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Author name code: froment
ADS astronomy entries on 2022-09-14
author:"Froment, Clara"
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Title: On the kinetics of inter-penetration of plasmas on the
boundaries of coronal holes
Authors: Krasnoselskikh, Vladimir; Dudok De Wit, Thierry; Zaslavsky,
Arnaud; Bale, Stuart; Froment, Clara; Artemiev, Anton; Agapitov,
Oleksiy
2022cosp...44.1457K Altcode:
The boundaries of coronal holes (CH) may create very favorable
conditions for the reconfiguration of the magnetic field. In
particular, mid-latitude CHs are known to rotate quasi-rigidly
although the photosphere rotates differentially. CH boundaries
(CHBs) separate two kinds of areas with different configurations:
CHs with open magnetic fields and surrounding quiet Sun with coronal
loops. The magnetic reconnection should be necessarily present at CHBs
otherwise rigid rotation of CHs could not exist when the surrounding
photospheric fields rotate differentially (Wang & Sheeley 1994;
Fisk et al. 1999). The process of reconnection may be rather slow, but
it necessarily leads to the inter-penetration of plasmas from different
origin, from closed and opened field lines. We describe this process
kinetically, similarly to (Gurevich, Pariiskaya & Pitaevskii,
1968) and show that the ion distribution functions formed as a result
of such mixture of plasmas have shapes very similar to those typically
observed in the solar wind (Pilip et al, 1987a,b, Marsch,2012). This
process occurs on the heights of the coronal loops thus its further
evolution towards larger heights may change important characteristics
of these distributions as the magnetic field may decrease significantly
faster than 1/r. We show that under certain conditions they may become
unstable and several instabilities such as firehose may develop.
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Title: Observations of switchbacks with Parker Solar Probe
Authors: Froment, Clara
2022cosp...44.1341F Altcode:
Parker Solar Probe observations reveal the ubiquitous presence of
localised magnetic deflections, often called "switchbacks" and known
previously as "microstreams", in the innermost heliosphere. Two main
class of theories have emerged in order to explain the formation of
these structures: the formation by processes occurring deep in the solar
atmosphere or directly in the solar wind. The origin of switchbacks
is currently unknown but their omnipresence, however, shows that they
could play an important role in the dynamics and heating of the young
solar wind. I will introduce the global context of these observations
and review some of the most recent observations and theories. I will
in particular talk about the characteristics of their boundaries that
can help us understanding their origins and evolution in the solar wind.
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Title: What is the role of whistler waves in shaping of the solar
wind electron function between 0.17 and 1 AU ?
Authors: Colomban, Lucas; Kretzschmar, Matthieu; Agapitov, Oleksiy;
Khotyaintsev, Yuri; Krasnoselskikh, Vladimir; Maksimovic, Milan;
Froment, Clara; Berthomier, Matthieu; Graham, Daniel; Bercic, Laura
2022cosp...44.1661C Altcode:
In the solar wind, whistler waves are thought to play an important
role on the evolution of the electron velocity distribution function
as a function of distance. In particular, oblique whistler waves may
diffuse the Strahl electrons into the halo population. Using AC magnetic
and electric field measured by the SCM (search coil magnetometer) and
electric antenna of Solar Orbiter and Parker Solar Probe, we search for
the presence of whistler waves at heliocentric distance between 0.17 and
1 AU. Spectral matrices computation and minimum variance analysis on
continuous waveforms make it possible to identify whistler wave modes
and to determine their direction of propagation with respect to the
ambiant magnetic field (angle and direction : sunward or anti-sunward)
. A statistical study of the inclination of these waves and of their
parameters is presented. Single events and calculation of the diffusion
coefficients are also presented.
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Title: Statistical investigation of switchbacks properties observed
by Parker Solar Probe
Authors: Bizien, Nina; Dudok De Wit, Thierry; Macdowall, Robert;
Krasnoselskikh, Vladimir; Bale, Stuart; Froment, Clara; Kasper,
Justin; Whittlesey, Phyllis; Larson, Davin; Case, Antony
2022cosp...44.1434B Altcode:
Magnetic switchbacks are sudden deflections of the magnetic field,
observed by Parker Solar Probe (PSP) in the pristine solar wind. Their
nature and origin are still unestablished. We aim to present a more
in-depth description of all magnetic deflections, including the largest
ones that are called switchbacks, conducting a statistical analysis over
the first ten solar encounters of PSP. We identify these deflections
using measurements from the MAG fluxgate magnetometer, which is part of
the FIELDS instrument suite. The detection is based on the deflection
of the magnetic field from the Parker spiral. We also use the electron
pitch-angle distributions measured by SWEAP/SPAN-E in order to check
the relative orientation of the strahl within the magnetic structures
and then validate their identification. In this study we concentrate
on the boundary of these structures and investigate their properties
(thickness, type of discontinuity, etc.) versus their distance from
the Sun. Indeed, these properties provide direct insight into the
dynamical evolution of these structures. Of particular interest is
their dependence on the magnitude of the deflection.
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Title: First Results From the SCM Search-Coil Magnetometer on Parker
Solar Probe
Authors: Dudok de Wit, T.; Krasnoselskikh, V. V.; Agapitov, O.;
Froment, C.; Larosa, A.; Bale, S. D.; Bowen, T.; Goetz, K.; Harvey,
P.; Jannet, G.; Kretzschmar, M.; MacDowall, R. J.; Malaspina, D.;
Martin, P.; Page, B.; Pulupa, M.; Revillet, C.
2022JGRA..12730018D Altcode:
Parker Solar Probe is the first mission to probe in situ the innermost
heliosphere, revealing an exceptionally dynamic and structured outer
solar corona. Its payload includes a search-coil magnetometer (SCM)
that measures up to three components of the fluctuating magnetic
field between 3 Hz and 1 MHz. After more than 3 years of operation,
the SCM has revealed a multitude of different wave phenomena in the
solar wind. Here we present an overview of some of the discoveries made
so far. These include oblique and sunward propagating whistler waves
that are important for their interaction with energetic electrons, the
first observation of the magnetic signature associated with escaping
electrons during dust impacts, the first observation of the magnetic
field component for slow extraordinary wave modes during type III radio
burst events, and more. This study focuses on the major observations
to date, including a description of the instrument and lessons learned.
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Title: Langmuir-Slow Extraordinary Mode Magnetic Signature
Observations with Parker Solar Probe
Authors: Larosa, A.; Dudok de Wit, T.; Krasnoselskikh, V.; Bale,
S. D.; Agapitov, O.; Bonnell, J.; Froment, C.; Goetz, K.; Harvey,
P.; Halekas, J.; Kretzschmar, M.; MacDowall, R.; Malaspina, David M.;
Moncuquet, M.; Niehof, J.; Pulupa, M.; Revillet, C.
2022ApJ...927...95L Altcode:
Radio emission from interplanetary shocks, planetary foreshocks,
and some solar flares occurs in the so-called "plasma emission"
framework. The generally accepted scenario begins with electrostatic
Langmuir waves that are driven by a suprathermal electron beam on the
Landau resonance. These Langmuir waves then mode-convert to freely
propagating electromagnetic emissions at the local plasma frequency
f <SUB> pe </SUB> and/or its harmonic 2f <SUB> pe </SUB>. However,
the details of the physics of mode conversion are unclear, and so far
the magnetic component of the plasma waves has not been definitively
measured. Several spacecraft have measured quasi-monochromatic Langmuir
or slow extraordinary modes (sometimes called z-modes) in the solar
wind. These coherent waves are expected to have a weak magnetic
component, which has never been observed in an unambiguous way. Here
we report on the direct measurement of the magnetic signature of these
waves using the Search Coil Magnetometer sensor of the Parker Solar
Probe/FIELDS instrument. Using simulations of wave propagation in an
inhomogeneous plasma, we show that the appearance of the magnetic
component of the slow extraordinary mode is highly influenced by
the presence of density inhomogeneities that occasionally cause the
refractive index to drop to low values where the wave has strong
electromagnetic properties.
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Title: Multi-Scale Variability of Coronal Loops Set by Thermal
Non-Equilibrium and Instability as a Probe for Coronal Heating
Authors: Antolin, Patrick; Froment, Clara
2022FrASS...920116A Altcode:
Solar coronal loops are the building blocks of the solar corona. These
dynamic structures are shaped by the magnetic field that expands
into the solar atmosphere. They can be observed in X-ray and extreme
ultraviolet (EUV), revealing the high plasma temperature of the
corona. However, the dissipation of magnetic energy to heat the
plasma to millions of degrees and, more generally, the mechanisms
setting the mass and energy circulation in the solar atmosphere are
still a matter of debate. Furthermore, multi-dimensional modelling
indicates that the very concept of a coronal loop as an individual
entity and its identification in EUV images is ill-defined due to
the expected stochasticity of the solar atmosphere with continuous
magnetic connectivity changes combined with the optically thin
nature of the solar corona. In this context, the recent discovery
of ubiquitous long-period EUV pulsations, the observed coronal rain
properties and their common link in between represent not only major
observational constraints for coronal heating theories but also major
theoretical puzzles. The mechanisms of thermal non-equilibrium (TNE)
and thermal instability (TI) appear in concert to explain these
multi-scale phenomena as evaporation-condensation cycles. Recent
numerical efforts clearly illustrate the specific but large parameter
space involved in the heating and cooling aspects, and the geometry of
the loop affecting the onset and properties of such cycles. In this
review we will present and discuss this new approach into inferring
coronal heating properties and understanding the mass and energy cycle
based on the multi-scale intensity variability and cooling properties
set by the TNE-TI scenario. We further discuss the major numerical
challenges posed by the existence of TNE cycles and coronal rain,
and similar phenomena at much larger scales in the Universe.
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Title: The role of asymmetries in coronal rain formation during
thermal non-equilibrium cycles
Authors: Pelouze, Gabriel; Auchère, Frédéric; Bocchialini, Karine;
Froment, Clara; Mikić, Zoran; Soubrié, Elie; Voyeux, Alfred
2022A&A...658A..71P Altcode: 2021arXiv211009975P
Context. Thermal non-equilibrium (TNE) produces several observables
that can be used to constrain the spatial and temporal distribution
of solar coronal heating. Its manifestations include prominence
formation, coronal rain, and long-period intensity pulsations in
coronal loops. The recent observation of abundant periodic coronal rain
associated with intensity pulsations allowed for these two phenomena
to be unified as the result of TNE condensation and evaporation
cycles. On the other hand, many observed intensity pulsation events
show little to no coronal rain formation. <BR /> Aims: Our goal is
to understand why some TNE cycles produce such abundant coronal
rain, while others produce little to no rain. <BR /> Methods:
We reconstructed the geometry of the periodic coronal rain event,
using images from the Extreme Ultraviolet Imager (EUVI) onboard the
Solar Terrestrial Relations Observatory (STEREO), and magnetograms
from the Helioseismic and Magnetic Imager (HMI). We then performed 1D
hydrodynamic simulations of this event for different heating parameters
and variations of the loop geometry (9000 simulations in total). We
compared the resulting behaviour to simulations of TNE cycles that do
not produce coronal rain. <BR /> Results: Our simulations show that
both prominences and TNE cycles (with and without coronal rain) can
form within the same magnetic structure. We show that the formation
of coronal rain during TNE cycles depends on the asymmetry of the
loop and of the heating. Asymmetric loops are overall less likely
to produce coronal rain, regardless of the heating. In symmetric
loops, coronal rain forms when the heating is also symmetric. In
asymmetric loops, rain forms only when the heating compensates for
the asymmetry. <P />Movie associated to Fig. 5 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140477/olm">https://www.aanda.org</A>
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Title: Survey of whistlers waves parameters in the pristine solar
wind from the first PSP orbit: wave amplitude, polarization, and
occurrence rates
Authors: Froment, Clara; Agapitov, Oleksiy; Krasnoselskikh, Vladimir;
Dudok de Wit, Thierry; Malaspina, David; Jagarlamudi, vamsee Krishna;
Kretzschmar, Matthieu; Larosa, Andrea; Bale, Stuart; Bonnell, John;
Case, Anthony; Goetz, Keith; Kasper, Justin; Korreck, Kelly; Larson,
Davin; Livi, Roberto; MacDowall, Robert; Moncuquet, Michel; Mozer,
Forrest; Pulupa, Marc; Revillet, Claire; Stevens, Michael; Whittlesey,
Phyllis
2021AGUFMSH34B..08F Altcode:
Whistlers waves are electromagnetic waves that are widely present
in the solar wind. These waves are a strong candidate for explaining
the scattering of the strahl electrons into the halo population and,
thus, for regulating the heat flux in the solar wind. Observations by
the Parker Solar Probe (PSP) mission of the solar wind at ~35.7 solar
radii reveal a significant increase of whistler wave activity (the
amplitudes and occurrence rate) in comparison with the observations
at 1AU. We present the parameters of whistlers waves in the young
solar wind based on the statistical processing of the cross spectra
(full spectral matrices) of the magnetic field collected during the
first encounter of PSP with the Sun. These data are captured by the
3-components Search-Coil Magnetometer (SCM) and produced by the Digital
Fields Board (DFB) that are part of the FIELDS experiment onboard
PSP. The SCM provides the cross-spectra measurements in the 20 Hz -
4.5 kHz frequency range covering the full range of whistler waves
(0.1-0.9 of the local electron gyrofrequency) at the heliospheric
distances from 35 to 59 solar radii. We report on the whistler waves
parameters in the young solar wind and present statistics of amplitudes,
occurrence rates, and whistler polarization properties compared to the
heliospheric distance. It is found in particular that while most of the
observed whistlers were quasi-parallel to the background magnetic field
(wave normal angle were around 0-30 degrees), a significant part (~10%)
of observed waves had oblique (> 45°) wave normal angles. Even if
modest, this amount of oblique whistlers could substantially contribute
to the strahl scattering.
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Title: New insight into the nature and origin of switchbacks thanks
to a comprehensive catalogue of events
Authors: Dudok de Wit, Thierry; Aschwanden, Markus; Bale, Stuart;
Froment, Clara; Krasnoselskikh, Vladimir; Larosa, Andrea; MacDowall,
Robert; Raouafi, Nour
2021AGUFMSH44B..05D Altcode:
One of the most intriguing observations made by Parker Solar Probe
is the omnipresence of sudden deflections of the magnetic field,
called switchbacks or jets. One of the pathways towards understanding
the nature and the origin of these structures consists in studying
their statistical properties. This can be pursued only if we have a
means for detecting and extracting each individual switchback. Here
we provide a robust technique that allows to automatically detect
and identify switchbacks based on their sudden deflection from the
Parker spiral. This allows us to build a comprehensive catalogue,
with thousands of events per solar encounter. Most importantly,
this catalogue does not only include full reversals, but also smaller
deflections, whose properties have been overlooked so far while they
are essential for building a complete picture. Using this catalogue
we provide new constraints on the origin of these structures and their
radial evolution.
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Title: On the kinetics of inter-penetration of plasmas on the
boundaries of coronal holes
Authors: Krasnoselskikh, Vladimir; Zaslavsky, Arnaud; Artemyev, Anton;
Dudok de Wit, Thierry; Froment, Clara
2021AGUFMSH32B..04K Altcode:
The boundaries of coronal holes (CH) may create very favorable
conditions for the reconfiguration of the magnetic field. In particular,
mid-latitude CHs can be connected with polar CHs. In this case they
are known to rotate quasi-rigidly although the photosphere rotates
differentially. CH boundaries (CHBs) separate two kinds of areas
with different configurations: CHs with open magnetic fields and
surrounding quiet Sun with coronal loops. The magnetic reconnection
should be necessarily present at CHBs otherwise rigid rotation of
CHs could not exist since the surrounding photospheric fields rotate
differentially (Wang & Sheeley 1994; Fisk et al. 1999). The process
of reconnection may be rather slow, but it necessarily leads to the
inter-penetration of plasmas from different origin, from closed and
opened field lines. We describe this process kinetically, similarly to
(Gurevich, Pariiskaya & Pitaevskii, 1968) and show that the ion
distribution functions formed as a result of such mixture of plasmas
have shapes very similar to those typically observed in the solar wind
(Pilip et al, 1987a,b, Marsch,2012). This process occurs on the heights
of the coronal loops thus its further evolution towards larger heights
may change important characteristics of these distributions as the
magnetic field may decrease significantly faster than 1/r. We show
that under certain conditions they may become unstable and several
instabilities such as firehose may develop. References Wang, Y. M.,
& Sheeley, N. R. 1994, ApJ, 430, 399; Fisk, L. A., Zurbuchen,
T. H., & Schwadron, N. A. 1999, ApJ, 521, 868; A.L. Gurevich,
L.I. Pariiskaya, L.P. Pitaevskii, ZhETF, Vol. 54, No. 3, p. 891,
September 1968; W.G. Pilipp, H. Miggenrieder, M.D. Montgomery,
K.-H. Mühlhäuser, H. Rosenbauer, R. Schwenn, J. Geophys. Res. 92,
1075--1092 (1987a); W.G. Pilipp, H. Miggenrieder, K.-H. Mühlhäuser,
H. Rosenbauer, R. Schwenn, F.M. Neubauer, J. Geophys. Res. 92,
1103--1118 (1987b); Marsch, E., Helios: Evolution of Distribution
Functions 0.3--1 AU, Space Sci Rev (2012) 172:23--39
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Title: Langumir/Slow extraordinary mode magnetic signatures with
Parker Solar Probe
Authors: Larosa, Andrea; Krasnoselskikh, Vladimir; Dudok de Wit,
Thierry; Bale, Stuart; Agapitov, Oleksiy; Bonnell, John; Froment,
Clara; Goetz, Keith; Harvey, Peter; Halekas, Jasper; Kretzschmar,
Matthieu; MacDowall, Robert; Mitchell, J. Grant; Niehof, Jonathan;
Pulupa, Marc; Revillet, Claire
2021AGUFMSH35C2081L Altcode:
Langmuir or slow extraordinary modes (sometimes called z-modes)
are continuously observed in the solar wind. These coherent waves
are expected to have a weak magnetic component, which had never
been observed so far. For the first time we reveal their magnetic
signature by using the SCM search-coil magnetometer onboard Parker Solar
Probe. Using simulations of wave propagation in inhomogeneous plasma,
we show that this magnetic component of the slow extraordinary mode is
primarily due to density inhomogeneities that occasionally cause the
refractive index to drop to low values. This drop, as we are going to
show, facilitate the observations of the magnetic signature which are
usually hidden in the noise floor.
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Title: Whistler Waves Bursts at Switchback Boundaries in the Young
Solar Wind: Generation Mechanisms and Effects for Superthermal
Electrons
Authors: Agapitov, Oleksiy; Drake, James; Swisdak, Marc; Froment,
Clara; Mozer, Forrest
2021AGUFMSH44B..06A Altcode:
Observations by the Parker Solar Probe mission of the solar wind at
~35.7 SR reveal the existence of intensive plasma wave bursts with
frequencies below 0.1 fce (from tens of Hz to 150 Hz in the spacecraft
frame) collocated with the local minima of the magnetic field magnitude
at switchbacks boundaries (localized sudden deflections of the magnetic
field). Sunward propagation with depletion of magnetic field magnitude
lead to a significant Doppler frequency downshift of whistler waves from
200-300 Hz to 20-80 Hz (from 0.2 fce to 0.5 fce). Their peak amplitudes
can be as large as 2 to 4 nT. Such values represent approximately 10-20%
of the background magnetic field. We have evaluated the properties of
these waves collocated with dips of magnetic field related to switchback
boundaries, the mechanisms of wave generation: the generation of these
waves is supported by the modified electron distribution with increased
transverse temperature anisotropy inside the magnetic holes; and the
effects on solar wind suprathermal particles from interaction with these
waves: sunward propagating whistler waves efficiently interact with
the high energy solar wind electrons (in the energy range up to 1 keV)
scattering the strahl population of suprathermal electrons into a halo
population due to the most efficient cyclotron resonance interaction.
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Title: Magnetic reconnection as a mechanism to produce multiple
proton populations and beams locally in the solar wind
Authors: Lavraud, Benoit; Kieokaew, Rungployphan; Fargette, Nais;
Louarn, Philippe; Fedorov, Andrei; Andre, Nicolas; Fruit, Gabriel;
Genot, Vincent; Reville, Victor; Rouillard, Alexis; Plotnikov, Illya;
Penou, Emmanuel; Barthe, Alain; Prech, Lubomir; Owen, Christopher;
Bruno, Roberto; Allegrini, Frederic; Berthomier, Matthieu; Kataria, D.;
Livi, Stefano; Raines, Jim; D'Amicis, Raffaella; Eastwood, Jonathan;
Froment, Clara; Laker, Ronan; Maksimovic, Milan; Marcucci, Maria;
Perri, Silvia; Perrone, Denise; Phan, Tai; Stansby, David; Stawarz,
Julia; Toledo-Redondo, Sergio; Vaivads, Andris; Verscharen, Daniel;
Zouganelis, Yannis; Angelini, Virginia; Evans, Vincent; Horbury,
Timothy; O'Brien, Helen
2021AGUFMSH25B2090L Altcode:
Spacecraft observations early revealed frequent multiple proton
populations in the solar wind. Decades of research on their origin have
focused on processes such as magnetic reconnection in the low corona
and wave-particle interactions in the corona and locally in the solar
wind. This study aims to highlight that multiple proton populations and
beams are also produced by magnetic reconnection occurring locally in
the solar wind. We use high resolution Solar Orbiter proton velocity
distribution function measurements, complemented by electron and
magnetic field data, to analyze the association of multiple proton
populations and beams with magnetic reconnection during a period of
slow Alfvénic solar wind on 16 July 2020. At least 6 reconnecting
current sheets with associated multiple proton populations and beams,
including a case of magnetic reconnection at a switchback boundary, are
found during this day. This represents 2% of the measured distribution
functions. We discuss how this proportion may be underestimated, and how
it may depend on solar wind type and distance from the Sun. Although
suggesting a likely small contribution, but which remains to be
quantitatively assessed, Solar Orbiter observations show that magnetic
reconnection must be considered as one of the mechanisms that produce
multiple proton populations and beams locally in the solar wind.
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Title: Whistler waves observed by Solar Orbiter/RPW between 0.5 AU
and 1 AU
Authors: Kretzschmar, M.; Chust, T.; Krasnoselskikh, V.; Graham,
D.; Colomban, L.; Maksimovic, M.; Khotyaintsev, Yu. V.; Soucek, J.;
Steinvall, K.; Santolík, O.; Jannet, G.; Brochot, J. -Y.; Le Contel,
O.; Vecchio, A.; Bonnin, X.; Bale, S. D.; Froment, C.; Larosa, A.;
Bergerard-Timofeeva, M.; Fergeau, P.; Lorfevre, E.; Plettemeier, D.;
Steller, M.; Štverák, Š.; Trávníček, P.; Vaivads, A.; Horbury,
T. S.; O'Brien, H.; Evans, V.; Angelini, V.; Owen, C. J.; Louarn, P.
2021A&A...656A..24K Altcode: 2021arXiv211005080K
Context. Solar wind evolution differs from a simple radial expansion,
while wave-particle interactions are assumed to be the major cause
for the observed dynamics of the electron distribution function. In
particular, whistler waves are thought to inhibit the electron heat
flux and ensure the diffusion of the field-aligned energetic electrons
(Strahl electrons) to replenish the halo population. <BR /> Aims: The
goal of our study is to detect and characterize the electromagnetic
waves that have the capacity to modify the electron distribution
functions, with a special focus on whistler waves. <BR /> Methods:
We carried out a detailed analysis of the electric and magnetic
field fluctuations observed by the Solar Orbiter spacecraft during
its first orbit around the Sun, between 0.5 and 1 AU. Using data from
the Search Coil Magnetometer and electric antenna, both part of the
Radio and Plasma Waves (RPW) instrumental suite, we detected the
electromagnetic waves with frequencies above 3 Hz and determined
the statistical distribution of their amplitudes, frequencies,
polarization, and k-vector as a function of distance. Here, we also
discuss the relevant instrumental issues regarding the phase between
the electric and magnetic measurements as well as the effective length
of the electric antenna. <BR /> Results: An overwhelming majority of
the observed waves are right-handed circularly polarized in the solar
wind frame and identified as outwardly propagating quasi-parallel
whistler waves. Their occurrence rate increases by a least a factor of
2 from 1 AU to 0.5 AU. These results are consistent with the regulation
of the heat flux by the whistler heat flux instability. Near 0.5 AU,
whistler waves are found to be more field-aligned and to have a smaller
normalized frequency (f/f<SUB>ce</SUB>), larger amplitude, and greater
bandwidth than at 1 AU.
---------------------------------------------------------
Title: Magnetic reconnection as a mechanism to produce multiple
thermal proton populations and beams locally in the solar wind
Authors: Lavraud, B.; Kieokaew, R.; Fargette, N.; Louarn, P.; Fedorov,
A.; André, N.; Fruit, G.; Génot, V.; Réville, V.; Rouillard,
A. P.; Plotnikov, I.; Penou, E.; Barthe, A.; Prech, L.; Owen, C. J.;
Bruno, R.; Allegrini, F.; Berthomier, M.; Kataria, D.; Livi, S.;
Raines, J. M.; D'Amicis, R.; Eastwood, J. P.; Froment, C.; Laker,
R.; Maksimovic, M.; Marcucci, F.; Perri, S.; Perrone, D.; Phan,
T. D.; Stansby, D.; Stawarz, J.; Toledo-Redondo, S.; Vaivads, A.;
Verscharen, D.; Zouganelis, I.; Angelini, V.; Evans, V.; Horbury,
T. S.; O'Brien, H.
2021A&A...656A..37L Altcode: 2021arXiv210911232L
Context. Spacecraft data revealed early on the frequent observation of
multiple near-thermal proton populations in the solar wind. Decades of
research on their origin have focused on processes such as magnetic
reconnection in the low corona and wave-particle interactions in the
corona and locally in the solar wind. <BR /> Aims: This study aims to
highlight the fact that such multiple thermal proton populations and
beams are also produced by magnetic reconnection occurring locally in
the solar wind. <BR /> Methods: We used high-resolution Solar Orbiter
proton velocity distribution function measurements, complemented by
electron and magnetic field data, to analyze the association of multiple
thermal proton populations and beams with magnetic reconnection during a
period of slow Alfvénic solar wind on 16 July 2020. <BR /> Results: At
least six reconnecting current sheets with associated multiple thermal
proton populations and beams, including a case of magnetic reconnection
at a switchback boundary, were found on this day. This represents 2%
of the measured distribution functions. We discuss how this proportion
may be underestimated, and how it may depend on solar wind type and
distance from the Sun. <BR /> Conclusions: Although suggesting a likely
small contribution, but which remains to be quantitatively assessed,
Solar Orbiter observations show that magnetic reconnection must be
considered as one of the mechanisms that produce multiple thermal
proton populations and beams locally in the solar wind.
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Title: Switchback systematic orientation near Sun and implications
for solar interchange reconnection preferential locations
Authors: Fargette, Nais; Lavraud, Benoit; Rouillard, Alexis; Reville,
Victor; Dudok de Wit, Thierry; Froment, Clara; Halekas, Jasper; Phan,
Tai; Malaspina, David; Bale, Stuart; Kasper, Justin; Louarn, Philippe;
Case, Anthony; Korreck, Kelly; Larson, Davin; Pulupa, Marc; Stevens,
Michael; Whittlesey, Phyllis; Berthomier, Matthieu
2021AGUFMSH33B..03F Altcode:
Near the Sun, the solar wind magnetic field is dominated by large
Alfvénic structures that often lead to reversals of the radial magnetic
field while keeping constant electron strahl properties as well as a
constant magnetic field amplitude. They are called magnetic switchbacks
and are interpreted as folds in the interplanetary magnetic field
with associated solar wind velocity spikes. They have been observed
by numerous missions (Wind, Ulysses, Solar Orbiter) but are most
remarkable in Parker Solar Probe data below 0.3 AU. Their origin is
still debated and scenarii include interchange reconnection near the
solar surface, propagation of alfvenic waves and turbulence driven
phenomena. In this work we present a statistical analysis that aims
to investigate a possible preferential orientation of the magnetic
switchbacks in the tangential direction of the RTN frame. We compare
the magnetic field orientation to the local Parker spiral direction
over all the encounters that are available to date. We find that
over several days, no obvious preferential direction arises. By
contrast, at temporal scales of several hours to a day, we frequently
find patches of switchback that display a systematic deflection in
one direction. These unidirectional patches are observed over all
encounters, and the clearest ones are observed near plasma sheets and
Heliospheric Current Sheet crossings. We discuss how these observations
are most likely consistent with the scenario of interchange reconnection
in the low atmosphere in a context of differential rotation and of the
reconnection process being regulated on supergranulation spatial scales.
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Title: Characteristic Scales of Magnetic Switchback Patches Near
the Sun and Their Possible Association With Solar Supergranulation
and Granulation
Authors: Fargette, Naïs; Lavraud, Benoit; Rouillard, Alexis P.;
Réville, Victor; Dudok De Wit, Thierry; Froment, Clara; Halekas,
Jasper S.; Phan, Tai D.; Malaspina, David M.; Bale, Stuart D.; Kasper,
Justin C.; Louarn, Philippe; Case, Anthony W.; Korreck, Kelly E.;
Larson, Davin E.; Pulupa, Marc; Stevens, Michael L.; Whittlesey,
Phyllis L.; Berthomier, Matthieu
2021ApJ...919...96F Altcode: 2021arXiv210901519F
Parker Solar Probe (PSP) data recorded within a heliocentric radial
distance of 0.3 au have revealed a magnetic field dominated by Alfvénic
structures that undergo large local variations or even reversals
of the radial magnetic field. They are called magnetic switchbacks,
they are consistent with folds in magnetic field lines within a same
magnetic sector and are associated with velocity spikes during an
otherwise calmer background. They are thought to originate either
in the low solar atmosphere through magnetic reconnection processes
or result from the evolution of turbulence or velocity shears in the
expanding solar wind. In this work, we investigate the temporal and
spatial characteristic scales of magnetic switchback patches. We define
switchbacks as a deviation from the nominal Parker spiral direction
and detect them automatically for PSP encounters 1, 2, 4, and 5. We
focus in particular on a 5.1 day interval dominated by switchbacks
during E5. We perform a wavelet transform of the solid angle between
the magnetic field and the Parker spiral and find periodic spatial
modulations with two distinct wavelengths, respectively consistent with
solar granulation and supergranulation scales. In addition we find
that switchback occurrence and spectral properties seem to depend on
the source region of the solar wind rather than on the radial distance
of PSP. These results suggest that switchbacks are formed in the low
corona and modulated by the solar surface convection pattern.
---------------------------------------------------------
Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
2021ExA...tmp...95P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability of
planets orbiting these host stars. Although the magnetic field at the
surface of the Sun is reasonably well characterised by observations,
the information on the magnetic field in the higher atmospheric layers
is mainly indirect. This lack of information hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution
and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
based on a 30 cm telescope that combines high throughput in the
extreme UV with polarimetry to connect the magnetic measurements
of the other two instruments. Placed in a near-Earth orbit, the data
downlink would be maximised, while a location at L4 or L5 would provide
stereoscopic observations of the Sun in combination with Earth-based
observatories. This mission to measure the magnetic field will finally
unlock the driver of the dynamics in the outer solar atmosphere and
thereby will greatly advance our understanding of the Sun and the
heliosphere.
---------------------------------------------------------
Title: Direct evidence for magnetic reconnection at the boundaries
of magnetic switchbacks with Parker Solar Probe
Authors: Froment, C.; Krasnoselskikh, V.; Dudok de Wit, T.;
Agapitov, O.; Fargette, N.; Lavraud, B.; Larosa, A.; Kretzschmar,
M.; Jagarlamudi, V. K.; Velli, M.; Malaspina, D.; Whittlesey, P. L.;
Bale, S. D.; Case, A. W.; Goetz, K.; Kasper, J. C.; Korreck, K. E.;
Larson, D. E.; MacDowall, R. J.; Mozer, F. S.; Pulupa, M.; Revillet,
C.; Stevens, M. L.
2021A&A...650A...5F Altcode: 2021arXiv210106279F
Context. The first encounters of Parker Solar Probe (PSP) with the Sun
revealed the presence of ubiquitous localised magnetic deflections in
the inner heliosphere; these structures, often called switchbacks, are
particularly striking in solar wind streams originating from coronal
holes. <BR /> Aims: We report the direct piece of evidence for magnetic
reconnection occurring at the boundaries of three switchbacks crossed
by PSP at a distance of 45 to 48 solar radii to the Sun during its
first encounter. <BR /> Methods: We analyse the magnetic field and
plasma parameters from the FIELDS and Solar Wind Electrons Alphas and
Protons instruments. <BR /> Results: The three structures analysed all
show typical signatures of magnetic reconnection. The ion velocity
and magnetic field are first correlated and then anti-correlated at
the inbound and outbound edges of the bifurcated current sheets with
a central ion flow jet. Most of the reconnection events have a strong
guide field and moderate magnetic shear, but one current sheet shows
indications of quasi anti-parallel reconnection in conjunction with
a magnetic field magnitude decrease by 90%. <BR /> Conclusions: Given
the wealth of intense current sheets observed by PSP, reconnection at
switchback boundaries appears to be rare. However, as the switchback
boundaries accomodate currents, one can conjecture that the geometry of
these boundaries offers favourable conditions for magnetic reconnection
to occur. Such a mechanism would thus contribute in reconfiguring the
magnetic field of the switchbacks, affecting the dynamics of the solar
wind and eventually contributing to the blending of the structures
with the regular wind as they propagate away from the Sun.
---------------------------------------------------------
Title: Whistler wave occurrence and the interaction with strahl
electrons during the first encounter of Parker Solar Probe
Authors: Jagarlamudi, V. K.; Dudok de Wit, T.; Froment, C.;
Krasnoselskikh, V.; Larosa, A.; Bercic, L.; Agapitov, O.; Halekas,
J. S.; Kretzschmar, M.; Malaspina, D.; Moncuquet, M.; Bale, S. D.;
Case, A. W.; Kasper, J. C.; Korreck, K. E.; Larson, D. E.; Pulupa,
M.; Stevens, M. L.; Whittlesey, P.
2021A&A...650A...9J Altcode: 2021arXiv210106723J
<BR /> Aims: We studied the properties and occurrence of narrowband
whistler waves and their interaction with strahl electrons
observed between 0.17 and 0.26 au during the first encounter of
Parker Solar Probe. <BR /> Methods: We used Digital Fields Board
band-pass filtered (BPF) data from FIELDS to detect the signatures
of whistler waves. Additionally parameters derived from the particle
distribution functions measured by the Solar Wind Electrons Alphas and
Protons (SWEAP) instrument suite were used to investigate the plasma
properties, and FIELDS suite measurements were used to investigate the
electromagnetic (EM) fields properties corresponding to the observed
whistler signatures. <BR /> Results: We observe that the occurrence
of whistler waves is low, nearly ~1.5% and less than 0.5% in the
analyzed peak and average BPF data, respectively. Whistlers occur
highly intermittently and 80% of the whistlers appear continuously
for less than 3 s. The spacecraft frequencies of the analyzed waves
are less than 0.2 electron cyclotron frequency (f<SUB>ce</SUB>). The
occurrence rate of whistler waves was found to be anticorrelated
with the solar wind bulk velocity. The study of the duration of the
whistler intervals revealed an anticorrelation between the duration
and the solar wind velocity, as well as between the duration and the
normalized amplitude of magnetic field variations. The pitch-angle
widths (PAWs) of the field-aligned electron population referred to as
the strahl are broader by at least 12 degrees during the presence of
large amplitude narrowband whistler waves. This observation points
toward an EM wave electron interaction, resulting in pitch-angle
scattering. PAWs of strahl electrons corresponding to the short
duration whistlers are higher compared to the long duration whistlers,
indicating short duration whistlers scatter the strahl electrons better
than the long duration ones. Parallel cuts through the strahl electron
velocity distribution function (VDF) observed during the whistler
intervals appear to depart from the Maxwellian shape typically found
in the near-Sun strahl VDFs. The relative decrease in the parallel
electron temperature and the increase in PAW for the electrons in the
strahl energy range suggests that the interaction with whistler waves
results in a transfer of electron momentum from the parallel to the
perpendicular direction.
---------------------------------------------------------
Title: Switchbacks: statistical properties and deviations from
Alfvénicity
Authors: Larosa, A.; Krasnoselskikh, V.; Dudok de Wit, T.; Agapitov,
O.; Froment, C.; Jagarlamudi, V. K.; Velli, M.; Bale, S. D.; Case,
A. W.; Goetz, K.; Harvey, P.; Kasper, J. C.; Korreck, K. E.; Larson,
D. E.; MacDowall, R. J.; Malaspina, D.; Pulupa, M.; Revillet, C.;
Stevens, M. L.
2021A&A...650A...3L Altcode: 2020arXiv201210420L
Context. Parker Solar Probe's first solar encounter has revealed the
presence of sudden magnetic field deflections in the slow Alfvénic
solar wind. These structures, which are often called switchbacks,
are associated with proton velocity enhancements. <BR /> Aims: We
study their statistical properties with a special focus on their
boundaries. <BR /> Methods: Using data from SWEAP and FIELDS,
we investigate particle and wavefield properties. The magnetic
boundaries are analyzed with the minimum variance technique. <BR
/> Results: Switchbacks are found to be Alfvénic in 73% of cases
and compressible in 27%. The correlations between magnetic field
magnitude and density fluctuations reveal the existence of both
positive and negative correlations, and the absence of perturbations
in the magnetic field magnitude. Switchbacks do not lead to a magnetic
shear in the ambient field. Their boundaries can be interpreted in
terms of rotational or tangential discontinuities. The former are more
frequent. <BR /> Conclusions: Our findings provide constraints on the
possible generation mechanisms of switchbacks, which have to be able
to also account for structures that are not purely Alfvénic. One
of the possible candidates, among others, manifesting the described
characteristics is the firehose instability.
---------------------------------------------------------
Title: Why switchbacks may be related to solar granulation
Authors: Fargette, Naïs; Lavraud, Benoit; Rouillard, Alexis; Réville,
Victor; Phan, Tai; Bale, Stuart D.; Dudok De Wit, Thierry; Froment,
Clara; Kasper, Justin; Halekas, Jasper S.; Louarn, Philippe; Case,
Anthony W.; Korreck, Kelly E.; Larson, Davin E.; Malaspina, David;
Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis L.; Berthomier,
Matthieu
2021EGUGA..2315707F Altcode:
Parker Solar Probe data below 0.3 AU have revealed a near-Sun magnetic
field dominated by Alfvénic structures that display back and forth
reversals of the radial magnetic field. They are called magnetic
switchbacks, they display no electron strahl variation consistent
with magnetic field foldings within the same magnetic sector,
and are associated with velocity spikes during an otherwise calmer
background. They are thought to originate either at the photosphere
through magnetic reconnection processes, or higher up in the corona
and solar wind through turbulent processes.In this work, we analyze
the spatial and temporal characteristic scales of these magnetic
switchbacks. We define switchbacks as a deviation from the parker
spiral direction and detect them automatically through perihelia
encounters 1 to 6. We analyze the solid angle between the magnetic
field and the parker spiral both over time and space. We perform a
fast Fourier transformation to the obtained angle and find a periodical
spatial variation with scales consistent with solar granulation. This
suggests that switchbacks form near the photosphere and may be caused,
or at least modulated, by solar convection.
---------------------------------------------------------
Title: Long-period EUV Pulsations & Coronal Rain: Multi-scale
manifestations of thermal non-equilibrium in the Solar atmosphere
Authors: Froment, Clara
2021cosp...43E.961F Altcode:
Solar coronal loops are the building blocks of the solar corona. They
can be observed in X-ray and extreme ultraviolet (EUV), revealing
the high plasma temperature (1 MK - 10 MK) of the corona. However,
it is still a matter of debate how the magnetic energy is dissipated
to heat the coronal plasma. In order to properly differentiate between
heating mechanisms, the location and frequency of the energy deposition,
in particular, must be properly constrained. We know from numerical
simulations that a heating that is quasi-steady and concentrated toward
the loop footpoints can lead to a state of thermal non-equilibrium. This
physical process can lead to the formation of cool material in the
hot solar corona, in the form of coronal condensations (T ~ 0,1 MK -
0,01 MK). The discovery of ubiquitous long-period EUV pulsations in the
solar corona and in particular in solar coronal loops, with SOHO and
then SDO, have brought a renewed attention on the importance of thermal
non-equilibrium in the solar atmosphere. I will give an overview of the
latest developments, on both observations and modelling of long-period
EUV pulsations in coronal loops and their relationship with coronal
rain events. I will show in particular that they are two aspects of the
same phenomenon and why understanding the characteristics of thermal
non-equilibrium cycles is essential to understand the circulation of
mass and energy in the corona.
---------------------------------------------------------
Title: Whistler wave properties during PSP encounter 1 - First
results from SCM cross spectral data
Authors: Froment, Clara; Dudok De Wit, Thierry; Krasnoselskikh,
Vladimir; Malaspina, David; Agapitov, Oleksiy
2021cosp...43E.938F Altcode:
Whistler waves were widely observed during the first solar encounters of
Parker Solar Probe. The interaction of these electromagnetic waves with
the Strahl electrons is known to affect the heat flux and PSP brings
the first opportunity to study them in the young solar wind. We present
several examples of whistler waves analysis observed during PSP's
1st encounter. We mainly use cross spectra (full spectral matrices)
of the magnetic field, as measured by the Search-Coil Magnetometer
(SCM) that is part of the FIELDS experiment. These cross-spectra cover
the 20 Hz - 4.5 kHz frequency band. We combine some of them with the
waveforms measurements in order to check the calibrations. For these few
selected cases, we demonstrate the determination of the wave properties
(planarity, ellipticity, polarization) from these data, and connect
these properties to their signatures in the electric field (EFI electric
field antennas). We eventually determine the wave characteristics
using the solar wind magnetic field (MAG Fluxgate Magnetometer) and
density from QTN (Quasi-Thermal Noise from FIELDS) and SWEAP.
---------------------------------------------------------
Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
2021arXiv210101566P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.
---------------------------------------------------------
Title: Whistler Waves in the Young Solar Wind: Properties, Origin,
and Consequences for Particles
Authors: Agapitov, O. V.; Dudok de Wit, T.; Drake, J. F.; Swisdak,
M.; Malaspina, D.; Mozer, F.; Froment, C.; Krasnoselskikh, V.; Bale,
S. D.; Bonnell, J. W.; Chaston, C. C.; Case, A. W.; Goetz, K.; Kasper,
J. C.; Korreck, K. E.; Larson, D.; Livi, K.; MacDowall, R. J.; Pulupa,
M.; Stevens, M. L.; Whittlesey, P. L.; Wygant, J. R.
2020AGUFMSH025..08A Altcode:
Observations by the Parker Solar Probe mission of the solar wind at
about 35 solar radii reveal the existence of whistler wave packets with
frequencies below 0.1fce (20-150 Hz in the spacecraft frame). These
waves bursts often coincide with local minima of the magnetic field
magnitude observed in the vicinity of the switchbacks boundaries. The
Poynting flux indicates sunward propagation that leads to a significant
Doppler frequency downshift from 200-300 Hz to 20-80 Hz (from 0.2fce to
0.5fce). The polarization of these waves varies from quasi-parallel to
significantly oblique. Their peak amplitude can be as large as 1-4 nT
(up to 20% of the background magnetic field magnitude). The generation
of these waves is supported by the modified electron distribution
with increased transverse temperature anisotropy inside the magnetic
hole. Sunward propagating whistler waves scatter the high energy solar
wind electrons in the energy range up to 1 keV and potentially play a
significant role in breaking the heat flux and scattering the Strahl
population of suprathermal electrons into a halo population.
---------------------------------------------------------
Title: Whistler wave properties and their occurrence during the
Parker Solar Probe's 1st and 2nd encounter
Authors: Jagarlamudi, V. K.; Dudok de Wit, T.; Froment, C.;
Krasnoselskikh, V.; Larosa, A.; Malaspina, D.; Agapitov, O. V.;
Bercic, L.; Issautier, K.; Kretzschmar, M.; Liu, M.; Moncuquet, M.;
Bale, S. D.; Case, A. W.; Kasper, J. C.; Larson, D.; Korreck, K. E.;
Stevens, M. L.; Whittlesey, P. L.
2020AGUFMSH052..06J Altcode:
We present the analysis of narrow-band whistler wave signatures
observed between the lower-hybrid and half of the electron cyclotron
frequency during the 1st and 2nd encounters of Parker Solar Probe
(PSP). These whistlers are identified using the band-pass filter data
from the Digital Fields Board on the PSP. We find that nearly 85% of
the whistlers are observed for less than three seconds consecutively,
the probability of occurrence of long-consecutive (> 60 s) whistler
intervals are rare. Using both the peak and mean band-pass filter data
we show that whistler waves occur intermittently and the majority of
the whistlers are of low amplitudes and occur for a short period (<
0.1 s). We investigate the dependence of the occurrence of whistlers and
their amplitudes with respect to different proton and electron plasma
parameters and with respect to magnetic field deflections. Several of
the observed whistler features are in line with the previous Helios
observations. We infer that the slower the velocity of the wind is,
the higher the occurrence of whistlers is.
---------------------------------------------------------
Title: Performances and First Results from the RPW/Search Coil
Magnetometer onboard Solar Orbiter
Authors: Kretzschmar, M.; Krasnoselskikh, V.; Dudok de Wit, T.;
Froment, C.; Jean-Yves, B.; Jannet, G.; Le Contel, O.; Maksimovic, M.;
Chust, T.; Soucek, J.; Vecchio, A.; Bale, S. D.; Khotyaintsev, Y.;
Lorfevre, E.; Plettemeier, D.; Steller, M.; Stverak, S.; Travnicek,
P.; Vaivads, A.
2020AGUFMSH0360021K Altcode:
The Search Coil Magnetometer (SCM) onboard Solar Orbiter is part of the
Radio and Plasma Waves (RPW) experiment. It measures magnetic field
fluctuations in the frequency range from a few Hz to 50 kHz on three
axes and between 1 kHz and 1MHz in one axis. RPW has been working nearly
continuously and SCM has recorded many interesting features, including
whistler and other types of waves as well as local characteristics of
turbulence. We will provide an overview of these observations as well
as a description of the in flight performances of SCM.
---------------------------------------------------------
Title: Whistler wave properties during PSP's encounter 1 - First
results from SCM cross-spectral data
Authors: Froment, C.; Krasnoselskikh, V.; Agapitov, O. V.; Dudok de
Wit, T.; Malaspina, D.; Jagarlamudi, V. K.; Kretzschmar, M.; Larosa,
A.; Bale, S. D.; Bonnell, J. W.; Case, A. W.; Goetz, K.; Kasper,
J. C.; Korreck, K. E.; Larson, D. E.; Livi, R.; MacDowall, R. J.;
Moncuquet, M.; Mozer, F.; Pulupa, M.; Revillet, C.; Stevens, M. L.;
Whittlesey, P. L.
2020AGUFMSH0490017F Altcode:
Whistler waves were widely observed during the first solar encounters
of Parker Solar Probe. The interaction of these electromagnetic waves
with the strahl electrons is known to affect the heat flux and PSP
brings the first opportunity to study them in the young solar wind. We
present several examples of whistler wave analysis during PSP's 1st
encounter. We mainly use cross spectra (full spectral matrices from 20
Hz - 4.5 kHz) of the magnetic field, as measured by the Search-Coil
Magnetometer (SCM) that is part of the FIELDS experiment. <P />In
this study, we 1) check the spectral matrices by comparing them
to waveforms (for the few low-frequency whistlers), 2) determine
their wave properties (planarity, ellipticity, polarization) and 3)
connect these properties to their signatures in the electric field
(EFI electric field antennas) and 4) eventually determine the wave
characteristics using the solar wind magnetic field (MAG Fluxgate
Magnetometer) and density from QTN (Quasi-Thermal Noise from FIELDS)
and SWEAP observations.
---------------------------------------------------------
Title: Switchbacks: statistical properties and deviation from
alfvenicity
Authors: Larosa, A.; Krasnoselskikh, V.; Dudok de Wit, T.; Agapitov,
O. V.; Froment, C.; Jagarlamudi, V. K.; Bale, S.; Bonnell, J. W.; Case,
A. W.; Goetz, K.; Harvey, P.; Kasper, J. C.; Korreck, K. E.; Larson,
D. E.; Livi, R.; MacDowall, R. J.; Malaspina, D.; Moncuquet, M.;
Mozer, F.; Pulupa, M.; Revillet, C.; Stevens, M. L.; Whittlesey, P. L.
2020AGUFMSH054..07L Altcode:
Switchbacks are probably the most prominent features observed by Parker
Solar Probe during its first encounter with the Sun. These magnetic
structures with reversed polarity have well defined boundaries, higher
proton velocity with respect to the surrounding plasma, enhanced wave
activity inside the structures and at the boundaries. Their duration
varies from a few seconds to tens of minutes. <P />We present an
extensive statistical study of their properties, with a particular
focus on their boundaries: orientation, type of discontinuity,
presence of wave activity, velocity orientation with respect to
the boundaries, and Poynting flux. We show that even though they are
commonly considered as Alfvénic structures a small percentage of them
show slow and fast mode-like correlations between the magnetic field
and the proton density.
---------------------------------------------------------
Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.
---------------------------------------------------------
Title: Localized Magnetic-field Structures and Their Boundaries in
the Near-Sun Solar Wind from Parker Solar Probe Measurements
Authors: Krasnoselskikh, V.; Larosa, A.; Agapitov, O.; de Wit,
T. Dudok; Moncuquet, M.; Mozer, F. S.; Stevens, M.; Bale, S. D.;
Bonnell, J.; Froment, C.; Goetz, K.; Goodrich, K.; Harvey, P.; Kasper,
J.; MacDowall, R.; Malaspina, D.; Pulupa, M.; Raouafi, N.; Revillet,
C.; Velli, M.; Wygant, J.
2020ApJ...893...93K Altcode: 2020arXiv200305409K
One of the discoveries of the Parker Solar Probe during its first
encounters with the Sun is ubiquitous presence of relatively
small-scale structures standing out as sudden deflections of the
magnetic field. They were named "switchbacks" since some of them show
a full reversal of the radial component of the magnetic field and
then return to "regular" conditions. We carried out an analysis of
three typical switchback structures having different characteristics:
I. Alfvénic structure, where the variations of the magnetic field
components take place while conserving the magnitude of the magnetic
field; II. Compressional structure, where the magnitude of the field
varies together with changes of its components; and III. Structure
manifesting full reversal of the magnetic field, presumably Alfvén,
which is an extremal example of a switchback. We analyzed the
properties of the magnetic fields of these structures and of their
boundaries. Observations and analyses lead to the conclusion that
they represent localized twisted magnetic tubes moving with respect
to surrounding plasma. An important feature is the existence of a
relatively narrow boundary layer at the surface of the tube that
accommodates flowing currents. These currents are closed on the
surface of the structure and typically have comparable azimuthal and
tube-axis-aligned components. They are supported by the presence of an
effective electric field due to strong gradients of the density and ion
plasma pressure. The ion beta is typically larger inside the structure
than outside. The surface of the structure may also accommodate
electromagnetic waves that assist particles in carrying currents.
---------------------------------------------------------
Title: Sunward-propagating Whistler Waves Collocated with Localized
Magnetic Field Holes in the Solar Wind: Parker Solar Probe
Observations at 35.7 R<SUB>⊙</SUB> Radii
Authors: Agapitov, O. V.; Dudok de Wit, T.; Mozer, F. S.; Bonnell,
J. W.; Drake, J. F.; Malaspina, D.; Krasnoselskikh, V.; Bale, S.;
Whittlesey, P. L.; Case, A. W.; Chaston, C.; Froment, C.; Goetz,
K.; Goodrich, K. A.; Harvey, P. R.; Kasper, J. C.; Korreck, K. E.;
Larson, D. E.; Livi, R.; MacDowall, R. J.; Pulupa, M.; Revillet, C.;
Stevens, M.; Wygant, J. R.
2020ApJ...891L..20A Altcode: 2020arXiv200209837A
Observations by the Parker Solar Probe mission of the solar wind at
∼35.7 solar radii reveal the existence of whistler wave packets
with frequencies below 0.1 f<SUB>ce</SUB> (20-80 Hz in the spacecraft
frame). These waves often coincide with local minima of the magnetic
field magnitude or with sudden deflections of the magnetic field
that are called switchbacks. Their sunward propagation leads to
a significant Doppler frequency downshift from 200-300 to 20-80 Hz
(from 0.2 to 0.5 f<SUB>ce</SUB>). The polarization of these waves
varies from quasi-parallel to significantly oblique with wave normal
angles that are close to the resonance cone. Their peak amplitude can
be as large as 2-4 nT. Such values represent approximately 10% of the
background magnetic field, which is considerably more than what is
observed at 1 au. Recent numerical studies show that such waves may
potentially play a key role in breaking the heat flux and scattering
the Strahl population of suprathermal electrons into a halo population.
---------------------------------------------------------
Title: Spectroscopic detection of coronal plasma flows in loops
undergoing thermal non-equilibrium cycles
Authors: Pelouze, Gabriel; Auchère, Frédéric; Bocchialini, Karine;
Froment, Clara; Parenti, Susanna; Soubrié, Elie
2020A&A...634A..54P Altcode: 2019arXiv191202538P
Context. Long-period intensity pulsations were recently detected in
the EUV emission of coronal loops and attributed to cycles of plasma
evaporation and condensation driven by thermal non-equilibrium
(TNE). Numerical simulations that reproduce this phenomenon
also predict the formation of periodic flows of plasma at coronal
temperatures along some of the pulsating loops. <BR /> Aims: We aim
to detect these predicted flows of coronal-temperature plasma in
pulsating loops. <BR /> Methods: We used time series of spatially
resolved spectra from the EUV imaging spectrometer (EIS) onboard
Hinode and tracked the evolution of the Doppler velocity in loops in
which intensity pulsations have previously been detected in images
of SDO/AIA. <BR /> Results: We measured signatures of flows that are
compatible with the simulations but only for a fraction of the observed
events. We demonstrate that this low detection rate can be explained
by line of sight ambiguities combined with instrumental limitations,
such as low signal-to-noise ratio or insufficient cadence. <P
/>Movies associated to Figs. 1, 4, 7, 10 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935872/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Switchbacks in the Near-Sun Magnetic Field: Long Memory and
Impact on the Turbulence Cascade
Authors: Dudok de Wit, Thierry; Krasnoselskikh, Vladimir V.; Bale,
Stuart D.; Bonnell, John W.; Bowen, Trevor A.; Chen, Christopher
H. K.; Froment, Clara; Goetz, Keith; Harvey, Peter R.; Jagarlamudi,
Vamsee Krishna; Larosa, Andrea; MacDowall, Robert J.; Malaspina, David
M.; Matthaeus, William H.; Pulupa, Marc; Velli, Marco; Whittlesey,
Phyllis L.
2020ApJS..246...39D Altcode: 2019arXiv191202856D
One of the most striking observations made by Parker Solar Probe
during its first solar encounter is the omnipresence of rapid polarity
reversals in a magnetic field that is otherwise mostly radial. These
so-called switchbacks strongly affect the dynamics of the magnetic
field. We concentrate here on their macroscopic properties. First,
we find that these structures are self-similar, and have neither a
characteristic magnitude, nor a characteristic duration. Their waiting
time statistics show evidence of aggregation. The associated long memory
resides in their occurrence rate, and is not inherent to the background
fluctuations. Interestingly, the spectral properties of inertial range
turbulence differ inside and outside of switchback structures; in the
latter the 1/f range extends to higher frequencies. These results
suggest that outside of these structures we are in the presence
of lower-amplitude fluctuations with a shorter turbulent inertial
range. We conjecture that these correspond to a pristine solar wind.
---------------------------------------------------------
Title: Multi-scale observations of thermal non-equilibrium cycles
in coronal loops
Authors: Froment, C.; Antolin, P.; Henriques, V. M. J.; Kohutova,
P.; Rouppe van der Voort, L. H. M.
2020A&A...633A..11F Altcode: 2019arXiv191109710F
Context. Thermal non-equilibrium (TNE) is a phenomenon that can
occur in solar coronal loops when the heating is quasi-constant and
highly-stratified. Under such heating conditions, coronal loops undergo
cycles of evaporation and condensation. The recent observations of
ubiquitous long-period intensity pulsations in coronal loops and their
relationship with coronal rain have demonstrated that understanding the
characteristics of TNE cycles is an essential step in constraining
the circulation of mass and energy in the corona. <BR /> Aims:
We report unique observations with the Solar Dynamics Observatory
(SDO) and the Swedish 1-m Solar Telescope (SST) that link the captured
thermal properties across the extreme spatiotemporal scales covered by
TNE processes. <BR /> Methods: Within the same coronal loop bundle,
we captured 6 h period coronal intensity pulsations in SDO/AIA and
coronal rain observed off-limb in the chromospheric Hα and Ca
II K spectral lines with SST/CRISP and SST/CHROMIS. We combined
a multi-thermal analysis of the cycles with AIA and an extensive
spectral characterisation of the rain clumps with the SST. <BR />
Results: We find clear evidence of evaporation-condensation cycles in
the corona which are linked with periodic coronal rain showers. The
high-resolution spectroscopic instruments at the SST reveal the
fine-structured rain strands and allow us to probe the cooling
phase of one of the cycles down to chromospheric temperatures. <BR />
Conclusions: These observations reinforce the link between long-period
intensity pulsations and coronal rain. They also demonstrate the
capability of TNE to shape the dynamics of active regions on the large
scales as well as on the smallest scales currently resolvable. <P
/>Movies associated to Figs. 3-5, and 8 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936717/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: First direct observation of a torsional Alfvén oscillation
at coronal heights
Authors: Kohutova, P.; Verwichte, E.; Froment, C.
2020A&A...633L...6K Altcode:
Context. Torsional Alfvén waves are promising candidates for
the transport of energy across different layers of the solar
atmosphere. They have been predicted theoretically for decades. Previous
detections of Alfvén waves so far have however mostly relied
on indirect signatures. <BR /> Aims: We present the first direct
observational evidence of a fully resolved torsional Alfvén oscillation
of a large-scale structure occurring at coronal heights. <BR /> Methods:
We analysed IRIS imaging and spectral observation of a surge resulting
from magnetic reconnection between active region prominence threads and
surrounding magnetic field lines. <BR /> Results: The IRIS spectral
data provide clear evidence of an oscillation in the line-of-sight
velocity with a 180° phase difference between the oscillation
signatures at opposite edges of the surge flux tube. This together
with an alternating tilt in the Si IV and Mg II k spectra across the
flux tube and the trajectories traced by the individual threads of
the surge material provide clear evidence of torsional oscillation of
the flux tube. <BR /> Conclusions: Our observation shows that magnetic
reconnection leads to the generation of large-scale torsional Alfvén
waves. <P />Movies attached to Figs. 1 and 2 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201937144/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Switchbacks in the near-Sun magnetic field: long-range
correlations and impact on the turbulence cascade
Authors: Dudok de Wit, T.; Bale, S.; Bonnell, J. W.; Bowen, T. A.;
Chen, C. H. K.; Froment, C.; Goetz, K.; Harvey, P.; Jagarlamudi,
V. K.; Krasnoselskikh, V.; Larosa, A.; MacDowall, R. J.; Malaspina,
D.; Matthaeus, W. H.; Pulupa, M.; Whittlesey, P. L.
2019AGUFMSH11A..08D Altcode:
One of the most striking observations made by Parker Solar Probe
during its first solar encounter is the omnipresence of rapid polarity
reversals in a magnetic field that is otherwise mostly radial. These
so-called switchbacks, which are associated with radial jets of plasma,
strongly affect the dynamics of the magnetic field. We concentrate
here on their macroscopic properties. <P />First, we find that
these structures are self-similar, and have neither a characteristic
magnitude, not a characteristic duration. The waiting time statistics
shows clear evidence for long-range correlations, with indications
that they are connected deep inside the corona. Interestingly, the
spectral scaling of inertial range turbulence differ when the switchback
structures are included or not in the analysis. These results suggest
that Kolmogorov-like scaling in the magnetic field fluctuations of
the solar wind spectrum is driven by the dynamics of the switchbacks,
and is not intrinsic to the fluctuations in the inner heliosphere.
---------------------------------------------------------
Title: First direct observation of a torsional Alfvén oscillation
at coronal heights
Authors: Kohutova, P.; Verwichte, E.; Froment, C.
2019arXiv191203954K Altcode:
Torsional Alfvén waves are promising candidates for transport of
energy across different layers of the solar atmosphere and have been
theoretically predicted for decades. Previous detections of Alfvén
waves so far have however mostly relied on indirect signatures. We
present a first direct observational evidence of a fully resolved
torsional Alfvén oscillation of a large-scale structure occurring at
coronal heights. We analyse IRIS imaging and spectral observation of
a surge resulting from magnetic reconnection between active region
prominence threads and surrounding magnetic fieldlines. The IRIS
spectral data provides clear evidence of an oscillation in the
line-of-sight velocity with a 180° phase difference between the
oscillation signatures at opposite edges of the surge flux tube. This
together with an alternating tilt in the Si IV and Mg II k spectra
across the flux tube and the trajectories traced by the individual
threads of the surge material provides clear evidence of torsional
oscillation of the flux tube. Our observation shows that magnetic
reconnection leads to the generation of large-scale torsional Alfvén
waves.
---------------------------------------------------------
Title: Formation of coronal rain triggered by impulsive heating
associated with magnetic reconnection
Authors: Kohutova, P.; Verwichte, E.; Froment, C.
2019A&A...630A.123K Altcode: 2019arXiv191007746K
Context. Coronal rain consists of cool plasma condensations
formed in coronal loops as a result of thermal instability. The
standard models of coronal rain formation assume that the heating
is quasi-steady and localised at the coronal loop footpoints. <BR
/> Aims: We present an observation of magnetic reconnection in the
corona and the associated impulsive heating triggering formation
of coronal rain condensations. <BR /> Methods: We analyse combined
SDO/AIA and IRIS observations of a coronal rain event following a
reconnection between threads of a low-lying prominence flux rope and
surrounding coronal field lines. <BR /> Results: The reconnection
of the twisted flux rope and open field lines leads to a release of
magnetic twist. Evolution of the emission of one of the coronal loops
involved in the reconnection process in different AIA bandpasses
suggests that the loop becomes thermally unstable and is subject to
the formation of coronal rain condensations following the reconnection
and that the associated heating is localised in the upper part of the
loop leg. <BR /> Conclusions: In addition to the standard models of
thermally unstable coronal loops with heating localised exclusively
in the footpoints, thermal instability and subsequent formation of
condensations can be triggered by the impulsive heating associated
with magnetic reconnection occurring anywhere along a magnetic
field line. <P />The movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936253/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: The Coronal Monsoon: Thermal Nonequilibrium Revealed by
Periodic Coronal Rain
Authors: Auchère, Frédéric; Froment, Clara; Soubrié, Elie; Antolin,
Patrick; Oliver, Ramon; Pelouze, Gabriel; Voyeux, Alfred
2018csc..confE.114A Altcode:
We report on the discovery of periodic coronal rain in an off-limb
sequence of SDO/AIA images. The showers are co-spatial and in phase
with periodic (6.6 hr) intensity pulsations of coronal loops of the
sort described by Auchère et al. (2014) and Froment et al. (2015,
2017. These new observations make possible a unified description of
both phenomena. Coronal rain and periodic intensity pulsations of loops
are two manifestations of the same physical process: evaporation /
condensation cycles resulting from a state of thermal nonequilibrium
(TNE). The fluctuations around coronal temperatures produce the
intensity pulsations of loops, and rain falls along their legs
if thermal runaway cools the periodic condensations down and below
transition-region (TR)temperatures. This scenario is in line with the
predictions of numerical models of quasi-steadily and footpoint heated
loops. This event of periodic coronal rain is compared with a similar
event showing only pulsations at coronal temperatures but no significant
cool rain fall. For both events we have stereoscopic observations from
the SDO and STEREO spacecraft which allows reconstruction of the 3D loop
geometries. Comparison with numerical simulations suggest that these two
events correspond to two regimes of TNE: one with "full condensations"
(coronal rain) and another in which "incomplete condensations" start
to develop but are pushed down one loop leg before they can reach
chromospheric temperatures. These new observations impose severe
constrains on the spatio-temporal distribution of coronal heating.
---------------------------------------------------------
Title: The Coronal Monsoon: Thermal Nonequilibrium Revealed by
Periodic Coronal Rain
Authors: Auchere, Frederic; Soubrie, Elie; Antolin, Patrick; Froment,
Clara; Oliver, Ramon; Pelouze, Gabriel
2018cosp...42E.144A Altcode:
We report on the discovery of periodic coronal rain in an off-limb
sequence of SDO/AIA images. The showers are co-spatial and in phase
with periodic (6.6 hr) intensity pulsations of coronal loops of the
sort described by Auchère et al. (2014) and Froment et al. (2015,
2017}. These new observations make possible a unified description of
both phenomena. Coronal rain and periodic intensity pulsations of loops
are two manifestations of the same physical process: evaporation /
condensation cycles resulting from a state of thermal nonequilibrium
(TNE). The fluctuations around coronal temperatures produce the
intensity pulsations of loops, and rain falls along their legs
if thermal runaway cools the periodic condensations down and below
transition-region (TR) temperatures. This scenario is in line with the
predictions of numerical models of quasi-steadily and footpoint heated
loops.This event of periodic coronal rain is compared with a similar
event showing only pulsations at coronal temperatures but no significant
cool rain fall. For both events we have stereoscopic observations from
the SDO and STEREO spacecraft which allows reconstruction of the 3D loop
geometries. Comparison with numerical simulations suggest that these two
events correspond to two regimes of TNE: one with "full condensations"
(coronal rain) and another in which "incomplete condensations" start
to develop but are pushed down one loop leg before they can reach
chromospheric temperatures.These new observations impose severe
constrains on the spatio-temporal distribution of coronal heating.
---------------------------------------------------------
Title: Search for predicted periodic flows in loops undergoing
thermal non-equilibrium
Authors: Pelouze, Gabriel; Parenti, Susanna; Bocchialini, Karine;
Soubrie, Elie; Auchere, Frederic; Froment, Clara
2018cosp...42E2623P Altcode:
Long-period intensity pulsations have been recently detected in
coronal loopswith EUV images of both SoHO/EIT (Auchère et al.,
2014) and SDO/AIA (Froment etal., 2015). These pulsations have
been interpreted as resulting from thermalnon-equilibrium (TNE),
thus providing a signature of a highly-stratified andquasi-constant
heating at the loops footpoints (Froment et al., 2017; Auchèreet al.,
2016). Depending on the adequacy between the geometry of the loop
andthe characteristics of the heating, this can result in either
complete (atchromospheric temperatures) or incomplete (> 1 MK)
condensation and evaporationcycles, that are responsible for the
observed intensity pulsations. Using 1Dhydrodynamic simulations,
Froment et al. (2017) were able to reproduce theobserved pulsations,
with incomplete condensation for the active region studiedin their
previous paper. The simulations also predict periodic plasma flowsalong
the loops footpoints, with velocities up to 40 km/s. We try to detect
these flows by using time series of spatially resolved spectrafrom
the EUV spectrometer Hinode/EIS. We systematically search for EIS
datasetsthat correspond to the observation of pulsation events among
the 3000+ thatwere detected in AIA data, between 2010 and 2016. For the
9 datasets that arefound, we derive series of Doppler velocity maps,
which allows us to track theevolution of the plasma velocity in the
loop over several pulsation periods. Wethen compare these data to the
results of previous simulations andobservations. However the expected
pulsations in velocity cannot be identifiedin any of the datasets that
we analysed. We demonstrate that line of sightambiguities, combined
with low signal to noise ratio or lack of time cadence,can explain
this non-detection.
---------------------------------------------------------
Title: On the Occurrence of Thermal Nonequilibrium in Coronal Loops
Authors: Froment, C.; Auchère, F.; Mikić, Z.; Aulanier, G.;
Bocchialini, K.; Buchlin, E.; Solomon, J.; Soubrié, E.
2018ApJ...855...52F Altcode: 2018arXiv180204010F
Long-period EUV pulsations, recently discovered to be common in active
regions, are understood to be the coronal manifestation of thermal
nonequilibrium (TNE). The active regions previously studied with
EIT/Solar and Heliospheric Observatory and AIA/SDO indicated that
long-period intensity pulsations are localized in only one or two
loop bundles. The basic idea of this study is to understand why. For
this purpose, we tested the response of different loop systems, using
different magnetic configurations, to different stratifications and
strengths of the heating. We present an extensive parameter-space study
using 1D hydrodynamic simulations (1020 in total) and conclude that the
occurrence of TNE requires specific combinations of parameters. Our
study shows that the TNE cycles are confined to specific ranges in
parameter space. This naturally explains why only some loops undergo
constant periodic pulsations over several days: since the loop geometry
and the heating properties generally vary from one loop to another in
an active region, only the ones in which these parameters are compatible
exhibit TNE cycles. Furthermore, these parameters (heating and geometry)
are likely to vary significantly over the duration of a cycle, which
potentially limits the possibilities of periodic behavior. This study
also confirms that long-period intensity pulsations and coronal rain are
two aspects of the same phenomenon: both phenomena can occur for similar
heating conditions and can appear simultaneously in the simulations.
---------------------------------------------------------
Title: The Coronal Monsoon: Thermal Nonequilibrium Revealed by
Periodic Coronal Rain
Authors: Auchère, Frédéric; Froment, Clara; Soubrié, Elie; Antolin,
Patrick; Oliver, Ramon; Pelouze, Gabriel
2018ApJ...853..176A Altcode: 2018arXiv180201852A
We report on the discovery of periodic coronal rain in an off-limb
sequence of Solar Dynamics Observatory/Atmospheric Imaging Assembly
images. The showers are co-spatial and in phase with periodic (6.6 hr)
intensity pulsations of coronal loops of the sort described by Auchère
et al. and Froment et al. These new observations make possible a unified
description of both phenomena. Coronal rain and periodic intensity
pulsations of loops are two manifestations of the same physical
process: evaporation/condensation cycles resulting from a state of
thermal nonequilibrium. The fluctuations around coronal temperatures
produce the intensity pulsations of loops, and rain falls along their
legs if thermal runaway cools the periodic condensations down and
below transition-region temperatures. This scenario is in line with
the predictions of numerical models of quasi-steadily and footpoint
heated loops. The presence of coronal rain—albeit non-periodic—in
several other structures within the studied field of view implies that
this type of heating is at play on a large scale.
---------------------------------------------------------
Title: Erratum: “On the Fourier and Wavelet Analysis of Coronal Time
Series” (<A href="https://doi.org/10.3847/0004-637x/825/2/110">2016,
ApJ, 825, 110</A>)
Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.;
Solomon, J.
2017ApJ...838..166A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Long-period Intensity Pulsations in Coronal Loops Explained
by Thermal Non-equilibrium Cycles
Authors: Froment, C.; Auchère, F.; Aulanier, G.; Mikić, Z.;
Bocchialini, K.; Buchlin, E.; Solomon, J.
2017ApJ...835..272F Altcode: 2017arXiv170101309F
In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon
that can occur when the heating is both highly stratified and
quasi-constant. Unambiguous observational identification of TNE
would thus permit us to strongly constrain heating scenarios. While
TNE is currently the standard interpretation of coronal rain, the
long-term periodic evolution predicted by simulations has never been
observed. However, the detection of long-period intensity pulsations
(periods of several hours) has been recently reported with the Solar
and Heliospheric Observatory/EIT, and this phenomenon appears to be very
common in loops. Moreover, the three intensity-pulsation events that we
recently studied with the Solar Dynamics Observatory/Atmospheric Imaging
Assembly (AIA) show strong evidence for TNE in warm loops. In this
paper, a realistic loop geometry from linear force-free field (LFFF)
extrapolations is used as input to 1D hydrodynamic simulations. Our
simulations show that, for the present loop geometry, the heating has
to be asymmetrical to produce TNE. We analyze in detail one particular
simulation that reproduces the average thermal behavior of one of the
pulsating loop bundle observed with AIA. We compare the properties of
this simulation with those deduced from the observations. The magnetic
topology of the LFFF extrapolations points to the presence of sites
of preferred reconnection at one footpoint, supporting the presence
of asymmetric heating. In addition, we can reproduce the temporal
large-scale intensity properties of the pulsating loops. This simulation
further strengthens the interpretation of the observed pulsations as
signatures of TNE. This consequently provides important information
on the heating localization and timescale for these loops.
---------------------------------------------------------
Title: Thermal Non-Equilibrium Revealed by Periodic Pulses of Random
Amplitudes in Solar Coronal Loops
Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.;
Solomon, J.
2016usc..confE.131A Altcode:
We recently detected variations in extreme ultraviolet intensity in
coronal loops repeating with periods of several hours. Models of loops
including stratified and quasi-steady heating predict the development
of a state of thermal non-equilibrium (TNE): cycles of evaporative
upflows at the footpoints followed by falling condensations at the
apex. Based on Fourier and wavelet analysis, we demonstrate that the
observed periodic signals are indeed not signatures of vibrational
modes. Instead, superimposed on the power law expected from the
stochastic background emission, the power spectra of the time series
exhibit the discrete harmonics and continua expected from periodic
trains of pulses of random amplitudes. These characteristics reinforce
our earlier interpretation of these pulsations as being aborted
TNE cycles.
---------------------------------------------------------
Title: Fourier and Wavelet Analysis of Coronal Time Series
Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.;
Solomon, J.
2016usc..confE.130A Altcode:
Using Fourier and wavelet analysis, we critically re-assess the
significance of our detection of periodic pulsations in coronal
loops. We show that the proper identification of the frequency
dependence and statistical properties of the different components of
the power spectra provies a strong argument against the common practice
of data detrending, which tends to produce spurious detections around
the cut-off frequency of the filter. In addition, the white and red
noise models built into the widely used wavelet code of Torrence &
Compo cannot, in most cases, adequately represent the power spectra of
coronal time series, thus also possibly causing false positives. Both
effects suggest that several reports of periodic phenomena should
be re-examined. The Torrence & Compo code nonetheless effectively
computes rigorous confidence levels if provided with pertinent models of
mean power spectra, and we describe the appropriate manner in which to
call its core routines. We recall the meaning of the default confidence
levels output from the code, and we propose new Monte-Carlo-derived
levels that take into account the total number of degrees of freedom
in the wavelet spectra. These improvements allow us to confirm that
the power peaks that we detected have a very low probability of being
caused by noise.
---------------------------------------------------------
Title: Long-period Intensity Pulsations as the Manifestation of the
Heating Stratification and Timescale in Coronal Loops
Authors: Froment, Clara; Auchère, Frédéric; Aulanier, Guillaume;
Mikić, Zoran; Bocchialini, Karine; Buchlin, Eric; Solomon, Jacques
2016usc..confE..47F Altcode:
In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon
that can occur when the heating is both highly-stratified and
quasi-constant. Unambiguous observational identification of TNE
would thus permit to strongly constrain heating scenarios. Up to
now, while TNE is the standard interpretation of coronal rain, it
was not believed to happen commonly in warm coronal loops. Recently,
the detection of long-period intensity pulsations (periods of several
hours) has been reported with SoHO/EIT. This phenomenon appears to be
very common in loops (Auchère et al. 2014). In Froment et al. 2015,
three intensity-pulsation events studied with SDO/AIA, show strong
evidence for TNE in warm loops. We use realistic loop geometries
from LFFF extrapolations for one of these events are used as input
to a 1D hydrodynamic simulation of TNE. A highly-stratified heating
function is chosen to reproduce the observed period of pulsation and
temperature of the loops. With these conditions, the heating function
has to be asymmetric. The magnetic topology of the LFFF extrapolations
points to the presence of sites of preferred reconnection at one
footpoint, supporting the presence of asymmetric heating. We compared
the properties of the simulated loop with the properties deduced
from observations. We found that the 1D hydrodynamic simulation
can reproduce the large temporal scale intensity properties of the
pulsating loops (Froment et al. 2016, submitted). This simulation
further strengthen the interpretation of the observed pulsations as
signatures of TNE. This implies that the heating for these loops is
highly-stratified and that the frequency of the heating events must
be high compared to the typical cooling time.
---------------------------------------------------------
Title: Long-period intensity pulsations as the manifestation of
heating stratification and timescale in solar coronal loops
Authors: Froment, Clara
2016PhDT.......115F Altcode:
Long-period EUV intensity pulsations (periods from 3 to 16 hours)
have been found recently to be very common in the solar corona and
especially in coronal loops. The heating mechanism(s) of solar coronal
loops that generate million-degree plasma and maintain it confined at
this temperature remain unknown. These intensity pulsations (extreme
ultraviolet) provide new constraints for loops models and thus to better
understand coronal loops dynamics and heating. The central topic of
this thesis is to explore the possible physical explanations for this
phenomenon. First, I used a detection code, initially developed for
SoHO/EIT images, on the SDO/AIA archive. I detected thousands of events
in the six years of data, half of them corresponding to active regions
and about the half of whom are identified as corresponding to coronal
loops. I selected three cases of long-period intensity pulsation events
in loops, with a clear detection signal and allowing to scan different
periods. Second, using the six coronal channels of AIA, I made a
detailed study of the thermal structure of these loops. I used both
differential emission measure (DEM) reconstructions and an analysis
of the time-lags between the intensities in the six channels. The
temperature and the density are found to be periodic with a time delay
between these two physical parameters of the plasma. This behavior is
characteristic of evaporation and condensation cycles of the plasma
and it allowed me to connect these intensity pulsations to thermal
non-equilibrium (TNE), a well-know phenomenon in numerical simulations
and for structures such as prominences and coronal rain. Moreover, an
analysis based only on the shape of power spectra allowed to confirm
this conclusion. TNE happens when the heating is highly-stratified
(mainly concentrated at low altitudes) and quasi-constant. Unambiguous
identification of TNE in coronal loops has thus important implications
for understanding coronal heating. Third, I aimed at reproducing the
observed intensity pulsations by simulations and at determining the
intrinsic properties of coronal loops that favor these particular cycles
of evolution. I made extrapolations of the magnetic field for the three
regions studied to determine the loops geometry. These geometries have
been then used as inputs for 1D hydrodynamic simulations. I conducted
a parameter space study that revealed that the TNE cycles occurrence is
sensitive to a combination of the loop geometry and heating parameters
(asymmetry and heating power). This allows me to explain why these
pulsations are encountered in some loops but not in all. I studied
one simulation in particular, matching the observed characteristics
of the plasma evolution. I derived the corresponding AIA synthetic
intensities which reproduced the main characteristics of the observed
pulsations. This model allows me to explain the observed pulsations
as evaporation and condensation cycles.
---------------------------------------------------------
Title: Thermal Non-equilibrium Revealed by Periodic Pulses of Random
Amplitudes in Solar Coronal Loops
Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.;
Solomon, J.
2016ApJ...827..152A Altcode: 2016arXiv160803789A
We recently detected variations in extreme ultraviolet intensity in
coronal loops repeating with periods of several hours. Models of loops
including stratified and quasi-steady heating predict the development
of a state of thermal non-equilibrium (TNE): cycles of evaporative
upflows at the footpoints followed by falling condensations at the
apex. Based on Fourier and wavelet analysis, we demonstrate that the
observed periodic signals are indeed not signatures of vibrational
modes. Instead, superimposed on the power law expected from the
stochastic background emission, the power spectra of the time series
exhibit the discrete harmonics and continua expected from periodic
trains of pulses of random amplitudes. These characteristics reinforce
our earlier interpretation of these pulsations as being aborted
TNE cycles.
---------------------------------------------------------
Title: On the Fourier and Wavelet Analysis of Coronal Time Series
Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.;
Solomon, J.
2016ApJ...825..110A Altcode: 2016arXiv160605251A
Using Fourier and wavelet analysis, we critically re-assess the
significance of our detection of periodic pulsations in coronal
loops. We show that the proper identification of the frequency
dependence and statistical properties of the different components of the
power spectra provides a strong argument against the common practice
of data detrending, which tends to produce spurious detections around
the cut-off frequency of the filter. In addition, the white and red
noise models built into the widely used wavelet code of Torrence &
Compo cannot, in most cases, adequately represent the power spectra of
coronal time series, thus also possibly causing false positives. Both
effects suggest that several reports of periodic phenomena should
be re-examined. The Torrence & Compo code nonetheless effectively
computes rigorous confidence levels if provided with pertinent models of
mean power spectra, and we describe the appropriate manner in which to
call its core routines. We recall the meaning of the default confidence
levels output from the code, and we propose new Monte-Carlo-derived
levels that take into account the total number of degrees of freedom
in the wavelet spectra. These improvements allow us to confirm that
the power peaks that we detected have a very low probability of being
caused by noise.
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Title: Evidence for Evaporation-incomplete Condensation Cycles in
Warm Solar Coronal Loops
Authors: Froment, C.; Auchère, F.; Bocchialini, K.; Buchlin, E.;
Guennou, C.; Solomon, J.
2015ApJ...807..158F Altcode: 2015arXiv150408129F
Quasi-constant heating at the footpoints of loops leads to evaporation
and condensation cycles of the plasma: thermal non-equilibrium
(TNE). This phenomenon is believed to play a role in the formation
of prominences and coronal rain. However, it is often discounted
as being involved in the heating of warm loops because the
models do not reproduce observations. Recent simulations have
shown that these inconsistencies with observations may be due to
oversimplifications of the geometries of the models. In addition,
our recent observations reveal that long-period intensity pulsations
(several hours) are common in solar coronal loops. These periods are
consistent with those expected from TNE. The aim of this paper is to
derive characteristic physical properties of the plasma for some of
these events to test the potential role of TNE in loop heating. We
analyzed three events in detail using the six EUV coronal channels
of the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We
performed both a differential emission measure (DEM) and a time-lag
analysis, including a new method to isolate the relevant signal from
the foreground and background emission. For the three events, the DEM
undergoes long-period pulsations, which is a signature of periodic
heating even though the loops are captured in their cooling phase,
as is the bulk of the active regions. We link long-period intensity
pulsations to new signatures of loop heating with strong evidence for
evaporation and condensation cycles. We thus simultaneously witness
widespread cooling and TNE. Finally, we discuss the implications of
our new observations for both static and impulsive heating models.
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Title: Observations and possible interpretations of very long period
intensity pulsations in solar coronal loops
Authors: Froment, Clara; Solomon, Jacques; Buchlin, Eric; Bocchialini,
Karine; Auchere, Frederic; Guennou, Chloe
2014cosp...40E.903F Altcode:
We discovered that intensity pulsations with periods ranging from 3
to 16 hours are common in solar coronal loops. Initially developed
for EIT/SOHO 195 nm images, the automatic detection algorithm is now
running on AIA/SDO data and allows detection of pulsation events in
six coronal bands simultaneously. From may 2010 to december 2013, we
detected more than 2000 events in the 6 EUV bands. We focus our study
on pulsations in active regions and in particular in solar coronal
loops where most of events are detected. A multi-wavelength analysis
of some characteristic events is presented to help understand their
physical nature. We perform a Differential Emission Measure analysis
on AIA time series in order to determine the temporal variations of the
thermal structure of the pulsating loops. This analysis gives important
clues to investigate possible physical interpretations in particular in
term of small perturbations of loops in static equilibrium and to study
how this can constraint coronal heating models. We will also compare
our observations to the results of a MHD turbulence and heating model
of coronal loops.