition region (TR) and lower corona. Here, we simulate the formation
of wave-driven (type-I) spicule phenomena in three dimensions and the
transmission of acoustic waves from the lower chromosphere and into
the corona. The outer atmosphere oscillates in response to the jet
formation, and in turn, we reveal the formation of a circular seismic
surface wave, which we name as a Transition Region Quake (TRQ). The TRQ
forms as a consequence of an upward propelling spicular wave train that
repeatedly punctures and energizes the TR. The steep density gradient
enables the TRQ to develop and radially fan outward from the location
where the spicular plasma column impinges the TR. We suggest the TRQ
formation as a formidable mechanism in continuously sustaining part of
the energy budget of the TR. We present a supporting numerical model
which allow us to determine the level of energy dumping at the TR by
upward-propagating p-modes. Upon applying a wavelet analysis on our
simulations we identify the presence of a chromospheric cavity which
resonates with the jet propagation and leaves behind an oscillatory
wake with a distinctive periodicity. Through our numerical analysis we
also discover type-I spicule turbulence leading to a convection-based
motion in the low corona.
Title: Torsional Alfvén waves: magneto-seismology in static and
dynamic coronal plasmas
Authors: Morton, R. J.; Ruderman, M. S.; Erdélyi, R.
Bibcode: 2011A&A...534A..27M
Altcode:
Aims: We study the properties of torsional Alfvén waves in
coronal loops so that they may be exploited for coronal seismological
applications.
Methods: The governing equation is obtained
for standing torsional Alfvén waves of a dynamic, gravitationally
stratified plasma. The footpoints are assumed to obey line-tying
conditions necessary for standing oscillations. Solutions are found
in a number of different but typical scenarios to demonstrate the
possibilities for both temporal and spatial magneto-seismology
exploitation of waveguides with the standing torsional Alfvén
oscillations.
Results: It is found that the frequency of the
standing Alfvén oscillation increases as the stratification of the
plasma increases. The ratio of the periods of the fundamental modeand
the first overtone is also found to change as the stratification of the
plasma increases. Further, the eigenfunctions of the higher overtones
of the standing oscillations are found to experience a shift of their
anti-nodes. The influence of a dynamic plasma on the amplitudes of the
mode is also investigated. The amplitude of the torsional Alfvén mode
is found to increase as the plasma within the coronal loop experiences
cooling.
Title: Frequency Filtering of Torsional Alfvén Waves by Chromospheric
Magnetic Field
Authors: Fedun, V.; Verth, G.; Jess, D. B.; Erdélyi, R.
Bibcode: 2011ApJ...740L..46F
Altcode:
In this Letter, we demonstrate how the observation of broadband
frequency propagating torsional Alfvén waves in chromospheric
magnetic flux tubes can provide valuable insight into their magnetic
field structure. By implementing a full nonlinear three-dimensional
magnetohydrodynamic numerical simulation with a realistic vortex driver,
we demonstrate how the plasma structure of chromospheric magnetic flux
tubes can act as a spatially dependent frequency filter for torsional
Alfvén waves. Importantly, for solar magnetoseismology applications,
this frequency filtering is found to be strongly dependent on magnetic
field structure. With reference to an observational case study of
propagating torsional Alfvén waves using spectroscopic data from the
Swedish Solar Telescope, we demonstrate how the observed two-dimensional
spatial distribution of maximum power Fourier frequency shows a strong
correlation with our forward model. This opens the possibility of
beginning an era of chromospheric magnetoseismology, to complement
the more traditional methods of mapping the magnetic field structure
of the solar chromosphere.
Title: Multiwavelength Observations of a Failed Flux Rope in the
Eruption and Associated M-Class Flare from NOAA AR 11045
Authors: Kumar, Pankaj; Srivastava, Ablishek K.; Filippov, B.;
Erdélyi, R.; Uddin, Wahab
Bibcode: 2011SoPh..272..301K
Altcode: 2011arXiv1107.0605K
We present the multiwavelength observations of a flux rope that
was trying to erupt from NOAA AR 11045 and the associated M-class
solar flare on 12 February 2010 using space-based and ground-based
observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT, and BBSO. While
the flux rope was rising from the active region, an M1.1/2F class
flare was triggered near one of its footpoints. We suggest that the
flare triggering was due to the reconnection of a rising flux rope
with the surrounding low-lying magnetic loops. The flux rope reached
a projected height of ≈0.15R⊙ with a speed of ≈90 km
s−1 while the soft X-ray flux enhanced gradually during
its rise. The flux rope was suppressed by an overlying field, and the
filled plasma moved towards the negative polarity field to the west of
its activation site. We found the first observational evidence of the
initial suppression of a flux rope due to a remnant filament visible
both at chromospheric and coronal temperatures that evolved a couple
of days earlier at the same location in the active region. SOHO/MDI
magnetograms show the emergence of a bipole ≈12 h prior to the flare
initiation. The emerged negative polarity moved towards the flux rope
activation site, and flare triggering near the photospheric polarity
inversion line (PIL) took place. The motion of the negative polarity
region towards the PIL helped in the build-up of magnetic energy at
the flare and flux rope activation site. This study provides unique
observational evidence of a rising flux rope that failed to erupt
due to a remnant filament and overlying magnetic field, as well as
associated triggering of an M-class flare.
Title: Damping of Longitudinal Magneto-Acoustic Oscillations in
Slowly Varying Coronal Plasma
Authors: Erdélyi, R.; Al-Ghafri, K. S.; Morton, R. J.
Bibcode: 2011SoPh..272...73E
Altcode: 2010arXiv1011.2617E; 2011SoPh..tmp..314E; 2011SoPh..tmp..184E;
2011SoPh..tmp..253E; 2011SoPh..tmp..289E
We investigate the propagation of MHD waves in a magnetised plasma
in a weakly stratified atmosphere, representative of hot coronal
loops. In most earlier studies, a time-independent equilibrium was
considered. Here we abandon this restriction and allow the equilibrium
to develop as a function of time. In particular, the background plasma
is assumed to be cooling due to thermal conduction. The cooling is
assumed to occur on a time scale greater than the characteristic travel
times of the perturbations. We investigate the influence of cooling of
the background plasma on the properties of magneto-acoustic waves. The
MHD equations are reduced to a 1D system modelling magneto-acoustic
modes propagating along a dynamically cooling coronal loop. A
time-dependent dispersion relation that describes the propagation of
the magneto-acoustic waves is derived using the WKB theory. An analytic
solution for the time-dependent amplitude of waves is obtained, and
the method of characteristics is used to find an approximate analytical
solution. Numerical calculations of the analytically derived solutions
are obtained to give further insight into the behaviour of the MHD waves
in a system with a variable, time-dependent background. The results show
that there is a strong damping of MHD waves and the damping also appears
to be independent of the position along the loop. Studies of MHD wave
behaviour in a time-dependent backgrounds seem to be a fundamental
and very important next step in the development of MHD wave theory
that is applicable to a wide range of situations in solar physics.
Title: Resonant MHD Waves in the Solar Atmosphere
Authors: Goossens, Marcel; Erdélyi, Robert; Ruderman, Michael S.
Bibcode: 2011SSRv..158..289G
Altcode: 2010SSRv..tmp..182G
The linear theory of MHD resonant waves in inhomogeneous plasmas
is reviewed. The review starts from discussing the properties of
driven resonant MHD waves. The dissipative solutions in Alfvén
and slow dissipative layers are presented. The important concept of
connection formulae is introduced. Next, we proceed on to non-stationary
resonant MHD waves. The relation between quasi-modes of ideal MHD and
eigenmodes of dissipative MHD are discussed. The solution describing
the wave motion in non-stationary dissipative layers is given. It is
shown that the connection formulae remain valid for non-stationary
resonant MHD waves. The initial-value problem for resonant MHD waves
is considered. The application of theory of resonant MHD waves to
solar physics is discussed.
Title: Magnetohydrodynamic Waves and Seismology of the Solar
Atmosphere
Authors: Erdélyi, Robertus; Goossens, Marcel
Bibcode: 2011SSRv..158..167E
Altcode: 2011SSRv..tmp..229E; 2011SSRv..tmp...84E; 2011SSRv..tmp..153E
No abstract at ADS
Title: Effects of Magnetic Fields in the Solar Atmosphere on Global
Oscillations
Authors: Pintér, Balázs; Erdélyi, Robert
Bibcode: 2011SSRv..158..471P
Altcode: 2011SSRv..tmp..250P; 2011SSRv..tmp..280P; 2011SSRv..tmp..157P;
2011SSRv..tmp..233P
Helioseismology is practically the only efficient experimental way of
probing the solar interior. Without it, the results of theoretical
solar models would remain untested and, consequently, less reliable
when applying them for investigating remote stars. Hence, having a firm
understanding of the applicability and reliability of helioseismology
and the awareness of its limits are essential in solar physics and
also in astrophysics. One of the weaknesses of the currently popular
helioseismic models is that they allow only limited interaction
between the global acoustic oscillation modes and the magnetic lower
solar atmosphere, although, observations confirm strong coupling of
helioseismic oscillations to the atmospheric magnetic field. The present
article overviews the attempts of taking into account atmospheric
magnetic effects in the theoretical models of global solar oscillations.
Title: Observational Signatures of Impulsively Heated Coronal Loops:
Power-Law Distribution of Energies
Authors: Taroyan, Y.; Erdélyi, R.; Bradshaw, S. J.
Bibcode: 2011SoPh..269..295T
Altcode: 2011SoPh..tmp...11T
It has been established that small scale heating events, known as
nanoflares, are important for solar coronal heating if the power-law
distribution of their energies has a slope α steeper than −2
(α<−2). Forward modeling of impulsively heated coronal loops with
a set of prescribed power-law indices α is performed. The power-law
distribution is incorporated into the governing equations of motion
through an impulsive heating term. The results are converted into
synthetic Hinode/EIS observations in the 40″ imaging mode, using
a selection of spectral lines formed at various temperatures. It is
shown that the intensities of the emission lines and their standard
deviations are sensitive to changes in α. A method based on a
combination of observations and forward modeling is proposed for
determining whether the heating in a particular case is due to small
or large scale events. The method is extended and applied to a loop
structure that consists of multiple strands.
Title: Observations of Sausage Modes in Magnetic Pores
Authors: Morton, R. J.; Erdélyi, R.; Jess, D. B.; Mathioudakis, M.
Bibcode: 2011ApJ...729L..18M
Altcode: 2010arXiv1011.2375M
We present here evidence for the observation of the magnetohydrodynamic
(MHD) sausage modes in magnetic pores in the solar photosphere. Further
evidence for the omnipresent nature of acoustic global modes is also
found. The empirical decomposition method of wave analysis is used to
identify the oscillations detected through a 4170 Å "blue continuum"
filter observed with the Rapid Oscillations in the Solar Atmosphere
(ROSA) instrument. Out of phase, periodic behavior in pore size and
intensity is used as an indicator of the presence of magnetoacoustic
sausage oscillations. Multiple signatures of the magnetoacoustic
sausage mode are found in a number of pores. The periods range from
as short as 30 s up to 450 s. A number of the magnetoacoustic sausage
mode oscillations found have periods of 3 and 5 minutes, similar to
the acoustic global modes of the solar interior. It is proposed that
these global oscillations could be the driver of the sausage-type
magnetoacoustic MHD wave modes in pores.
Title: On the triggering of M-class solar flare due to loop-loop
interaction in AR NOAA 10875
Authors: Kumar, Pankaj; Srivastava, Abhishek K.; Somov, B. V.;
Manoharan, P. K.; Erdélyi, R.; Uddin, Wahab
Bibcode: 2011ASInC...2..315K
Altcode: 2011arXiv1109.4730K
We present multiwavelength analysis of an M7.9 /1N solar flare which
occurred on 27 April 2006 in AR NOAA 10875. The flare was triggered
due to the interaction of two loop systems. GOES soft X-ray and TRACE
195 Å image sequences show the observational evidences of 3-D X-type
loop-loop interaction with converging motion at the interaction site. We
found the following characteristics during the loop-loop interaction:
(i) a short duration/impulsive flare obeying the Neupart effect, (ii)
double peak structure in radio flux profiles (in 4.9 and 8.8 GHz),
(iii) quasi-periodic oscillations in the radio flux profiles for
the duration of ∼3 min, (iv) absence of CME and type III radio
burst. The above characteristics observed during the flare are in
agreement with the theory and simulation of current loop coalescence
by Sakai et al. (1986). These are unique multiwavelength observations,
which provide the evidences of loop-loop interaction and associated
triggering of solar flare without CME.
Title: Numerical Modeling of Footpoint-driven Magneto-acoustic Wave
Propagation in a Localized Solar Flux Tube
Authors: Fedun, V.; Shelyag, S.; Erdélyi, R.
Bibcode: 2011ApJ...727...17F
Altcode:
In this paper, we present and discuss results of two-dimensional
simulations of linear and nonlinear magneto-acoustic wave propagation
through an open magnetic flux tube embedded in the solar atmosphere
expanding from the photosphere through to the transition region
and into the low corona. Our aim is to model and analyze the
response of such a magnetic structure to vertical and horizontal
periodic motions originating in the photosphere. To carry out
the simulations, we employed our MHD code SAC (Sheffield Advanced
Code). A combination of the VALIIIC and McWhirter solar atmospheres
and coronal density profiles were used as the background equilibrium
model in the simulations. Vertical and horizontal harmonic sources,
located at the footpoint region of the open magnetic flux tube,
are incorporated in the calculations, to excite oscillations in the
domain of interest. To perform the analysis we have constructed a
series of time-distance diagrams of the vertical and perpendicular
components of the velocity with respect to the magnetic field lines
at each height of the computational domain. These time-distance
diagrams are subject to spatio-temporal Fourier transforms allowing
us to build ω-k dispersion diagrams for all of the simulated regions
in the solar atmosphere. This approach makes it possible to compute
the phase speeds of waves propagating throughout the various regions
of the solar atmosphere model. We demonstrate the transformation of
linear slow and fast magneto-acoustic wave modes into nonlinear ones,
i.e., shock waves, and also show that magneto-acoustic waves with a
range of frequencies efficiently leak through the transition region
into the solar corona. It is found that the waves interact with the
transition region and excite horizontally propagating surface waves
along the transition region for both types of drivers. Finally, we
estimate the phase speed of the oscillations in the solar corona and
compare it with the phase speed derived from observations.
Title: Evidence of Solar Flare Triggering Due to Loop-loop Interaction
Caused by Footpoint Shear Motion
Authors: Kumar, Pankaj; Srivastava, A. K.; Somov, B. V.; Manoharan,
P. K.; Erdélyi, R.; Uddin, Wahab
Bibcode: 2010ApJ...723.1651K
Altcode: 2010arXiv1009.1202K
We analyze multi-wavelength data of an M7.9/1N class solar flare which
occurred on 2006 April 27 in AR NOAA 10875. GOES soft X-ray images
provide the most likely signature of two interacting loops and their
reconnection, which triggers the solar flare. TRACE 195 Å images also
reveal the loop-loop interaction and the formation of "X" points with
converging motion (~30 km s-1) at the reconnection site
in between this interacting loop system. This provides evidence of
progressive reconnection and flare maximization at the interaction
site in the active region. The absence of type III radio bursts during
this time period indicates no opening of magnetic field lines during
the flare energy release, which implies that the change of field line
connectivity/orientation occurred only during the loop-loop interaction
and reconnection process. The Ondrejov dynamic radio spectrum shows
an intense decimetric (DCIM) radio burst (2.5-4.5 GHz, duration ~3
minutes) during the flare initiation, which reveals the signature
of particle acceleration from the reconnection site during loop-loop
interaction. The double-peak structures at 4.9 and 8.8 GHz provide the
most likely confirmatory signature of the loop-loop interaction at the
flare site in the active region. RHESSI hard X-ray images also show the
loop-top and footpoint sources of the corresponding two-loop system,
which act like current-carrying flux tubes with resultant opposite
magnetic fields and net force of attraction, and their coalescence
during the flare maximum. We also suggest that the shear motion/rotation
of the footpoint of the smaller loop, which is anchored in the opposite
polarity spot, may be responsible for the flare energy buildup and
its eventual release due to the loop-loop interaction.
Title: An analytic interface dynamo over a shear layer of finite depth
Authors: Petrovay, K.; Kerekes, A.; Erdelyi, R.
Bibcode: 2010GApFD.104..619P
Altcode: 2010arXiv1007.1634P
Parker's analytic Cartesian interface dynamo is generalized to the case
of a shear layer of finite thickness and low resistivity ("tachocline"),
bounded by a perfect conductor ("radiative zone") on the one side, and
by a highly diffusive medium ("convective zone") supporting an α-effect
on the other side. In the limit of high diffusivity contrast between
the shear layer and the diffusive medium, thought to be relevant for
the Sun, a pair of exact dispersion relations for the growth rate and
frequency of dynamo modes is analytically derived. Graphic solution of
the dispersion relations displays a somewhat unexpected, non-monotonic
behavior, the mathematical origin of which is elucidated. The dependence
of the results on the parameter values (dynamo number and shear layer
thickness) is investigated. The implications of this result for the
solar dynamo problem are discussed.
Title: Application of the theory of damping of kink oscillations by
radiative cooling of coronal loop plasma
Authors: Morton, R. J.; Erdélyi, R.
Bibcode: 2010A&A...519A..43M
Altcode:
Aims: We present here a first comparative study between the
observed damping of numerous fast kink oscillations and the theoretical
model of their damping due to the cooling of coronal loops. The theory
of damping of kink oscillations due to radiation of the solar plasma
with a temporally varying background is applied here to all known
cases of coronal kink oscillations.
Methods: A recent dynamic
model of cooling coronal loops predicts that transverse oscillations of
such loops could be significantly damped due to the radiative cooling
process (Morton & Erdélyi 2009, ApJ, 707, 750). The cooling of the
loop plasma also has the consequence that the kink oscillation has a
time-dependent frequency. The theory is applied to a relatively large
number of known and reported examples of TRACE observations of damped
kink oscillations.
Results: We find that, for cooling timescales
that are typical of EUV loops (500-2000 s), the observed damping of
the transversal (i.e. kink) oscillations can be accounted for almost
entirely by the cooling process in half of the examples. No other
dissipative mechanism(s) seems to be needed to model the damping. In
the remaining other examples, the cooling process does not appear to
be able to account fully for the observed damping, though could still
have a significant influence on the damping. In these cases another
mechanism(s), e.g. resonant absorption, may be additionally required
to account for the complete decay of oscillations. Also, we show that
because of the dynamic nature of the background plasma, allowing for
a time-dependent frequency provides a better fit profile for the data
points of observations than a fit profile with a constant frequency,
opening novel avenues for solar magneto-seismology.
Title: Magneto-Acoustic Waves in Compressible Magnetically Twisted
Flux Tubes
Authors: Erdélyi, Robert; Fedun, Viktor
Bibcode: 2010SoPh..263...63E
Altcode: 2010SoPh..tmp...60E; 2010SoPh..tmp...48E
The oscillatory modes of a magnetically twisted compressible flux tube
embedded in a compressible magnetic environment are investigated in
cylindrical geometry. Solutions to the governing equations to linear
wave perturbations are derived in terms of Whittaker's functions. A
general dispersion equation is obtained in terms of Kummer's functions
for the approximation of weak and uniform internal twist, which is a
good initial working model for flux tubes in solar applications. The
sausage, kink and fluting modes are examined by means of the derived
exact dispersion equation. The solutions of this general dispersion
equation are found numerically under plasma conditions representative of
the solar photosphere and corona. Solutions for the phase speed of the
allowed eigenmodes are obtained for a range of wavenumbers and varying
magnetic twist. Our results generalise previous classical and widely
applied studies of MHD waves and oscillations in magnetic loops without
a magnetic twist. Potential applications to solar magneto-seismology
are discussed.
Title: Magnetoseismology: Eigenmodes of Torsional Alfvén Waves in
Stratified Solar Waveguides
Authors: Verth, G.; Erdélyi, R.; Goossens, M.
Bibcode: 2010ApJ...714.1637V
Altcode:
There have recently been significant claims of Alfvén wave observation
in the solar chromosphere and corona. We investigate how the radial and
longitudinal plasma structuring affects the observational properties
of torsional Alfvén waves in magnetic flux tubes for the purposes of
solar magnetoseismology. The governing magnetohydrodynamic equations
of these waves in axisymmetric flux tubes of arbitrary radial and
axial plasma structuring are derived and we study their observable
properties for various equilibria in both thin and finite-width
magnetic flux tubes. For thin flux tubes, it is demonstrated that
observation of the eigenmodes of torsional Alfvén waves can provide
temperature diagnostics of both the internal and surrounding plasma. In
the finite-width flux tube regime, it is shown that these waves are the
ideal magnetoseismological tool for probing radial plasma inhomogeneity
in solar waveguides.
Title: Propagating magneto-hydrodynamic waves in a cooling homogenous
coronal plasma
Authors: Morton, R. J.; Hood, A. W.; Erdélyi, R.
Bibcode: 2010A&A...512A..23M
Altcode:
Aims: We present an investigation into how the cooling of the
background plasma influences the propagation of slow and fast MHD
wave modes supported by an unbounded, homogenous plasma. Previous
investigations have suggested that the cooling of the plasma and a
reduction in density could lead to the damping of fast magneto-acoustic
oscillations. We aim to investigate whether cooling of the background
plasma at a constant density may be responsible for the damping of
slow and fast modes.
Methods: The plasma is assumed homogeneous
and the background temperature (pressure) is decreasing with time. The
temperature change is assumed to be due to optically thin radiation. A
special case of the radiative function is chosen to allow an analytical
assessment of the effects of cooling on magneto-acoustic MHD modes
and ensures the temperature evolution of the background plasma
due to this radiation also matches the observed cooling profile of
coronal loops.
Results: A time-dependent dispersion relation
is obtained on the slow timescale of cooling and full time-dependent
solutions are found. Leading order equations for the amplitude of the
waves are obtained and solved analytically for the slow and fast MHD
modes. The cooling of the plasma is found to cause the frequency of the
magneto-acoustic modes to decrease with time. The slow modes are found
to experience a greater change in frequency than the fast modes. More
importantly, the radiative losses also provide a significant damping
of the slow mode and a small damping of the component of the fast mode
perpendicular to the magnetic field. The damping of the slow mode is
found to be strong within typical lifetimes of oscillations observed in
coronal structures. Cooling could have important consequences and needs
to be assessed when trying to determine what mechanism is responsible
for the observed damping of coronal oscillations.
Title: A spectroscopic analysis of macrospicules .
Authors: Scullion, E.; Doyle, J. G.; Erdélyi, R.
Bibcode: 2010MmSAI..81..737S
Altcode:
We explore the nature of macrospicule structures, both off-limb
and on-disk, and their possible relation to explosive events in the
mid-solar atmosphere. We use high resolution spectroscopy obtained with
the SoHO/SUMER instrument. We present a highly resolved spectroscopic
analysis and line parameter study of time series data for such jets. We
focus on two interesting off-limb events which rapidly propagate
between the mid-transition region N IV 765 Å line formation (140
000 K) and the lower corona Ne VIII 770 Å line formation (630 000
K). In one example, a strong jet-like event is associated with a cool
feature not present in the Ne VIII 770 Å line radiance or Doppler
velocity maps. Our data reveals fast, repetitive plasma outflows
with blue-shift velocities of ≈ 145 km s-1 in the lower
solar atmosphere. The data suggests a strong role for smaller jets
(spicules), as a precursor to macrospicule formation, which may have
a common origin with explosive events.
Title: Waves in the Transition Region
Authors: Scullion, E.; Erdélyi, R.; Doyle, J. G.
Bibcode: 2010ASSP...19..426S
Altcode: 2010mcia.conf..426S
Fundamental questions concerning coronal heating and the origin of
the fast solar wind may be answered through greater understanding of
fine structures in the lower solar atmosphere. We present results
from a 2.5-D ideal-MHD simulation from a new numerical code, plus
new supportive observational material. The simulation was run with
the Sheffield Advanced Code (SAC, Shelyag et al. 2008, A&A, 486,
655) and is supported by multi-instrument evidence of a surface wave
obtained from co-alignment of observations with Hinode/EIS and SoHO/MDI.
Title: MHD Wave Heating Diagnostics
Authors: Taroyan, Y.; Erdélyi, R.
Bibcode: 2010ASSP...19..287T
Altcode: 2010mcia.conf..287T
Analyzing the structure of solar coronal loops is crucial to our
understanding of the processes that heat and maintain the coronal
plasma at multimillion degree temperatures. The determination of the
physical parameters of coronal loops remains both an observational
and theoretical challenge. A novel diagnostic technique for quiescent
coronal loops based on the analysis of power spectra of Doppler-shift
time series is developed and proposed to test on real data.
Title: Oscillations and Waves in Solar Spicules
Authors: Zaqarashvili, T. V.; Erdélyi, R.
Bibcode: 2009SSRv..149..355Z
Altcode: 2009arXiv0906.1783Z
Since their discovery, spicules have attracted increased attention
as energy/mass bridges between the dense and dynamic photosphere
and the tenuous hot solar corona. Mechanical energy of photospheric
random and coherent motions can be guided by magnetic field lines,
spanning from the interior to the upper parts of the solar atmosphere,
in the form of waves and oscillations. Since spicules are one of the
most pronounced features of the chromosphere, the energy transport
they participate in can be traced by the observations of their
oscillatory motions. Oscillations in spicules have been observed for
a long time. However the recent high-resolution and high-cadence space
and ground based facilities with superb spatial, temporal and spectral
capacities brought new aspects in the research of spicule dynamics. Here
we review the progress made in imaging and spectroscopic observations
of waves and oscillations in spicules. The observations are accompanied
by a discussion on theoretical modelling and interpretations of these
oscillations. Finally, we embark on the recent developments made on
the presence and role of Alfvén and kink waves in spicules. We also
address the extensive debate made on the Alfvén versus kink waves in
the context of the explanation of the observed transverse oscillations
of spicule axes.
Title: Transverse Oscillations of a Cooling Coronal Loop
Authors: Morton, R. J.; Erdélyi, R.
Bibcode: 2009ApJ...707..750M
Altcode:
Here we present an investigation into how cooling of the plasma
influences the oscillation properties (e.g., eigenfunctions and
eigenfrequencies) of transverse (i.e., kink) magnetohydrodynamic
(MHD) waves in a compressible magnetic flux tube embedded in a
gravitationally stratified and uniformly magnetized atmosphere. The
cooling is introduced via a temperature-dependent density profile. A
time-dependent governing equation is derived and an approximate
zeroth-order solution is then obtained. From this the influence of
cooling on the behavior of the eigenfrequencies and eigenfunctions
of the transverse MHD waves is determined for representative
cooling timescales. It is shown analytically, as the loop cools,
how the amplitude of the perturbations is found to decrease as time
increases. For cooling timescales of 900-2000 s (as observed in
typical EUV loops), it is shown that the cooling has important and
relevant influence on the damping times of loop oscillations. Next,
the theory is put to the test. The damping due to cooling is fitted
to a representative observation of standing kink oscillation of EUV
loops. It is also shown with an explicit approximate analytical form,
how the period of the fundamental and first harmonic of the kink
mode changes with time as the loop cools. A consequence of this is
that the value of the period ratio P 1/P 2,
a tool that is popular in magneto-seismological studies in coronal
diagnostics, decreases from the value of a uniform loop, 2, as
the temperature decreases. The rate of change in P 1/P
2 is dependent upon the cooling timescale and is well
within the observable range for typical EUV loops. Further to this,
the magnitude of the anti-node shift of the eigenfunctions of the
first harmonic is shown to continually increase as the loop cools,
giving additional impetus to the use of spatial magneto-seismology
of the solar atmosphere. Finally, we suggest that measurements of
the rate of change in the eigenfunctions and eigenfrequencies of MHD
oscillations can provide values for the cooling timescale and a further
insight into the physics of coronal loops.
Title: Foreword
Authors: Nakariakov, V. M.; Erdélyi, R.
Bibcode: 2009SSRv..149....1N
Altcode:
No abstract at ADS
Title: Numerical Simulation of Acoustic Wave Propagation in the
Solar Sub-Photosphere with Localized Magnetic Field Concentration
Authors: Shelyag, S.; Zharkov, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
Bibcode: 2009ASPC..416..167S
Altcode:
The results of numerical simulations of acoustic wave propagation and
dispersion in the solar sub-photosphere with a localised magnetic
field concentration are presented. The initial equilibrium density
and pressure stratifications are derived from a standard solar
model and adjusted to maintain magnetohydrostatic and convective
stability. Acoustic waves are generated by a perturbation located
at the height corresponding to the visible surface of the Sun. The
time-distance diagram of the vertical velocity perturbation at the level
corresponding to the visible solar surface shows that the magnetic
field perturbs and scatters acoustic waves and absorbs the acoustic
power of the wave packet.
Title: Heating Diagnostics with MHD Waves
Authors: Taroyan, Y.; Erdélyi, R.
Bibcode: 2009SSRv..149..229T
Altcode:
The heating of the solar atmosphere is a fundamental problem
of modern solar and astrophysics. A review of the seismological
aspects of magnetohydrodynamic (MHD) waves with an emphasis on
standing longitudinal waves in the context of coronal heating is
presented. Efforts made recently may be split into two categories:
forward modelling and data inversion. Forward modelling can be
applied to predict the observational footprints of various heating
scenarios. A new diagnostic method based on the analysis of Doppler
shift time series is outlined with specific application to solar
coronal conditions. The power of the method is demonstrated and tested
using synthetic data and comparing them with actual high-resolution
(e.g. SoHO/SUMER) observations. Further, related recent examples of
standing longitudinal oscillations in coronal loop structures observed
with the new Hinode/EIS instrument are also presented. These latter
observations provide an advanced ground for MHD seismology as a tool
for plasma heating diagnostics in the atmosphere of the Sun.
Title: Coronal Seismology by Means of Kink Oscillation Overtones
Authors: Andries, J.; van Doorsselaere, T.; Roberts, B.; Verth, G.;
Verwichte, E.; Erdélyi, R.
Bibcode: 2009SSRv..149....3A
Altcode:
The detection of overtones of coronal loop kink oscillations has been
an important advance in the development of coronal seismology. It has
significantly increased the potential of coronal seismology and has
thus initiated important theoretical and observational improvements. New
detections of overtones have been made and a reduction of the error bars
has been obtained. The efforts of theoreticians to extend eigenmode
studies to more general coronal loop models is no longer a matter
of checking the robustness of the model but now also allows for the
estimation of certain equilibrium parameters. The frequencies of
the detected (longitudinal) overtones are in particular sensitive to
changes in the equilibrium properties along the loop, especially the
density and the magnetic field expansion. Also, attempts have been
made to use the limited longitudinal resolution in combination with
the theoretical eigenmodes as an additional seismological tool.
Title: Transverse Oscillations of Coronal Loops
Authors: Ruderman, Michael S.; Erdélyi, Robert
Bibcode: 2009SSRv..149..199R
Altcode:
On 14 July 1998 TRACE observed transverse oscillations of a coronal
loop generated by an external disturbance most probably caused by a
solar flare. These oscillations were interpreted as standing fast kink
waves in a magnetic flux tube. Firstly, in this review we embark on the
discussion of the theory of waves and oscillations in a homogeneous
straight magnetic cylinder with the particular emphasis on fast kink
waves. Next, we consider the effects of stratification, loop expansion,
loop curvature, non-circular cross-section, loop shape and magnetic
twist. An important property of observed transverse coronal loop
oscillations is their fast damping. We briefly review the different
mechanisms suggested for explaining the rapid damping phenomenon. After
that we concentrate on damping due to resonant absorption. We describe
the latest analytical results obtained with the use of thin transition
layer approximation, and then compare these results with numerical
findings obtained for arbitrary density variation inside the flux
tube. Very often collective oscillations of an array of coronal
magnetic loops are observed. It is natural to start studying this
phenomenon from the system of two coronal loops. We describe very recent
analytical and numerical results of studying collective oscillations
of two parallel homogeneous coronal loops. The implication of the
theoretical results for coronal seismology is briefly discussed. We
describe the estimates of magnetic field magnitude obtained from the
observed fundamental frequency of oscillations, and the estimates of
the coronal scale height obtained using the simultaneous observations
of the fundamental frequency and the frequency of the first overtone
of kink oscillations. In the last part of the review we summarise the
most outstanding and acute problems in the theory of the coronal loop
transverse oscillations.
Title: Jets in Polar Coronal Holes
Authors: Scullion, E.; Popescu, M. D.; Banerjee, D.; Doyle, J. G.;
Erdélyi, R.
Bibcode: 2009ApJ...704.1385S
Altcode:
Here, we explore the nature of small-scale jet-like structures and
their possible relation to explosive events and other known transient
features, like spicules and macrospicules, using high-resolution
spectroscopy obtained with the Solar and Heliospheric Observatory/Solar
Ultraviolet Measurements of Emitted Radiation instrument. We present
a highly resolved spectroscopic analysis and line parameter study
of time-series data for jets occurring on-disk and off-limb in
both a northern and a southern coronal hole. The analysis reveals
many small-scale transients which rapidly propagate between the
mid-transition region (N IV 765 Å line formation: 140,000 K) and
the lower corona (Ne VIII 770 Å line formation: 630,000 K). In one
example, a strong jet-like event is associated with a cool feature
not present in the Ne VIII 770 Å line radiance or Doppler velocity
maps. Another similar event is observed, but with a hot component,
which could be perceived as a blinker. Our data reveal fast, repetitive
plasma outflows with blueshift velocities of ≈145 km s-1
in the lower solar atmosphere. The data suggest a strong role for
smaller jets (spicules), as a precursor to macrospicule formation,
which may have a common origin with explosive events.
Title: Photospheric high-frequency acoustic power excess in sunspot
umbra: signature of magneto-acoustic modes
Authors: Zharkov, S.; Shelyag, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
Bibcode: 2009arXiv0909.5332Z
Altcode:
We present observational evidence for the presence of MHD waves in
the solar photosphere deduced from SOHO/MDI Dopplergram velocity
observations. The magneto-acoustic perturbations are observed as
acoustic power enhancement in the sunspot umbra at high-frequency bands
in the velocity component perpendicular to the magnetic field. We use
numerical modelling of wave propagation through localised non-uniform
magnetic field concentration along with the same filtering procedure
as applied to the observations to identify the observed waves. Guided
by the results of the numerical simulations we classify the observed
oscillations as magneto-acoustic waves excited by the trapped
sub-photospheric acoustic waves. We consider the potential application
of the presented method as a diagnostic tool for magnetohelioseismology.
Title: Oscillatory Response of the 3D Solar Atmosphere to the Leakage
of Photospheric Motion
Authors: Fedun, Viktor; Erdélyi, Robert; Shelyag, Sergiy
Bibcode: 2009SoPh..258..219F
Altcode:
The direct propagation of acoustic waves, driven harmonically at
the solar photosphere, into the three-dimensional solar atmosphere is
examined numerically in the framework of ideal magnetohydrodynamics. It
is of particular interest to study the leakage of 5-minute global solar
acoustic oscillations into the upper, gravitationally stratified and
magnetised atmosphere, where the modelled solar atmosphere possesses
realistic temperature and density stratification. This work aims to
complement and bring further into the 3D domain our previous efforts
(by Erdélyi et al., 2007, Astron. Astrophys. 467, 1299) on the
leakage of photospheric motions and running magnetic-field-aligned
waves excited by these global oscillations. The constructed model
atmosphere, most suitable perhaps for quiet Sun regions, is a VAL
IIIC derivative in which a uniform magnetic field is embedded. The
response of the atmosphere to a range of periodic velocity drivers is
numerically investigated in the hydrodynamic and magnetohydrodynamic
approximations. Among others the following results are discussed in
detail: i) High-frequency waves are shown to propagate from the lower
atmosphere across the transition region, experiencing relatively low
reflection, and transmitting most of their energy into the corona;
ii) the thin transition region becomes a wave guide for horizontally
propagating surface waves for a wide range of driver periods, and
particularly at those periods that support chromospheric standing
waves; iii) the magnetic field acts as a waveguide for both high- and
low-frequency waves originating from the photosphere and propagating
through the transition region into the solar corona.
Title: Acoustic wave propagation in the solar sub-photosphere with
localised magnetic field concentration: effect of magnetic tension
Authors: Shelyag, S.; Zharkov, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
Bibcode: 2009A&A...501..735S
Altcode: 2009arXiv0901.3680S
Aims: We analyse numerically the propagation and dispersion of acoustic
waves in the solar-like sub-photosphere with localised non-uniform
magnetic field concentrations, mimicking sunspots with various
representative magnetic field configurations.
Methods: Numerical
simulations of wave propagation through the solar sub-photosphere
with a localised magnetic field concentration are carried out using
SAC, which solves the MHD equations for gravitationally stratified
plasma. The initial equilibrium density and pressure stratifications
are derived from a standard solar model. Acoustic waves are generated
by a source located at the height corresponding approximately to
the visible surface of the Sun. By means of local helioseismology we
analyse the response of vertical velocity at the level corresponding
to the visible solar surface to changes induced by magnetic field in
the interior.
Results: The results of numerical simulations of
acoustic wave propagation and dispersion in the solar sub-photosphere
with localised magnetic field concentrations of various types are
presented. Time-distance diagrams of the vertical velocity perturbation
at the level corresponding to the visible solar surface show that the
magnetic field perturbs and scatters acoustic waves and absorbs the
acoustic power of the wave packet. For the weakly magnetised case, the
effect of magnetic field is mainly thermodynamic, since the magnetic
field changes the temperature stratification. However, we observe
the signature of slow magnetoacoustic mode, propagating downwards,
for the strong magnetic field cases.
Title: The effect of elliptic shape on the period ratio
P1/P2 of emerging coronal loops
Authors: Morton, R. J.; Erdélyi, R.
Bibcode: 2009A&A...502..315M
Altcode:
Aims: We determine the effect of an elliptical shape on the period
ratio for the standing transversal oscillations of a longitudinally
stratified coronal loop throughout its emergence from the low solar
atmosphere into the ubiquitously magnetised corona.
Methods:
Under the assumption that elliptical curvature has a negligible effect
on eigenfrequencies, the equation that describes the projection of a
density profile onto a magnetic flux tube with elliptical shape is
obtained in a gravitationally stratified atmosphere. The effect of
the elliptical shape on the period ratio of the fundamental mode to
the first harmonic (P1/P2) at various stages
of emergence is determined, assuming that the oscillation periods are
much shorter than the characteristic time scale of loop emergence.
Results: We find that there are two separate cases of elliptical shape
that occur, the minor ellipse and the major ellipse. It is then shown
how the period ratio P1/P2 is dependent upon the
ellipticity (ɛ), the parameter characterising the stage of emergence
(λ) and the density scale height (H). Ellipticity is found to make an
important contribution to P1/P2 for the minor
ellipse when compared to its counterpart of standing oscillations of
stratified loops with semi-circle or circle-arc shape. The major ellipse
was found to have a lesser effect on the period ratio of standing
oscillations. We also find the value of P1/P2 is
dependent upon the stage of emergence of the loop, where the greatest
contribution from emergence to the ratio of P1/P2
is when the loop is almost fully emerged. The important implication for
magneto-seismological interpretations of the observations of oscillating
coronal loops is that measurements of ellipticity and stage of emergence
should supplement observations of oscillation periods and should be
considered when applying observed frequencies of the fundamental
mode and first harmonic to determine the diagnostic properties of
these oscillating loops, e.g. the density scale height or strength of
magnetic field. Neglecting the determination of ellipticity and stage of
emergence may result in a 35% error in estimating density scale height.
Title: Alfvén Waves in the Lower Solar Atmosphere
Authors: Jess, David B.; Mathioudakis, Mihalis; Erdélyi, Robert;
Crockett, Philip J.; Keenan, Francis P.; Christian, Damian J.
Bibcode: 2009Sci...323.1582J
Altcode: 2009arXiv0903.3546J
The flow of energy through the solar atmosphere and the heating of the
Sun’s outer regions are still not understood. Here, we report the
detection of oscillatory phenomena associated with a large bright-point
group that is 430,000 square kilometers in area and located near the
solar disk center. Wavelet analysis reveals full-width half-maximum
oscillations with periodicities ranging from 126 to 700 seconds
originating above the bright point and significance levels exceeding
99%. These oscillations, 2.6 kilometers per second in amplitude,
are coupled with chromospheric line-of-sight Doppler velocities
with an average blue shift of 23 kilometers per second. A lack of
cospatial intensity oscillations and transversal displacements rules
out the presence of magneto-acoustic wave modes. The oscillations
are a signature of Alfvén waves produced by a torsional twist of
±22 degrees. A phase shift of 180 degrees across the diameter of the
bright point suggests that these torsional Alfvén oscillations are
induced globally throughout the entire brightening. The energy flux
associated with this wave mode is sufficient to heat the solar corona.
Title: Magnetohydrodynamic waves in a compressible magnetic flux
tube with elliptical cross-section
Authors: Erdélyi, R.; Morton, R. J.
Bibcode: 2009A&A...494..295E
Altcode:
Aims: The propagation of magnetohydrodynamic (MHD) waves in a finite,
compressible magnetic flux tube with an elliptical cross-section
embedded in a magnetic environment is investigated.
Methods: We
present the derivation of the general dispersion relation of linear
magneto-acoustic wave propagation for a compressible magnetic flux
tube with elliptical cross-section in a plasma with finite beta. The
wave modes of propagation for the n=0 (symmetric) sausage and n=1
(anti-symmetric) kink oscillations are then examined within the limit
of the thin flux tube approximation.
Results: It is shown that
a compressible magnetic tube with elliptical cross-section supports
slow and fast magneto-acoustic waves. In the thin tube approximation,
the slow sausage mode and the slow and fast kink modes are found in
analogue to a circular cross-section. However, the kink modes propagate
with different phase speeds depending on whether the axial displacement
takes place along the major or minor axis of the ellipse. This feature
is present in both the slow and the fast bands, providing two infinite
sets of slow kink modes and two infinite sets of fast kink modes,
i.e. each corresponding cylindrical mode splits into two sets of modes
due to the ellipticity. The difference between the phase speeds along
the different axis is dependent on the ratio of the lengths of the two
axes. Analytical expressions for the phase speeds are found. We show
that the sausage modes do not split due to the introduced ellipticity
and only the phase speed is modified when compared to the appropriate
cylindrical counterpart. The percentage difference between the periods
of the circular and elliptical cross-sections is also calculated, which
reaches up to 21% for oscillations along the major axis. The level of
difference in period could be very important in magneto-seismological
applications, when observed periods are inverted into diagnostic
properties (e.g. magnetic field strength, gravitational scale height,
tube expansion parameter). Also shown is the perturbation of focal
points of the elliptical cross-section for different modes. It is
found that the focal points are unperturbed for the sausage mode,
but are perturbed for all higher modes.
Title: Dissipation of Longitudinal Oscillations in Stratified
Nonisothermal Hot Coronal Loops
Authors: Erdélyi, R.; Luna-Cardozo, M.; Mendoza-Briceño, C. A.
Bibcode: 2008SoPh..252..305E
Altcode: 2008SoPh..tmp..177E
We investigate the damping of longitudinal (i.e., slow or acoustic)
waves in nonisothermal, hot (T≥ 5.0 MK), gravitationally stratified
coronal loops. Motivated by SOHO/SUMER and Yohkoh/SXT observations, and
by taking into account a range of dissipative mechanisms such as thermal
conduction, compressive viscosity, radiative cooling, and heating,
the nonlinear governing equations of one-dimensional hydrodynamics
are solved numerically for standing-wave oscillations along a magnetic
field line. A semicircular shape is chosen to represent the geometry
of the coronal loop. It was found that the decay time of standing
waves decreases with the increase of the initial temperature, and the
periods of oscillations are affected by the different initial footpoint
temperatures and loop lengths studied by the numerical experiments. In
general, the period of oscillation of standing waves increases and
the damping time decreases when the parameter that characterises the
temperature at the apex of the loop increases for a fixed footpoint
temperature and loop length. A relatively simple second-order scaling
polynomial between the damping time and the parameter determining the
apex temperature is found. This scaling relation is proposed to be
tested observationally. Because of the lack of a larger, statistically
relevant number of observational studies of the damping of longitudinal
(slow) standing oscillations, it can only be concluded that the
numerically predicted decay times are well within the range of values
inferred from Doppler shifts observed by SUMER in hot coronal loops.
Title: Refined Magnetoseismological Technique for the Solar Corona
Authors: Verth, G.; Erdélyi, R.; Jess, D. B.
Bibcode: 2008ApJ...687L..45V
Altcode:
We present a step-by-step guide of a refined magnetoseismological
technique for plasma diagnostics in the Sun's corona. Recently developed
MHD wave theory which models a coronal loop as an expanding magnetic
flux tube with an arbitrary longitudinal plasma density profile is
applied to TRACE observations of fast kink oscillations. The theory
predicts that using the observed ratio of the first overtone and
fundamental mode to predict the plasma density scale height and not
taking account of loop expansion will lead to an overestimation of scale
height. For the first time, the size of this correction is quantified
directly from observation and for the particular case study presented
here, it is found that the overestimation is approximately by a factor
of 2.
Title: Chapter 5: Waves and Oscillations in the Solar Atmosphere
Authors: Erdélyi, Robert
Bibcode: 2008psa..book...61E
Altcode:
The actual operating heating process that generates and sustains the
hot solar corona has so far defied a quantitative understanding despite
efforts spanning over half a century. Particular attention is paid
here towards the exploration of the coronal heating problem from the
perspectives of MHD waves and oscillations. Do MHD waves play any role
in the heating of the solar atmosphere? In order to attempt answering
this question, first we need do embark on the key properties of the
heating of the solar atmosphere...
Title: Transverse Oscillations of Longitudinally Stratified Coronal
Loops with Variable Cross Section
Authors: Ruderman, M. S.; Verth, G.; Erdélyi, R.
Bibcode: 2008ApJ...686..694R
Altcode:
We consider transverse oscillations of coronal loops that have both
variable circular cross-sectional area and plasma density in the
longitudinal direction. The primary focus of this paper is to study the
eigenmodes of these oscillations. Implementing the method of asymptotic
expansions with the ratio of the loop radius to length as a small
parameter, a second-order ordinary differential equation is derived
describing the displacement of the loop axis. Together with the boundary
conditions at the tube ends that follow from the frozen-in condition,
this equation constitutes the Sturm-Liouville problem determining
the eigenfrequencies and eigenmodes. Our results are relevant to the
magnetoseismological method of estimating the coronal density scale
height by using the observed ratio of the fundamental frequency and
first overtone of loop kink oscillations. It is shown that this method
is very sensitive to the tube expansion factor, which is the ratio of
the tube radii at the apex and footpoints. The estimated scale height
is a monotonically decreasing function of the expansion factor.
Title: Hinode EUV spectroscopic observations of coronal oscillations
Authors: Erdélyi, R.; Taroyan, Y.
Bibcode: 2008A&A...489L..49E
Altcode:
Context: Waves offer a unique opportunity to understand and diagnose
the properties of the solar coronal plasma.
Aims: Hinode/EIS
observations are analysed to detect wave and oscillatory motions in
the solar corona.
Methods: The EIS observations were carried
out using a selection of EUV lines. Hinode/XRT images are taken
concurrently.
Results: Two examples of oscillations in active
regions are presented. We analysed the evolution of the intensities
and Doppler shifts. The Hinode/XRT images suggest that both events
occurred along loop-like structures. The first event is interpreted
as a slow sausage (acoustic) type wave with a period of 1.2 mHz. The
second example is associated with a transverse, most likely kink type,
wave with a period of 3 mHz. The EUV line ratios were then used to
determine the value of the coronal magnetic field.
Title: Global Acoustic Resonance in a Stratified Solar Atmosphere
Authors: Taroyan, Y.; Erdélyi, R.
Bibcode: 2008SoPh..251..523T
Altcode: 2008SoPh..tmp...47T
The upward propagation of linear acoustic waves in a gravitationally
stratified solar atmosphere is studied. The wave motion is governed
by the Klein - Gordon equation, which contains a cutoff frequency
introduced by stratification. The acoustic cutoff may act as a potential
barrier when the temperature decreases with height. It is shown that
waves trapped below the barrier could be subject to a resonance that
extends into the entire unbounded atmosphere of the Sun. The parameter
space characterizing the resonance is explored.
Title: Effects of Random Flows on the Solar f Mode: II. Horizontal
and Vertical Flow
Authors: Kerekes, Andrea; Erdélyi, Róbert; Mole, Nils
Bibcode: 2008SoPh..251..469K
Altcode: 2008SoPh..tmp..129K
We study the influence of horizontal and vertical random flows on the
solar f mode in a plane-parallel, incompressible model that includes a
static atmosphere. The incompressible limit is an adequate approximation
for f-mode type of surface waves that are highly incompressible. The
paper revisits and extends the problem investigated earlier by Murawski
and Roberts (Astron. Astrophys.272, 601, 1993).
Title: Effects of Random Flows on the Solar f Mode: I. Horizontal Flow
Authors: Mole, Nils; Kerekes, Andrea; Erdélyi, Robert
Bibcode: 2008SoPh..251..453M
Altcode: 2008SoPh..tmp..150M
We examine the effect of random horizontal flows on the dispersion
relation of high-degree solar f modes. We follow the approach of
Murawski and Roberts (Astron. Astrophys.272, 595, 1993), addressing some
limitations of that paper, and extending the results to include damping
and to apply for a general turbulent spectrum. We find a reduction in
frequency below the classical result that is about three times that
observed. For large wavenumber the damping rate is larger than the
frequency correction by a factor of the order of the nondimensional
wavenumber, which appears to be consistent with observation.
Title: A Novel Approach to the Solar Interior-Atmosphere Eigenvalue
Problem
Authors: Kerekes, A.; Erdélyi, R.; Mole, N.
Bibcode: 2008ApJ...683..527K
Altcode:
In this paper we introduce a new approach to study the interaction
of solar eigenoscillations, with particular emphasis on the f-mode,
with random inhomogeneities caused by flows and magnetic field near
the solar surface. We present an initial value method to derive a
general dispersion relation for a class of models where the magnetic
atmosphere is overlying an arbitrary static solar interior. In these
models the interior part is treated parametrically and does not need
to be specified before we obtain the dispersion relation. In order to
demonstrate the applicability of the proposed method, an analytical
solution of the dispersion relation is given for an incompressible
interior with constant density.
Title: Effect of longitudinal magnetic and density inhomogeneity on
transversal coronal loop oscillations
Authors: Verth, G.; Erdélyi, R.
Bibcode: 2008A&A...486.1015V
Altcode:
Context: Observations of post-flare transversal coronal loop
oscillations by TRACE have given us an excellent opportunity to
implement magneto-seismological techniques for probing the plasma fine
structure of the Sun's upper atmosphere.
Aims: We investigate
the combined effect of magnetic and density stratification on
transversal coronal loop oscillations.
Methods: A coronal loop
will be modelled as an expanding magnetic flux tube with arbitrary
longitudinal plasma density. The governing equation of the fast
kink body mode is derived and solved by analytical approximation and
numerical methods.
Results: It is found that even a relatively
small coronal loop expansion can have a significant and pronounced
effect on the accuracy of the plasma density scale height measurements
derived from observation of loop oscillations.
Conclusions:
To conduct more accurate and realistic magneto-seismology of coronal
loops, the magnetic field divergence should be taken into account.
Title: Magnetohydrodynamic code for gravitationally-stratified media
Authors: Shelyag, S.; Fedun, V.; Erdélyi, R.
Bibcode: 2008A&A...486..655S
Altcode:
Aims: We describe a newly-developed magnetohydrodynamic (MHD)
code with the capacity to simulate the interaction of any arbitrary
perturbation (i.e., not necessarily limited to the linearised limit)
with a magnetohydrostatic equilibrium background.
Methods: By
rearranging the terms in the system of MHD equations and explicitly
taking into account the magnetohydrostatic equilibrium condition,
we define the equations governing the perturbations that describe
the deviations from the background state of plasma for the density,
internal energy and magnetic field. We found it was advantageous to use
this modified form of the MHD equations for numerical simulations of
physical processes taking place in a stable gravitationally-stratified
plasma. The governing equations are implemented in a novel way in
the code. Sub-grid diffusion and resistivity are applied to ensure
numerical stability of the computed solution of the MHD equations. We
apply a fourth-order central difference scheme to calculate the
spatial derivatives, and implement an arbitrary Runge-Kutta scheme
to advance the solution in time.
Results: We have built the
proposed method, suitable for strongly-stratified magnetised plasma,
on the base of the well-documented Versatile Advection Code (VAC)
and performed a number of one- and multi-dimensional hydrodynamic and
MHD tests to demonstrate the feasibility and robustness of the code
for applications to astrophysical plasmas.
Title: Waves & Oscillations in the Solar Atmosphere: Heating
and Magneto-Seismology
Authors: Erdélyi, Robert; Mendoza-Briceno, César A.
Bibcode: 2008IAUS..247.....E
Altcode:
Preface; Organizing committee; Conference participants; Address by
the Scientific Organizing Committee R. Erdélyi; Progress in coronal
seismology B. Roberts; Session 1. Waves and oscillations in solar
and stellar interior Robert Erdélyi; Session 2. Coupling of global
solar and stellar motions into the lower atmosphere Bernard Roberts;
Session 3. Seismology of the lower solar atmosphere and stellar
chromospheres Siraj S. Hasan; Session 4. Seismology of open versus
closed magnetic structures Marcel Goossens; Session 5. Prominence
seismology Jose Luis Ballester; Session 6. Dynamical processes and
coupling in the magnetic atmosphere of Sun and stars Miguel Ibañez;
Session 7. Wave-particle interactions in magnetized plasmas Cesar
A. Mendoza-Briceño; Session 8. Solar and stellar global coronal
seismology Viggo Hansteen; Session 9. Fundamental physical processes
in coronae: waves, turbulence, reconnection Saku Tsuneta; Session
10. Waves and instabilities in atmospheric plasmas Arnold O. Benz;
Summary of meeting Cesar A. Mendoza-Briceño; Concluding remarks
A. O. Benz; Late papers; Author index.
Title: Discovery of Spatial Periodicities in a Coronal Loop Using
Automated Edge-Tracking Algorithms
Authors: Jess, D. B.; Mathioudakis, M.; Erdélyi, R.; Verth, G.;
McAteer, R. T. J.; Keenan, F. P.
Bibcode: 2008ApJ...680.1523J
Altcode: 2008arXiv0802.1971J
A new method for automated coronal loop tracking, in both spatial
and temporal domains, is presented. Applying this technique to TRACE
data, obtained using the 171 Å filter on 1998 July 14, we detect a
coronal loop undergoing a 270 s kink-mode oscillation, as previously
found by Aschwanden et al. However, we also detect flare-induced,
and previously unnoticed, spatial periodicities on a scale of 3500 km,
which occur along the coronal loop edge. Furthermore, we establish a
reduction in oscillatory power for these spatial periodicities of 45%
over a 222 s interval. We relate the reduction in detected oscillatory
power to the physical damping of these loop-top oscillations.
Title: Waves and Oscillations in the Solar Atmosphere (IAU S247)
Authors: Erdélyi, Robert; Mendoza-Briceno, César A.
Bibcode: 2008wosa.book.....E
Altcode:
Preface; Organizing committee; Conference participants; Address by
the Scientific Organizing Committee R. Erdélyi; Progress in coronal
seismology B. Roberts; Session 1. Waves and oscillations in solar
and stellar interior Robert Erdélyi; Session 2. Coupling of global
solar and stellar motions into the lower atmosphere Bernard Roberts;
Session 3. Seismology of the lower solar atmosphere and stellar
chromospheres Siraj S. Hasan; Session 4. Seismology of open versus
closed magnetic structures Marcel Goossens; Session 5. Prominence
seismology Jose Luis Ballester; Session 6. Dynamical processes and
coupling in the magnetic atmosphere of Sun and stars Miguel Ibañez;
Session 7. Wave-particle interactions in magnetized plasmas Cesar
A. Mendoza-Briceño; Session 8. Solar and stellar global coronal
seismology Viggo Hansteen; Session 9. Fundamental physical processes
in coronae: waves, turbulence, reconnection Saku Tsuneta; Session
10. Waves and instabilities in atmospheric plasmas Arnold O. Benz;
Summary of meeting Cesar A. Mendoza-Briceño; Concluding remarks
A. O. Benz; Late papers; Author index.
Title: Identification of linear slow sausage waves in magnetic pores
Authors: Dorotovič, I.; Erdélyi, R.; Karlovský, V.
Bibcode: 2008IAUS..247..351D
Altcode: 2007IAUS..247..351D
The analysis of an 11-hour series of high resolution white light
observations of a large pore in the sunspot group NOAA 7519, observed
on 5 June 1993 with the Swedish Vacuum Solar Telescope at La Palma
on Canary Islands, has been recently described by Dorotovič et
al. (2002). Special attention was paid to the evolution of a filamentary
region attached to the pore, to horizontal motions around the pore, and
to small-scale morphological changes. One of the results, relevant to
out work here, was the determination of temporal area evolution of the
studied pore where the area itself showed a linear trend of decrease
with time at an average rate of -0.23 Mm2h-1
during the entire observing period. Analysing the time series of the
are of the pore, there is strong evidence that coupling between the
solar interior and magnetic atmosphere can occur at various scales
and that the referred decrease of the area may be connected with
a decrease of the magnetic field strength according to the magnetic
field-to-size relation. Periods of global acoustic, e.g. p-mode, driven
waves are usually in the range of 5 10 minutes, and are favourite
candidates for the coupling of interior oscillations with atmospheric
dynamics. However, by assuming that magneto-acoustic gravity waves
may be there too, and may act as drivers, the observed periodicities
(frequencies) are expected to be much longer (smaller), falling well
within the mMHz domain. In this work we determine typical periods of
such range in the area evolution of the pore using wavelet analysis. The
resulted periods are in the range of 20 70 minutes, suggesting that
periodic elements of the temporal evolution of the area of this studied
pore could be linked to, and considered as, observational evidence of
linear low-frequency slow sausage (magneto-acoustic gravity) waves in
magnetic pores. This would give us further evidence on the coupling
of global solar oscillations to the overlaying magnetic atmosphere.
Title: Wave propagation in steady stratified one-dimensional
cylindrical waveguides
Authors: Erdélyi, R.; Hargreaves, J.
Bibcode: 2008A&A...483..285E
Altcode:
Aims: This paper studies the propagation of longitudinal magnetic tube
waves in a stratified isothermal flux tube with an internal equilibrium
background flow.
Methods: The governing differential equation
is solved by means of Laplace transforms and temporal and spatial
solutions are developed, with boundary conditions given by various
footpoint drivers, namely a monochromatic source, a delta function
pulse, and a sinusoidal pulse. The effect of the background flow is to
introduce an increase in amplitude of the wave perturbation and changes
in phase shift when compared with the corresponding static case.
Results: Results are presented and applied to conditions in the
solar atmosphere. When the source is driven continuously, the forced
atmospheric oscillations are shown to have large percentage differences
when compared to the corresponding static case. For the free atmospheric
oscillations, percentage increases in amplitude merely a few percent
are found and vary greatly in height but are practically unaltered in
time. Phase shifts up to a radian are introduced and weakly depend on
both height and time.
Conclusions: The results presented in this
paper may have interesting observational consequences, especially when
using the tools of magnetic seismology of solar atmospheric wave guides
(i.e. flux tubes from photosphere to corona) in light of the present
and near-future high spatial and temporal resolution space missions,
e.g. Hinode, Solar Dynamics Observatory, or Solar Orbiter.
Title: Solar feature tracking in both spatial and temporal domains
Authors: Jess, D. B.; Mathioudakis, M.; Erdélyi, R.; Verth, G.;
McAteer, R. T. J.; Keenan, F. P.
Bibcode: 2008IAUS..247..288J
Altcode: 2007IAUS..247..288J
A new method for automated coronal loop tracking, in both spatial and
temporal domains, is presented. The reliability of this technique
was tested with TRACE 171 Å observations. The application of this
technique to a flare-induced kink-mode oscillation, revealed a 3500
km spatial periodicity which occur along the loop edge. We establish
a reduction in oscillatory power, for these spatial periodicities,
of 45% over a 322 s interval. We relate the reduction in oscillatory
power to the physical damping of these loop-top oscillations.
Title: Radiative damping of standing acoustic waves in solar
coronal loops
Authors: Bradshaw, S. J.; Erdélyi, R.
Bibcode: 2008A&A...483..301B
Altcode:
Context: A detailed understanding of the physical processes that
determine the damping timescales of magneto-acoustic waves is
essential to interpret diagnostic results from the application of solar
magneto-seismology.
Aims: The influence of the transition region
and the importance of radiative emission, arising from equilibrium and
non-equilibrium ionisation balances, for the damping timescale of the
fundamental mode standing acoustic wave is investigated.
Methods:
An extensive numerical study, in the framework of the field-aligned
hydrodynamic approximation, is carried out of the damping of the
fundamental mode standing wave in a solar coronal loop, for a wide
range of loop lengths and apex temperatures.
Results: It was found
that the radiative emission arising from a non-equilibrium ionisation
balance will always act to reduce the damping timescale (in comparison
to the equilibrium case) and may do so by up to ~10%. The physics of the
transition region is most crucial in determining the magnitude of the
reduction of the damping timescale when a non-equilibrium ionisation
balance is properly accounted for.
Conclusions: The methods
of solar magneto-seismology, in particular the tools of coronal
seismology, may be used to estimate loop lengths to a reasonable
degree of accuracy, although estimates of the apex temperature
are significantly less reliable, and one should use alternative
(e.g. spectroscopic) diagnostics instead.
Title: Damping of non-isothermal hot coronal loops oscillations
Authors: Luna-Cardozo, M.; Erdélyi, R.; Mendoza-Briceño, César A.
Bibcode: 2008IAUS..247..316L
Altcode: 2007IAUS..247..316L
Here we investigate longitudinal waves in non-isothermal hot (T
≥ 5.0 MK) coronal loops. Motivated by SOHO SUMER and Yohkoh SXT
observations and taking into account gravitational stratification,
thermal conduction, compressive viscosity, radiative cooling,
and heating, the governing equations of 1D hydrodynamics is solved
numerically for standing wave oscillations along a magnetic field
line. A semicircular shape is chosen to represent a coronal loop. It
was found that the decay time of standing waves decreases with the
increase of the initial temperature and the periods of oscillations
are affected by the different initial velocities and loop lengths
studied by the numerical experiments. The predicted decay times are
within the range of values inferred from Doppler-shift oscillations
observed by SUMER in hot coronal loops.
Title: Resonant acoustic waves in a stratified atmosphere
Authors: Taroyan, Y.; Erdélyi, R.
Bibcode: 2008IAUS..247...86T
Altcode: 2007IAUS..247...86T
The upward propagation of linear acoustic waves in a gravitationally
stratified atmosphere is studied. The wave motion is governed by the
Klein-Gordon equation which contains a cut-off frequency introduced by
stratification. The acoustic cut-off may act as a potential barrier when
the temperature decreases with height. It is shown that waves trapped
below the barrier could be subject to a resonance which extends into
the entire unbounded atmosphere. The parameter space characterizing
the resonance is explored.
Title: Kink oscillations in magnetic tubes with twisted annulus
Authors: Carter, B. K.; Erdélyi, R.
Bibcode: 2008A&A...481..239C
Altcode:
Aims:We study kink waves in a magnetic flux tube modelled as a straight
core surrounded by a magnetically twisted annulus, both embedded in a
straight ambient external field, and derive the dispersion relation for
this configuration.
Methods: The existence and behaviour of the
kink modes are examined with specific attention to the effect that the
addition of magnetic twist has on phase speeds and periods. Analytic
expansions to the short and long wavelength approximations are also
considered.
Results: The magnetic twist is found to introduce
of an infinite set of body modes into solutions of the dispersion
relation not present in the untwisted case. Moreover, for the kink
modes, the width of interval of this infinite set, generally found to
occupy phase speeds around the annulus' longitudinal Alfvén speed,
increases for longer wavelengths. Two surface modes are also present
in the solution, one at each surface: the internal and the external
edges of the annulus. The magnetic twist is found to increase or
decrease the phase speeds of these surface modes that are depending
on the ratio of internal and external Alfvén speeds in the flux
tube.
Conclusions: The magnetic twist of the annulus region of
a flux tube is found to have a marked effect on the phase speeds of
occurring modes. A straight annulus layer increased (or decreased)
the periods of the surface modes for a tube modelled as a density
(magnetic) enhancement. The addition of twist reduces the periods of
the modes in both cases.
Title: Are There Alfvén Waves in the Solar Atmosphere?
Authors: Erdélyi, R.; Fedun, V.
Bibcode: 2007Sci...318.1572E
Altcode:
The Sun’s outer coronal layer exists at a temperature of millions
of kelvins, much hotter than the solar surface we observe. How this
high temperature is maintained and what energy sources are involved
continue to puzzle and fascinate solar researchers. Recently, the Hinode
spacecraft was launched to observe and measure the plasma properties
of the Sun’s outer layers. The data collected by Hinode reveal much
about the role of magnetic field interactions and how plasma waves
might transport energy to the corona. These results open a new era in
high-resolution observation of the Sun.
Title: Direct Propagation of Photospheric Acoustic p Modes into
Nonmagnetic Solar Atmosphere
Authors: Malins, C.; Erdélyi, R.
Bibcode: 2007SoPh..246...41M
Altcode:
Solar p modes are one of the dominant types of coherent signals in
Doppler velocity in the solar photosphere, with periods showing a
power peak at five minutes. The propagation (or leakage) of these
p-mode signals into the higher solar atmosphere is one of the key
drivers of oscillatory motions in the higher solar chromosphere
and corona. This paper examines numerically the direct propagation
of acoustic waves driven harmonically at the photosphere, into the
nonmagnetic solar atmosphere. Erdélyi et al. (Astron. Astrophys.467,
1299, 2007) investigated the acoustic response to a single point-source
driver. In the follow-up work here we generalise this previous study to
more structured, coherent, photospheric drivers mimicking solar global
oscillations. When our atmosphere is driven with a pair of point drivers
separated in space, reflection at the transition region causes cavity
oscillations in the lower chromosphere, and amplification and cavity
resonance of waves at the transition region generate strong surface
oscillations. When driven with a widely horizontally coherent velocity
signal, cavity modes are caused in the chromosphere, surface waves
occur at the transition region, and fine structures are generated
extending from a dynamic transition region into the lower corona,
even in the absence of a magnetic field.
Title: Preface: A Topical Issue in Honor of Professor Bernard Roberts
Authors: Ballester, J. L.; Erdélyi, R.; Hood, A. W.; Leibacher,
J. W.; Nakariakov, V. M.
Bibcode: 2007SoPh..246....1B
Altcode:
No abstract at ADS
Title: Present and Future Observing Trends in Atmospheric
Magnetoseismology
Authors: Banerjee, D.; Erdélyi, R.; Oliver, R.; O'Shea, E.
Bibcode: 2007SoPh..246....3B
Altcode:
With modern imaging and spectral instruments observing in the visible,
EUV, X-ray, and radio wavelengths, the detection of oscillations
in the solar outer atmosphere has become a routine event. These
oscillations are considered to be the signatures of a wave phenomenon
and are generally interpreted in terms of magnetohydrodynamic (MHD)
waves. With multiwavelength observations from ground- and space-based
instruments, it has been possible to detect waves in a number of
different wavelengths simultaneously and, consequently, to study their
propagation properties. Observed MHD waves propagating from the lower
solar atmosphere into the higher regions of the magnetized corona
have the potential to provide excellent insight into the physical
processes at work at the coupling point between these different regions
of the Sun. High-resolution wave observations combined with forward MHD
modeling can give an unprecedented insight into the connectivity of the
magnetized solar atmosphere, which further provides us with a realistic
chance to reconstruct the structure of the magnetic field in the solar
atmosphere. This type of solar exploration has been termed atmospheric
magnetoseismology. In this review we will summarize some new trends in
the observational study of waves and oscillations, discussing their
origin and their propagation through the atmosphere. In particular,
we will focus on waves and oscillations in open magnetic structures
(e.g., solar plumes) and closed magnetic structures (e.g., loops and
prominences), where there have been a number of observational highlights
in the past few years. Furthermore, we will address observations of
waves in filament fibrils allied with a better characterization of
their propagating and damping properties, the detection of prominence
oscillations in UV lines, and the renewed interest in large-amplitude,
quickly attenuated, prominence oscillations, caused by flare or
explosive phenomena.
Title: Effect of the steady flow on spatial damping of small-amplitude
prominence oscillations
Authors: Singh, K. A. P.; Erdelyi, R.; Dwivedi, B. N.
Bibcode: 2007arXiv0711.2353S
Altcode:
Aims. Taking account of steady flow in solar prominences, we study
its effects on spatial damping of small-amplitude non-adiabatic
magnetoacoustic waves in a homogeneous, isothermal, and unbounded
prominence plasma. Methods. We model the typical feature of
observed damped oscillatory motion in prominences, removing the
adiabaticity assumption through thermal conduction, radiation
and heating. Invoking steady flow in MHD equations, we linearise
them under small-amplitude approximation and obtain a new general
dispersion relation for linear non-adiabatic magnetoacoustic waves in
prominences Results. The presence of steady flow breaks the symmetry
of forward and backward propagating MHD wave modes in prominences. The
steady flow has dramatic influence on the propagation and damping of
magnetoacoustic and thermal waves. Depending upon the direction and
strength of flow the magnetoacoustic and thermal modes can show both
the features of wave amplification and damping. At the wave period of
5 min where the photospheric power is maximum, the slow mode shows wave
amplification. However, in the absence of steady flow the slow mode wave
shows damping. Conclusions. For the wave period between 5 min and 15
min, the amplification length for slow mode, in the case of prominence
regime 1.1, varies between 3.4*10^11 m to 2*10^12 m. Dramatic influence
of steady flow on small-amplitude prominence oscillations is likely to
play an important role in both wave detection and prominence seismology.
Title: Spatial magneto-seismology: effect of density stratification
on the first harmonic amplitude profile of transversal coronal
loop oscillations
Authors: Verth, G.; Van Doorsselaere, T.; Erdélyi, R.; Goossens, M.
Bibcode: 2007A&A...475..341V
Altcode:
Context: The new generation of extreme-ultraviolet (EUV) imagers onboard
missions such as the Solar Dynamics Observatory (SDO) and Solar Orbiter
(SO) will provide the most accurate spatial measurements of post-flare
coronal loop oscillations yet. The amplitude profiles of these loop
oscillations contain important information about plasma fine structure
in the corona.
Aims: We show that the position of the anti-nodes
of the amplitude profile of the first harmonic of the standing fast kink
wave of a coronal loop relate to the plasma density stratification of
that loop.
Methods: The MHD kink transversal waves of coronal
loops are modelled both numerically and analytically. The numerical
model implements the implicit finite element code pollux. Dispersion
relations are derived and solved analytically. The results of
the two methods are compared and verified.
Results: Density
stratification causes the anti-nodes of the first harmonic to shift
towards the loop footpoints. The greater the density stratification,
the larger the shift. The anti-node shift of the first harmonic of
a semi-circular coronal loop with a density scale height H=50 Mm and
loop half length L=100 Mm is approximately 5.6 Mm. Shifts in the Mm
range are measureable quantities providing valuable information about
the subresolution structure of coronal loops.
Conclusions:
The measurement of the anti-node shift of the first harmonic of the
standing fast kink wave of coronal loops is potentially a new tool in
the field of solar magneto-seismology, providing a novel complementary
method of probing plasma fine structure in the corona.
Title: Sausage and kink oscillations in incompressible annular
magnetic cylinders
Authors: Carter, B. K.; Erdélyi, R.
Bibcode: 2007A&A...475..323C
Altcode:
Aims:The propagation of MHD waves in a structured magnetic flux
tube embedded within a straight magnetic environment is studied
analytically. The motivation for this analysis comes from the
observations of damped loop oscillations indicating the possibility
that only part of the loop is homogeneous in the radial direction and
from the observation of two simultaneous waves with different speeds
in the same magnetic loop in the solar atmosphere.
Methods:
The general dispersion relation of longitudinal wave propagation
is derived for a flux tube configuration consisting of a core,
annulus and external region each with straight distinct magnetic
field. Modes of oscillation are examined from the general dispersion
relation that is suitable for obtaining information not just on
oscillations but also on some instability properties of this complex
tube structure. Specific attention is given to the modification of the
phase speeds and oscillation periods caused by the annulus structure,
compared to a single monolithic tube.
Results: It is shown that
two purely surface modes arise. The relative change in periods due to
the additional annulus layer is shown to be rather significant (up to
20% in some cases). In particular we found that in photospheric type
annular tubes, periods are less than their counterparts in a monolithic
loop while for a dense flux tube in the majority of cases the period was
greater than the period of the counterpart monolithic flux tube. Both
short and long wavelength approximations are considered for both
the symmetrical (sausage) and kink modes.
Conclusions: Annular
structuring of a magnetic flux tube will reduce or increase periods of
the allowed oscillations depending on the type of flux tube considered
(either as a magnetic or as a density enhancement). The results are
relevant to further our knowledge of solar magneto-seismology. In
particular, the obtained results for the kink oscillations may be
applicable from photosphere to corona, while the case for the sausage
mode is more relevant in the lower part of the solar atmosphere.
Title: Linear MHD Sausage Waves in Compressible Magnetically Twisted
Flux Tubes
Authors: Erdélyi, Robert; Fedun, Viktor
Bibcode: 2007SoPh..246..101E
Altcode:
Oscillations of magnetic flux tubes are of great importance as they
contain information about the geometry and fine structure of the
flux tubes. Here we derive and analytically solve in terms of Kummer's
functions the linear governing equations of wave propagation for sausage
surface and body modes (m=0) of a magnetically twisted compressible flux
tube embedded in a compressible uniformly magnetized plasma environment
in cylindrical geometry. A general dispersion relation is obtained
for such flux tubes. Numerical solutions for the phase velocity are
obtained for a wide range of wavenumbers and for varying magnetic
twist. The effect of magnetic twist on the period of oscillations
of sausage surface modes for different values of the wavenumber and
vertical magnetic field strength is calculated for representative
photospheric and coronal conditions. These results generalize and
extend previous studies of MHD waves obtained for incompressible or
for compressible but nontwisted flux tubes. It is found that magnetic
twist may change the period of sausage surface waves of the order of a
few percent when compared to counterparts in straight nontwisted flux
tubes. This information will be most relevant when high-resolution
observations are used for diagnostic exploration of MHD wave guides in
analogy to solar-interior studies by means of global eigenoscillations
in helioseismology.
Title: Heating of the solar and stellar coronae: a review
Authors: Erdélyi, R.; Ballai, I.
Bibcode: 2007AN....328..726E
Altcode:
Despite great advances in observations and modelling, the problem of
solar and stellar heating still remains one of the most challenging
problems of space physics. To find a definite answer to what sort of
mechanisms act to heat the plasma to a few million degrees requires
a collaborative effort of small scales observations, large capacity
numerical modelling and complicated theoretical approaches. A unique
theory should incorporate aspects such as the generation of energy,
its transport and dissipation. Up to now, the first two problems are
rather clarified. However, the modality of transfer of magnetic or
kinetic energy into heat is a question still awaiting for an answer. In
the present paper we review the various popular heating mechanisms
put forward in the existing extensive literature. The heating
processes are, somewhat arbitrarily, classified as hydrodynamic,
magnetohydrodynamic or kinetic based on the characteristics of the
model medium. These mechanisms are further divided based on the time
scales of the ultimate dissipation involved (i.e. AC and DC heating,
turbulent heating). In particular, special attention is paid to discuss
shock dissipation, mode coupling, resonant absorption, phase mixing,
and, reconnection. Finally, we briefly review the various heating
mechanisms proposed to heat other stars.
Title: Forward modelling of sub-photospheric flows for time-distance
helioseismology
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
Bibcode: 2007A&A...469.1101S
Altcode: 2007astro.ph..3067S
Context: The results of forward modelling of acoustic wave propagation
in a realistic solar sub-photosphere with two cases of steady
horizontal flows are presented and analysed by the means of local
helioseismology.
Aims: This paper is devoted to an analysis
of the influence of steady flows on the propagation of sound waves
through the solar interior.
Methods: The simulations are based
on fully compressible ideal hydrodynamical modelling in a Cartesian
grid. The initial model is characterised by solar density and pressure
stratifications taken from the standard Model S and is adjusted in
order to suppress convective instability. Acoustic waves are excited
by a non-harmonic source located below the depth corresponding to
the visible surface of the Sun. Numerical experiments with coherent
horizontal flows of linear and Gaussian dependences of flow speed on
depth are carried out. These flow fields may mimic horizontal motions
of plasma surrounding a sunspot, differential rotation or meridional
circulation. An inversion of the velocity profiles from the simulated
travel time differences is carried out. The inversion is based on
the ray approximation. The results of inversion are then compared
with the original velocity profiles.
Results: The results
of forward modelling of acoustic wave propagation in a realistic
solar sub-photosphere with two cases of steady horizontal flows are
presented. The influence of steady flow on the propagation of sound
waves through the solar interior is analysed. A time-distance analysis
technique is applied to compute the direct observable signatures of
the background bulk motions on travel times and phase shifts. This
approach allows direct comparison with observational data. Further,
we propose a method of obtaining the travel-time differences for the
waves propagating in sub-photospheric solar regions with horizontal
flows. The method employs directly the difference between travel-time
diagrams of waves propagating with and against the background flow.
Conclusions: The analysis shows that the flow speed profiles obtained
from inversion based on the ray approximation differ from the original
ones. The difference between the original and observed profiles is
caused by the fact that the wave packets propagate along the ray
bundle, which has a finite extent, and thus reach deeper regions of
the sub-photosphere in comparison with ray theory.
Title: Leakage of photospheric acoustic waves into non-magnetic
solar atmosphere
Authors: Erdélyi, R.; Malins, C.; Tóth, G.; de Pontieu, B.
Bibcode: 2007A&A...467.1299E
Altcode:
Aims:This paper aims to look at the propagation of synthetic
photospheric oscillations from a point source into a two-dimensional
non-magnetic solar atmosphere. It takes a particular interest in
the leakage of 5-min global oscillations into the atmosphere, and
aims to complement efforts on the driving of chromospheric dynamics
(e.g. spicules and waves) by 5-min oscillations.
Methods: A
model solar atmosphere is constructed based on realistic temperature
and gravitational stratification. The response of this atmosphere to
a wide range of adiabatic periodic velocity drivers is numerically
investigated in the hydrodynamic approximation.
Results: The
findings of this modelling are threefold. Firstly, high-frequency waves
are shown to propagate from the lower atmosphere across the transition
region experiencing relatively low reflection and transmitting energy
into the corona. Secondly, it is demonstrated that driving the upper
solar photosphere with a harmonic piston driver at around the 5 min
period may generate three separate standing modes with similar periods
in the chromosphere and transition region. In the cavity formed
by the chromosphere and bounded by regions of low cut-off period
at the photospheric temperature minimum and the transition region
this is caused by reflection, while at either end of this region in
the lower chromosphere and transition region the standing modes are
caused by resonant excitation. Finally, the transition region becomes
a guide for horizontally propagating surface waves for a wide range
of driver periods, and in particular at those periods which support
chromospheric standing waves. Crucially, these findings are the results
of a combination of a chromospheric cavity and resonant excitation in
the lower atmosphere and transition region.
Title: Trapped Eigenoscillations in the Lower Solar Atmosphere:
Is there a Resonant Coupling?
Authors: Erdélyi, R.; Fedun, V.; Malins, Ch.; Pintér, B.
Bibcode: 2007ASPC..368..187E
Altcode:
Magnetic coupling through MHD waves and oscillations at the solar
interior - lower corona interface is studied here. First, the
effect of a magnetic solar atmosphere on solar global oscillations is
investigated. Frequency shifts of acoustic eigenmodes are found due to
the presence of the chromospheric and coronal magnetic fields. Potential
application to local magneto-seismology is highlighted. Next, the
propagation and leakage of global acoustic waves is studied in a
multi-dimensional realistic model of the lower solar magnetized
atmosphere with temperature, pressure and density profiles based on
the VAL IIIc model. The higher atmosphere, on the other hand, is the
McWhirter atmospheric model. Acoustic waves, mainly identified by
solar global oscillations, manifest at photospheric heights. Their
leakage into the lower atmosphere is approximated by a harmonic point
velocity driver at a range of realistic driver periods measured at
photospheric heights, positioned just above the temperature minimum in
the photosphere. Convective instability may thus be ignored. The
excited high-frequency waves are seen to propagate through the lower
atmosphere to the transition region, and, dependant on the wave period,
are transmitted into the lower corona. It was found that for periods
close to the lower atmospheric resonant cavity period, reflection from
the transition region and trapping in the cavity formed right below the
transition region is manifested in the form of chromospheric standing
waves. We urge observers to justify these standing waves in the region
between the photosphere and transition region by carrying out space
or ground-based high-resolution and high-cadence observations. Further, it is observed in the simulations that waves driven below
the cut-off period propagate through into the higher atmosphere with
only a slight reflected component. Waves driven at a higher period, in
contrast, are largely trapped in the lower atmosphere, with some leakage
through the transition region. For specific drivers of around 5 minutes,
clear evidence of standing waves being set up in the lower atmospheric
cavity is found, and the formation of surface waves travelling outwards
along the transition region is demonstrated. When the lower
atmospheric magnetic canopy is also considered, global oscillations can
resonantly interact at a much wider range of frequencies as opposed
to quiet Sun regions. The properties of this interaction allow us
to carry out local magneto-seismology, i.e. to derive diagnostic
information about the chromospheric magnetic field. This technique
can be further used to improve the missing details of wave leakage,
spicule and chromospheric jet formation.
Title: Observation And Simulation Of P-mode Propagation Into The
Solar Corona
Authors: Marsh, Michael; Malins, C.; Erdelyi, R.
Bibcode: 2007AAS...210.2413M
Altcode: 2007BAAS...39..130M
Observations have shown the connection between oscillations within the
sunspot photosphere and photospheric p-modes. In the strong, vertical,
magnetic field regions of sunspot umbrae, it is thought that these
acoustic p-modes undergo mode conversion to slow-magnetoacoustic waves,
and that these slow-magnetoacoustic p-modes may be waveguided from the
photosphere into the solar corona along the magnetic field. Observations
are presented of the propagation of these waves and their channelling
into the coronal parts of magnetic loops, originally emerging from a
sunspot region. These observations are combined with 2-D MHD numerical
simulations of wave leakage and direct propagation within the model
sunspot atmosphere. The simulations are driven at the photospheric level
by the Doppler velocity field of p-modes observed within the sunspot,
and the response of forward modelling of the atmosphere is compared to
observations. In the future, this combined approach of observation and
theoretical modelling may be exploited to allow magneto-seismology of
the solar atmosphere above sunspots or active regions. M.S. Marsh
supported through the NASA post doctoral program.
Title: Forward Modeling of Hot Loop Oscillations Observed by SUMER
and SXT
Authors: Taroyan, Y.; Erdélyi, R.; Wang, T. J.; Bradshaw, S. J.
Bibcode: 2007ApJ...659L.173T
Altcode:
An example of hot active region loop oscillations observed by SUMER
and SXT is presented. The hypothesis that a fundamental mode standing
slow sausage (acoustic) wave is initiated by a footpoint microflare is
tested and confirmed using a forward modeling approach. The oscillation
is set up immediately after the heating pulse. The duration, temporal
behavior, and total heat input of the microflare are estimated using
the oscillation parameters. The rapid energy release is followed by
cooling. The time-distance profile of the heating rate along the loop
is recovered using the intensity and Doppler-shift time series. Hot
loop oscillations are mainly observed in the Doppler shift. The absence
of intensity oscillations in this and similar cases is explained. It
is also found that the intensity oscillation, unlike the Doppler
shift oscillation, undergoes half a period phase variation when the
background intensity passes through its maximum, thus making it more
difficult to detect.
Title: Global oscillations in a magnetic solar model. II. Oblique
propagation
Authors: Pintér, B.; Erdélyi, R.; Goossens, M.
Bibcode: 2007A&A...466..377P
Altcode:
The coupling of solar global acoustic oscillations to a magnetised
solar atmosphere is studied here. The solar interior - atmosphere
interface is modelled by a non-magnetic polytrope interior overlayed
by a planar atmosphere embedded in non-uniform horizontal atmospheric
magnetic field. Pintér & Goossens (1999, A&A, 347, 321) showed
that parallel propagating acoustic waves can couple resonantly to
local magnetohydrodynamic (MHD) slow continuum modes only. In general,
global acoustic modes can, however, propagate in arbitrary directions
with respect to local atmospheric fields giving rise to an additional
efficient coupling mechanism that has consequences on mode damping and
atmospheric energetics. In this paper we study obliquely propagating
global modes that can couple also to local MHD Alfvén continuum
modes. The atmospheric magnetic effects on global mode frequencies are
still much of a debate. In particular, the resulting frequency shifts
and damping rates of global modes caused by the resonant interaction
with both local Alfvén and slow waves are investigated. We found the
coupling of global f and p modes and the Lamb mode, that penetrate into
the magnetic solar atmosphere, will strongly depend on the direction of
propagation with respect to the solar atmospheric magnetic field. These
frequency shifts, as a function of the propagation direction, give us
a further elegant tool and refinement method of local helioseismology
techniques. Finally we briefly discuss the importance of studying
obliquely propagating waves and discuss the results in the context of
possible helioseismic observations. Appendix A is only available
in electronic form at http://www.aanda.org
Title: Leakage of photospheric motions into the magnetic solar
atmosphere: new prospects of magneto-seismology
Authors: Erdélyi, R.; Pintér, B.; Malins, C.
Bibcode: 2007AN....328..305E
Altcode:
The leakage and coupling of solar global oscillations to the overlaying
magnetized solar atmosphere is investigated in this paper. Solar
global acoustic oscillations may couple through resonant absorption to
atmospheric local magnetic eigenoscillations ({i}) resulting in small
shifts of the order of μHz in the real part of their frequencies
as compared to their non-magnetic counterparts, and ({ii}) causing
dissipation of wave energy and a consequent line broadening of the
modes. Alternatively, global modes may also penetrate deeply into
the magnetized solar atmosphere through leakage along magnetic field
lines causing small-scale structuring in the transition region and low
corona. By analyzing the dynamic fragmentation generated by direct
wave propagations, one may deduce diagnostic information about the
geometric and physical properties of the local magnetic environment
in the atmosphere. A few numerical examples are presented here to
demonstrate the leakage of global oscillations and its influence and
omnipotence on the dynamics of the lower solar atmosphere.
Title: The Effect of Abnormal Granulation on Acoustic Wave Travel
Times and Mode Frequencies
Authors: Petrovay, K.; Erdélyi, R.; Thompson, M. J.
Bibcode: 2007SoPh..240..197P
Altcode: 2007astro.ph..2076P
Observations indicate that in plage areas (i.e. in active regions
outside sunspots) acoustic waves travel faster than in the quiet Sun,
leading to shortened travel times and higher p-mode frequencies. Coupled
with the 11-year variation of solar activity, this may also explain the
solar cycle variation of oscillation frequencies. While it is clear
that the ultimate cause of any difference between the quiet Sun and
plage is the presence of magnetic fields of order 100 G in the latter,
the mechanism by which the magnetic field exerts its influence has
not yet been conclusively identified. One possible such mechanism is
suggested by the observation that granular motions in plage areas tend
to be slightly "abnormal", dampened compared to the quiet Sun.
Title: The effect of density stratification on the amplitude profile
of transversal coronal loop oscillations
Authors: Erdélyi, R.; Verth, G.
Bibcode: 2007A&A...462..743E
Altcode:
Context: Measuring how the density of the plasma in the Sun's corona
varies along fine structures such as coronal loops using emission
measure is very difficult as the exact value of the line of sight
filling factor and the correct amount of background subtraction are
unknown.
Aims: To investigate if magnetohydrodynamic (MHD)
wave theory can be used to complement existing observational methods
to obtain diagnostic information about the density structure of
coronal loops by measuring the amplitude profile of the fundamental
standing mode of the fast kink wave.
Methods: Analytical and
numerical approaches are used to show how the amplitude profile
of the fundamental fast kink mode changes by varying the amount of
density stratification in a coronal loop.
Results: Increasing
the amount of density stratification in a coronal loop will increase
the difference in amplitude profile from one of constant longitudinal
density. For a semi-circular TRACE 171 Å temperature loop of length
200 Mm and density scale height, H=50 Mm, the maximum change in
amplitude profile is of the order of 50 km. It is also found that
the amplitudes of these oscillations are effectively negligible
at altitudes lower than the transition region.
Conclusions:
.The effect of density stratification on the amplitude profile of the
fundamental standing kink mode of a TRACE 171 Å temperature loop may
be very subtle. Unfortunately, the observational signatures of this
effect are likely to be well below the resolution of the best currently
available extreme-ultraviolet (EUV) imagers. Only loops with homogeneous
magnetic fields have been addressed here, but inhomogeneous magnetic
fields may well dominate over the effect of density stratification on
the amplitude profile.
Title: Analysis of power spectra of Doppler shift time series as a
diagnostic tool for quiescent coronal loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.; Bradshaw, S. J.
Bibcode: 2007A&A...462..331T
Altcode:
Context: Analysing the structure of solar coronal loops is crucial
to our understanding of the processes which heat and maintain the
coronal plasma at multimillion degree temperatures. The determination
of the physical parameters of the loops remains both an observational
and theoretical challenge.
Aims: The present work is aimed at
tackling some of these challenges such as the determination of the
average loop temperature and its distribution along a given loop.
Methods: A novel diagnostic technique for quiescent coronal loops
based on the analysis of power spectra of Doppler shift time series
is proposed. It is assumed that the loop is heated randomly both in
space and time by small-scale discrete impulsive events of unspecified
nature. The loop evolution is characterised by longitudinal motions
caused by the random heating events. These random motions can be
represented as a superposition of the normal modes of the loop,
i.e., its standing acoustic wave harmonics. The idea is borrowed
from helioseismology where a similar approach resulted in a deep
understanding of the solar interior.
Results: It is shown that
depending on the heliographic position of the loop and its geometrical
orientation, various harmonics can be identified in the power spectra
of the line shift time series. The highest power peak corresponds
to the fundamental mode. The peaks become smaller as the frequency
increases. The frequencies of the harmonics are determined by the
loop length and temperature and thus are suggested to be used as a
temperature diagnostic tool. It is demonstrated that the analysis of
the power spectra allows the distinction between uniformly heated
loops from loops heated near their footpoints and to estimate the
average energy of a single heating event. The proposed new method
could in principle be used to study the multithermal structure of
coronal loops.
Conclusions: .The power spectrum analysis is a
potentially powerful technique for coronal loop diagnostics.
Title: Forward Modeling of Acoustic Wave Propagation in the Quiet
Solar Subphotosphere
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
Bibcode: 2006ApJ...651..576S
Altcode:
The results of numerical simulations of acoustic wave propagation
and dispersion in the nonmagnetic solar subphotosphere are
presented. Initial equilibrium density and pressure stratifications are
taken from a standard solar model but modified to suppress convective
instabilities in fully compressible two-dimensional ideal hydrodynamical
modeling. Acoustic waves are generated by sources located below the
height corresponding to the visible solar surface. The dynamic response
of the solar interior to two acoustic source types, namely a harmonic
source and one representing downward-propagating photospheric plumes,
is studied. A large number of randomly distributed localized cooling
sources with random amplitudes is also introduced. The methods used to
analyze the simulation data are similar to ones used in observational
studies in local helioseismology. Time-distance diagrams of the pressure
and vertical velocity perturbations at the level corresponding to the
solar surface show the appearance of wave packets propagating with
different speeds, which are reflected at different depths beneath the
subphotosphere. The (ω, kh) power spectra, derived from the
vertical velocity data, show the existence of g-, f-, and p-modes p-mode
ridges are identifiable up to high radial orders of n~11 g-modes appear
in the simulations, unlike in the real Sun, where they cannot propagate
in the convectively unstable solar subphotosphere. Cross-correlation
analysis of vertical velocity perturbations shows a good correspondence
with the observed time-distance helioseismic data for quiet Sun. Thus,
the ability of the implemented approach of forward modeling to
investigate propagation of acoustic, internal, and surface gravity
waves in a realistic solar interior model is shown.
Title: Sausage MHD Waves in Incompressible Flux Tubes with Twisted
Magnetic Fields
Authors: Erdélyi, Robert; Fedun, Viktor
Bibcode: 2006SoPh..238...41E
Altcode: 2006SoPh..tmp...36E
Twisted magnetic flux tubes are of considerable interest because of
their natural occurrence from the Sun's interior, throughout the
solar atmosphere and interplanetary space up to a wide range of
applicabilities to astrophysical plasmas. The aim of the present
work is to obtain analytically a dispersion equation of linear
wave propagation in twisted incompressible cylindrical magnetic
waveguides and find appropriate solutions for surface, body and
pseudobody sausage modes (i.e. m = 0) of a twisted magnetic flux
tube embedded in an incompressible but also magnetically twisted
plasma. Asymptotic solutions are derived in long- and short-wavelength
approximations. General solutions of the dispersion equation for
intermediate wavelengths are obtained numerically. We found, that in
case of a constant, but non-zero azimuthal component of the equilibrium
magnetic field outside the flux tube the index ν of Bessel functions
in the dispersion relation is not integer any more in general. This
gives rise to a rich mode-structure of degenerated magneto-acoustic
waves in solar flux tubes. In a particular case of a uniform magnetic
twist the total pressure is found to be constant across the boundary of
the flux tube. Finally, the effect of magnetic twist on oscillation
periods is estimated under solar atmospheric conditions. It was
found that a magnetic twist will increase, in general, the periods of
waves approximately by a few percent when compared to their untwisted
counterparts.
Title: Helioseismology of sub-photospheric flows
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
Bibcode: 2006ESASP.624E.123S
Altcode: 2006soho...18E.123S
No abstract at ADS
Title: Helioseismic modes in a magnetic atmospheric solar model
Authors: Pintér, B.; Erdélyi, R.
Bibcode: 2006ESASP.624E..72P
Altcode: 2006soho...18E..72P
No abstract at ADS
Title: Propagation of p-modes into the solar atmosphere
Authors: Taroyan, Y.; Erdélyi, R.; Malins, C.
Bibcode: 2006ESASP.624E.135T
Altcode: 2006soho...18E.135T
No abstract at ADS
Title: Magnetic seismology of the lower solar atmosphere
Authors: Erdélyi, R.
Bibcode: 2006ESASP.624E..15E
Altcode: 2006soho...18E..15E
No abstract at ADS
Title: Intermittent Coronal Loop Oscillations by Random Energy
Releases
Authors: Mendoza-Briceño, César A.; Erdélyi, Robert
Bibcode: 2006ApJ...648..722M
Altcode:
High-resolution observations by the SOHO and TRACE spacecraft have
confirmed the existence of coronal loop oscillations and waves. In a
recent work, Mendoza-Briceño et al. studied the heating response of
coronal plasma to energy pulses randomly distributed in time and space
along coronal loops. In this paper we focus on the oscillatory patterns
and other features, such as cool gas blobs traveling along the loop,
during the evolution of spatiotemporal randomly heated flux tubes in
the corona. The nature of these oscillatory patterns is investigated
using wavelet analysis. Periodic features, such as wave packets, with
periods of 150-220, 500-600, and 800-1000 s are found. It is also found
that the periods increase with the loop length and decrease with the
length of the loop segments along which the pulses are injected. On
the other hand, the randomly driven intermittent cool plasma blobs that
propagate from one footpoint to the other are analyzed. Although plenty
of coronal loop oscillations are detected by the cohort of the current
high-resolution satellites, there are more controversial observational
evidences about the predicted cold plasma blobs.
Title: Wave propagation in incompressible MHD wave guides: the
twisted magnetic Annulus
Authors: Erdélyi, R.; Carter, B. K.
Bibcode: 2006A&A...455..361E
Altcode:
The propagation of MHD waves in a structured magnetic flux
tube embedded within a straight vertical magnetic environment is
studied analytically. The motivation of this analysis comes from the
observations of damped loop oscillations showing that possibly only
part of the loop is homogeneous in the radial direction. The general
dispersion relation of longitudinal wave propagation is derived for
a fully magnetically twisted configuration consisting of a core,
annulus and external region each with magnetic field of uniform, yet
distinct, twist. Next, a simplified case representing coronal loops
is analysed in detail considering magnetic twist just in the annulus,
the internal and external regions having straight magnetic field. Modes
of oscillations are examined from the general dispersion relation that
is suitable for obtaining information on not just oscillations but
also on some instability properties of this complex tube structure. It
is shown that there are purely surface (i.e. evanescent) and hybrid
(spatially oscillatory in the twisted annulus, otherwise evanescent)
modes. Except for small wavenumbers, the surface waves show little
dispersion; a property making them more suitable for observations. The
hybrid modes show a more complex character. Though the frequency range
seems to be rather limited, there is a continuum band of frequencies
for a given wavenumber. Both short and long wavelength approximations
are considered for the symmetrical (sausage) mode and with small twist
in particular.
Title: Sound Wave Travel Times in Plage Areas - The Effect of
Abnormal Granulation
Authors: Petrovay, K.; Erdélyi, R.; Thompson, M. J.
Bibcode: 2006ESASP.617E..73P
Altcode: 2006soho...17E..73P
No abstract at ADS
Title: Absolute and convective instabilities of parallel propagating
circularly polarized Alfvén waves: numerical results
Authors: Simpson, D.; Ruderman, M. S.; Erdélyi, R.
Bibcode: 2006A&A...452..641S
Altcode: 2009arXiv0911.2565J
Context: .The stability of parallel propagating circularly polarized
Alfvén waves (pump waves) has been studied for more than four decades
with the use of normal mode analysis. It is well known that the normal
mode analysis does not answer the question if a pump wave looks stable
or unstable in a particular reference frame. To answer this question it
is necessary to find out if the instability is absolute or convective
in this reference frame.
Aims: .We extend our previous study
of absolute and convective instabilities of pump waves with small
amplitude to pump waves with arbitrary amplitude.
Methods: .To
study the absolute and convective instabilities of pump waves with
arbitrary amplitude we numerically implement Brigg's method.
Results: .We show that the wave is absolutely unstable in a reference
frame moving with the velocity U with respect to the rest plasma if
U satisfies the inequality Ul < U < Ur
and convectively unstable otherwise, and calculate the dependences of
Ul and Ur on the dimensionless wave amplitude
a . We also calculate the dependence of the increment of the absolute
instability on U for different values of a . When the instability is
convective (U < Ul or U > U_r) we study the signalling
problem. We show that spatially amplifying waves exist only when the
signalling frequency is in two symmetric frequency bands, and calculate
the dependences of the boundaries of these bands on U for different
values of a . We also obtain the dependences of the maximum spatial
amplification rate on U for different values of a . The implication of
these results on the interpretation of observational data from space
missions is discussed. In particular, it is shown that circularly
polarized Alfvén waves propagating in the solar wind are convectively
unstable in a reference frame of any realistic spacecraft.
Title: Introduction
Authors: Erdélyi, Robert
Bibcode: 2006RSPTA.364..289E
Altcode:
No abstract at ADS
Title: Magnetic coupling of waves and oscillations in the lower
solar atmosphere: can the tail wag the dog?
Authors: Erdélyi, Robert
Bibcode: 2006RSPTA.364..351E
Altcode:
No abstract at ADS
Title: The nature of moss and lower atmospheric seismology
Authors: de Pontieu, B.; Erdélyi, R.
Bibcode: 2006RSPTA.364..383D
Altcode:
No abstract at ADS
Title: MHD waves in magnetically twisted solar atmospheric flux tubes
Authors: Erdélyi, Robert; Fedun, Viktor
Bibcode: 2006IAUS..233..134E
Altcode:
The propagation of surface and body linear MHD modes in a twisted
magnetic flux tube embedded in a magnetically twisted plasma environment
is considered. The dispersion relation for surface and body modes is
derived assuming constant external twisted field. Analytic approximate
solutions to the dispersion equation are found for the long and short
wave length cases.It was found, that in case the twisted component of
the magnetic field in the environment of the flux tube is constant the
index of Bessel functions ν in the corresponding dispersion relation
is not integer. In the particular case of a homogen magnetic twist
the total pressure is found to be constant across the boundary of the
flux tube.
Title: Seismology of quiescent coronal loops
Authors: Taroyan, Y.; Erdélyi, R.
Bibcode: 2006IAUS..233..191T
Altcode:
The determination of the physical parameters of coronal loops remains
both an observational and a theoretical challenge. A new diagnostic
technique for quiescent dynamically heated coronal loops, based on
the analysis of the power spectra of Doppler shift time series, is
proposed. It is assumed that a given loop is heated randomly both in
space and time by small-scale discrete impulsive events of unspecified
nature. It is shown here that, depending on the heliographic position
of the loop and the orientation of the observing instrument, various
harmonics can be identified in the power spectra of line shift time
series. The frequency peaks are sensitive to changes in the average
loop temperature and are proposed to use as a temperature diagnostic
tool. The analysis of the power spectra also allows to distinguish
uniformly heated loops from loops heated near their footpoints.
Title: Nonlinear wave time dependent dynamic evolution in solar
flux tubes
Authors: Fedun, V.; Erdelyi, R.
Bibcode: 2005AGUFMSH53A1239F
Altcode:
The aim of the present work is to investigate the excitation,
time dependent dynamic evolution and interaction of weakly nonlinear
propagating (i.e. solitary) waves on vertical cylindrical magnetic flux
tubes in a compressible solar atmospheric plasma. The axisymmetric
flux tube has a field strength of 1000 G at its footpoint what is
typical for photospheric regions. Solitons are excited by a footpoint
driver. The propagation of the nonlinear signal is investigated by
solving numerically a set of fully nonlinear 2D MHD equations in
cylindrical coordinates. For the initial conditions the solutions of
the linear dispersion relation for wave modes (in the present case we
focus on the sausage mode) in a magnetic flux tube is applied. This
dispersion relation is solved numerically for a range of plasma
parameters. We compare our results with the works of Roberts [1],
Wilson [2] (dispersion relation), Molotovshchikov [3] (nonlinear
slow sausage waves) and Weisshaar [4] (numerical solutions of the
Leibovich-Prichard-Roberts equation). (1) We found solitary solutions
and investigate solitary propagating with external sound speed by
solving the full MHD equations. (2) We also found a solitary wave
propagating with the tube speed. A natural application of our studies
may be spicule formation in the chromosphere, as suggested by Roberts
[5], where it was demonstrated theoretically, that a solar photospheric
magnetic flux tube can support the propagation of solitons governed by
the Benjamin-Ono (slow mode) equations. Future possible improvements in
modeling and the relevance of the photospheric chromospheric transition
region coupling by spicules is suggested. [1] B. Roberts and A. Webb,
Sol. Phys., 1978, v. 56, p. 5 [2] P.R. Wilson, Astron. Astrophys., 1980,
v. 87, p. 121 [3] A.L. Molotovshchikov and M.S. Ruderman, Sol. Phys.,
1987, v. 109, p. 247 [4] E. Weisshaar, Phys. Fluids A, 1989, v. 1(8),
p. 1406 [5] B. Roberts and A. Mangeney, Royal Astronomical Society,
Monthly Notices, 1982, v. 198, p.7P
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A. G.; de Pontieu, B.; Erdélyi, R.
Bibcode: 2005ESASP.600E..14D
Altcode: 2005ESPM...11...14D; 2005dysu.confE..14D
No abstract at ADS
Title: Acoustic Wave Propagation in the Solar Subphotosphere
Authors: Shelyag, S.; Erdelyi, R.; Thompson, M. J.
Bibcode: 2005AGUFMSH53A1237S
Altcode:
Local time-distance helioseismology aims to get an information about the
internal structure of subphotospheric region of the Sun, like flows and
sound speed perturbations, by investigation of observed travel times
of the oscillatory responses of subphotosphere to a perturbation. We
present the results of simulations of acoustic wave propagation and
dispersion in the non-magnetic solar subphotosphere. We use methods
similar to the observational ones to produce results aiming to reproduce
observational data from local helioseismology. The VAC code (G. Toth)
is used to carry out the simulations. The code can solve the full system
of ideal hydrodynamic equations in two or three dimensions. All the
results presented are carried out in 2D. The simulations use realistic
solar density and pressure stratifications and are based on fully
compressible ideal hydrodynamical model. Acoustic waves are produced
by perturbations located near the layer corresponding to the visible
surface of the Sun. The simulation domain is 150 Mm wide and 52.6 Mm
deep, and has a resolution of 600x4000 grid points; the upper boundary
of the domain is near the temperature minimum. The density profile for
the initial plane-parallel model is taken from Christensen-Dalsgaard's
standard Model S. We suppress convective motions of the fluid in the
domain by slight change of adiabatic index γ_1. This approach has
an advantage among other approaches because the waves we study, while
they propagate through the quiescent medium, can be clearly observed
far from the source undisturbed by convective fluid motions. First
we study the propagation of acoustic waves produced by a harmonic
pressure perturbation, then, in order to follow the criteria of realism
we introduce more involved perturbation source, described as a source
in the energy equation of the HD system of equations. The source used
corresponds to a localized cooling event causing mass inflow and
sound waves extinction (M. Rast, 1999). In order to reproduce the
helioseismogram of the quiet Sun we introduce a number of randomly
distributed sources with random amplitudes and present a comparison
of the simulated data with the observations.
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A.; de Pontieu, B.; Erdélyi, R.
Bibcode: 2005ESASP.596E..33D
Altcode: 2005ccmf.confE..33D
No abstract at ADS
Title: On the Nature of Coronal EIT Waves
Authors: Ballai, I.; Erdélyi, R.; Pintér, B.
Bibcode: 2005ApJ...633L.145B
Altcode:
Large-scale eruption events in the solar atmosphere can generate
global waves, i.e., waves that propagate over distances comparable to
the solar radius. In the low solar corona, global waves observed by
SOHO EIT, generated by coronal mass ejections or flares, are usually
referred to as ``EIT waves.'' The nature of these global waves is the
subject of strong debate, and opinions are divided between different
interpretations (e.g., fast magnetohydrodynamic waves, shock waves,
nonwave feature, etc.). In the present Letter, we studied TRACE EUV
data to show that these global coronal disturbances are indeed waves
with a well-defined period. Supposing that the EIT waves transfer all
their energy to interacting loops, we also estimate the minimum energy
threshold carried by EIT waves.
Title: Footpoint excitation of standing acoustic waves in coronal
loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.; Bradshaw, S. J.
Bibcode: 2005A&A...438..713T
Altcode:
A new theoretical model for the study of slow standing sausage mode
oscillations in hot (T > 6 MK) active region coronal loops is
presented. These oscillations are observed by the SUMER spectrometer on
board the SoHO satellite. The model contains the transition region and
the upper chromosphere which enables us to study the entire process of
hot loop oscillations - from the impulsive footpoint excitation phase
to the rapid damping phase. It is shown that standing acoustic waves
can be excited by an impulsive heat deposition at the chromospheric
footpoint of a loop if the duration of the pulse matches the fundamental
mode period. The pulse is immediately followed by a standing wave
consistent with the SUMER observations in hot loops. The amount of
released energy determines the oscillation amplitude. The combined
effects of thermal conduction and radiation on the behaviour of the
standing acoustic waves in hot gravitationally stratified loops are
investigated. In addition to damping, these effects lead to downflows
which are superimposed on the oscillations. The implications of the
results in coronal seismology are discussed.
Title: Towards the future - Birmingham UKSP 2005
Authors: Chaplin, W. J.; Erdélyi, R.
Bibcode: 2005A&G....46c..15C
Altcode:
This year's annual UK Solar Physics Meeting was held in parallel with
the National Astronomy Meeting in Birmingham, from 4-8 April 2005. Bill
Chaplin and Robert Erdélyi report on proceedings.
Title: Heating of the Solar Corona: Review
Authors: Erdélyi, R.
Bibcode: 2005PADEU..15....7E
Altcode:
The heating of solar and stellar chromospheres and coronae are one
of the key fundamental and yet unresolved questions of modern space
and plasma physics. In spite of the multi-fold efforts spanning over
half a century including the many superb technological advances
and theoretical developments (both analytical and computational)
the unveiling of the subtles of coronal heating still remained an
exciting job for the 21st century! In the present paper I review
the various popular heating mechanisms put forward in the existing
extensive literature. The heating processes are, somewhat arbitrarily,
classified as hydrodynamic (HD), magnetohydrodynamic (MHD) or kinetic
based on the model medium. These mechanisms are further divided based
on the time scales of the ultimate dissipation involved (i.e. AC and
DC heating, turbulent heating). In particular, attention is paid to
discuss shock dissipation, Landau damping, mode coupling, resonant
absorption, phase mixing, and, reconnection. Finally, I briefly review
the various observational consequences of the many proposed heating
mechanisms and confront them with high-resolution ground-based and
satellite data currently available.
Title: Catastrophic Cooling of Impulsively Heated Coronal Loops
Authors: Mendoza-Briceño, César A.; Sigalotti, Leonardo Di G.;
Erdélyi, Robert
Bibcode: 2005ApJ...624.1080M
Altcode:
The physical mechanisms that cause the heating of the solar corona
are still far from being completely understood. However, recent
highly resolved observations with the current solar missions have
shown clear evidence of frequent and very localized heating events
near the chromosphere that may be responsible for the observable
high temperatures of the coronal plasma. In this paper, we perform
one-dimensional hydrodynamic simulations of the evolution of a
hypothetical loop model undergoing impulsive heating through the release
of localized Gaussian energy pulses near the loop's footpoints. We
find that when a discrete number of randomly spaced pulses is released,
loops of length L=5 and 10 Mm heat up and stay at coronal temperatures
for the whole duration of the impulsive heating stage, provided that
the elapsed time between successive heat injections is <~175 and
<~215 s, respectively. The precise value of the critical elapsed
time is sensitive to the loop length. In particular, we find that for
increased loop lengths of 20 and 30 Mm, the critical elapsed time rises
to about 240 and 263 s, respectively. For elapsed times longer than
these critical values, coronal temperatures can no longer be maintained
at the loop apex in spite of continued impulsive heating. As a result,
the loop apex undergoes runaway cooling well below the initial state,
reaching chromospheric temperatures (~104 K) and leading
to the typical hot-cool temperature profile characteristic of a cool
condensation. For a large number of pulses (up to ~1000) having a fully
random spatiotemporal distribution, the variation of the temperature
along the loop is highly sensitive to the spatial distribution of the
heating. As long as the heating concentrates more and more at the loop's
footpoints, the temperature variation is seen to make a transition from
that of a uniformly heated loop to a flat, isothermal profile along the
loop length. Concentration of the heating at the footpoints also results
in a more frequent appearance of rapid and significant depressions of
the apex temperature during the loop evolution, most of them ranging
from ~1.5×106 to ~104 K and lasting from about
3 to 10 minutes. This behavior bears a tight relation with the strong
variability of coronal loops inferred from SOHO observations in active
regions of the solar atmosphere.
Title: Tracing Coronal Waves Back to the Photosphere
Authors: De Pontieu, B.; Erdelyi, R.; De Moortel, I.; Metcalf, T.
Bibcode: 2005AGUSMSH11C..03D
Altcode:
There are now many observations of waves with periods around 5 minutes
in the outer atmosphere of the Sun. We provide an observational
overview of 5 minute periodicity in chromospheric spicules in active
region plage, upper transition region moss and the low legs of coronal
loops. Using a numerical model, we show that all of these phenomena
are connected: normally evanescent photospheric oscillations can
propagate into the low atmosphere as long as they are guided along
magnetic field lines that are inclined away from the vertical. The
leaked photospheric oscillations develop into shocks and lead to
periodic upward chromospheric flows, which we have identified as
active region spicules. These shocks continue upwards and enter
into the corona. We suggest that TRACE observations of propagating
acoustic waves in the corona are shocked and tunneled photospheric
oscillations. Using SOHO/MDI, TRACE and Imaging Vector Magnetograph
(Hawaii) data we explore how these coronal waves can be exploited to
determine the connectivity between photosphere and corona,and thus
allow seismology of the lower solar atmosphere.
Title: How to Channel Photospheric Oscillations into the Corona
Authors: De Pontieu, B.; Erdélyi, R.; De Moortel, I.
Bibcode: 2005ApJ...624L..61D
Altcode:
There are now many observations of waves in the solar corona with
periods around 5 minutes. The source of these waves is uncertain,
although global p-modes in the photosphere are an obvious candidate,
given the similarity of the dominant periods. However, p-modes are
traditionally considered evanescent in the upper photosphere, and it
has been unclear how they could propagate through the chromosphere
into the corona. Using a numerical model, we show that photospheric
oscillations with periods around 5 minutes can actually propagate into
the corona so long as they are guided along an inclined magnetic flux
tube. The nonverticality of the flux tube increases the acoustic cutoff
period to values closer to the dominant periods of the photospheric
oscillations, thus allowing tunneling or even direct propagation into
the outer atmosphere. The photospheric oscillations develop into shocks,
which drive chromospheric spicules and reach the corona. We suggest
that Transition Region and Coronal Explorer (TRACE) observations of
propagating magnetoacoustic waves in the corona represent these shocked
and tunneled photospheric oscillations. We also explore how seismology
of these waves could be exploited to determine the connectivity between
photosphere and corona.
Title: Influence of random magnetic field on solar global
oscillations: The incompressible f-mode
Authors: Erdélyi, R.; Kerekes, A.; Mole, N.
Bibcode: 2005A&A...431.1083E
Altcode:
The discrepancies between theoretically predicted and observed
frequencies of solar global oscillations (e.g. p- and f-modes)
have attracted major attention in the past decades. The f-mode is
essentially a surface wave hence the mode frequencies are less likely
to be influenced by the solar stratification. Most probably then the
discrepancies are the result of some near surface mechanism(s) such as
interactions with surface or sub-surface magnetic fields and flows. In
the following we explore whether the small-scale photospheric magnetic
fields, sometimes also called the magnetic carpet, may be part of the
explanation for the apparent frequency paradox.
Title: Impulse Excitation and Damping of Slow Standing Mode
Oscillations in Hot Coronal Loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.
Bibcode: 2004ESASP.575..443T
Altcode: 2004soho...15..443T
No abstract at ADS
Title: Can ion-neutral damping help to form spicules?. II. Random
driver
Authors: Erdélyi, R.; James, S. P.
Bibcode: 2004A&A...427.1055E
Altcode:
The possible mechanism of generation of spicules by Alfvénic
disturbances is studied in dissipative MHD where dissipation is mainly
caused by ion-neutral collision damping, as suggested by Haerendel
(\cite{haerendel}). Ion-neutral damping becomes non-negligible in the
upper chromosphere at high cyclic frequencies of typically greater than
0.1 Hz, and the potential role played by this effect in both forming and
supporting solar spicules is investigated. The propagation of randomly
generated Alfvénic disturbances on vertically open solar magnetic flux
tubes is considered. The flux tubes are taken to be axisymmetric and
initially untwisted with the field strength declining from 1600 G in the
photosphere to 20 G in the corona. Their propagation is investigated
by numerically solving a set of fully nonlinear, dissipative 1.5D MHD
equations with waves being generated by a continuous random driver
introduced into the equation of angular momentum in the low atmosphere
of the Sun. This work is a continuation of James et al. (\cite{james2})
which studied the results for a continuous, monochromatic sinusoidal
driver. As with the previous study, spicule-like structures were
formed. The formation was again found to be primarily caused by
the impact of a series of slow shocks generated by the continuous
interaction between the upward propagating driven disturbance and
the downward propagating disturbances reflected by the transition
region. The formation was aided by the increased thermal pressure
gradient caused by Joule heating due to ion-neutral collisions. There
is some indication that an analogue of the momentum transfer effect
suggested by Haerendel (\cite{haerendel}) for simple sinusoidal waves
is at work, but this effect on it's own is at best only of a similar
order as the reduction in height caused by including damping in the
first place. However, the effect is highly sensitive to the level of
ionisation and therefore to the energy balance. Including the effects of
thermal conduction and radiation may well lead to different results and
thus it would be premature to dismiss the mechanism completely at this
point. Significant damping and heating was again observed, strengthening
the previously made suggestions that ion-neutral damping may play a
more important role in the dynamics of the upper chromosphere than
normally assumed in numerical simulations (where it is often neglected
completely), although a treatment of radiative losses must be included
before this can be confirmed. The heating provided by ion-neutral
damping may be an appropriate counter to the low temperatures suffered
by other mechanisms better able to reproduce spicule dynamics.
Title: Wave Propagation in Twisted Magnetic Annulus
Authors: Carter, B. K.; Erdélyi, R.
Bibcode: 2004ESASP.575..378C
Altcode: 2004soho...15..378C
No abstract at ADS
Title: Photospheric Oscillations in the Solar Atmosphere: Driving
Chromospheric Spicules and Coronal Waves
Authors: De Pontieu, B.; Erdelyi, R.; De Moortel, I.; Metcalf, T.
Bibcode: 2004AGUFMSH13A1142D
Altcode:
There are now many observations of oscillations and waves with periods
around 5 minutes in the solar transition region and corona. We provide
an observational overview of 5 minute periodicity in upper transition
region moss, the low legs of coronal loops, and chromospheric spicules
in active region plage. The source of the 5 minute periodicity is
unclear, since photospheric p-modes are evanescent in the upper
photosphere which should prevent them from propagating into the
chromosphere, transition region and corona. Using a numerical model
we show that photospheric oscillations can propagate into the low
atmosphere as long as they are guided along a magnetic flux tube that is
inclined away from the vertical. The leaked photospheric oscillations
develop non-linearly into shocks at low chromospheric heights because
of the density decrease with height. The upward traveling shocks and
resulting rebound shocks of the chromosphere lead to periodic upward
chromospheric flows, which in a recent paper we have identified as
the periodic spicules that we observe in active region plage. After
passage through the spicule, these shocked photospheric oscillations
propagate into the corona. We suggest that TRACE observations of
propagating acoustic waves in the corona are shocked and tunneled
photospheric oscillations. We also explore whether these coronal waves
can be exploited to determine the connectivity between photosphere
and corona, and thus perform seismology of the lower solar atmosphere.
Title: Coronal Loop Heating and Catastrophic Cooling
Authors: Erdélyi, R.; Mendoza-Briceño, C. A.; Sigalotti, L. Di G.
Bibcode: 2004ESASP.575..300E
Altcode: 2004soho...15..300E
No abstract at ADS
Title: Coronal heating: Heating in the solar atmosphere
Authors: Erdélyi, Robert
Bibcode: 2004A&G....45d..34E
Altcode:
The solar coronal plasma, mainly confined in magnetic flux tubes,
is maintained at temperatures of several millions of K. The heating
process that generates and sustains the hot corona has so far
defied a quantitative understanding despite efforts spanning over
half a century. In this paper I review the most popular and viable
mechanisms of heating the solar atmosphere, from low chromospheric
levels through the transition region up to the corona. I address two
principal questions: What is the source of plasma heating in the solar
(and stellar) atmosphere? How do perturbations dissipate efficiently,
resulting in hot plasmas? The latest results of theoretical and
observational studies provide some answers, but there remains much to
be learned.
Title: Solar chromospheric spicules from the leakage of photospheric
oscillations and flows
Authors: De Pontieu, Bart; Erdélyi, Robert; James, Stewart P.
Bibcode: 2004Natur.430..536D
Altcode:
Spicules are dynamic jets propelled upwards (at speeds of
~20kms-1) from the solar `surface' (photosphere) into the
magnetized low atmosphere of the Sun. They carry a mass flux of 100
times that of the solar wind into the low solar corona. With diameters
close to observational limits (< 500km), spicules have been largely
unexplained since their discovery in 1877: none of the existing models
can account simultaneously for their ubiquity, evolution, energetics and
recently discovered periodicity. Here we report a synthesis of modelling
and high-spatial-resolution observations in which numerical simulations
driven by observed photospheric velocities directly reproduce the
observed occurrence and properties of individual spicules. Photospheric
velocities are dominated by convective granulation (which has been
considered before for spicule formation) and by p-modes (which are
solar global resonant acoustic oscillations visible in the photosphere
as quasi-sinusoidal velocity and intensity pulsations). We show that
the previously ignored p-modes are crucial: on inclined magnetic flux
tubes, the p-modes leak sufficient energy from the global resonant
cavity into the chromosphere to power shocks that drive upward flows
and form spicules.
Title: Meeting report: Core to corona: UKSP 2004
Authors: Fletcher, Lyndsay; Erdelyi, Robert
Bibcode: 2004A&G....45c..33F
Altcode:
The UK solar physics community gathered with the MIST community in
Edinburgh from 29 March - 1 April 2004, with a programme that reflected
the strength and diversity of UK research in the field. Lyndsay Fletcher
and Robert Erdelyi report.
Title: British-Hungarian N+N Workshop for Young Researchers On
Computer processing and use of satellite data in astronomy and
astrophysics and 3rd Workshop of Young Researchers in Astronomy
& Astrophysics
Authors: Forgács-Dajka, E.; Petrovay, K.; Erdélyi, R.
Bibcode: 2004PADEU..14.....F
Altcode:
The N+N Young Researchers' Workshop scheme, initiated and funded by the
British Council, aims to provide an opportunity for young researchers
to exchange ideas, knowledge and information by coming together in the
form of N+N workshops and meetings. Here the term N+N workshop refers
to a workshop involving a number of researchers from the UK and an
equal number of local researchers. The workshops are followed by real
and virtual networking to sustain the contacts made with a view to
produce a proposal for longer term externally funded collaboration or
applications for further funding. As at the Department of Astronomy
of the Eötvös University we have had a tradition of national
workshops of young researchers in astronomy and astrophysics with
similar characteristics, the call for meeting proposals by the British
Council seemed an ideal way to extend the geographical scope of our
meeting, while still maintaining its general format and spirit. Thus,
this year's Hungarian Young Researchers' Workshop in Astronomy and
Astrophysics was held in tandem with the British-Hungarian N+N workshop,
and the contributions are also presented together in this volume. For
the topic of this year's meeting we chose "Computer processing and use
of satellite data in astronomy and astrophysics". The reason for this
is that, thanks to a high number of space probes, in the past decades
a vast amount data has been collected from the extraterrestrial world,
from the magnetosphere to the most distant galaxies and beyond. We are
now in a situation where the amount data grows much faster than the
speed by which they can be processed and duly analyzed. The workshop was
devoted to methods aimed at improving on this situation, as well as to
scientific results born out of the use of space data. The workshop was
open to post-doctoral scientists and engineers and those tenured for
five years or less. PhD students in an advanced phase of their project
were also admitted. The number of participants from the U.K. was nine,
while a total of 13 applications were accepted from Hungary for the
N+N workshop (with many more participants at the adjoining national
workshop). It is to be noted that from the nine UK participants, only
four were British citizens, the rest hailing from Armenia, Germany,
Hungary, and Italy. Nevertheless, all have been residing in the UK for
years, and this composition reflects well the international character
and openness of current British academic research.
Title: Influence of random magnetic field on solar global oscillations
Authors: Erdélyi, R.; Kerekes, A.
Bibcode: 2004PADEU..14..141E
Altcode:
The discrepancies between theoretically predicted and observed
frequencies of solar global oscillations (e.g. p- and f-modes) have
attracted major attention in the past two decades. In the following we
wish to explore further whether the solar atmosphere may account for
the apparent frequency paradox. Magnetic flux is continuously emerging
at photospheric levels and expanding into the solar atmosphere. We
investigate the possible effects of an atmospheric random magnetic
field on the solar fundamental mode (f-mode).
Title: The Effects of Stratification on Oscillating Coronal Loops
Authors: Mendoza-Briceño, César A.; Erdélyi, Robert; Sigalotti,
Leonardo Di G.
Bibcode: 2004ApJ...605..493M
Altcode:
Recent observations by the Solar and Heliospheric Observatory
(SOHO) and the Transition Region and Coronal Explorer (TRACE) have
confirmed previous theoretical predictions that coronal loops may
oscillate. These oscillations and their damping are of fundamental
importance, because they can provide diagnostics of the coronal
plasma. In the present paper, we perform numerical hydrodynamic
calculations of a one-dimensional loop model to investigate the
effects of stratification on damping of longitudinal waves in the
hot coronal loops observed by the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) on board the SOHO satellite. In particular,
we study the dissipation by thermal conduction and by compressive
viscosity of standing slow magnetosonic disturbances in loops of
semicircular shape. For the parameter regime that characterizes the
SUMER hot loops, we find that stratification results in a ~10%-20%
reduction of the wave-damping time compared to the nonstratified loop
models because of increased dissipation by compressive viscosity due
to gravity. We show that temperature oscillations are more strongly
dissipated by thermal conduction, while density and velocity waves are
mostly damped by compressive viscosity. However, the decay time of the
oscillations is always governed by the thermal conduction timescale. The
scalings of the decay time with wave period, temperature, and loop
length all point toward higher dissipation rates in the stratified,
hotter loops because of the increased effects of thermal conduction
and compressive viscosity.
Title: Hall-magnetohydrodynamic surface waves in solar wind
flow-structures
Authors: Miteva, Rossitsa; Zhelyazkov, Ivan; Erdélyi, Robert
Bibcode: 2004NJPh....6...14M
Altcode:
This paper investigates the parallel propagation of agnetohydrodynamic
(MHD) surface waves travelling along an ideal steady plasma slab
surrounded by a steady plasma environment in the framework of Hall
magnetohydrodynamics. The magnitudes of the ambient magnetic field,
plasma density and flow velocity inside and outside the slab are
different. Two possible directions of the relative flow velocity
(in a frame of reference co-moving with the ambient flow) have been
studied. In contrast to the conventional MHD surface waves which
are usually assumed to be pure surface or pseudo-surface waves,
the Hall-MHD approach makes it necessary to treat the normal MHD
slab's modes as generalized surface waves. The latter have to be
considered as a superposition of two partial waves, one of which is
a pure/pseudo-surface-wave whereas the other constitutive wave is a
leaky one. From the two kinds of surface-wave modes that can propagate,
notably sausage and kink ones, the dispersion behaviour of the kink
mode turns out to be more complicated than that of the sausage mode. In
general, the flow increases the waves' phase velocities comparing with
their magnitudes in a static Hall-MHD plasma slab. The applicability of
the results to real solar wind flow-structures is briefly discussed. EHPRG Award Lecture.
Title: Influence of Random Magnetic Field on Photospheric Surface
Waves
Authors: Erdélyi, R.; Kerekes, A.; Mole, N.; Ruderman, M. S.
Bibcode: 2004ESASP.547...69E
Altcode: 2004soho...13...69E
The discrepancies between theoretically predicted and observed
frequencies of solar global oscillations (e.g. pand f-modes) have
attracted major attention in the past two decades. In the following
we wish to explore whether the solar atmosphere may account for the
apparent frequency paradox. Magnetic flux is continuously emerging
at photospheric levels and expanding into the solar atmosphere. We
investigate the possible effects of an atmospheric random magnetic
field on the solar fundamental mode (f-mode).
Title: Episodic Coronal Loop Heating
Authors: Mendoza-Briceño, C. A.; Erdélyi, R.
Bibcode: 2004ESASP.547..261M
Altcode: 2004soho...13..261M
Coronal loop temperatures are known to be of a few millions degrees
but the nature of the energy source remains as a longstanding
fundamental problem for solar (and stellar) physics. Observations
of solar atmospheric plasma show clear evidence of frequent very
localised heating events, which may be statistically responsible for
heating of the solar upper atmosphere. One heating theory indicates
that these micro-scale events are driven by localized magnetic field
reconnection. In this paper, we present the results of numerical
calculations that describe the response of the coronal plasma to
small-scale heating pulses in a magnetic loop. In particular, we study
the effects of energy input pulses injected randomly near the two
footpoints of a semi-circular loop. We have found that increasing the
elapsing time between successive pulses, the overall loop temperature
decreases. When a critical elapsing time is reached the loop can no
longer be maintained at typical coronal temperatures. These features
have some support from SOHO-CDS observations of coronal loops which
seem to undergo strong variability especially in active regions
of the solar atmosphere (Kjeldseth-Moe &Brekke, 1998). We also
have found that successive random pulses can statistically maintain
the average plasma temperature at typical coronal values. Due to the
randomness of the heat injections, the resulting temperature profiles
show thermal bumps that could be connected to intermittent behaviour
in the transition region and the low corona.
Title: Random Flow Effects on Surface Waves
Authors: Erdélyi, R.; Kerekes, A.; Mole, N.
Bibcode: 2004ESASP.547...75E
Altcode: 2004soho...13...75E
Studying the properties of surface waves is probably the simplest wave
tool for diagnosing a medium. Surface waves are observed e.g. as the
fundamental global oscillations (called the f-mode), and have also been
detected at the boundaries of various solar structures (e.g. sunspot
filaments, coronal loops, coronal funnels, solar wind tubes, etc.). SOHO
and TRACE have demonstrated that the solar atmosphere and its magnetic
structures are highly inhomogeneous at almost all spatial and time
scales. The question naturally arises: does the random nature of
the medium influence the propagation characteristics of the surface
modes? Murawski &Roberts (1993) investigated the effect of a random
velocity field on the dispersion relation for fmodes propagating on
the solar surface. Here we follow their general approach, which is a
valuable one, but correct errors which appeared in that paper. We still
find, as they did, that the simple model used gives a deviation of the
f-modes from the theoretically predicted parabolic ridges which agrees
qualitatively with observations. We find that turbulent background
flows can reduce the eigenfrequencies of global solar f-modes by
several per cent as found in observations at high spherical degree.
Title: Time-Distance Helioseismology and the Magnetic Atmosphere of
the Sun
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.
Bibcode: 2004ESASP.547...33T
Altcode: 2004soho...13...33T
No abstract at ADS
Title: Oscillations of Coronal Loops with Elliptic Cross-Sections
Authors: Ruderman, M. S.; Erdélyi, R.
Bibcode: 2004ESASP.547..507R
Altcode: 2004soho...13..507R
No abstract at ADS
Title: MHD Wave Propagation in Open Flux Tubes in the Low Solar
Atmosphere
Authors: James, S. P.; Erdélyi, R.
Bibcode: 2004ESASP.547..131J
Altcode: 2004soho...13..131J
The propagation of Alfvénic disturbances in open magnetic flux
tubes in the low solar atmosphere is considered. Their evolution is
studied numerically in a fully non-linear 1.5D MHD regime under the
thin flux-tube approximation. In particular, the slippage between
ion species, which are directly affected by changes in magnetic and
electric fields, and the neutral fluids, which are affected only
indirectly by collisional coupling, is considered. This slippage
becomes non-negligible in the upper chromosphere for high frequency
Alfvén waves (typically for frequencies of the order of 0.1 Hz)
and the resulting wave damping and dissipation is included in our
treatment. The disturbances are generated in the photosphere or low
chromosphere by both Alfvén wave and random drivers, and over a wide
range of parameters. Comparison is drawn with observed solar phenomena,
particularly solar spicules.
Title: Damping of Coronal EIT Waves as a Tool for Plasma Diagnostics
Authors: Ballai, I.; Erdélyi, R.
Bibcode: 2004ESASP.547..433B
Altcode: 2004soho...13..433B
Observations with the Extreme-Ultraviolet Imaging Telescope (EIT)
on-board SOHO have revealed the existence of transient coronal
waves generated by an impulsive event (e.g. flare or coronal mass
ejection) that propagates across the visible solar disk over very long
distances. The present work aims to discuss one of the most remarkable
properties of waves, namely how to obtain diagnostic information about
the medium in which these waves propagate. By extracting information
from EIT wave observations (propagation speed, damping length,
etc.) we use these waves for plasma diagnostics, i.e. global coronal
seismology. Applying a simple coronal model, we find average values
of magnetic field at the propagation height of EIT waves, as well as
average values for the coefficient of kinematic viscosity. Using TRACE
data we show that EIT waves are indeed waves with a well defined period.
Title: Absolute and convective instabilities in open shear
layers. II. Magnetohydrodynamic equilibrium
Authors: Terra-Homem, M.; Erdélyi, R.
Bibcode: 2004A&A...413....7T
Altcode:
The present paper is the continuation of our study of absolute and
convective instabilities in open shear layers \citep{ter03}. In this
paper the effects of a magnetic field are included and a series of fully
non-linear ideal polytropic 2D MHD numerical simulations is carried
out. The amount of mean flow required to sweep away the perturbation
before it grows and destroys the whole flow is calculated for various
configurations of the magnetic field. The analytical results obtained
by \citet{fej64} for a velocity discontinuity were recovered with a
very good accuracy. The study focused on uniform, discontinuous and
sheared magnetic fields. We found that the value of mean flow needed
for a perturbation to become convectively unstable (critical mean flow)
decreased with decreasing value of the plasma β. We also found that
the low β value side, of a discontinuous and sheared magnetic field,
is predominant in the behaviour of the instability. Finally we show
the thickness of the magnetic shear layer has no effect on the value
of critical mean flow.
Title: Damping of Loop Oscillations in the Stratified Corona
Authors: Erdélyi, R.; Mendoza-Briceño, C. A.
Bibcode: 2004ESASP.547..441E
Altcode: 2004soho...13..441E
SOHO and TRACE observations have confirmed the theoretical predictions
by Roberts et al. (1984) almost two solar cycles ago, namely, coronal
loops may oscillate. These oscillations, and in particular their
damping, are of fundamental importance for solar physics since they
can provide diagnostics of the plasma medium. In the present paper we
apply this concept to hot and stratified and nonisothermal coronal
loops observed by e.g. TRACE or SUMER on-board SOHO. We investigate
the effect of stratification on (i) the damping of standing waves and
(ii) on propagating coherent disturbances (i.e. basically slow MHD
waves). The effect of stratification results, if we may say so, in
an approximate 15-20% of reduction in damping time for the parameter
regime that characterise hot SUMER or TRACE loops. This is a good news
as theoretical speculations in the literature usually suffer from an
over-estimate of the damping of oscillations caused by e.g. thermal
conduction or viscosity in the non-stratified atmosphere approach.
Title: Solitary Wave Propagation from the Photosphere into the
Solar Corona
Authors: Erdélyi, R.; Fedun, V.
Bibcode: 2004ESASP.547...63E
Altcode: 2004soho...13...63E
In the present paper we study the excitation and time dependent dynamic
evolution of vertically propagating weakly nonlinear (i.e. solitary)
waves on vertically open cylindrical magnetic flux tubes in a stratified
plasma. The axisymmetric flux tubes have a typical field strength
of 1500 G at their photospheric roots, reducing to 20-30 G in the
corona. Solitons are excited by a footpoint driver. The propagation
of the solitary signal is investigated by solving numerically a set
of fully nonlinear 2.5D MHD equations. We compare our results with the
analytical solutions of Molotovshchikov &Ruderman (1987) obtained by
using the method of multi-scale expansion. The model could be applied
to spicule formation in the chromosphere, as suggested by Roberts
&Mangeney (1982), where it was demonstrated theoretically, that a
solar photospheric magnetic flux tube can support the propagation of
two types of soliton, governed either by the Benjamin-Ono (slow mode)
or by the Korteweg-de Vries (fast mode) equations. Future possible
improvements in modelling and the relevance of the photospheric
chromospheric transition region coupling by spicules is suggested.
Title: Turbulence, Waves and Instabilities in the Solar Plasma
Authors: Erdélyi, R.; Petrovay, K.; Roberts, B.; Aschwanden, M.
Bibcode: 2003twis.book.....E
Altcode:
Significant advances have been made recently in both the theoretical
understanding and observation of small-scale turbulence in different
layers of the Sun, and in the instabilities that give rise to them. The
general development of solar physics, however, has led to such a
degree of specialization as to hinder interaction between workers in
the field. This book therefore presents studies of different layers
and regions of the Sun, but from the same aspect, concentrating on
the study of small-scale motions. The main emphasis is on the common
theoretical roots of these phenomena, but the book also contains
an extensive treatment of the observational aspects. Link: http://www.springer.com/east/home?SGWID=5-102-22-3362=5696-0&changeHeader=true
Title: Intensity Oscillations in the upper transition region above
active region plage
Authors: de Pontieu, B.; Erdelyi, R.; de Wijn, A.; Loefdahl, M.
Bibcode: 2003AGUFMSH42B0540D
Altcode:
Although there are now many observations showing the presence
of oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (so-called
moss) above active region plage. Here we report on a wavelet analysis
of observations (made with TRACE, the Transition Region and Coronal
Explorer) of strong ( ∼ 5-15%) intensity oscillations in the upper
TR footpoints of hot coronal loops. They show a range of periods from
200 to 600 seconds, typically persisting for 4 to 7 cycles. These
oscillations are not associated with sunspots, as they usually occur at
the periphery of plage regions. A majority of the upper TR oscillations
are directly associated with upper chromospheric oscillations observed
in Hα , i.e., periodic flows in spicular structures. The presence of
such strong oscillations at low heights (of order 3,000 km) provides
an ideal opportunity to study the propagation of oscillations from
photosphere and chromosphere into the TR and corona, and improve
our understanding of the magnetic connectivity in the chromosphere
and TR. In addition, we use new high resolution observations of the
photosphere and chromosphere, taken with the Swedish Solar Telescope, to
shed light on the source of chromospheric mass flows such as spicules.
Title: Linear and non-linear MHD wave propagation in steady-state
magnetic cylinders
Authors: Terra-Homem, M.; Erdélyi, R.; Ballai, I.
Bibcode: 2003SoPh..217..199T
Altcode:
The propagation of linear and non-linear magnetohydrodynamic (MHD)
waves in a straight homogeneous cylindrical magnetic flux tube embedded
in a homogeneous magnetic environment is investigated. Both the tube and
its environment are in steady state. Steady flows break the symmetry of
forward (field-aligned) and backward (anti-parallel to magnetic field)
propagating MHD wave modes because of the induced Doppler shifts. It is
shown that strong enough flows change the sense of propagation of MHD
waves. The flow also induces shifts in cut-off values and phase-speeds
of the waves. Under photospheric conditions, if the flow is strong
enough, the slow surface modes may disappear and the fast body modes
may become present. The crossing of modes is also observed due to
the presence of flows. The effect of steady-state background has
to be considered particularly carefully when evaluating observation
signatures of MHD waves for diagnostics in the solar atmosphere.
Title: Intensity Oscillations in the Upper Transition Region above
Active Region Plage
Authors: De Pontieu, B.; Erdélyi, R.; de Wijn, A. G.
Bibcode: 2003ApJ...595L..63D
Altcode:
Although there are now many observations showing the presence of
oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (the
so-called moss) above active region plage. Here we report on a wavelet
analysis of observations (made with the Transition Region and Coronal
Explorer) of strong (~5%-15%) intensity oscillations in the upper TR
footpoints of hot coronal loops. They show a range of periods from 200
to 600 s, typically persisting for 4-7 cycles. These oscillations are
not associated with sunspots, as they usually occur at the periphery
of plage regions. A preliminary comparison to photospheric vertical
velocities (using the Michelson Doppler Imager on board the Solar and
Heliospheric Observatory) reveals that some upper TR oscillations
show a correlation with p-modes in the photosphere. In addition,
a majority of the upper TR oscillations are directly associated with
upper chromospheric oscillations observed in Hα, i.e., periodic flows
in spicular structures. The presence of such strong oscillations at
low heights (of the order of 3000 km) provides an ideal opportunity to
study the propagation of oscillations from photosphere and chromosphere
into the TR and corona. It can also help us understand the magnetic
connectivity in the chromosphere and TR and shed light on the source
of chromospheric mass flows such as spicules.
Title: MHD resonant flow instability in the magnetotail
Authors: Erdélyi, R.; Taroyan, Y.
Bibcode: 2003AIPC..679..355E
Altcode:
Resonant flow instability (RFI) and Kelvin-Helmholtz instability
(KHI) are investigated as possible wave generating mechanisms in
the mantle-like boundary layer of the Earth's magnetotail where all
equilibrium quantities transition continuously from magnetosheath values
to values more characteristic of the tail lobe. It is shown that as in
the case of a sharp interface the KHI requiring high flow speeds in the
magnetosheath is unlikely to be operative under typical conditions. RFI
which is physically distinct from KHI may appear at lower flow speeds
due to the inhomogeneity of the mantle-like boundary layer. It is
shown that RFI can be important when the variation length-scale
of the flow velocity is smaller than the variation length-scales
of other equilibrium quantities such as density and magnetic field
strength. Interpretation in terms of the wave energy flux is presented
and the applicability to the magnetotail is discussed. The obtained
results could explain the observed low power of ULF waves in the tail
lobes compared with other parts of the magnetosphere.
Title: Impulsive heating in coronal loops
Authors: Mendoza-Briceño, César A.; Sigalotti, Leonardo Di G.;
Erdélyi, Robert
Bibcode: 2003AdSpR..32..995M
Altcode:
Observations of the solar-chromosphere transition region plasma show
evidence of frequent microscale events, which have been proposed to
be responsible for the heating of the solar atmosphere. One heating
theory indicates that these small-scale events are driven by localized
magnetic field reconnection. In this paper, we present the results
of numerical calculations that describe the response of the coronal
plasma to microscale heating pulses in a magnetic loop. In particular,
we study the effects of energy input pulses injected randomly near
the two footpoints of a semi-circular loop. We find that successive
random pulses can maintain the plasma temperature on average at typical
coronal values. Due to the randomness of the pulse injections, the
resulting temperature profiles show temporal thermal bumps that could
be connected to intermittent behavior in the transition region and
the low corona of the quiet Sun.
Title: Can ion-neutral damping help to form spicules?
Authors: James, S. P.; Erdélyi, R.; De Pontieu, B.
Bibcode: 2003A&A...406..715J
Altcode:
The possible mechanism of generation of spicules by Alfvénic
waves is studied in dissipative MHD where dissipation is mainly
caused by ion-neutral collision damping, as suggested by Haerendel
(\cite{haerendel}). Ion-neutral damping becomes non-negligible at
the high cyclic frequencies involved, typically greater than 0.1unit
{Hz}, and the potential role played by this effect in both forming
and supporting solar spicules is investigated. The propagation of
high frequency Alfvén waves on vertically open solar magnetic flux
tubes is considered. The flux tubes are taken to be axisymmetric and
initially untwisted with the field strength declining from 1600unit {G}
in the photosphere to 10-40unit {G} in the corona. Their propagation
is investigated by numerically solving a set of fully nonlinear,
dissipative 1.5D MHD equations with the waves being generated by a
continuous sinusoidal driver introduced into the equation of angular
momentum in the low atmosphere of the Sun. Spicule-like structures with
heights of up to 7000unit {km} were formed. The formation was found
to be caused by the impact of a series of slow shocks generated by
the continuous interaction between the upward propagating driven wave
train and the downward propagating train of waves created by reflection
off the transition region and aided by the increased thermal pressure
gradient caused by Joule heating due to ion-neutral collisions. The
adiabatic results suggest that ion-neutral damping may not support
spicules as described by Haerendel (\cite{haerendel}). However, the
effect is highly sensitive to the level of ionisation and therefore
to the energy balance. Including the effects of thermal conduction
and radiation may well lead to different results and thus it would
be premature to dismiss the mechanism completely at this point. In
addition, the relatively high chromospheric temperatures obtained,
even at frequencies for which ion-neutral damping and heating might
be expected to be unimportant, suggest intriguing possibilities for
combining the mechanism with others that are better able to recreate
spicule dynamics but suffer from unrealistically low temperatures.
Title: Steady state excitation of field line resonances by global
waveguide modes in the magnetosphere
Authors: Taroyan, Y.; ErdéLyi, R.
Bibcode: 2003JGRA..108.1301T
Altcode:
A major shortcoming of theories of long-period magnetic pulsations is
the separate treatment of the problems of wave excitation and resonant
coupling. This could account for many substantial discrepancies between
the waveguide/cavity mode theories and observations. A unified approach
leading to a new type of field line resonance excitation mechanism is
presented. It is shown that in a steady state the direct coupling of the
waveguide modes to the local field line oscillations provides a natural
and very efficient transfer of energy from the magnetosheath flow
to the shear Alfvén waves deep within the magnetosphere even in the
ideal magnetohydrodynamic limit. The role of ionospheric dissipation is
examined, and many well-known observational features are recovered. The
e-folding lengths of the generated waves are estimated. The presented
mechanism of energy transport from the velocity shear into resonant
Alfvén waves could play an important role in many applications of
solar-terrestrial physics and astrophysics.
Title: UKSP: Solar physics in Dublin
Authors: Erdélyi, R.; Fletcher, L.; Doyle, G. J.
Bibcode: 2003A&G....44c..13E
Altcode:
This year's annual UK Solar Physics meeting took place in Dublin from
7-11 April 2003, overlapping with the National Astronomy Meeting. R
Erdélyi, L Fletcher and G J Doyle summarize.
Title: Correlations on Arcsecond Scales between Chromospheric and
Transition Region Emission in Active Regions
Authors: De Pontieu, B.; Tarbell, T.; Erdélyi, R.
Bibcode: 2003ApJ...590..502D
Altcode:
The discovery of active region moss, i.e., dynamic and bright upper
transition region (TR) emission at chromospheric heights above active
region plage, provides a powerful diagnostic to probe the structure,
dynamics, energetics, and coupling of the magnetized solar chromosphere
and TR. Here we present an observational study of the interaction
of the chromosphere with the upper TR, by studying correlations (or
lack thereof) between emission at varying temperatures: from the low
chromosphere (Ca II K line), to the middle and upper chromosphere (Hα),
to the low TR (C IV λ1550 at 0.1 MK) and the upper TR (Fe IX/X λ171
at 1 MK and Fe XII λ195 at 1.5 MK). We use several data sets at high
cadence (24-42 s) obtained with the Swedish Vacuum Solar Telescope
(SVST, La Palma) and the Transition Region and Coronal Explorer
(TRACE). This correlation analysis from low chromosphere to upper
TR in active region plage quantifies and considerably expands on
previous studies. Our results elucidate various issues, such as (1)
how the heating mechanisms of the chromosphere and lower and upper TR
are related (if at all), (2) how important heating of spicular jets is
for the energy balance of the lower TR, (3) which timescales dominate
the dynamic behavior of the active region TR, and (4) whether the
spatial and temporal variability of moss can be used as a diagnostic
for coronal heating.
Title: Absolute and convective instabilities in open shear
layers. I. Hydrodynamic equilibrium
Authors: Terra-Homem, M.; Erdélyi, R.
Bibcode: 2003A&A...403..425T
Altcode:
In the present paper we study the absolute and convective nature of
instabilities in open shear flows by carrying out fully non-linear
adiabatic 2-D hydrodynamic numerical simulations. The purpose is to
identify what influences an instability to become from absolutely
to convectively unstable or vice-versa. First we study the case of
incompressible fluid approximation and compare our results with the
analytic solution of Huerre & Monkewitz (\cite{mon85}). Next we
derive the effect of compressibility and of viscosity on the transition
from absolute to convective instability of an open shear flow. We
found, numerically, the value of the mean flow for which perturbations
change from absolutely to convectively unstable. We fully recover the
results of the approximate analytic solution. We found that an inviscid
incompressible fluid is the most unstable configuration. We also found
that compressibility and viscosity decrease the value of the mean flow
for which the transition from absolute to convective instability occurs,
and that viscosity has a stronger influence than compressibility.
Title: Observations of the propagation and photospheric source of
waves at the upper transition region footpoints of coronal loops
Authors: de Pontieu, B.; Erdelyi, R.
Bibcode: 2003EAEJA.....5890D
Altcode:
We study the lower and upper transition region (TR) at the footpoints of
coronal loops anchored in active region plage. Using wavelet analysis,
we look for the presence of waves in images of C IV 1550 A (0.1 MK)
and Fe IX/X 171 A (1 MK) taken with the Transition Region and Coronal
Explorer (TRACE). We present several examples of strong intensity
oscillations in active region plage at varying temperatures, and
study wave power as a function of wave period, as well as propagation
effects. We also show, for the first time, an example of correlated
oscillations of the upper TR at the opposite ends of a coronal loop,
and use this to determine magnetic connectivity, propagation speed and
coronal properties. Co-aligned spectra from the SOHO/SUMER spectrometer
are used to determine whether correlated velocity oscillations
are also present. Co-aligned photospheric dopplergrams taken with
SOHO/MDI help us shed light on the possible source of these waves. We
find several examples of a correlation between photospheric and upper
TR oscillations, which has not been observed before in active region
plage. We discuss a theoretical model that can explain such coupling of
global helioseismic acoustic oscillations into the upper TR or corona
through the mechanism of resonant absorption.
Title: Challenges in Coronal Moreton waves
Authors: Ballai, I.; Erdélyi, R.
Bibcode: 2003PADEU..13..121B
Altcode:
Observations with the Extreme Ultraviolet Imaging Telescope (EIT)
onboard SOHO have revealed the existence of transient coronal waves
which propagate across the visible solar disc and are generated by an
impulsive event. Using observational quantities (propagation speed,
attenuation length) we derive average values for magnetic field
intensity and viscosity in the low corona, i.e. we develop global
coronal seismology.
Title: Impulsive heating in the solar atmosphere
Authors: Mendoza-Briceno, C. A.; Erdélyi, R.
Bibcode: 2003PADEU..13..171M
Altcode:
Observations of the solar chromosphere-corona transition region plasma
show evidence of small, short-lived dynamic phenomena called e.g.,
explosive events, blinkers, micro- and nano-flares. These events
may serve as the basic building blocks of the heating mechanism(s)
of the solar atmosphere. In this paper we study the heating of the
solar corona by numerous micro-scale randomly highly localized events
representing the energy dissipation found by observations. We found,
that typical loop temperature structures seen by e.g. TRACE are
recovered when the energy release occurs close to the footpoints of
the loop. Implications of these results upon the latest coronal loop
observations are addressed.
Title: Contributions to NATO Advanced Research Workshop Turbulence,
Waves, and Instabilities in the Solar Plasma
Authors: Forgács-Dajka, E.; Petrovay, K.; Erdélyi, R.
Bibcode: 2003PADEU..13.....F
Altcode:
This volume contains focus reviews, oral contributions and poster
papers presented at the NATO Advanced Research Workshop ``Turbulence,
Waves, and Instabilities in the Solar Plasma'', held at Hotel Normafa,
Budapest, 16-20 September, 2002. The more exensive invited reviews
presented at the same meeting are published by Kluwer in a companion
volume, with the same title as that of the meeting. The purpose of the
workshop was to facilitate interchange and communication between diverse
groups studying different layers and regions of the Sun but from the
same aspect, concentrating on the study of small-scale motions. While
the emphasis was on the common theoretical roots of these phenomena,
observational aspects were not excluded either. The selection of
invited speakers concentrated on the researchers currently most
active in the field, mostly on a post-doctoral/tenure/fresh faculty
position level. A number of senior experts and PhD students were
also invited. Scientists from NATO partner countries were especially
encouraged to apply. Altogether, 50 scientists from 11 different
countries participated in the workshop. The relative isolation of the
venue, as well as the fact that the participants all lived at the same
place, where the conference was also held, contributed to the success
of the meeting, offering plenty of opportunities to meet and exchange
ideas. We are convinced that many of the papers in the present volume
will prove to be a very useful reference for some rarely discussed
chapters of solar physics.
Title: Spicule Formation by Ion-neutral Damping
Authors: James, S. P.; Erdélyi, R.
Bibcode: 2003PADEU..13..133J
Altcode:
The possible generation of spicules by Alfvénic waves is studied in MHD
where dissipation is mainly caused by ion-neutral collision damping, as
suggested by tet{haerendel}. The propagation of high frequency Alfvén
waves on vertically open solar magnetic flux tubes is considered by
numerically solving a set of fully nonlinear, dissipative 1.5D MHD
equations with the waves being generated by a continuous sinusoidal
driver in the low atmosphere of the Sun. Spicule-like structures
with heights of around 4,000-10,000 unit{km} were formed, primarily
by the impact of a series of slow shocks generated by the continuous
interaction between the upward propagating driven and reflected wave
trains rather than the predicted ion-neutral damping mechanism.
Title: Absolute and Convective Instabilities in Open Shear Flow Layers
Authors: Homem, M. T.; Erdélyi, R.
Bibcode: 2003PADEU..13...77H
Altcode:
In the present paper we study the absolute and convective nature of
instabilities in open shear flows by carrying out fully non-linear
adiabatic 2-D hydrodynamic numerical simulations. We found the
value of mean flow for which perturbations change from absolute
to convective unstable. We fully recover the results of a previous
analytic solution. We found that (i) an inviscid incompressible fluid
is the most unstable configuration; (b) compressibility and viscosity
decrease the value of mean flow necessary for the transition from
absolute to convective instability; (c) even a viscosity has dominant
influence over compressibility.
Title: On resonantly excited MHD waves in the magnetotail
Authors: ErdéLyi, R.; Taroyan, Y.
Bibcode: 2003JGRA..108.1043E
Altcode:
The resonant flow instability (RFI) and the Kelvin-Helmholtz instability
(KHI) are investigated as possible wave-generating mechanisms in
the mantle-like boundary layer of the Earth's magnetotail where all
equilibrium quantities transit continuously from magnetosheath values
to values more characteristic of the tail lobe. It is shown that as in
the case of a sharp interface, the KHI requiring high flow speeds in the
magnetosheath is unlikely to be operative under typical conditions. The
RFI which is physically distinct from the KHI may appear at lower flow
speeds owing to the inhomogeneity of the mantle-like boundary layer. It
is shown that the RFI can be important when the variation length-scale
of the flow velocity is smaller than the variation length-scales of
other equilibrium quantities such as the density and the magnetic
field strength. Interpretation in terms of the wave energy flux is
presented and the applicability to the magnetotail is discussed.
Title: Episodic footpoint heating of coronal loops: does it work?
Authors: Mendoza-Briceño, César A.; Erdélyi, Robert; Sigalotti,
Leonardo Di G.
Bibcode: 2002ESASP.506..697M
Altcode: 2002ESPM...10..697M; 2002svco.conf..697M
Short answer: YES! And in mor details..: Coronal loop temperatures
are known to be of a few millions degrees but the nature of the
energy source remains as a longstanding fundamental problem for
solar and stellar physics. Observations of solar chromosphere-corona
transition region plasma show evidence of small, short-lived dynamic
phenomena called e.g., explosive events, blinkers, micro-flares and
nano-flares. These events may serve as the basic building blocks of
the heating mechanism(s) of the solar atmosphere. In this paper,
we study the heating of the solar corona by numerous micro-scale
randomly localized events representing the energy dissipation found
by observations. It is found that these energy input distributions can
maintain the plasma along the loop at typical coronal temperatures. We
also found, that typical loop temperature structures seen by e.g. Trace
are recovered when the energy release occurs close to the foot points
of the loop. Implications of these results upon the lastest coronal
loop observations are addressed.
Title: Effects of the atmosphere and of sub-surface flows on solar
oscillation modes (Invited review)
Authors: Erdélyi, R.
Bibcode: 2002ESASP.506..869E
Altcode: 2002ESPM...10..869E; 2002svco.conf..869E
In helioseismology effects caused by the solar atmosphere on global
eigenmodes are gathered in the so-called surface-term. Variations
in chromospheric magnetic field, canopy height, temperature or the
presence of equilibrium bulk motions all may cause observable frequency
shifts of the solar p/f-modes. Surface random or sub-surface global
motions (e.g. differential rotation, meridional flow motion) below the
solar surface may also have measurable effects on the properties of
helioseismic eigenmodes. When both an atmospheric magnetic field and
sub-surface flows (i.e. steady state) are present, a complex picture
of competition between these two effects is found. The theoretically
predicted frequency shifts show promise of explaining some recent GONG,
MDI and BiSON observations.
Title: Spicule formation by ion-neutral damping
Authors: James, S. P.; Erdélyi, R.
Bibcode: 2002ESASP.506..649J
Altcode: 2002ESPM...10..649J; 2002svco.conf..649J
The possible mechanism of generation of spicules by Alfvénic
waves is studied in dissipative MHD where dissipation is mainly
caused by ion-neutral collision damping, as suggested by Haerendel
(1992). Ion-neutral damping becomes non-negligible at the high cyclic
frequencies involved, typically greater than 0.1 Hz, and the potential
role played by this effect in both forming and supporting solar
spicules is investigated. The propagation of high frequency Alfvén
waves on vertically open solar magnetic flux tubes is considered by
numerically solving a set of 1.5D MHD equations. Spicule-like structures
with heights of around 4000-10000 km were formed. The formation was
found to be primarily caused by the impact of a series of slow shocks
generated by the continuous interaction between the upward propagating
driven wave train and the downward propagating train of waves created by
reflection off the transition region. At the lower end of frequencies
considered the heating due to ion-neutral damping was found to provide
only a small benefit due to the increased thermal pressure gradient. At
higher frequencies, whilst the heating effect becomes stronger, the
much reduced wave amplitude reaching the transition region hinders
spicules formation. The adiabatic results suggest that ion-neutral
damping may not support spicules as described by Haerendel (1992).
Title: Coronal Loop Heating by Random Energy Releases
Authors: Mendoza-Briceño, César A.; Erdélyi, Robert; Di
G. Sigalotti, Leonardo
Bibcode: 2002ApJ...579L..49M
Altcode:
It was suggested by Parker that the solar corona is heated by numerous
small localized events called nanoflares. High-resolution satellites
(the Solar and Heliospheric Observatory and Transition Region and
Coronal Explorer [TRACE]) have shown a kind of very small scale activity
at transition region temperatures (i.e., explosive events, microflares,
blinkers, etc.). These events may serve as the building blocks of the
heating mechanism(s) of the solar atmosphere. In this Letter we present
the results of numerical calculations that detail the response of the
coronal plasma to microscale heating pulses in a magnetic loop. The
energy input pulses are at periodical and random injections, located
near the footpoint where the temperature is ~104 K. It
is found that these successive energy inputs can maintain the plasma
along the loop at typical coronal temperatures. This result is in good
qualitative agreement with TRACE observations studied by Aschwanden
et al.
Title: Spicule formation by ion-neutral damping
Authors: James, S. P.; Erdélyi, R.
Bibcode: 2002A&A...393L..11J
Altcode:
The possible mechanism of generation of spicules by Alfvénic
waves is studied in dissipative MHD where dissipation is mainly
caused by ion-neutral collision damping, as suggested by Haerendel
(\cite{haerendel}). Ion-neutral damping becomes non-negligible at
the high cyclic frequencies involved, typically greater than 0.1
Hz, and the potential role played by this effect in both forming
and supporting solar spicules is investigated. The propagation of
high frequency Alfvén waves on vertically open solar magnetic flux
tubes is considered. The flux tubes are taken to be axisymmetric
and initially untwisted with the field strength declining from
1600 G in the photosphere to 20 G in the corona. Their propagation
is investigated by numerically solving a set of fully nonlinear,
dissipative 1.5D MHD equations with the waves being generated by a
continuous sinusoidal driver introduced into the equation of angular
momentum in the low atmosphere of the Sun. Spicule-like structures
with heights of around 5000-6000 km were formed. The formation was
found to be primarily caused by the impact of a series of slow shocks
generated by the continuous interaction between the upward propagating
driven wave train and the downward propagating train of waves created by
reflection off the transition region. At the lower end of frequencies
considered the heating due to ion-neutral damping was found to
provide only a small benefit due to the increased thermal pressure
gradient. At higher frequencies, whilst the heating effect becomes
stronger, the much reduced wave amplitude reaching the transition
region hinders spicule formation. The adiabatic results suggest that
ion-neutral damping may not support spicules as described by Haerendel
(\cite{haerendel}). However, the effect is highly sensitive to the level
of ionisation and therefore the energy balance. Including the effects
of thermal conduction and radiation may well lead to different results
and thus it would be premature to dismiss the mechanism at this point.
Title: What is the real nature of blinkers?
Authors: Marik, D.; Erdélyi, R.
Bibcode: 2002A&A...393L..73M
Altcode:
In the present paper a simple physical model of blinkers based on the
process of magnetic reconnection is developed. Blinkers were first
found in transition region lines (e.g. He I, O III, O IV, O V and Mg
IX) by SOHO CDS. Their typical lifetime is approximately 16 min, the
intensity enhancement ratios are around 1.8, and they appear at 1-20
s-1 on the solar disk. According to observations, blinker
events seem to be increases in density and/or filling factor rather than
increases in temperature. Most blinkers have a repetitive nature and a
high percentage of these events occur above unipolar magnetic fields.\
Magnetic reconnection in the lower transition region of the solar
atmosphere is numerically simulated by solving the fully nonlinear,
time-dependent, dissipative, radiative 2D MHD equations. Setting the
initial parameters describing transition region explosive events as
in Roussev et al. (\cite{rou01a},b,c), we computed the evolution of
the reconnection jets. Taking into account the limit of the spatial and
temporal resolution of the CDS camera and converting the high-resolution
numerical results into ``CDS-resolution'', the propagating reconnection
jets are found to have similar properties as those described by CDS
blinker observations. These results suggest SOHO CDS may actually
observe reconnection driven explosive events as blinkers.
Title: Ducted compressional waves in the magnetosphere in the
double-polytropic approximation
Authors: Ballai, I.; Erdélyi, R.; Roberts, B.
Bibcode: 2002AnGeo..20.1553B
Altcode:
Small-amplitude compressional magnetohydrodynamic-type waves are studied
in the magnetosphere. The magnetosphere is treated as a rarefied plasma
with anisotropy in the kinetic pressure distribution. The parallel and
perpendicular pressures are defined by general polytropic pressure
laws. This double-polytropic model can be considered as a natural
extension of the magnetohydrodynamic (MHD) model when the plasma is
collisionless.
Title: Resonant MHD wave instabilities in the solar atmosphere
Authors: Erdélyi, Robert
Bibcode: 2002ESASP.505..145E
Altcode: 2002IAUCo.188..145E; 2002solm.conf..145E
Resonant MHD waves occur naturally in inhomogeneous plasmas like
the solar atmosphere. When there is a plasma bulk motion present
the wave-steady plasma interaction may result in increasing wave
amplitude and the wave carrying energy away instead of the usual damping
(and heating of the inhomogeneous plasma). This phenomenon is called
resonant flow instability (RFI). Such situation may occur in blinkers,
in sunspot penumbrae, at the boundary of coronal loops and coronal
holes, in the shear layers of slow and fast solar wind or at the
magneto- and heliopause. We report on the negative energy character
and on the unstable nature of waves in shear flows throughout solar
atmospheric conditions.
Title: Heating of coronal loops by random micro-scale energy releases
Authors: Mendoza-Briceño, César A.; Erdélyi, Robert; Sigalotti,
Leonardo Di G.
Bibcode: 2002ESASP.505..257M
Altcode: 2002solm.conf..257M; 2002IAUCo.188..257M
It was suggested by Parker (1988) that the solar corona is heated by
numerous small localized events called nano-flares. High-resolution
satellites (SOHO and TRACE) have shown a kind of very small-scale
activity at transition-region temperatures (i.e., explosive events,
micro-flares, blinkers, etc.). These events may serve as the building
blocks of the heating mechanism of the solar atmosphere. In this
paper, we present the results of numerical calculations that detail
the response of the coronal plasma to micro-scale heating pulses in a
magnetic loop. The energy input pulses are at periodical and random
injections, located near the footpoint where the temperature is
≍104K. It is found that these successive energy inputs
can maintain the plasma at typical coronal temperatures along the
loop. The implications of the results upon the latest coronal loop
observations are also discussed.
Title: Meeting report: Steel MIST and UKSP together at Sheffield
Authors: Arnold, Neil; Bailey, Graham; Erdélyi, Robert
Bibcode: 2002A&G....43c..27A
Altcode:
The annual UK Solar Physics meeting this year joined a MIST meeting for
the first time. The two drew together the considerable UK solar and
solar-terrestrial physics community for discussion and debate at the
University of Sheffield from 9-12 April 2002. Neil Arnold and Graham
Bailey (MIST) and Robert Erdélyi (UKSP) report on this innovative
joint meeting.
Title: What blinkers really are?
Authors: Marik, D.; Erdélyi, R.
Bibcode: 2002ESASP.508..315M
Altcode: 2002soho...11..315M
The transition region blinkers, according to the present model, may
play a significant role not only in the solar transition region and the
solar atmospheric plasma heating but may even contribute to the solar
wind mass flux. They were mainly found, e.g., in He I, O III, O IV,
O V and Mg IX, respectively (Harrison, 1997). Their typical lifetime
is approximately 16s, the intensity enhancement ratios are around 1.8,
and they appear at 1 - 20 s-1 on the Sun. Blinker events
seem to be increases in density and/or filling factor rather then to be
increases in temperature. Most of the blinkers have repetitive nature
and high percentage of these events occur above unipolar magnetic
field. A simple physical model of blinkers based on the process of
magnetic reconnection is developed. In the present paper results of
solving the fully nonlinear, time-dependent, dissipative, radiative 2-D
MHD equations are shown. By setting the initial parameters describing
blinkers and taking into account the limit of the spatial resolution
of SOHO CDS propagating reconnection jets are found to have properties
described by CDS observations. Results may suggest SOHO CDS observes
explosive events as blinkers in some cases.
Title: Numberical Simulations of Blinker Events
Authors: Marik, D.; Erdélyi, R.
Bibcode: 2002PADEU..12...13M
Altcode:
The transition region blinkers are one of the most controversial
phenomena in the lower solar atmosphere observed in the past five
years. According to our model these small-scale bright intensity
enhancements may play a significant role not only in the solar
transition region but even in the solar wind acceleration and the
solar atmospheric plasma heating. They were mainly found, e.g., in
HeI (584.33A), OIII (599.52A), OIV (554.52A), OV (629.73A) and MgIX
(368.06A), respectively (Harrison). Their typical parameters are: the
mean lifetime is approximately 16 s, the intensity enhancement ratios
are around 1.8, and the appearing frequency on the whole solar surface
is at 1 - 20 1/s. Blinker events appear to be increases in density or
filling factor rather then to be increases in temperature. Most of the
blinkers have repetitive nature and high percentage of these events
occur above regions where one magnetic polarity dominates. We have
developed a simple physical model of blinkers based on the process
of magnetic reconnection (Priest). In the present paper we show our
results of solving the fully nonlinear, time-dependent, dissipative,
radiative 2-D MHD equations using a staggered mesh. By setting the
initial parameters describing blinkers we found propagating jets with
similar properties found by observations.
Title: Impulsive random energy heating in coronal loops
Authors: Mendoza-Briceno, C.; Erdelyi, R.; Sigalotti, L.
Bibcode: 2002cosp...34E1402M
Altcode: 2002cosp.meetE1402M
The heating of the solar corona by numerous micro-scale randomly
localized events is considered. High-resolution satellites (SOHO and
TRACE) have recently shown traces of micro-scale activity at transition
region temperatures (e.g., explosive events, micro-flares, blinkers,
etc.). These events may serve as the basic building blocks of the
heating mechanism(s) of the solar atmosphere. Results of a series of
numerical simulations with detailed response of the coronal plasma in a
magnetic loop to microscale heating pulses are presented. Energy input
pulses, located near the footpoint with an approx. temperature 10^4 K,
are distributed at periodical and random injections. It is found that
these successive energy inputs can maintain the plasma along the loop
at typical coronal temperatures. Implications of these results upon
the latest coronal loop observation will be discussed.
Title: Fast MHD oscillations in prominence fine structures
Authors: Díaz, A. J.; Oliver, R.; Erdélyi, R.; Ballester, J. L.
Bibcode: 2001A&A...379.1083D
Altcode:
High-resolution observations suggest that quiescent solar prominences
are made of small-scale fibrils stacked one after another in both the
vertical and horizontal directions. These fibrils are interpreted as the
cool, highermost part of much larger coronal loops which are rooted in
the solar photosphere. On the other hand, there is some evidence showing
that small amplitude oscillations in prominences can affect individual
or groups of fibrils, which vibrate with their own periods. Using
a simple magnetostatic model to represent the fibril structure
of quiescent solar prominences, Joarder et al. (\cite{joarder})
investigated some oscillatory properties of the Alfvén and fast
magnetohydrodynamic modes. In this paper, with a proper treatment of
boundary conditions, we reexamine their configuration and explore more
deeply the basic features (mainly frequency and spatial structure)
of the fast mode. The main conclusion is that, for reasonable values
of the fibril's width, perturbations extend far away from its axis
and, therefore, a single oscillating fibril can excite oscillations
in neighbouring ones.
Title: Modelling of solar explosive events in 2D
environments. III. Observable consequences
Authors: Roussev, I.; Doyle, J. G.; Galsgaard, K.; Erdélyi, R.
Bibcode: 2001A&A...380..719R
Altcode:
We examine the response via line synthesis of two representative
transition region lines, namely C IV 1548.2 Å and O VI 1031.9 Å,
in various physical environments representing the ``quiet'' Sun to
magnetic reconnection events. Our calculations of ion populations allow
for departures from equilibrium ionization (EI), which is critical
in studies of transient events. Both lines reveal highly blue- and
red-shifted Doppler components, and some of the results are examined in
the context of solar explosive events. The observable consequences of
magnetic reconnection are subtle in the various physical circumstances
examined here and differ from one emission line to another, because
of the difference in their formation temperatures.
Title: Rotational splitting of helioseismic modes influenced by a
magnetic atmosphere
Authors: Pintér, B.; New, R.; Erdélyi, R.
Bibcode: 2001A&A...378L...1P
Altcode:
In the present paper the splitting of sectoral (m=+/- l) helioseismic
eigenmodes (f- and p-modes) is studied in the presence of a
magnetic atmosphere. The solar interior is in a steady state, with
sub-photospheric plasma flow along the equator representing solar
rotation. The Cartesian geometry employed restricts the present study
to sectoral modes, m=+/- l. We work with l >= 50, which guarantees
that the modes do not deeply penetrate into the solar interior and
therefore experience an approximately uniform rotation. Potentially
observable effects are predicted and developments of the model to aid
detections are discussed.
Title: Modelling of explosive events in the solar transition region
in a 2D environment. II. Various MHD experiments
Authors: Roussev, I.; Galsgaard, K.; Erdélyi, R.; Doyle, J. G.
Bibcode: 2001A&A...375..228R
Altcode:
We examine the response of various physical environments representing
the solar atmosphere to a magnetic reconnection event. The reconnection
is driven by a localized increase of the magnetic diffusivity in the
current concentration formed between two magnetic fluxes of opposite
polarity. The time dependent evolution is then followed by numerically
solving the 2-dimensional (2D) dissipative magnetohydrodynamic (MHD)
equations, including also effects of thermal conduction, radiative
losses, and volumetric heating.\ This work continues a previous related
study (Roussev et al. 2001a), and compares results obtained from
exploring different initial states. The choice of the initial states
is found to be crucial to the dynamics of the reconnection jets. The
numerical experiments are aimed at modelling transient events on the
quiet Sun, with an emphasis on explosive events. The 2D reconnection
experiments presented in this paper are the basis for a detailed
analysis on the line synthesis in transition region resonant lines,
presented by Roussev et al. (\cite{rou01b}).
Title: Damping of helioseismic modes in steady state
Authors: Pintér, B.; Erdélyi, R.; New, R.
Bibcode: 2001A&A...372L..17P
Altcode:
The effects of an equilibrium flow in the internal regions of the
Sun are studied on the damping of helioseismic f- and p-modes. The
Sun is modeled as a multi-layered plasma, where the upper parts,
representing the chromosphere and corona, are embedded in a horizontally
unidirectional though vertically inhomogeneous magnetic field, while
the lower part, representing the sub-photospheric polytropic region,
is in a steady equilibrium state. The steady state sub-surface region
can be considered as a first approximation of dynamic motions (e.g.,
differential rotation, sub-surface flows, meridional flows, convective
motion, etc.). The frequencies and the line-widths of eigenmodes
are affected by sub-surface flow and atmospheric magnetic fields. A
key contribution to the effects comes from the universal mechanism
of resonant absorption. When both atmospheric magnetic field and
sub-surface flows are present, a complex picture of competition between
these two effects is found. The theoretically predicted frequency
shifts in a steady state show promise of explaining the observed
effects. Changes in damping of f- and p-modes caused by changes
(e.g. cyclic, if any) of steady state flows are predicted.
Title: Modelling of explosive events in the solar transition region
in a 2D environment. I. General reconnection jet dynamics
Authors: Roussev, I.; Galsgaard, K.; Erdélyi, R.; Doyle, J. G.
Bibcode: 2001A&A...370..298R
Altcode:
The aim of the present study is to investigate the reconnection
jets formed during the process of magnetic flux cancellation
in the physical environment of the solar transition region. The
emission properties of these jets are then computed for two resonance
transition region lines, C iv 1548.2 Å and O vi 1031.9 Å, under the
assumption of non-equilibrium ionization. The numerical modelling
involves 2-dimensional (2D) dissipative, radiative, nonlinear
magnetohydrodynamics. The nonlinear anisotropic thermal conduction,
radiative losses, and volumetric heating are taken into account in order
to assess their role in the physical situation examined. This work is a
continuation of previous related simulations where small-scale energy
depositions were modelled in 1D radiative hydrodynamics. Having an
X-point reconnection in the mid-transition region gives blue-shifts
of the order of ~ 100 km s-1, however, the red-shift can
be up to one order of magnitude less.
Title: Nonlinear resonant absorption of fast magnetoacoustic waves
due to coupling into slow continua in the solar atmosphere
Authors: Erdélyi, R.; Ballai, I.; Goossens, M.
Bibcode: 2001A&A...368..662E
Altcode:
Nonlinear resonant absorption of fast magnetoacoustic (FMA) waves in
inhomogeneous weakly dissipative, isotropic and anisotropic plasmas
in static and steady equilibria is studied. Both isotropic and
anisotropic plasmas are considered and for the background equilibrium
state 1D planar static and steady models are used. The equilibrium
configuration consists of three layers, where an inhomogeneous
magnetised plasma slab is surrounded by two homogeneous magnetised
semi-infinite plasma regions. The propagating FMA waves are partly
absorbed due to coupling to local nonlinear slow magnetohydrodynamic
(MHD) waves in the inhomogeneous layer, and are partly reflected. The
coefficient of wave energy resonant absorption is derived using two
simplifying assumptions (i) weak nonlinearity and (ii) the thickness
of the inhomogeneous layer is small compared to the wavelength of the
waves, i.e. the so-called long-wavelength approximation is used.
Title: Effects of steady flow on magnetoacoustic-gravity surface waves
Authors: Varga, Emese; Erdelyi, Robert
Bibcode: 2001PADEU..11...83V
Altcode:
The linearized theory for the parallel propagation of
magnetoacoustic-gravity (MAG) surface waves is developed for an
isothermal interface of a horizontally magnetised plasma above a
field-free medium with a constant steady flow parallel to the field
lines. The dispersion relation is derived and studied in detail for
two distributions of magnetic field strength. The effect of flow is
found to be twofold: %We found that the effect of flow is twofold: the
frequencies of the modes and the permitted regions of propagation are
both shifted causing some modes to disappear, and others to appear. The
backward propagating slow mode changes its direction of propagation
and couples to its forward propagating counterpart.
Title: Effect of a Steady Flow and an Atmospheric Magnetic Field on
the Solar p- and f-Modes
Authors: Erdélyi, R.; Taroyan, Y.
Bibcode: 2001IAUS..203..208E
Altcode:
The combined effect of a chromospheric uniform magnetic field
and a photospheric steady flow on the p- and f-modes is evaluated
theoretically for a simple model of the solar plasma. The introduced
flow is parallel to the horizontal magnetic field. This model may serve
as a first approximation to assess the effects of the observed highly
dynamical solar interior (e.g., subsurface meridional flows, convective
motion, etc.) especially for high degree l. Frequency changes due to
the magnetic atmosphere and the steady flow are derived analytically in
the long wavelength limit and are detemined numerically for arbitrary
wavelengths. The results reveal the influence of flow on the p- and
f-modes is more dominant than the influence of the atmospheric magnetic
field for the small wavenumber limit. However for arbitrary wavelengths
the effect of magnetic field might be stronger than frequency shifts
caused by a steady flow. The understanding of the effect of subsurface
flows on the p- and f-modes might help us to contribute to the solution
for the puzzle of helioseismic frequency shifts.
Title: Helioseismic frequency shifts due to steady states
Authors: Erdélyi, R.; Taroyan, Y.
Bibcode: 2001ESASP.464..203E
Altcode: 2001soho...10..203E
A three layer model of the Sun is presented for the study of p-
and f-modes. Frequency shifts due to the combined effects of an
atmospheric magnetic field and subsurface equilibrium flows are
evaluated by deriving and solving the dispersion relation. An increase
in the chromospheric temperature can not only reduce but also raise
the frequencies of p- and f-modes when a background magnetic field
is present. Beside flow effects the effect of changing the height of
the magnetic canopy is also examined. A comparison of our theoretical
results with recent observational data shows an excellent agreement.
Title: Influence of equilibrium flows and the atmospheric magnetic
field on solar oscillation modes
Authors: Pintér, B.; Erdélyi, R.; New, R.; Goossens, M.
Bibcode: 2001ESASP.464..227P
Altcode: 2001soho...10..227P
The competing effects of an atmospheric magnetic field and an
equilibrium flow in the internal regions of the Sun are studied on
the helioseismic f- and p-modes. The Sun is modeled as a multi-layered
plasma, where the upper parts, representing the chromosphere and corona,
are embedded in a unidirectional though inhomogeneous magnetic field,
meanwhile the lower part, representing the sub-photospheric polytropic
region, is in a steady equilibrium state. The steady state sub-surface
region can be considered as a first approximation of dynamic motions
(e.g., convective motion, differential rotation, sub-surface flows,
meridional flows, etc.). The obtained frequency shifts of the different
eigenmodes are associated with flow and magnetic effects. We also found
damping of the eigenfrequencies which apparently can be associated with
the universal mechanism of resonant absorption. Resonant absorption
(already known as a viable heating mechanism in the solar corona)
is present due to inhomogeneities in the atmosphere which give rise
to Alfvén and slow continua. Damping of helioseismic modes occurs
when the modes are coupled into these continua. When both atmospheric
magnetic field and sub-surface flows are present, a complex picture of
competition of these two effects is found. The theoretically predicted
frequency shifts in a steady state are in excellent agreement with the
observed values. For related works see also the papers by Erdélyi &
Taroyan and Varga & Erdélyi in the present Volume.
Title: Effects of steady flow on magnetoacoustic-gravity surface waves
Authors: Varga, E.; Erdélyi, R.
Bibcode: 2001ESASP.464..255V
Altcode: 2001soho...10..255V
We developed the linearized theory for the parallel propagation
of magnetoacoustic-gravity (MAG) surface waves at an isothermal
interface of a uniformly magnetised plasma above a field-free plasma
with a constant steady flow parallel to the field lines. The dispersion
relation is derived and studied in detail. We found that the effect of
flow is twofold: the frequencies of the modes and the permitted regions
of propagation are both shifted causing some modes to disappear,
and others to appear. The backward propagating slow mode changes
its direction of propagation and couples to its forward propagating
counterpart giving rise to an upper bound of the permitted wavenumber
range for propagation.
Title: Micro-scale Heating Blocks: SUMER-TRACE-La Palma Observations
and Their Modelling (CD-ROM Directory: contribs/erdelyi2)
Authors: Erdélyi, R.; de Pontieu, B.; Roussev, I.
Bibcode: 2001ASPC..223..619E
Altcode: 2001csss...11..619E
No abstract at ADS
Title: Nonlinear Resonant MHD Waves in the Atmosphere of the Sun
(CD-ROM Directory: contribs/erdelyi1)
Authors: Erdélyi, R.; Ballai, I.
Bibcode: 2001ASPC..223..613E
Altcode: 2001csss...11..613E
No abstract at ADS
Title: Linear and nonlinear waves in dilute plasmas
Authors: Ballai, István; Erdélyi, Róbert; Goossens, Marcel
Bibcode: 2000AIPC..537..152B
Altcode: 2000wdss.conf..152B
Small-amplitude magnetohydrodynamic (MHD) waves are studied in a dilute
collisionless plasma with an anisotropic pressure distribution. The
parallel and perpendicular pressure are defined with the aid of
two polytropic pressure laws. For specific values of the polytropic
indices, previous results obtained with the usual Chew-Goldberger-Low
(CGL) double-adiabatic (i) and double-isothermal (ii) models are
recovered. The double-polytropic model can be considered as the
counterpart of the single-polytropic model. Dispersion relations for
the linear waves are derived and analyzed in the presence of pressure
anisotropy. The weakly nonlinear dynamics is shown to be governed by
the Benjamin-Ono equation. The results are discussed in the CGL and
double-isothermal limits. .
Title: Absorption of fast magnetosonic waves in the solar atmosphere
in the limit of weak nonlinearity
Authors: Ballai, István; Erdélyi, Róbert; Goossens, Marcel
Bibcode: 2000AIPC..537..144B
Altcode: 2000wdss.conf..144B
We study the resonant absorption of fast magnetoacoustic (FMA) waves in
inhomogeneous weakly dissipative, isotropic and anisotropic plasmas. The
equilibrium states on which the waves are superimposed is static
or stationary and are assumed to be in a 1-D planar geometry. The
equilibrium model consists of three layers with an inhomogeneous
magnetized plasma surrounded by two homogeneous magnetized semi-infinite
plasmas. The propagating FMA waves are partly absorbed and partly
reflected by coupling to local nonlinear slow magnetohydrodynamic
(MHD) waves in the inhomogeneous layer. The dissipation acts only in a
narrow layer called the dissipative layer which embraces the resonant
magnetic surface. In linear theory it has been shown that in the
vicinity of the resonant surface the energy density, the amplitudes
of waves and the spatial gradients become large, suggesting that in
this region nonlinearity might be important. The wave motions far from
the dissipative layer are described by the linear, ideal MHD equations,
while inside this layer the wave motions are governed by the full system
of the dissipative, nonlinear MHD equations. The coefficient of wave
energy resonant absorption is derived assuming weak nonlinearity and
long-wavelength approximation. .
Title: Interaction of sound waves with inhomogeneous magnetized
plasma in strongly nonlinear resonant slow wave layer
Authors: Ruderman, Michael S.; Erdélyi, Robert
Bibcode: 2000AIPC..537..279R
Altcode: 2000wdss.conf..279R
We consider slow resonant MHD waves in 1D planar equilibria with
the unidirectional magnetic field. A nonlinear equation governing
this waves in a slow resonant layer is derived. A periodic solution
in the form of propagating wave with a permanent shape is found in
the limiting case, where nonlinearity dominates dissipation. This
solution is used to derive a connection formula that connects the
values of the normal component of the velocity at two sides of the
resonant layer. This connection formula is, in turn, used to study
the interaction of an incoming sound wave with a slab containing an
inhomogeneous magnetized plasma. The coefficient of the wave energy
resonant absorption is calculated and compared with its counterpart
obtained on the basis of linear theory. .
Title: Slow surface wave damping in plasmas with anisotropic viscosity
and thermal conductivity
Authors: Ruderman, M. S.; Oliver, R.; Erdélyi, R.; Ballester, J. L.;
Goossens, M.
Bibcode: 2000A&A...354..261R
Altcode:
This paper studies the damping of slow surface MHD waves propagating
along the equilibrium magnetic field on a finite-thickness magnetic
interface. The plasma is assumed to be strongly magnetised, and the
full Braginskii's expressions for viscosity and the heat flux are
used. The primary focus of the paper is on the competition between
resonant absorption in the thin dissipative layer embracing the ideal
resonant position and the bulk wave damping due to viscosity and thermal
conductivity as damping mechanisms for surface MHD waves. The dependence
of the wave damping decrement on the wave length and the dissipative
coefficients is studied. Application of the obtained results to the
surface MHD wave damping in the solar chromosphere is discussed.
Title: Modelling of Explosive Events in the Solar Transition Region:
Importance of Radiative Losses and Thermal Conduction
Authors: Roussev, I.; Erdélyi, R.; Doyle, J. G.; Galsgaard, K.
Bibcode: 1999ESASP.448..641R
Altcode: 1999mfsp.conf..641R; 1999ESPM....9..641R
No abstract at ADS
Title: New Insight in Transition Region Dynamics as Derived from
SUMER Observations and Numerical Modelling
Authors: Teriaca, L.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.;
Banerjee, D.
Bibcode: 1999ESASP.448..379T
Altcode: 1999ESPM....9..379T; 1999mfsp.conf..379T
No abstract at ADS
Title: The Influence of a Steady State on p- and f-Modes
Authors: Erdélyi, R.; Taroyan, Y. A.
Bibcode: 1999ESASP.448...81E
Altcode: 1999mfsp.conf...81E; 1999ESPM....9...81E
No abstract at ADS
Title: Multiwavelength Observations (SOHO, TRACE, La Palma) and
Modelling of Explosive Events
Authors: Erdélyi, R.; de Pontieu, B.; Sarro, L. M.
Bibcode: 1999ESASP.448.1345E
Altcode: 1999ESPM....9.1345E; 1999mfsp.conf.1345E
No abstract at ADS
Title: Magnetoacoustic-Gravity Surface Waves in Steady Plasmas
Authors: Erdélyi, R.; Varga, E.; Zétényi, M.
Bibcode: 1999ESASP.448..269E
Altcode: 1999ESPM....9..269E; 1999mfsp.conf..269E
No abstract at ADS
Title: New insight into transition region dynamics via SUMER
observations and numerical modelling
Authors: Teriaca, L.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.
Bibcode: 1999A&A...352L..99T
Altcode:
We explore the idea that the occurrence of nano-flares in a magnetic
loop around the O vi formation temperature could explain the
observed red-shift of mid-low transition region lines as well as the
blue-shift observed in low coronal lines (T > 6x 105\
K). Observations are compared to numerical simulations of the response
of the solar atmosphere to an energy perturbation of 4x 1024
ergs representing an energy release during magnetic reconnection
in a 1-D semi-circular flux tube. The temporal evolution of the
thermodynamic state of the loop is converted into C iv 1548, O vi 1032
and Ne viii 770 line profiles in non-equilibrium ionization. Performing
an integration over the entire period of simulations, a redshift of ~
6\ km\ s-1 is found in C iv, while a blue-shift of ~ 2\ km\
s-1 and ~ 10\ km\ s-1 were derived for O vi and
Ne viii, respectively, in reasonable agreement with observations.
Title: Strongly Nonlinear Resonant MHD Waves in the Steady Solar
Magnetic Canopy
Authors: Erdélyi, R.; Ballai, I.; Ruderman, M. S.
Bibcode: 1999ESASP.448..263E
Altcode: 1999ESPM....9..263E; 1999mfsp.conf..263E
No abstract at ADS
Title: Modelling explosive events in the solar atmosphere
Authors: Sarro, L. M.; Erdélyi, R.; Doyle, J. G.; Pérez, M. E.
Bibcode: 1999A&A...351..721S
Altcode:
High-resolution ultraviolet (UV) spectra of the outer solar
atmosphere show transient brightenings often referred to as explosive
events. These are localized regions of small spatial extent that
show sudden enhancements in the intensities of lines formed between
20,000 and 200,000 K, accompanied by strong non-gaussian profiles. The
present work is an attempt to extract observational consequences from
computational simulations of the dynamic response of a coronal loop to
energy perturbations. Explosive events are simulated in semi-circular
magnetic flux tubes. Thermal energy perturbations drive flows along
the flux tube giving rise to thermodynamic phenomena. The temporal
evolution of the thermodynamic state of the loop is converted into C iv
lambda 1548.2 Ä line profiles in (non)-equilibrium ionization. Time
dependent carbon ion populations are obtained in the non-equilibrium
conditions derived from the thermodynamic variables by means of
an adaptive grid code. Most important, departures from ionization
equilibrium are assessed for the first time under conditions such as
those encountered in explosive events.
Title: Nonlinear Resonant MHD Waves In The Atmosphere Of The Sun
Authors: Ballai, Istvan; Erdelyi, Robert
Bibcode: 1999ESASP.446..155B
Altcode: 1999soho....8..155B
We consider driven resonant nonlinear MHD waves in dissipative steady
plasmas to study the effect of steady flows on the nonlinear resonant
heating behaviour of MHD waves The nonlinear analogue of the connection
formulae for slow MHD waves are derived. The nonlinear theory of
driven MHD developed is then used to study the interaction of sound
waves with one-dimensional isotropic steady plasmas modelling, e.g.,
the wave interaction in the magnetic canopy. We find that a steady
equilibrium shear flow can significantly influence the nonlinear
resonant absorption in the limits of thin inhomogeneous layer and weak
nonlinearity. The presence of an equilibrium flow may therefore be
important for the nonlinear resonant MHD wave phenomena. A parametric
analysis also shows the nonlinear part of resonant absorption can be
strongly enhanced by the equilibrium flow.
Title: Observation and modelling of small-scale energetic transients
in the solar atmosphere.
Authors: Erdelyi, R.; Sarro, L. M.
Bibcode: 1999ESASP.446..299E
Altcode: 1999soho....8..299E
SOHO and TRACE give new opportunities for studying phenomena on
rapid time-scale variability, such as the UV transition region
transients, e.g., microflares, explosive events or blinkers. These
events are localised regions with small spatial extent that show
sudden enhancements of line intensities associated with strong
non-Gaussian broadenings at wide temperature ranges. We believe these
events may serve as the building blocks of the heating mechanism
of the solar atmosphere. The present work describes the progress
made on their observations and numerical modelling based on a
reconnection-type physical process. MHD simulations are performed
to explore the properties of these micro-scale events and their
relevance to heating. In order to assess the physical model involved
the numerical results of MHD simulations are converted into observable
UV line profiles in non-equilibrium ionisation. The confrontation of
theoretical studies with observational data show an excellent agreement
between theory and SOHO observations.
Title: Resonant Absorption of Nonlinear Slow MHD Waves in Isotropic
Steady Plasmas - II. Application: Resonant Acoustic Waves
Authors: Erdélyi, Róbert; Ballai, István
Bibcode: 1999SoPh..186...67E
Altcode:
Nonlinear theory of driven magnetohydrodynamic (MHD) waves in the
slow dissipative layer in isotropic steady plasmas developed by Ballai
and Erdélyi (Solar Phys. 180 (1998)) is used to study the nonlinear
interaction of sound waves with one-dimensional isotropic steady
plasmas. An inhomogeneous magnetic slab with field-aligned plasma
flow is sandwiched by a homogeneous static magnetic-free plasma
and by a homogeneous steady magnetic plasma. Sound waves launched
from the magnetic-free plasma propagate into the inhomogeneous region
interacting with the localised slow dissipative layer and are partially
reflected, dissipated or transmitted by this region. The nonlinearity
parameter, introduced by Ballai and Erdélyi, is assumed to be small
and a regular perturbation method is used to obtain analytical wave
solutions. Analytical studies of resonant absorption of sound waves
show that the efficiency of the process of resonant absorption strongly
depends on both the equilibrium parameters and the characteristics of
the resonant wave. We also find that a steady equilibrium shear flow
can significantly influence the nonlinear resonant absorption in the
limits of thin inhomogeneous layer and weak nonlinearity. The presence
of an equilibrium flow may therefore be important for the nonlinear
resonant MHD wave phenomena. A parametric analysis also shows that the
nonlinear part of resonant absorption can be strongly enhanced by the
equilibrium flow.
Title: Explosive events in the solar atmosphere
Authors: Pérez, M. E.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.
Bibcode: 1999A&A...342..279P
Altcode:
Two examples of explosive events observed with SUMER in transition
region spectral lines are reported here; one detected in C iv 1548
Angstroms, in a region within the northern polar coronal hole, and the
other in O vi 1032 Angstroms, in an active region. The event measured
in C iv lasted ~ 3 min and extended approximately a region of 8 arc sec
along the slit (N-S) and 8 arc sec in the E-W direction. Velocities
reached around 150 km s(-1) in the blue wing and 100 km s(-1) in the
red wing. The active region events were more energetic and in total
lasted ~ 6 min. At the point of maximum activity, a region of 8 arc
sec along the slit is covered by one explosive event located in the
northern section of the observed region, while in the southern section
we observe two events very closely located and extended over a maximum
of 14 arc sec along the slit. More precisely, in the northern section
we have at least two consecutive events occurring in a short time
interval ( ~ 12 min) separated by ~ 3 arc sec. In the E-W direction
the raster length covered by each of these events was approximately
4 arc sec. The explosive events seen in O vi showed a very complex
structure of subsonic and supersonic velocity flows, both red-shifted
and blue-shifted. The apparent maximum velocity reached in the blue
wing was approximately 250 km s(-1) and 215 km s(-1) in the red wing.
Title: Center-to-limb line width measurements of solar chromospheric,
transition region and coronal lines
Authors: Erdelyi, R.; Doyle, J. G.; Perez, M. E.; Wilhelm, K.
Bibcode: 1998A&A...337..287E
Altcode:
Line widths derived from observational data obtained by SUMER
onboard SOHO in August 1996 at disk center and at the limb are used
to confront those derived via assuming Alfven and/or magneto-acoustic
wave heating. The observational data clearly shows a center-to-limb
variation in the upper chromospheric and transition region lines,
with only a marginal difference in the coronal lines in the sense of
additional broadening further from disk center. Numerical estimations
based on linear MHD, favour the existence of Alfven wave heating
over magneto-acoustic heating, although further calculations are
required. For example, non-linear effects could change the wave
characteristics which in turn can have a major effect on the overall
line broadening.
Title: Resonant Absorption of Alfvén Waves in Steady Coronal Loops
Authors: Erdélyi, Róbert
Bibcode: 1998SoPh..180..213E
Altcode:
The effect of equilibrium flow on linear Alfvén resonances in coronal
loops is studied in the compressible viscous MHD model. By means of a
finite element code, the full set of linearised driven MHD equations are
solved for a one-dimensional equilibrium model in which the equilibrium
quantities depend only on the radial coordinate. Computations of
resonant absorption of Alfvén waves for two classes of coronal
loop models show that the efficiency of the process of resonant
absorption strongly depends on both the equilibrium parameters and the
characteristics of the resonant wave. We find that a steady equilibrium
shear flow can also significantly influence the resonant absorption
of Alfvén waves in coronal magnetic flux tubes. The presence of
an equilibrium flow may therefore be important for resonant Alfvén
waves and coronal heating. A parametric analysis also shows that the
resonant absorption can be strongly enhanced by the equilibrium flow,
even up to total dissipation of the incoming wave.
Title: Resonant Absorption of Nonlinear Slow MHD Waves in Isotropic
Steady Plasmas - I. Theory
Authors: Ballai, István; Erdélyi, Róbert
Bibcode: 1998SoPh..180...65B
Altcode:
This paper considers driven resonant nonlinear slow magnetohydrodynamic
(MHD) waves in dissipative steady plasmas. A theory developed by
Ruderman, Hollweg, and Goossens (1997) is used and extended to study
the effect of steady flows on the nonlinear resonant behaviour of slow
MHD waves in slow dissipative layers. The method of matched asymptotic
expansions is used to describe the behaviour of the wave variables in
the slow dissipative layer. The nonlinear analogue of the connection
formulae for slow MHD waves obtained previously by Goossens, Hollweg,
and Sakurai (1992) and Erdélyi (1997) in linear MHD, are derived. The
effect of an equilibrium flow results partly in a Doppler shift of the
available frequency for slow resonance and partly in the modification
of the width of the dissipative layer.
Title: Resonant flow instability of MHD surface waves
Authors: Tirry, W. J.; Cadez, V. M.; Erdelyi, R.; Goossens, M.
Bibcode: 1998A&A...332..786T
Altcode:
We study the effect of velocity shear on the spectrum of MHD surface
waves. A nonuniform intermediate region is taken into account,
so that the surface wave can be subject to resonant absorption. In
order to deal in a mathematically and also physically consistent
manner with the resonant wave excitation, we analytically derive
the dissipative solution around the resonant surface in resistive
MHD. Using these analytical solutions in our eigenvalue code, the
effect of the velocity shear on the damping rate of the surface
wave can easily be investigated with limited numerical effort. The
presence of the flow can both increase and decrease the efficiency
of resonant absorption. We also show how the resonance can lead to
instability of the global surface mode for a certain range of values
for the velocity shear. The resonant flow instabilities, which are
physically distinct from the nonresonant Kelvin-Helmholz instabilities
can occur for velocity shears significantly below the Kelvin-Helmholz
threshold. Although resonant absorption as dissipation mechanism is
present, the amplitude of the surface mode grows in time. The resonant
flow instability can be explained in terms of negative energy waves :
to get an unstable negative energy wave, some dissipative process is
required to ensure energy dissipation.
Title: Nonlinear theory of slow dissipative layers in anisotropic
plasmas
Authors: Ballai, I.; Ruderman, M. S.; Erdélyi, R.
Bibcode: 1998PhPl....5..252B
Altcode:
The solar coronal plasma is a well-known example of a plasma with
strongly anisotropic dissipative coefficients. The main dissipative
processes in the solar corona are strongly anisotropic thermal
conductivity and viscosity. Ruderman and Goossens [Astrophys. J. 471,
1015 (1996)] developed a linear theory of driven slow resonant
waves in plasmas with strongly anisotropic viscosity and thermal
conductivity. Linear theory shows that in the slow dissipative layer
the amplitudes of oscillations become very large for high Reynolds and
Pecklet numbers, so that nonlinearity may be important. In the present
paper the nonlinear behavior of driven magnetohydrodynamic waves in the
slow dissipative layer in plasmas with strongly anisotropic viscosity
and thermal conductivity is studied. The nonlinear governing equation
for wave variables in the dissipative layer is derived. The nonlinear
connection formulae, which are extensions of the linear connection
formulae first introduced in the theory of resonant magnetohydrodynamic
waves by Sakurai, Goossens, and Hollweg [Solar Phys. 133, 127 (1991)],
are derived.
Title: Explosive events modelled in the view of SOHO observations
Authors: Erdélyi, R.; Sarro, L. B.; Doyle, J. G.
Bibcode: 1998ESASP.421..207E
Altcode: 1998sjcp.conf..207E
No abstract at ADS
Title: Observations of Explosive Events in the Solar Atmosphere
Authors: Perez, E. P.; Doyle, J. G.; Erdelyi, R.
Bibcode: 1998ASPC..154..666P
Altcode: 1998csss...10..666P
Two ultraviolet explosive events are reported here; one which lasted
over 2 mins and was detected in a region within the northern polar
coronal hole and a second event which lasted over 4 mins and was
detected within an active region. The coronal hole event first showed
a mass upflow, followed by blue and red-shifted plasma, then finally
a red-shifted plasma. Velocities reached ~120 km s^{-1}. The active
region event was more energetic, showing a second injection after
about 2 mins. The maximum velocity reached 300 km s^{-1}. Towards the
end of each of these events, the location of the mass upflow/downflow
had shifted by 3-4 arcsec compared to the initial location.
Title: Modeling of Explosive Events in the Solar Atmosphere
Authors: Sarro, L. M.; Doyle, J. G.; Montesinos, B.; Erdelyi, R.;
de Sterck, H.
Bibcode: 1998ASPC..154..693S
Altcode: 1998csss...10..693S
High-resolution ultraviolet (UV) spectra show transient brightenings ---
often referred to as explosive events --- in the solar atmosphere. The
present work describes the progress made on their numerical
simulations. Using semi-circular magnetic flux tubes we find that
thermal energy perturbations drive flows along the flux tube. The time
evolution of our simulations first shows a sudden rise in temperature
at the perturbation site followed by the ejection of cool dense gas
bullets and the generation of sound waves. This is then followed by
the appearance of ``new'' transition regions moving at different
velocities. Our computational results are converted into UV line
profiles in (non)-equilibrium ionization. Observational signatures
(e.g., emission measures) are calculated as a function of time at
different locations on the solar disk.
Title: Absorption of magnetosonic waves in presence of resonant slow
waves in the solar atmosphere.
Authors: Cadez, V. M.; Csik, A.; Erdelyi, R.; Goossens, M.
Bibcode: 1997A&A...326.1241C
Altcode:
The resonant absorption of slow and fast magnetosonic waves in a
nonuniform magnetic plasma is studied for a simple planar equilibrium
model. Propagating slow and fast magnetosonic waves are launched
upwards in a lower uniform layer. They are partially absorbed by
coupling to local resonant waves in an overlying nonuniform plasma
layer at the magnetic surface where the frequency of the incoming wave
equals the local Alfven continuum frequency or the local slow continuum
frequency. The slow magnetosonic waves can only be coupled to resonant
slow continuum waves. For the fast magnetosonic waves there are three
possibilities as they can be coupled to resonant Alfven continuum waves
alone, resonant Alfven continuum waves combined with resonant slow
continuum waves, and resonant slow continuum waves alone. The present
paper focuses on the absorption of magnetosonic waves by coupling
to resonant slow continuum waves either alone or in combination with
resonant Alfven continuum waves. The results show that the resonant
absorption of slow and fast magnetosonic waves at the slow resonance
position strongly depends on the characteristics of the equilibrium
model and of the driving wave. The absorption can produce efficient
local heating of plasma under conditions as in the solar atmosphere.
Title: Nonthermal Velocities in the Solar Transition Zone and Corona
Authors: Doyle, J. G.; O'Shea, E.; Erdélyi, R.; Dere, K. P.; Socker,
D. G.; Keenan, F. P.
Bibcode: 1997SoPh..173..243D
Altcode:
Nonthermal velocities are presented for spectral lines covering the
temperature range 10 4-10 6 K, measured from high-spectral-resolution
data for several solar features observed at the limb by the high
resolution telescope and spectrograph (HRTS), including a coronal hole,
`quiescent regions' and several small-scale active regions. These
results are compared with predictions based on acoustic waves and
heating via Alfvén waves. It is likely that more than one mechanism is
operating simultaneously, in particular, resonant Alfvén wave heating,
which is very sensitive to background plasma motions.
Title: Effect of Flow on Resonant Absorption of Slow MHD Waves in
Coronal Arcades
Authors: Csík, Árpád; Erdélyi, Róbert; Čadež, Vladimir M.
Bibcode: 1997SoPh..172...61C
Altcode: 1997ESPM....8...61C
Resonant absorption of slow MHD waves is studied numerically by using
the SGH method and is applied to a model of a coronal arcade in the
presence of equilibrium plasma flows. The arcade is approximated by
a 1D horizontal magnetic slab that is non-uniform along the vertical
direction and which is surrounded by two homogeneous media. While
propagating from the photosphere upwards into the corona, the
magneto-acoustic waves can be resonantly absorbed in the inhomogeneous
region of the arcade. Computational results show that the resonant
absorption of the impinging waves strongly depends on the equilibrium
model and on the characteristics of the driving wave. The results
also indicate that the presence of an equilibrium plasma flow along
the magnetic field of the arcade reduces the resonant absorption for
the flow speed parameters considered.
Title: Analytical Solutions for Cusp Resonance in Dissipative MHD
Authors: ERDÉLYI, RÓBERT
Bibcode: 1997SoPh..171...49E
Altcode:
The present paper considers resonant slow waves in 1D non-uniform
magnetic flux tubes in dissipative MHD. Analytical solutions are
obtained for the Lagrangian displacement and the Eulerian perturbation
of the total pressure for both static and stationary equilibrium
states. From these analytical solutions we obtain the fundamental
conservation law and the jump conditions for resonant slow waves
in dissipative MHD. The validity of the ideal conservation law and
jump conditions obtained by Sakurai, Goossens, and Hollweg (1991)
for static equilibria and Goossens, Hollweg, and Sakurai (1992) for
stationary equilibria is justified in dissipative MHD.
Title: MHD Waves Observed (?) by SOHO: MHD Wave Heating
Authors: Erdélyi, R.; Perez, E. P.; Doyle, J. G.
Bibcode: 1997ESASP.404..357E
Altcode: 1997cswn.conf..357E
No abstract at ADS
Title: Explosive Events Observed by SOHO
Authors: Erdélyi, R.; Perez, E. P.; Doyle, J. G.
Bibcode: 1997ESASP.404..353E
Altcode: 1997cswn.conf..353E
No abstract at ADS
Title: Modelling of Explosive Events in the Solar Atmosphere
Authors: Sarro, I. M.; de Sterk, H.; Erdélyi, R.; Montesinos, B.;
Doyle, J. G.
Bibcode: 1997ESASP.404..657S
Altcode: 1997cswn.conf..657S
No abstract at ADS
Title: Resonant Absorption in the Solar Corona
Authors: Erdélyi, R.
Bibcode: 1997ESASP.404..347E
Altcode: 1997cswn.conf..347E
No abstract at ADS
Title: Flow-effect on Resonant Absorption of p-modes in Sunspots
Authors: Erdelyi, R.
Bibcode: 1997ASPC..118...34E
Altcode: 1997fasp.conf...34E
The effect of an equilibrium flow on resonant absorption of p-mode
oscillations in sunspots is studied in compressible viscous MHD. We
show that an equilibrium shear flow can significantly influence the
absorption suffered by the acoustic driving waves.
Title: Dissipative instability of the MHD tangential discontinuity in
magnetized plasmas with anisotropic viscosity and thermal conductivity
Authors: Ruderman, M. S.; Verwichte, E.; Erdélyi, R.; Goossens, M.
Bibcode: 1996JPlPh..56..285R
Altcode:
The stability of the MHD tangential discontinuity is studied in
compressible plasmas in the presence of anisotropic viscosity and
thermal conductivity. The general dispersion equation is derived,
and solutions to this dispersion equation and stability criteria are
obtained for the limiting cases of incompressible and cold plasmas. In
these two limiting cases the effect of thermal conductivity vanishes,
and the solutions are only influenced by viscosity. The stability
criteria for viscous plasmas are compared with those for ideal plasmas,
where stability is determined by the Kelvin—Helmholtz velocity
VKH as a threshold for the difference in the equilibrium
velocities. Viscosity turns out to have a destabilizing influence when
the viscosity coefficient takes different values at the two sides of
the discontinuity. Viscosity lowers the threshold velocity V below
the ideal Kelvin—Helmholtz velocity VKH, so that there is a range
of velocities between V and VKH where the overstability is
of a dissipative nature.
Title: Effects of flow on resonant absorption of MHD waves in
viscous MHD.
Authors: Erdelyi, R.; Goossens, M.
Bibcode: 1996A&A...313..664E
Altcode:
The effect of an equilibrium flow on resonant absorption of linear MHD
waves in cylindrical magnetic flux tubes is studied in compressible
viscous MHD. We treat the problem numerically with an application of
the FEM combined with the Galerkin technique. The singularities of
the ideal MHD equations are removed by incorporating a dissipative
effect, namely the classical viscosity. We show that an equilibrium
shear flow can significantly influence the absorption suffered by
the incoming driving waves. The presence of an equilibrium flow may
therefore be very determinant for resonant absorption. A parametric
analysis shows that there are values of the equilibrium velocity
field for which the absorption rate becomes zero, even for rather
small velocity shears. We also found negative absorption of wave
power which apparently can be attributed to the resonant instability
found by Hollweg et al. (1990). For other values of the equilibrium
flow we find that the resonant absorption can be strongly enhanced,
even up to total absorption of the incoming wave.