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The slow solar wind can be separated into at least two different components: a dense, variable wind produced by helmet streamers and a more tenuous and Alfvénic component emitted by coronal holes. Previous studies have shown that the slow Alfvénic wind is associated with enhanced alpha particle abundances, strong proton beams, and large alpha-to-proton temperature ratios: typical properties of the fast wind known to originate from inside large coronal holes. Recent combined in-situ and remote-observation campaigns by the Solar Orbiter mission exploiting the Proton and Alpha particle Sensor (SWA-PAS) can help us to study the relationship between the Alfvénic slow wind and coronal holes. We exploit these latest observations in conjunction with the newly-developed multi-species IRAP Solar Atmospheric Model (ISAM) model to study the coronal conditions that favour the production of an Alfvénic slow wind. ISAM simulates the coupled transport of both neutral and charged particles between the chromosphere and the corona, including a self-consistent treatment of collisional and ionisation processes, as well as detailed energy and heat flux conservation equations. In this study we discuss how the simulated alpha to proton ratios are modulated in response to different coronal heating rates and discuss these simulation results in light of recent Solar Orbiter measurements. The results presented here were funded by the European Research Council through the SLOW SOURCE project grant number DLV-819189.

In order to monitor space weather events and their impacts, ground magnetic field data has proven to be a long-lasting and powerful source of information. For the determination of the impact of solar events it is essential to extract their signatures from the magnetic field signal. However, as the geomagnetic field is a superposition of sources that cover a broad amplitude and frequency spectrum, it is not trivial to isolate storm signatures. The major source is the intrinsically produced magnetic field that changes within years and is called the secular variation. In sub-auroral regions, it is well known that during times of minimum solar forcing the solar quiet current system induces smooth daily variations with strong dependency on season and local time.In this work we apply signal filtering techniques on time-series magnetic data from ground observatories in sub-auroral regions to extract the various sources. We then use these filter outputs to inspect their dependency and sensitivity to solar forcing. Additionally, statistical parameters are sought after to determine storm signatures.

Solar wind interactions with the Earth’s magnetosphere cause geomagnetic storms and thereby induce ionospheric storms. This study investigates the spatio-temporal evolution of the ionospheric Total Electron Content (TEC) during a moderate but long duration storm driven by solar wind high-speed streams (HSSs) and associated co-rotating interaction region (CIR) during 14-21 March 2016. The storm starts with a strong storm sudden commencement (SSC) with a peak close to 19 UT on 14 March 2016. The GNSS/TEC maps are obtained from the Madrigal database. The associated field-aligned currents (FACs) from AMPERE, ionospheric convection maps from SuperDARN, and the O/N2 ratio from TIMED/GUVI are also studied for understanding the physics behind the different features observed in TEC during the storm.The study predominantly focuses on the changes of TEC at high and middle latitudes. The storm induced changes in the TEC were extracted by removing the quiet time background (mean of five quietest days of the month) from the TEC maps. During the initial phase, TEC enhancements and depletions are found mainly at high latitudes within the auroral oval and close to the cusp, plausibly associated with auroral precipitation and variations in the upward and downward field-aligned currents (FACs). After the onset of the main phase, the TEC is enhanced at mid-latitudes and auroral ovals with a maximum of ~10 TECU. Meanwhile, a significant decrease in TEC is observed in the polar cap region. During the main phase, we observe the evolution of a storm-enhanced-density (SED) plume and a transient enhancement of TEC in the polar cap. Later during the storm, a strong TEC depletion at high and middle latitudes is found on the dayside and in the evening sector. The depletion of O/N2 ratio, triggered by Joule heating and atmospheric upwelling, could be a plausible reason for the TEC depletion. The possible physical mechanisms associated with the observed TEC variations will be discussed.

International audience; The geomagnetic field is composed of a variety of sources that act on a wide range of timescales and amplitudes. The separation of magnetic storm effects from quiet variations is needed to accurately quantify impacts of space weather events. The extraction of such quiet contributions within geomagnetic measurements is achieved by the determination of baselines, which, ideally, is done by a simple algorithm which captures quiet sources suitably well, while being applicable to an extensive network of magnetic observatories independent of the period of time. In this work, we apply signal filtering techniques on the horizontal components of geomagnetic field measurements from low- and mid-latitude observatories to determine baselines. The variations within the baseline are investigated for magnetically quiet periods between 1991 and 2019, focusing on long-term trends, seasonal and local time dependencies, and day-to-day variability. The analysis confirms that the contributing quiet sources include the secular variation and the solar quiet (Sq) current system. The non-negligible day-to-day variability, that is typical for Sq in low- and mid-latitudes, is embedded within the baseline. Thus, the filter approach extracts quiet magnetic field variations well. Comparisons with other baseline methods show good agreements. We conclude that the filter approach can be used to determine baselines automatically during magnetically quiet periods without the need of further apriori information and is applicable on a wide network of magnetic observatories. It marks the first step for deriving magnetic indices for (near) real-time space weather applications.

Magnetic storms are caused by the interactions between the solar wind and the Earth’s magnetosphere. Many studies have been carried out for strong magnetic storms. However, moderate or weak storms and their impacts on the ionosphere are less explored. This study investigates the large-scale and mesoscale structures in ionospheric total electron content (TEC) during a moderate storm (Sym-H index minimum: -63 nT) driven by two interacting solar wind high-speed streams (HSSs) and associated co-rotating interaction regions (CIRs) during 14-21 March 2016. For the solar wind, the IMF Bz minimum is -20 nT and the solar wind speed maximum 612 km/s. The long storm starts with a strong storm sudden commencement (SSC) with a peak close to 19 UT on 14 March 2016. The GNSS/TEC maps are obtained from the Madrigal database. The associated field-aligned currents (FACs) from AMPERE, ionospheric convection maps from SuperDARN, and the O/N2 ratio from TIMED/GUVI are also studied for understanding the physics behind.The focus of the study is on the changes of TEC at high and middle latitudes and the possible coupling between the two. To better characterize the changes, we subtract from the TEC maps the quiet time background (13 March 2016). Our analysis shows the different responses of TEC changes during the storm initial, main, and recovery phases. During the initial phase, TEC enhancements and depletions are found mainly at high latitudes within the auroral oval and close to the cusp, plausibly associated with auroral precipitation and variations in the upward and downward field-aligned currents (FACs). After the onset of the main phase, the TEC is enhanced at mid-latitudes with a maximum of ~10 TECU. During the main phase, we observe the evolution of a storm-enhanced-density (SED) plume and a transient enhancement of TEC in the polar cap. During the late main and the recovery phases, a strong TEC depletion at high and middle latitudes is found on the dayside and in the evening sector. The depletion is associated with the decrease of the O/N2 ratio indicating upwelling of the neutral atmosphere. The possible physical mechanisms associated with the observed TEC variations will be discussed.

In order to monitor space weather events and their impacts, ground magnetic field data has proven to be a long-lasting and powerful source of information. For the determination of space weather effects, it is essential to extract and understand the evolution of the quiet-time magnetic field. However, the data shows a high degree of complexity since the Earth’s magnetic field is a superposition of sources that cover a broad amplitude and frequency spectrum. In sub-auroral regions, it is well understood that the solar quiet current system contributes to the quiet signal with smooth patterns that depend on season and local time, having distinct periods of 24 hours and beneath.In this work, we apply signal filtering techniques on time-series magnetic data from ground observatories in sub-auroral regions. In order to extract the solar quiet current contributions, we use its specific periods of 24h and beneath and analyse the results with respect to season, local time, and day-to-day variability between 1991 and 2019. Careful investigations and interpretation of the contributing sources are given, confirming the main contribution to the filtered signal is the solar quiet current system. This implies that the filter approach is able to extract the quiet magnetic field variations and due to its simplicity may be used for real-time determination of the quiet magnetic field, including magnetic baselines.

The IRAP Plasmasphere Ionosphere Model (IPIM) is an ionospheric model which describes the transport equations of ionospheric plasma species along magnetic closed field lines. The development of a new operational version of IPIM as part of the EUHFORIA project to monitor and forecast space weather conditions and hazards includes using in-situ solar wind observations from the OMNI data set, ionospheric radar data of plasma motions from the Super Dual Auroral Radar Network (SuperDARN), and precipitation data from the Ovation model, as inputs to the model. A new conductivity module has also been developed for help in the simulation of geomagnetically induced currents based on a simplified version of IPIM. This model uses the photochemical module of IPIM in place of the fluid module and the full kinetic module, so that inter-hemispheric transport of suprathermal electrons is accounted for in the ion production term. As the main contribution to the conductivities comes from the lower ionosphere (typically below 150km) where the chemistry dominates, neglecting the field-aligned transport contribution in the fluid module does not alter significantly the conductivities. Based on the conductivities, the neutral wind and the electric field, ionospheric horizontal currents are computed. The ionospheric currents are used as an input for the Biot and Savart module to compute the resulting magnetic perturbations at the ground. We present the first results from this version which explores the ionosphere's response to different conditions in different regions in mid and high latitudes.

The IRAP Plasmasphere Ionosphere Model (IPIM) describes the transport equations ofionospheric plasma species along magnetic closed field lines. As input, the previous iterationof IPIM used basic models to provide estimations of the solar wind conditions, convection,and precipitation within the ionosphere. In this presentation, we discuss the development ofa new operational version of IPIM as part of the EUHFORIA project to monitor and forecastspace weather conditions and hazards. The developments of the model include using in-situsolar wind observations from the OMNI data set, ionospheric radar data of plasma motionsfrom the Super Dual Auroral Radar Network (SuperDARN), and precipitation data from theOvation model, as inputs to the model. We present the first results from the latest IPIMversion, focussing on case study coronal mass ejections on 14th December 2006 and 14thJuly 2012 which featured clear magnetic clouds and long-lasting southward magnetic field.For these events, we explore simulations of plasma densities, temperature, and motions,and compare with observations from EISCAT ionospheric radars and ionosonde launches.With these results in mind, we will discuss the skill of using IPIM as a space weatherforecasting and analysis tool.

International audience; We present the first long-term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in-situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60-90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV.

The last 60 years of space exploration have shown that the interplanetary medium is continually perturbed by a myriad of different solar winds and storms that transport solar material across the whole heliosphere. If there is a consensus on the source of the fast solar wind that is known to originate in coronal holes, the question is still largely debated on the origin of the slow solar wind (SSW). The abundance of heavy ions measured in situ provides a precious diagnostic of potential source regions, because the composition is established very low in the solar atmosphere at the interface between the dense chromosphere and the tenuous corona and remains invariant during transport in the collisionless solar wind. The similar composition measured in situ in the SSW and spectroscopically in coronal loops suggests that a significant fraction of the SSW originates as plasma material that was initially trapped along corona loops and subsequently released in the solar wind. The recent observations from the Parker Solar Probe (PSP) mission also provide new insights on the nascent solar wind. A great challenge remains to explain both the composition and bulk properties of the SSW in a self-consistent manner. For this purpose we exploit and develop models with various degrees of complexity. This context constitutes the backbone of this thesis which is structured in four major steps: we begin by presenting a new technique that exploits white-light (WL) observations of the SSW taken from multiple vantage points to constrain global models of the solar atmosphere. We then exploit the first images taken by the Wide-Field Imager for Solar PRobe (WISPR) from inside the solar corona to test our global models at smaller scales because WISPR offers an unprecedented close-up view of the fine structure of streamers and of the nascent SSW. This work provides further evidence for the transient release of plasma trapped in coronal loops into the solar wind that we interpret by exploiting high-resolution magneto-hydro-dynamics (MHD) simulations. Finally we develop and exploit a new multi-species model of coronal loops called the Irap Solar Atmosphere Model (ISAM) to provide an in-depth analysis of the plasma transport mechanisms at play between the chromosphere and the corona. ISAM solves for the coupled transport of the main constituents of the solar wind with minor ions through a comprehensive treatment of collisions as well as partial ionization and radiative cooling/heating mechanisms near the top of the chromosphere. We use this model to study the different mechanisms that can preferentially extract ions according to their first-ionization-potential (FIP), from the chromosphere to the corona. In this process we compare the relative roles of thermal-diffusive effects and the ponderomotive force induced by Alfvén waves in enriching coronal loops with low-FIP elements that could be subsequently expelled in the SSW through the mechanisms discussed in the first part of this thesis.; Les 60 dernières années d'exploration spatiale ont montré que le milieu interplanétaire est continuellement perturbé par une myriade de vents et de tempêtes solaires qui transportent de la matière solaire dans toute l'héliosphère. S'il existe un consensus sur la source du vent solaire rapide dont on sait qu'il provient des trous coronaux, la question de l'origine du vent solaire lent (SSW) est encore largement débattue. L'abondance des ions lourds mesurée in situ fournit un précieux diagnostic des potentielles régions sources, car la composition est établie très bas dans l'atmosphère solaire à l'interface entre la dense chromosphère et la couronne ténue et reste invariable pendant le transport dans le vent solaire sans collisions. La composition similaire mesurée in situ dans le SSW et par spectroscopie dans les boucles coronales suggère qu'une fraction significative du SSW provient de plasma qui a été initialement piégé le long des boucles coronales et ensuite libéré dans le vent solaire. Les observations récentes de la sonde Parker Solar Probe (PSP) fournissent également de nouvelles informations sur le vent solaire naissant. Un grand défi reste à être relevé pour expliquer à la fois la composition et les propriétés macroscopiques du SSW d'une manière autoconsistante. À cette fin, nous exploitons et développons des modèles de différents degrés de complexité. Ce contexte constitue le fil conducteur de cette thèse qui est structurée en quatre grands axes: nous commençons par présenter une nouvelle technique qui exploite les observations en lumière blanche (WL) du SSW prises depuis de multiples points d'observation afin de mieux contraindre les modèles globaux de l'atmosphère solaire. Nous exploitons ensuite les premières images en lumière blanche du télescope Wide-Field Imager for Solar PRobe (WISPR) à bord de PSP, prises depuis l'intérieur de la couronne solaire dans le but de tester nos modèles globaux à des plus petites échelles, car WISPR offre une vue rapprochée inédite de la structure fine des streamers et du SSW encore naissant. Ce travail fournit des preuves supplémentaires d'une éjection intermittente de plasma initiallement piégé dans les boucles coronales, dans le vent solaire que nous interprétons en exploitant des simulations magnéto-hydro-dynamiques (MHD) à haute résolution. Enfin, nous développons et exploitons un nouveau modèle multi-espèces de boucles coronales appelé ISAM (Irap Solar Atmosphere Model) pour fournir une analyse approfondie des mécanismes de transport du plasma en action entre la chromosphère et la couronne. ISAM résout le transport couplé des principaux constituants du vent solaire avec les ions mineurs par un traitement complet des collisions ainsi que des mécanismes d'ionisation partielle et de refroidissement/chauffage radiatif qui sont importants dans la partie haute de la chromosphère. Nous utilisons ce modèle pour étudier les différents mécanismes qui peuvent extraire préférentiellement les ions de la chromosphère vers la couronne, en fonction de leur potentiel de première ionisation (FIP). Dans ce processus, nous comparons les rôles relatifs des effets thermo-diffusifs et de la force ponderomotrice induite par les ondes d'Alfvén dans l'enrichissement des boucles coronales avec des éléments à faible FIP qui pourraient ensuite être expulsés dans le SSW par les mécanismes discutés dans la première partie de cette thèse.