Role of hard X-ray emission in ionospheric D-layer disturbances during solar flares

Any disturbance of the ionosphere may affect operational activities based on HF communication. The electron density is a critical parameter that controls levels of HF-signal absorption. A significant part of the HF absorption takes place in the D-layer. The increase of X radiations during solar flares generates noticeable perturbations of the electron density of the D-layer. However, the ionosphere reacts with some delay to the solar forcing. Several studies have addressed this question of ionospheric sluggishness from the time delay between VLF narrow-band transmissions and soft X-ray emissions during solar flares. Our study initially considers the interpretation of the VLF amplitude time profile. In particular, we show that the maximum of X-ray emission can be associated with a reversal in the VLF amplitude variation with time, i.e. exhibiting a peak or a trough. Then, building on this insight, we perform estimates of the time delay between VLF and soft X-rays during 67 events between 2017 and 2021, thus including the major flares of 2017. We show that the time delay can become negative for flares above X2, proving that soft X-rays are not the initial source of ionization in the case of major flares. From a careful analysis of RHESSI data for some events of September 2017, we demonstrate that radiation above 40 keV (i.e. hard X-rays) is an important forcing source of the ionosphere. This is of crucial interest in the frame of space weather forecasting since the hard X-rays are produced several minutes before the peak of soft X-rays

STEREO database of interplanetary Langmuir electric waveforms

International audienceThis paper describes a database of electric waveforms that is available at the Centre de Données de la Physique des Plasmas (CDPP, http://cdpp.eu/). This database is specifically dedicated to waveforms of Langmuir/Z-mode waves. These waves occur in numerous kinetic processes involving electrons in space plasmas. Statistical analysis from a large data set of such waves is then of interest, e.g., to study the relaxation of high-velocity electron beams generated at interplanetary shock fronts, in current sheets and magnetic reconnection region, the transfer of energy between high and low frequencies, the generation of electromagnetic waves. The Langmuir waveforms were recorded by the Time Domain Sampler (TDS) of the WAVES radio instrument on board the STEREO mission. In this paper, we detail the criteria used to identify the Langmuir/Z-mode waves among the whole set of waveforms of the STEREO spacecraft. A database covering the November 2006 to August 2014 period is provided. It includes electric waveforms expressed in the normalized frame inline image with B and Vsw the local magnetic field and solar wind velocity vectors, and the local magnetic field in the variance frame, in an interval of ±1.5 min around the time of the Langmuir event. Quicklooks are also provided that display the three components of the electric waveforms together with the spectrum of E∥, together with the magnitude and components of the magnetic field in the 3 min interval, in the variance frame. Finally, the distribution of the Langmuir/Z-mode waves peak amplitude is also analyzed

The relativistic solar particle event on 28 October 2021: Evidence of particle acceleration within and escape from the solar corona

Aims. We analyse particle, radio, and X-ray observations during the first relativistic proton event of solar cycle 25 detected on Earth. The aim is to gain insight into the relationship between relativistic solar particles detected in space and the processes of acceleration and propagation in solar eruptive events.Methods. To this end, we used ground-based neutron monitor measurements of relativistic nucleons and space-borne measurements of electrons with similar speed to determine the arrival times of the first particles at 1 AU and to infer their solar release times. We compared the release times with the time histories of non-thermal electrons in the solar atmosphere and their escape to interplanetary space, as traced by radio spectra and X-ray light curves and images.Results. Non-thermal electrons in the corona are found to be accelerated in different regions. Some are confined in closed magnetic structures expanding during the course of the event. Three episodes of electron escape to the interplanetary space are revealed by groups of decametric-to-kilometric type III bursts. The first group appears on the low-frequency side of a type II burst produced by a coronal shock wave. The two latter groups are accompanied at higher frequencies by bursts with rapid drifts to both lower and higher frequencies (forward- or reverse-drifting bursts). They are produced by electron beams that propagate both sunward and anti-sunward. The first relativistic electrons and nucleons observed near Earth are released with the third group of type III bursts, more than ten minutes after the first signatures of non-thermal electrons and of the formation of the shock wave in the corona. Although the eruptive active region is near the central meridian, several tens of degrees east of the footpoint of the nominal Parker spiral to the Earth, the kilometric spectrum of the type III bursts and the in situ detection of Langmuir waves demonstrate a direct magnetic connection between the L1 Lagrange point and the field lines onto which the electron beams are released at the Sun.Conclusions. We interpret the forward- and reverse-drifting radio bursts as evidence of reconnection between the closed expanding magnetic structures of an erupting flux rope and ambient open magnetic field lines. We discuss the origin of relativistic particles near the Earth across two scenarios: (1) acceleration at the CME-driven shock as it intercepts interplanetary magnetic field lines rooted in the western solar hemisphere and (2) an alternative where the relativistic particles are initially confined in the erupting magnetic fields and get access to the open field lines to the Earth through these reconnection events.</p

Accumulation of Polychlorinated Biphenyls in Adipocytes: Selective Targeting to Lipid Droplets and Role of Caveolin-1

Background : Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that preferentially accumulate in lipid-rich tissues of contaminated organisms. Although the adipose tissue constitutes a major intern reservoir of PCBs and recent epidemiological studies associate PCBs to the development of obesity and its related disorders, little is known about the mechanisms involved in their uptake by the adipose tissue and their intracellular localization in fat cells

Flare-related radio emission: a kinetic point-of-view

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Solar activity I: aspects of magnetic activity

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Strong Magnetic field: from theory to observations

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Soleil et microphysique des plasmas naturels

Le mémoire se compose de deux grands chapitres. Le premier traite de mes travaux de recherche et instrumentaux en physique solaire. Il traite notamment des mesures de spectro-polarimétrie dans le domaine visible, appliquées à l'études de l'évolution spatiale et temporelle du champ magnétique des régions actives. Le second chapitre aborde mes travaux en physique des plasma spatiaux. Il présente les aspects de simulations numériques cinétiques (Vlasov) appliqués à l'étude des structures cohérentes observées dans le vent solaire et la magnétosphère terrestre. Il expose également les résultats de l'exploitation des données radio de la mission STEREO

Langmuir waves: a tool to diagnose space plasma

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Coherent electrostatic structures in the solar wind: Observations to Vlasov simulations

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