explanation      blue bibcodes open ADS page with paths to full text
Author name code: froment
ADS astronomy entries on 2022-09-14
author:"Froment, Clara" 

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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>

---------------------------------------------------------
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 (&gt; 45°) wave normal angles. Even if
  modest, this amount of oblique whistlers could substantially contribute
  to the strahl scattering.

---------------------------------------------------------
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.

---------------------------------------------------------
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 &amp; 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 &amp; 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.,
  &amp; Sheeley, N. R. 1994, ApJ, 430, 399; Fisk, L. A., Zurbuchen,
  T. H., &amp; 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

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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 &amp; 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 (&gt; 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 (&lt;
  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 (&gt; 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 &amp;
  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 &amp; 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 &amp;
  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 &amp; 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: 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.

---------------------------------------------------------
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.