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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 pe and/or its harmonic 2f pe . 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 Bibcode: 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 Bibcode: 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.
Aims: Our goal is to understand why some TNE cycles produce such abundant coronal rain, while others produce little to no rain.
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.
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.

Movie associated to Fig. 5 is available at https://www.aanda.org 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 Bibcode: 2021AGUFMSH34B..08F Altcode: Whistlers waves are electromagnetic waves that are widely present in the solar wind. These waves are a strong candidate for explaining the scattering of the strahl electrons into the halo population and, thus, for regulating the heat flux in the solar wind. Observations by the Parker Solar Probe (PSP) mission of the solar wind at ~35.7 solar radii reveal a significant increase of whistler wave activity (the amplitudes and occurrence rate) in comparison with the observations at 1AU. We present the parameters of whistlers waves in the young solar wind based on the statistical processing of the cross spectra (full spectral matrices) of the magnetic field collected during the first encounter of PSP with the Sun. These data are captured by the 3-components Search-Coil Magnetometer (SCM) and produced by the Digital Fields Board (DFB) that are part of the FIELDS experiment onboard PSP. The SCM provides the cross-spectra measurements in the 20 Hz - 4.5 kHz frequency range covering the full range of whistler waves (0.1-0.9 of the local electron gyrofrequency) at the heliospheric distances from 35 to 59 solar radii. We report on the whistler waves parameters in the young solar wind and present statistics of amplitudes, occurrence rates, and whistler polarization properties compared to the heliospheric distance. It is found in particular that while most of the observed whistlers were quasi-parallel to the background magnetic field (wave normal angle were around 0-30 degrees), a significant part (~10%) of observed waves had oblique (> 45°) wave normal angles. Even if modest, this amount of oblique whistlers could substantially contribute to the strahl scattering. 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 Bibcode: 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 Bibcode: 2021AGUFMSH32B..04K Altcode: The boundaries of coronal holes (CH) may create very favorable conditions for the reconfiguration of the magnetic field. In particular, mid-latitude CHs can be connected with polar CHs. In this case they are known to rotate quasi-rigidly although the photosphere rotates differentially. CH boundaries (CHBs) separate two kinds of areas with different configurations: CHs with open magnetic fields and surrounding quiet Sun with coronal loops. The magnetic reconnection should be necessarily present at CHBs otherwise rigid rotation of CHs could not exist since the surrounding photospheric fields rotate differentially (Wang & Sheeley 1994; Fisk et al. 1999). The process of reconnection may be rather slow, but it necessarily leads to the inter-penetration of plasmas from different origin, from closed and opened field lines. We describe this process kinetically, similarly to (Gurevich, Pariiskaya & Pitaevskii, 1968) and show that the ion distribution functions formed as a result of such mixture of plasmas have shapes very similar to those typically observed in the solar wind (Pilip et al, 1987a,b, Marsch,2012). This process occurs on the heights of the coronal loops thus its further evolution towards larger heights may change important characteristics of these distributions as the magnetic field may decrease significantly faster than 1/r. We show that under certain conditions they may become unstable and several instabilities such as firehose may develop. References Wang, Y. M., & Sheeley, N. R. 1994, ApJ, 430, 399; Fisk, L. A., Zurbuchen, T. H., & Schwadron, N. A. 1999, ApJ, 521, 868; A.L. Gurevich, L.I. Pariiskaya, L.P. Pitaevskii, ZhETF, Vol. 54, No. 3, p. 891, September 1968; W.G. Pilipp, H. Miggenrieder, M.D. Montgomery, K.-H. Mühlhäuser, H. Rosenbauer, R. Schwenn, J. Geophys. Res. 92, 1075--1092 (1987a); W.G. Pilipp, H. Miggenrieder, K.-H. Mühlhäuser, H. Rosenbauer, R. Schwenn, F.M. Neubauer, J. Geophys. Res. 92, 1103--1118 (1987b); Marsch, E., Helios: Evolution of Distribution Functions 0.3--1 AU, Space Sci Rev (2012) 172:23--39 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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.
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.
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.
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/fce), 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. Bibcode: 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.
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.
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.
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.
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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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.
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.
Methods: We analyse the magnetic field and plasma parameters from the FIELDS and Solar Wind Electrons Alphas and Protons instruments.
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%.
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. Bibcode: 2021A&A...650A...9J Altcode: 2021arXiv210106723J
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.
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.
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 (fce). 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. Bibcode: 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.
Aims: We study their statistical properties with a special focus on their boundaries.
Methods: Using data from SWEAP and FIELDS, we investigate particle and wavefield properties. The magnetic boundaries are analyzed with the minimum variance technique.
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.
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 Bibcode: 2021EGUGA..2315707F Altcode: Parker Solar Probe data below 0.3 AU have revealed a near-Sun magnetic field dominated by Alfvénic structures that display back and forth reversals of the radial magnetic field. They are called magnetic switchbacks, they display no electron strahl variation consistent with magnetic field foldings within the same magnetic sector, and are associated with velocity spikes during an otherwise calmer background. They are thought to originate either at the photosphere through magnetic reconnection processes, or higher up in the corona and solar wind through turbulent processes.In this work, we analyze the spatial and temporal characteristic scales of these magnetic switchbacks. We define switchbacks as a deviation from the parker spiral direction and detect them automatically through perihelia encounters 1 to 6. We analyze the solid angle between the magnetic field and the parker spiral both over time and space. We perform a fast Fourier transformation to the obtained angle and find a periodical spatial variation with scales consistent with solar granulation. This suggests that switchbacks form near the photosphere and may be caused, or at least modulated, by solar convection. Title: Long-period EUV Pulsations & Coronal Rain: Multi-scale manifestations of thermal non-equilibrium in the Solar atmosphere Authors: Froment, Clara Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2020AGUFMSH052..06J Altcode: We present the analysis of narrow-band whistler wave signatures observed between the lower-hybrid and half of the electron cyclotron frequency during the 1st and 2nd encounters of Parker Solar Probe (PSP). These whistlers are identified using the band-pass filter data from the Digital Fields Board on the PSP. We find that nearly 85% of the whistlers are observed for less than three seconds consecutively, the probability of occurrence of long-consecutive (> 60 s) whistler intervals are rare. Using both the peak and mean band-pass filter data we show that whistler waves occur intermittently and the majority of the whistlers are of low amplitudes and occur for a short period (< 0.1 s). We investigate the dependence of the occurrence of whistlers and their amplitudes with respect to different proton and electron plasma parameters and with respect to magnetic field deflections. Several of the observed whistler features are in line with the previous Helios observations. We infer that the slower the velocity of the wind is, the higher the occurrence of whistlers is. Title: Performances and First Results from the RPW/Search Coil Magnetometer onboard Solar Orbiter Authors: Kretzschmar, M.; Krasnoselskikh, V.; Dudok de Wit, T.; Froment, C.; Jean-Yves, B.; Jannet, G.; Le Contel, O.; Maksimovic, M.; Chust, T.; Soucek, J.; Vecchio, A.; Bale, S. D.; Khotyaintsev, Y.; Lorfevre, E.; Plettemeier, D.; Steller, M.; Stverak, S.; Travnicek, P.; Vaivads, A. Bibcode: 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. Bibcode: 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.

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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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⊙ 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. Bibcode: 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 fce (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 fce). 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 Bibcode: 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.
Aims: We aim to detect these predicted flows of coronal-temperature plasma in pulsating loops.
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.
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.

Movies associated to Figs. 1, 4, 7, 10 are available at https://www.aanda.org 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. Bibcode: 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. Bibcode: 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.
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.
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.
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.
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.

Movies associated to Figs. 3-5, and 8 are available at https://www.aanda.org Title: First direct observation of a torsional Alfvén oscillation at coronal heights Authors: Kohutova, P.; Verwichte, E.; Froment, C. Bibcode: 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.
Aims: We present the first direct observational evidence of a fully resolved torsional Alfvén oscillation of a large-scale structure occurring at coronal heights.
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.
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.
Conclusions: Our observation shows that magnetic reconnection leads to the generation of large-scale torsional Alfvén waves.

Movies attached to Figs. 1 and 2 are available at https://www.aanda.org 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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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.
Aims: We present an observation of magnetic reconnection in the corona and the associated impulsive heating triggering formation of coronal rain condensations.
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.
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.
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.

The movie associated to Fig. 1 is available at https://www.aanda.org 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 Bibcode: 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 Bibcode: 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 Bibcode: 2018cosp...42E2623P Altcode: Long-period intensity pulsations have been recently detected in coronal loopswith EUV images of both SoHO/EIT (Auchère et al., 2014) and SDO/AIA (Froment etal., 2015). These pulsations have been interpreted as resulting from thermalnon-equilibrium (TNE), thus providing a signature of a highly-stratified andquasi-constant heating at the loops footpoints (Froment et al., 2017; Auchèreet al., 2016). Depending on the adequacy between the geometry of the loop andthe characteristics of the heating, this can result in either complete (atchromospheric temperatures) or incomplete (> 1 MK) condensation and evaporationcycles, that are responsible for the observed intensity pulsations. Using 1Dhydrodynamic simulations, Froment et al. (2017) were able to reproduce theobserved pulsations, with incomplete condensation for the active region studiedin their previous paper. The simulations also predict periodic plasma flowsalong the loops footpoints, with velocities up to 40 km/s. We try to detect these flows by using time series of spatially resolved spectrafrom the EUV spectrometer Hinode/EIS. We systematically search for EIS datasetsthat correspond to the observation of pulsation events among the 3000+ thatwere detected in AIA data, between 2010 and 2016. For the 9 datasets that arefound, we derive series of Doppler velocity maps, which allows us to track theevolution of the plasma velocity in the loop over several pulsation periods. Wethen compare these data to the results of previous simulations andobservations. However the expected pulsations in velocity cannot be identifiedin any of the datasets that we analysed. We demonstrate that line of sightambiguities, combined with low signal to noise ratio or lack of time cadence,can explain this non-detection. Title: On the Occurrence of Thermal Nonequilibrium in Coronal Loops Authors: Froment, C.; Auchère, F.; Mikić, Z.; Aulanier, G.; Bocchialini, K.; Buchlin, E.; Solomon, J.; Soubrié, E. Bibcode: 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 Bibcode: 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” (2016, ApJ, 825, 110) Authors: Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.; Solomon, J. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2016usc..confE.130A Altcode: Using Fourier and wavelet analysis, we critically re-assess the significance of our detection of periodic pulsations in coronal loops. We show that the proper identification of the frequency dependence and statistical properties of the different components of the power spectra provies a strong argument against the common practice of data detrending, which tends to produce spurious detections around the cut-off frequency of the filter. In addition, the white and red noise models built into the widely used wavelet code of Torrence & Compo cannot, in most cases, adequately represent the power spectra of coronal time series, thus also possibly causing false positives. Both effects suggest that several reports of periodic phenomena should be re-examined. The Torrence & Compo code nonetheless effectively computes rigorous confidence levels if provided with pertinent models of mean power spectra, and we describe the appropriate manner in which to call its core routines. We recall the meaning of the default confidence levels output from the code, and we propose new Monte-Carlo-derived levels that take into account the total number of degrees of freedom in the wavelet spectra. These improvements allow us to confirm that the power peaks that we detected have a very low probability of being caused by noise. Title: Long-period Intensity Pulsations as the Manifestation of the Heating Stratification and Timescale in Coronal Loops Authors: Froment, Clara; Auchère, Frédéric; Aulanier, Guillaume; Mikić, Zoran; Bocchialini, Karine; Buchlin, Eric; Solomon, Jacques Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2016ApJ...825..110A Altcode: 2016arXiv160605251A Using Fourier and wavelet analysis, we critically re-assess the significance of our detection of periodic pulsations in coronal loops. We show that the proper identification of the frequency dependence and statistical properties of the different components of the power spectra provides a strong argument against the common practice of data detrending, which tends to produce spurious detections around the cut-off frequency of the filter. In addition, the white and red noise models built into the widely used wavelet code of Torrence & Compo cannot, in most cases, adequately represent the power spectra of coronal time series, thus also possibly causing false positives. Both effects suggest that several reports of periodic phenomena should be re-examined. The Torrence & Compo code nonetheless effectively computes rigorous confidence levels if provided with pertinent models of mean power spectra, and we describe the appropriate manner in which to call its core routines. We recall the meaning of the default confidence levels output from the code, and we propose new Monte-Carlo-derived levels that take into account the total number of degrees of freedom in the wavelet spectra. These improvements allow us to confirm that the power peaks that we detected have a very low probability of being caused by noise. 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. Bibcode: 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 Bibcode: 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.