Response of the low ionosphere to X-ray and Lyman-a solar flare emissions

International audience[1] Using soft X-ray measurements from detectors onboard the Geostationary Operational Environmental Satellite (GOES) and simultaneous high-cadence Lyman-a observations from the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy 2 (PROBA2) ESA spacecraft, we study the response of the lower part of the ionosphere, the D region, to seven moderate to medium-size solar flares that occurred in February and March of 2010. The ionospheric disturbances are analyzed by monitoring the resulting sub-ionospheric wave propagation anomalies detected by the South America Very Low Frequency (VLF) Network (SAVNET). We find that the ionospheric disturbances, which are characterized by changes of the VLF wave phase, do not depend on the presence of Lyman-a radiation excesses during the flares. Indeed, Lyman-a excesses associated with flares do not produce measurable phase changes. Our results are in agreement with what is expected in terms of forcing of the lower ionosphere by quiescent Lyman-a emission along the solar activity cycle. Therefore, while phase changes using the VLF technique may be a good indicator of quiescent Lyman-a variations along the solar cycle, they cannot be used to scale explosive Lyman-a emission during flares

The effect of flares on total solar irradiance

Flares are powerful energy releases occurring in stellar atmospheres. Solar flares, the most intense energy bursts in the solar system, are however hardly noticeable in the total solar luminosity. Consequently, the total amount of energy they radiate 1) remains largely unknown and 2) has been overlooked as a potential contributor to variations in the Total Solar Irradiance (TSI), i.e. the total solar flux received at Earth. Here, we report on the detection of the flare signal in the TSI even for moderate flares. We find that the total energy radiated by flares exceeds the soft X-ray emission by two orders of magnitude, with an important contribution in the visible domain. These results have implications for the physics of flares and the variability of our star.Comment: accepted in Nature Physic

HelioSwarm: A Multipoint, Multiscale Mission to Characterize Turbulence

HelioSwarm (HS) is a NASA Medium-Class Explorer mission of the Heliophysics Division designed to explore the dynamic three-dimensional mechanisms controlling the physics of plasma turbulence, a ubiquitous process occurring in the heliosphere and in plasmas throughout the universe. This will be accomplished by making simultaneous measurements at nine spacecraft with separations spanning magnetohydrodynamic and sub-ion spatial scales in a variety of near-Earth plasmas. In this paper, we describe the scientific background for the HS investigation, the mission goals and objectives, the observatory reference trajectory and instrumentation implementation before the start of Phase B. Through multipoint, multiscale measurements, HS promises to reveal how energy is transferred across scales and boundaries in plasmas throughout the universe

Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Temperature Dependence of the Flare Fluence Scaling Exponent

International audienceSolar flares result in an increase of the solar irradiance at all wavelengths. While the distribution of the flare fluence observed in coronal emission has been widely studied and found to scale as , with slightly below 2, the distribution of the flare fluence in chromospheric lines is poorly known. We used the solar irradiance measurements observed by the SDO/EVE instrument at a 10 s cadence to investigate the dependency of the scaling exponent on the formation region of the lines (or temperature). We analyzed all flares above the C1 level since the start of the EVE observations (May 2010) to determine the flare fluence distribution in 16 lines covering a wide range of temperatures, several of which were not studied before. Our results show a weak downward trend with temperature of the scaling exponent of the PDF that reaches from above 2 at lower temperature (a few ) to for hot coronal emission (several ). However, because colder lines also have fainter contrast, we cannot exclude that this behavior is caused by including more noise for smaller flares for these lines. We discuss the method and its limitations and tentatively associate this possible trend with the different mechanisms responsible for the heating of the chromosphere and corona during flares

On the energy released in the extreme ultraviolet range by solar flares

International audienceAs the result of different physical processes taking place at various heights in the solar atmosphere, solar flares radiate energy at all wavelengths with different contrast and absolute energy. Because of the lack of simultaneous observations for many flares, the spectral distribution of the flare energy and its dependence on the flare magnitude are still poorly know. In this work, we perform a statistical analysis of many flares observed by the SDO/EVE instrument, which measures the Sun-as-a-star extreme-ultraviolet spectrum with unprecedented temporal and spectral resolution. In particular, we will estimate the energy released in various part sof the EUV spectrum and look at its dependance on the flare magnitude

Caractérisation et Modélisation du flux solaire EUV

he study of solar-terrestrial connections is a challenging science, because of the physical problems it implies and because of its growing impact on our societies, this last point being illustrated by the expansion of the study of space weather. In this context, this work aims to improve the knowledge and the modelling of the solar extreme ultraviolet flux which is the major cause for the existence of the planetary (and in particular terrestrial) ionosphere. An original processing of the measurements of the SUMER spectrometer onboard SOHO allows the retrieval of an important statistic of the solar emission lines intensities emitted in the quiet regions and the coronal holes of the solar atmosphere, during a significant part of the solar cycle. The amount of collected data permits the study of the transition region network and its variation during the solar cycle; no major changes of the cells and network elements structure is found with the activity. Using these results, we compute synthetic spectra through diffential emission measures (DEM) for the 2 regions of the solar atmosphere cited above. The comparison between TIMED/SEE data and a computation based on these 2 synthetic spectra and the one from an active region shows good agreement. Finally, we extend the DEM concept to the whole sun, and compute the solar EUV irradiance spectrum from the measurements of 5 solar lines, for a 100 day period. Comparisons at other wavelengths with the TIMED/SEE data reveal close similarities.L'étude des relations Soleil-Terre est une science en pleine effervescence, tant à cause des problèmes physiques qu'elle souléve que par son impact grandissant sur nos sociétés, ce dernier cas étant illustré par l'émergence de la météorologie de l'espace. Dans ce cadre, cette thèse s'emploie à mieux connaître et modéliser le flux extrême ultraviolet (EUV) solaire, principal créateur de l'ionosphère diurne terrestre et plus généralement planétaire. Un traitement routinier original des mesures du spectromètre SUMER à bord de SOHO permet d'obtenir une statistique considérable sur l'émission des raies EUV dans les régions calmes et les trous coronaux de l'atmosphère solaire, répartie sur une fraction significative du cycle d'activité solaire de onze ans. La quantité de données réduites permet ensuite l'étude du réseau de la zone de transition au cours du cycle, montrant qu'il n'est pas observé de variations importantes de la structure réseau/cellules avec l'activité solaire. En utilisant ces résultats, nous calculons les mesures différentielles d'émissions (DEM), puis les spectres EUV synthétiques pour les 2 composantes de l'atmosphère solaire citées plus haut. La comparaison avec les données TIMED/SEE d'un calcul du flux solaire EUV basé sur ces 2 spectres et sur celui d'une région active rend la démarche convaincante. Nous étendons ensuite le concept de la DEM au soleil entier, et calculons ainsi le flux EUV à partir de la mesure de l'irradiance de 5 raies solaires, sur 100 jours. La comparaison sur l'ensemble du spectre avec les données de TIMED/SEE est encourageante

Solar spectral irradiance variability: what do we (not) know ?

International audienceSolar spectral irradiance is an important driver for the Earth's atmosphere. The irradiance spectrum received by the Earth varies at all time scale and the amplitude of the (relative or absolute) depends strongly on the considered wavelengths. We will make a review of our current knowledge of solar irradiance variability based on observations, models and solar proxy, trying to identify points where no general agreement exists in the community. In more details, we will focus on the cycle and longer-term variations of the spectrum, based on the past and present observations and their agreement with models. We will also discuss the assumption behind the models and how proxy are used to estimate solar irradiance variations in the past. The research leading to these results has received funding from the European Community's Seventh Framework Program (FP7 2012) under grant agreement n • 313188 (SOLID

Le soleil en ligne de mire

International audienceReconnu internationalement pour la très haute technologie de ses instruments de mesure, le LPC2E est à bord de la missionSolar Orbiter pour un long voyage avant l’exploration du proche environnement solaire