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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 Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express, which operates between 0.1 and 5.5 MHz, suffered from a complete blackout for 10 days in September 2017 when observing on the nightside (a rare occurrence). Moreover, the Shallow Radar (SHARAD) onboard the Mars Reconnaissance Orbiter, which operates at 20 MHz, also suffered a blackout for three days when operating on both dayside and nightside. We propose that these blackouts are caused by solar energetic particles of few tens of keV and above associated with an extreme space weather event between 10 and 22 September 2017, as recorded by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Numerical simulations of energetic electron precipitation predict that a lower O-2(+) nighttime ionospheric layer of magnitude similar to 10(10) m(-3) peaking at similar to 90-km altitude is produced. Consequently, such a layer would absorb radar signals at high frequencies and explain the blackouts. The peak absorption level is found to be at 70-km altitude. Plain Language Summary Several instrument operations, as well as communication systems with rovers at the surface, depend on radio signals that propagate throughout the atmosphere of Mars. This is the case also for two radars that are currently working in Mars' orbit, sounding the ionosphere, surface, and subsurface of the planet. In mid-September 2017, a powerful solar storm hit Mars, producing a large amount of energetic particle precipitation over a 10-day period. We have found that high-energy electrons ionized the atmosphere of Mars, creating a dense layer of ions and electrons at similar to 90 km on the Martian nightside. This layer attenuated radar signals continuously for 10 days, stopping the radars to receive any signal from the planetary surface. In this work, we assess the properties of this layer in order to understand the implications of this kind of phenomenon for radar performance and communications.

The dynamics of the Kronian magnetosphere is controlled by the complex interplay of the planet’s fast rotation, its solar-wind interaction and its main plasma sources at Enceladus and other moons. At the ionospheric level, these MIT coupling processes can be characterized by a set of key parameters which include ionospheric conductances, currents and electric fields, exchanges of particles along field lines and auroral emissions. Knowledge of these key parameters in turn makes it possible to estimate the net deposition/extraction of momentum and energy into/out of the Kronian upper atmosphere. In this talk we will apply to Cassini high-inclination, F-ring and Grand Finale orbits the method developed and tested by Wang et al. (JGR 2021, under review) for Juno studies. We will combine Cassini multi-instrument data (MAG, CAPS, MIMI, UVIS and RPWS) with adequate modelling tools and data bases to retrieve these key parameters along the Cassini magnetic footprint and across the north and south auroral ovals. We will present preliminary distributions of conductances, electric currents and electric fields obtained from these orbits and will compare them with model predictions.

Mars Express has been exploring Mars since late 2003 giving us fascinating views of the red planet as well as unique science insights. The long-life of Mars Express is an asset in order to understand the long-term evolution of the atmosphere of Mars, and in particular, of the ionosphere and upper atmosphere. Currently, we have about 16 years of ionospheric observations at Mars, which cover near two cycles of solar activity. This is the first time that such a long time series observations can be investigated in other planet rather than Earth. In particular, this work focuses on Mars’ ionospheric behaviour during two consecutive solar minima (23/24 and 24/25) using the same dataset. We use the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express to investigate the total electron content behaviour of the whole atmosphere in relation to key parameters, such as the solar flux, solar illumination, dust storms and Sun-Mars distance. The topside variability of the ionosphere is also investigated through variations in the neutral scale height, and results are supported by ionospheric modelling. The main goal of this study is to investigate whether the ionosphere during the recent solar minimum 24/25 was similar (and to which degree) to the ionosphere at solar minimum 23/24, which was characterised by a pronounced reduction of both the topside and bottomside regions.

We present the first long-term characterization of the lower ionosphere of Mars, a region previously inaccessible to orbital observations, based on an analysis of radar echo blackouts observed by MARSIS on Mars Express and SHARAD on the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly to fully attenuated for portions of an observation. Enhanced ionization at altitudes of 60 to 90 km, below the main ionospheric electron density peak, results in the absorption of the radar signal, leading to a radar blackout. MARSIS, operating at frequencies between 1.8 and 5 MHz suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz). More events are seen during solar maximum while there is no apparent relationship between blackout occurrence and crustal magnetic fields. Blackouts do occur during both nightside and dayside observations, and have an interesting variation with solar zenith angle. Analysis of MAVEN Solar Energetic Particle (SEP) electron counts between 20 and 200 keV during selected events demonstrates that these electrons are responsible for such events, and we investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars observe a radar blackout at the same time, the SEP electron fluxes are at their highest. For certain events, we find that the average spectrum responsible for a blackout is particularly enhanced at the higher energy end of the spectrum, i.e. above 70 keV . This study is, therefore, important for future communications for human exploration of Mars.

The Earth’s magnetic field as measured from ground-based magnetometers is composed of a variety of fields generated by diverse sources, spanning a broad amplitude and frequency spectrum. Long-term variable sources induce smooth changes, whereas short-term variable sources are able to induce rapid spikes in the geomagnetic field. An important aspect of Space Weather research is to understand the contribution and impact of each of these sources. In particular, knowing the amplitude and frequency of steady-like sources, like diurnal variations, enables us to determine the impact of sudden and hazardous events such as solar storms. The basic approach to this challenge is to identify the quiet magnetic field information within the recorded time-varying signal.In this work, we examine the variance of the magnetically quiet diurnal and semi-diurnal components of the geomagnetic field, as recorded by ground-based magnetic observatories of the INTERMAGNET network. These variations are extracted by applying appropriately designed digital filters on the geomagnetic field time series. The residual signal is analysed in terms of local time and seasonal variations for selected locations under quiet magnetic conditions. This approach allows us to evaluate the applicability of the introduced filtering method. The obtained results improve our understanding of the driving sources of quiet currents such as the Sq current and the variations of their distributions with respect to regular solar irradiance variations. They will also contribute to a better extraction and description of the remaining/residual signal related to solar wind stimuli (e.g. ICMEs, CIRs) causing magnetic storms.

The objective of this White Paper, submitted to ESA’s Voyage 2050 call, is to get a more holistic knowledge of the dynamics of the Martian plasma system, from its surface up to the undisturbed solar wind outside of the induced magnetosphere. This can only be achieved with coordinated multi-point observations with high temporal resolution as they have the scientific potential to track the whole dynamics of the system (from small to large scales), and they constitute the next generation of the exploration of Mars analogous to what happened at Earth a few decades ago. This White Paper discusses the key science questions that are still open at Mars and how they could be addressed with coordinated multipoint missions. The main science questions are: (i) How does solar wind driving impact the dynamics of the magnetosphere and ionosphere? (ii) What is the structure and nature of the tail of Mars’ magnetosphere at all scales? (iii) How does the lower atmosphere couple to the upper atmosphere? (iv) Why should we have a permanent in-situ Space Weather monitor at Mars? Each science question is devoted to a specific plasma region, and includes several specific scientific objectives to study in the coming decades. In addition, two mission concepts are also proposed based on coordinated multi-point science from a constellation of orbiting and ground-based platforms, which focus on understanding and solving the current science gaps. Part of a collection: Voyage 2050 – science themes for ESA’s long-term plan for the science programme: Solar Systems, ours and others (Part 2).

The Mars' ionospheric behavior during two consecutive solar minima (23/24 and 24/25) is investigated with the same dataset. In particular, we use the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express to investigate the total electron content behavior of the whole atmosphere in relation to the solar irradiance (EUV and X-ray fluxes), the solar zenith angle and the heliocentric distance. The topside variability of the electron density profiles is also investigated through variations in the peak density and neutral scale height. Moreover, the equations of the NeMars empirical model of the Martian ionosphere for low solar activity are tested for both minima. We have found that the topside ionosphere of Mars behaved similarly at both solar minima. However, when considering the bottomside, a pronounced reduction in ionization in particular cases is suggested. In addition, larger TEC values are found during the solar minimum 24/25 in the nightside sector that may indicate possible larger plasma transport than during the minimum 23/24. Finally, this study confirms that the ionospheric empirical NeMars model equations derived by Sanchez-Cano et al. (2016) for the low solar activity period during the solar minimum 23/24 are also valid and accurate for the solar minimum 24/25. The long duration of Mars Express is a critical factor for determining the long-term Martian ionospheric variability, which in turn, is essential for understanding the global evolution of the planet's atmosphere.

We present an analysis of radar blackouts observed by MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter for the interval 2006 – 2017. The period of interest encompasses the extended solar minimum between solar cycles 23 and 24 as well as the solar maximum of cycle 24. Blackouts have been identified by eye through scanning daily plots of the surface reflection for both radars. A blackout occurs when, for no apparent instrumental reason, the surface reflection normally expected is either not observed (total) or when the surface reflection is seen for only part of the orbit or the surface reflection is both weaker and spread over a significant time delay (partial). Such blackouts are caused by enhanced ionisation at altitudes below the main ionospheric electron density peak resulting in increased absorption of the radar signal. There are more occurrences observed by MARSIS than SHARAD, which is expected due to the lower absorption at the higher operating frequency of SHARAD. We also observe more blackouts during solar maximum than solar minimum. Indeed, there are no total blackouts during the extended solar minimum, although both radars do have partial blackouts. There is no apparent relationship between blackout occurrence and crustal magnetic fields. Following previous work, which has indicated that solar energetic particles, specifically electrons are responsible for the enhanced ionisation in the atmosphere, we also present the analysis of the MAVEN SEP electrons between 20 keV and 2 MeV during events when all three spacecraft were operational. We find that the SEP electron flux-energy relationship is much enhanced during the total blackouts, in particular where both radars are impacted, while for partial blackouts the flux-energy spectrum is closer to those from orbits where no blackout occurs. We also find that for certain events, the average spectrum which result in a blackout is particularly enhanced at the higher energy end of the spectrum, above 50 keV. The average spectra from each condition is presented. We conclude that there is a higher probability of a radar blackout during solar maximum, that crustal magnetic fields play no apparent role in the their observational occurrence, that the higher energy (< 50 keV) electrons are responsible, and that for events where both radars observe a radar blackout the SEP electron fluxes are at their highest.

The loss of signal detection by the sub surface radars currently operational on Mars Express and Mars Reconnaissance Orbiter can be evidence of enhanced ionisation at lower altitudes in the Martian atmosphere as a result of solar energetic particles penetrating to these altitudes. The MARSIS instrument on Mars Express and SHARAD on MRO operate at different frequencies, with MARSIS up to 5 MHz and SHARAD between 10 and 20 MHZ. In addition MARSIS can operate in an additional mode as an Active Ionospheric Sounder, although here we focus only on the sub surface mode. We present an analysis of the data during the lifetimes of both instruments, extending from 2005 to 2018. Here we identify the radar blackouts as either total or partial and investigate their occurrence as a function of solar cycle. We find a clear solar cycle dependence with more events occurring during the solar maximum years, as expected. However, we also note the duration of events is often much longer than expected, in excess of several days, sometimes reaching 10 – 14 days. Investigation of other data sets, notably from the MAVEN SEP instrument complements the analysis. We finally compare our observations at Mars with similar observations at Earth.

TARANIS (Tool for the Analysis of RAdiations from lightNIngs and Sprites) is a French CNES microsatellite dedicated to the study of the impulsive energy transfer between the Earth’s atmosphere and the space environment as widely observed above the active thunderstorm regions. After years of development and testing, the satellite is approaching to its launch (expected in June 2020). The comprehensive satellite scientific payload incorporates optical, field, and particle sensors including the energetic electron instrument (IDEE) with very high sensitivity and time resolution. Its main scientific tasks are: to measure high resolution energetic electron spectra (70 keV to 4MeV) and pitch angle distributions, to separate upward accelerated electrons and downward precipitated electrons, to detect burst of electrons associated with Terrestrial Gamma ray Flashes, to identify Lightning-induced Electron Precipitation (LEP), and to provide alert signals about high-energy electron bursts to other TARANIS experiments. The aim of this contribution is to describe the final design and expected performance of the IDEE experiment, including the data products. We also want to show how we are going to enhance the today’s scientific knowledge of the thunderstorm related phenomena in synergy with other ground-based and space-born experiments.

Solar wind High-Speed Streams (HSSs) affect the auroral ionosphere in many ways, and several separate studies have been conducted of the different effects seen e.g. on aurora, geomagnetic disturbances, F-region behavior, and energetic particle precipitation. In this work, we study an HSS event in the solar cycle (24), which was associated with a co-rotating interaction region (CIR) that hit the Earth’s magnetopause at about 17:20 UT on 14 March 2016. The associated magnetic storm lasted for seven days, and the Dst index reached -56 nT. We use a very comprehensive set of measurements to study the whole period of this storm, following day by day for the magnetic indices and solar wind parameters and relating its consequences on ionospheric plasma parameters. We use EISCAT radar data from Tromsø and Svalbard stations to see the response in plasma parameters at different altitudes, riometer data for cosmic noise absorption, and IMAGE magnetometers to see the intensities of auroral electrojets. TomoScand ionospheric tomography provides us with electron densities over a wide region in Scandinavia and AMPERE data the global field-aligned currents. We identified 13 local substorms in the Scandinavian sector from the IL (IMAGE lower) index. Altogether, there were 11 global substorms, for which the AE index reaches 1000 nT. We discuss the development of currents, as well as E and D region precipitation during the course of this long-duration storm and compare local versus global behavior.

The NASA InSight mission is operating from the surface of Mars for more than a year. RISE (for Rotation and Interior Structure Experiment) is one of the scientific payloads of InSight. This radio-science experiment consisting in an X-band transponder and two horn-antennas enabling two-way coherent radio-link between Mars and the Earth [Folkner et al., 2018]. The main goal of RISE is to measure the slight modulations of the nutational motion of the spin axis of Mars induced by the liquid core of the planet in order to constrain its interior structure and core properties. To increase our chance to achieve this challenging goal, we must calibrate the RISE Doppler data by accounting to 2nd order effects like the Mars atmospheric noise. This study shows the predicted contribution of the Martian ionosphere to the RISE data collected so far. To do so, we use a new empirical model of the Mars’ ionosphere called MoMo [Bergeot et al. 2019]. This model is based on the large database of Total Electron Content (TEC) derived from the subsurface mode of the Mars Express MARSIS radar. The model provides the vertical TEC as a function of solar zenith angle, solar activity, solar longitude and the location. Using MoMo, we produce vTEC maps for Mars that are then used to estimate the slant TEC in the Earth line of sight, enabling to infer the phase delay and Doppler shift affecting the RISE X-band measurements. These computed effects are shown to be of the order of 10-3mm.s-1 in Doppler observables, with a larger effect around sunrise and sunset. This is about one order of magnitude below the typical measurement noise of RISE, but it is comparable to the contribution of the liquid core in the Doppler (~10-3-10-2mm.s-1).The MoMo model is suitable for any Mars radio-science data calibration, and in particular the forthcoming ExoMars 2020 LaRa measurements [Dehant et al. 2019]. The predictions made with MoMo will be of great use either for the data corrections or to define the timing of observations in order to avoid operating when the TEC rapidly varies (i.e. close to sunrise and sunset). The model output is further discussed here in terms of climatologic behavior of the Mars’ ionosphere. For comparison, we also investigate the contribution of the Earth ionosphere using Global Ionospheric Maps (GIMs) based on GNSS data.

International audience; On 19 October 2014, Mars experienced a close encounter with Comet C/2013 A1 Siding Spring. Using data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express (MEX), we assess the interaction of the Martian ionosphere with the comet's coma and possibly magnetic tail during the orbit of their closest approach. The topside ionospheric electron density profile is evaluated from the altitude of the peak density of the ionosphere up to the Mars Express altitude. We find complex and rapid variability in the ionospheric profile along the MEX orbit, not seen even after the impact of a large coronal mass ejection. Before closest approach, large electron density reductions predominate, which could be caused either by comet water‐damping, or comet magnetic field interactions. After closest approach, a substantial electron density rise predominates. Moreover, several extra topside layers are visible along the whole orbit at different altitudes, which could be related to different processes as we discuss.

The response of the Martian ionosphere to solar activity is analyzed by taking into account variations in a range of parameters during four phases of the solar cycle throughout 2005–2012. Multiple Mars Express data sets have been used (such as Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) in Active Ionospheric Sounding, MARSIS subsurface, and MaRS Radio Science), which currently cover more than 10 years of solar activity. The topside of the main ionospheric layer behavior is empirically modeled through the neutral scale height parameter, which describes the density distribution in altitude, and can be used as a dynamic monitor of the solar wind-Martian plasma interaction, as well as of the medium's temperature. The main peak, the total electron content, and the relationship between the solar wind dynamic pressure and the maximum thermal pressure of the ionosphere with the solar cycle are assessed. We conclude that the neutral scale height was different in each phase of the solar cycle, having a large variation with solar zenith angle during the moderate-ascending and high phases, while there is almost no variation during the moderate-descending and low phases. Between end-2007 and end-2009, an almost permanent absence of secondary layer resulted because of the low level of solar X-rays. Also, the ionosphere was more likely to be found in a more continuously magnetized state. The induced magnetic field from the solar wind, even if weak, could be strong enough to penetrate more than at other solar cycle phases.

Aims: Several scientific landers and rovers have reached the Martian surface since the 1970s. Communication between the asset (i.e., lander or rover) and Mars orbiters or Earth antennas uses radio signals in UHF to X-band frequencies passing through the Mars’ ionosphere. It is consequently necessary to take into account electron density variation in the Mars’ ionosphere to correct the refraction of the signal transmitted. Methods: We developed a new empirical model of the Mars’ ionosphere called MoMo. It is based on the large database of Total Electron Content (TEC) derived from the subsurface mode of the Mars Express MARSIS radar. The model provides vertical TEC as a function of solar zenith angle, solar activity, solar longitude and location. For validation, the model is compared with Mars Express radio occultation data as well as with the numerical model IPIM (IRAP Plasmasphere-Ionosphere Model). Results: We discussed the output of the model in terms of climatology behaviour of the Mars’ ionosphere. The output of MoMo is then uses to quantify the impact of the Martian ionosphere for radio-science experiments. From our results, the effect is of the order of 10−3 mm s−1 in Doppler observables especially around sunrise and sunset. Consequently, this new model could be used to support the data analysis of any radio-science experiment and especially for present InSight RISE and futur ExoMars LARA instruments aiming at better understand the deep-interior of Mars.

A set of EISCAT UHF and VHF observations is used for calibrating a coupled fluid-kinetic model of the ionosphere. The data gathered in the period 1200- 2400 UT on 24 March 1995 had various intervals of interest for such a calibration. The magnetospheric activity was very low during the afternoon, allowing for a proper examination of a case of quiet ionospheric conditions. The radars entered the auroral oval just after 1900 UT: a series of dynamic events probably associated with rapidly moving auroral arcs was observed until after 2200 UT. No attempts were made to model the dynamical behaviour during the 1900–2200 UT period. In contrast, the period 2200–2400 UT was characterised by quite steady precipitation: this latter period was then chosen for calibrating the model during precipitation events. The adjustment of the model on the four primary parameters observed by the radars (namely the electron concentration and temperature and the ion temperature and velocity) needed external inputs (solar fluxes and magnetic activity index) and the adjustments of a neutral atmospheric model in order to reach a good agreement. It is shown that for the quiet ionosphere, only slight adjustments of the neutral atmosphere models are needed. In contrast, adjusting the observations during the precipitation event requires strong departures from the model, both for the atomic oxygen and hydrogen. However, it is argued that this could well be the result of inadequately representing the vibrational states of N2 during precipitation events, and that these factors have to be considered only as ad hoc corrections.

International audience; This paper is a phenomenological description of multi‐spacecraft observations of energetic particles caused by the close flyby of comet C/2013 A1 Siding‐Spring with Mars on 19 October 2014. This is the first time that cometary energetic particles have been observed at Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) Solar Energetic Particle (SEP) and the Mars Odyssey High Energy Neutron Detector (HEND) instruments recorded evidence of precipitating particles, that are likely O+ pick‐up ions, during the ~10 hours that Mars was within the region of the comet's coma. O+ pick‐up ions were also detected several hours after, although whether their origin is the comet or space weather is not conclusive. We discuss the possible origin of those particles, and also, the cause of an additional shower of energetic particles that HEND observed between 22 and 35 h after the comet's closest approach, which may be related to dust impacts from the comet's dust tail. An O+ pick‐up ion energy flux simulation is performed with representative solar wind and cometary conditions, together with a simulation of their energy deposition profile in the atmosphere of Mars. Results indicate that the O+ pick‐up ion fluxes observed by SEP were deposited in the ionosphere around 105‐120 km altitude, and they are compared with pre‐comet flyby estimations of cometary pick‐up ions. The comet's flyby deposited a significant fluence of energetic particles into Mars' upper atmosphere, at a similar level to a large space weather event.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., We analyze 10 years of Mars Express total electron content (TEC) data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument. We describe the spatial, seasonal, and solar cycle behavior of the Martian TEC. Due to orbit evolution, data come mainly from the evening, dusk terminator and postdusk nightside. The annual TEC profile shows a peak at Ls = 25–75° which is not related to the solar irradiance variation but instead coincides with an increase in the thermospheric density, possibly linked with variations in the surface pressure produced by atmospheric cycles such as the CO or water cycles. With the help of numerical modeling, we explore the contribution of the ion species to the TEC and the coupling between the thermosphere and ionosphere. These are the first observations which show that the TEC is a useful parameter, routinely measured by Mars Express, of the dynamics of the lower-upper atmospheric coupling and can be used as tracer for the behavior of the thermosphere.©2018. The Authors., B. S. -C. and M. L. acknowledge support through STFC grant ST/N000749/1. ESA-ESTEC Faculty and Europlanet funding are also gratefully acknowledged. MEX MARSIS RDR and EDR data can be downloaded from the ESA-PSA archive, TIMED-SEE data at the University of Colorado's website (http://lasp.colorado.edu/lisird/index.html), REMS data at the NASA Planetary Data System (http://atmos.nmsu.edu/PDS/data/mslrem_1001/DATA/), the MCD model at the Mars Climate Database web interface (http://www-mars.lmd.jussieu.fr/mars/access.html), and the IPIM model at the IRAP CDPP web interface (http://transplanet.irap.omp.eu/).

Performance Based Navigation (PBN) is a concept developed by ICAO (International Civil Aviation Organization) that specifies the operational performance required in an airspace, route or approach procedure. A Satellite Based Augmentation System (SBAS) enhances the performances of the existing satellite navigation system. It is used to deploy Global Navigation Satellite System (GNSS) approach for PBN procedures. The required performance level for vertical guidance is directly linked to approach category criteria. The real performance provided by an SBAS for a single-frequency user depends on the physical characteristics of the ionospheric layer. As Sub-Saharan Africa corresponds to geomagnetic equator region, the question of ionosphere dynamics characterization in equatorial zone is central to gauge what SBAS performance level can be achievable. In the equatorial zone the dynamics of the ionosphere is subject to complex physical phenomena, involving rapid recombination of ion-electron pairs. Moreover these phenomena are transient with high local spatial and temporal gradients. These zones promote the occurrence of scintillation phenomena, bubbles (strong local fall of TEC (Total Electron Content)), and small scale gradients, which must be evaluated for the ionosphere modeling and integrity data generation. Based on a large volume of GNSS measurements covering more than four years of data collected, Thales Alenia Space associated with IRAP (Astrophysics and Planetology Research Institute, Toulouse, France), present a panorama of observed physical events through the ionosphere in Sub-Saharan Africa zone. The main purpose of this study is to establish a clear view on the physical mechanisms that drive the equatorial ionosphere dynamics and the effects on GNSS measurements. This study is supported by information coming from TEC values, TEC gradients amplitudes, and the nature of scintillation events as intensity, impact area and occurrence in time. Conclusion of these activities is to highlight that ionosphere conditions above sub-Saharan area are consistent with the performances level of SBAS approach with vertical guidance. Indeed scientific analyses show that a precise service level is possible on this zone with a very good level of availability above the main airports.

18th EISCAT symposiumSession E2: Future infrastructure & facilities (EISCAT_3D user meeting)May 29 (Mon), NIPR Auditorium

18th EISCAT symposiumSession E7: Space weather and modellingMay 27 (Sat), Poster Session

On 1 August 2008, a total solar eclipse occurred and the footprint of its umbra passed North–East of the Svalbard archipelago, where the EISCAT Svalbard Radars (ESR) are installed. This eclipse is peculiar because it was seen at high-latitude, thus with large solar zenith angles and it was the first time that incoherent scatter radars were able to sound the ionospheric response at such a high latitude. The ESR data, after correction, show the typical signatures of a solar eclipse: depletion in electron density in the E- and F-regions, a decrease in electron temperature in the F-region, and a downflow of ions. Also, the UHF dish of the mainland EISCAT system measured a decrease in the same parameters, showing the influence of the penumbra (partial eclipse) on the ionosphere. We have modelled the response of the high-latitude ionosphere to this solar eclipse with the TRANSCAR code. Our simulations reproduce rather well the observations above the UHF radar in Tromso and the ESR on Svalbard. In particular, we show the influence of particle precipitation above the ESR and we suspect an effect above Tromso of the photoelectrons coming from the opposite hemisphere. Another interesting and quite unusual feature is the observation of the summer ionospheric cusp undergoing the eclipse. Radar data show structures of enhanced electron temperature, due to soft particle precipitation through the polar cusp.

Solar cycle variations in solar radiation create notable changes in the Martian ionosphere, which have been analysed with Mars Express plasma datasets in this paper. In general, lower densities and temperatures of the ionosphere are found during the low solar activity phase, while higher densities and temperatures are found during the high solar activity phase. In this paper, we assess the degree of influence of the long term solar flux variations in the ionosphere of Mars.

TARANIS (Tool for the Analysis of RAdiation from lightNIng and Sprites) is a microsatellite aimed to atmospheric storms study. It embarks among other instruments IDEE (Instrument Detecteur d'Electron Energetique) which is dedicated to energetic electron characterization in the range from 70keV to 4Mev. To cover such awide ran ge, two types of detectors are required: Silicon (Si) and Cadmium Telluride (CdTe) based detector for the 70keV to 700keV and for the 300keV to 4MeV respectively. Si detectors are placed in front of CdTe detectors for angle measurement. Although the readout architecture of both detectors are similar, the time constants involved in collection of the charges for Si and CdTe are differents by almost 21 decades (60ns for Si and 3f.1s for CdTe). Two different readout circuits are thus required. CdTe type channels need to make use of Pole Zero Cancellation (PZC) technique in order not to impede the frequency of operation. Performance of the design has been characterized on a test board as well as interfaced with detectors. Finally, results of its characterized Single Event Latchup (SEL) performance is given.

Since 2005 the Mars Advanced Radar and Ionospheric Sounding experiment (MARSIS) aboard Mars Express has acquired a unique dataset on the ionosphere of Mars made up of ionospheric soundings taken by the instrument working in its active ionospheric sounding (AIS) mode. These soundings play a role similar to those of modern Terrestrial digisondes in the analysis of our planet ionosphere and have allowed us to dramatically improve our knowledge about the Martian ionosphere. This paper describes this kind of data, which are available from the public Planetary Science Archive, and introduces the MAISDAT tool developed by the European Space Agency to analyze and derive the vertical profile of electron density. Comparisons with radio occultation profiles obtained from Mars Express Radio Science instrument are performed to validate the procedure used in this study.

The work presents a data-model synthesis examining the response of the auroral F-region ion temperature, composition, and density to short time scale (

International audience; We present a conjunction between the Swarm fleet and the European Incoherent Scatter Svalbard Radar (ESR) on 9 January 2014. The Swarm orbit in the early phase of the mission gives us the unique opportunity of sequencing the temporal evolution of the observed field-aligned current system in the nightside, near magnetic local midnight. These field-aligned currents are seen to move poleward through the radar field of view and to affect the observed ionosphere. The upward field-aligned current (FAC) is responsible, at least in part, for the heating of the ionospheric electrons. It is less clear whether the downward FAC cools the ionosphere. We use the TRANSCAR model of the ionosphere to quantify the thermoelectric effect that comes into play. Finally, we compare the plasma parameters measured by the Langmuir probe on board Swarm and the ESR and conclude on an agreement within the errors.

Photochemical processes in the upper atmosphere are known to create significant amounts of energetic oxygen atoms or "hot O". In this research we simulate the effects of ionized hot oxygen, hot O+, on the ionosphere. We find that hot O+ is not able to maintain a temperature substantially above the ambient ion temperature at most altitudes, the exception being around the F-region ion density peak. However, the thermalization of hot O+, due to Coulomb collisions, represents an important heating process for the ambient ions. A time-dependent, fluid-kinetic model of the ionosphere (TRANSCAR) is used to self-consistently simulate hot O+ by considering it to be a separate species from O+. A Maxwellian neutral hot O population having characteristics consistent with current knowledge is added to TRANSCAR. The production of the hot O+ is then computed by considering ion charge exchange with the neutral hot O population that we have assumed. Loss of hot O+ results from these charge exchange reactions and from reactions with molecular atoms.

International audience; The DEMETER Langmuir probe experiment, called “Instrument Sonde de Langmuir” (ISL), has been designed for in situ measurements of the bulk parameters of the ionospheric thermal plasma. The ISL instrument is comprised of two sensors: (i) a classical cylindrical sensor and (ii) a spherical sensor with its surface divided in seven segments: six spherical caps electrically isolated and the rest of the sphere which is used as a guard electrode. The two main parameters measured by ISL are the electron density and temperature; they are obtained with a 1 s time-resolution. In addition, the ion density and its variation can be derived from the current-voltage characteristics of the probe, but it requires an a-priori knowledge of the ion composition and a more sophisticated processing than the one currently implemented. The novel design for the spherical sensor has been called the segmented Langmuir probe (SLP). The SLP current can be measured individually on each of the seven segments, thus providing angular sensitivity to the ram direction of the incoming ion flow. The SLP was flown for the first time onboard the DEMETER satellite for in-flight validation of this novel concept, but the main sensor used routinely during the mission is the cylindrical probe. The design of the instrument and the analysis technique for the cylindrical probe are described. A brief description of the SLP and of its capabilities is provided. An overview of the currently available ISL data products on the DEMETER Mission Science Data Centre is given. Selected examples of some “classical” ionospheric features as being observed by ISL are discussed.

We show that heating by large amplitude E-region plasma waves at high latitudes can at times substantially enhance the electro-dynamical response of the ionosphere. This is made manifest through an increase in parallel current densities and parallel electric fields generated at the edge of arcs in the E and lower F-region of the ionosphere, in response to sharp cutoffs in precipitation with an otherwise uniform differential energy flux. The enhancement is rooted in a reduction in electron recombination that occurs in response to higher electron temperatures triggered by the generation of strong electric fields near the edge of the arc. The reduced recombination rate, in turn, leads to enhanced conductivity gradients near the edge of the arc, which, in turn, drives more intense parallel currents and stronger local electric fields. Keywords. Ionosphere (Electric fields and curents; Plasma temperature and density) – Space plasma physics (Numerical simulation studies)

The NEtlander Ionosphere and Geodesy Experiment (NEIGE) of the Netlander mission to Mars will measure Doppler shifts affecting the radio links between ground stations and an orbiter. The experiment has two complementary scientific objectives which are the monitoring of the structure and dynamics of the ionosphere of Mars and the precise determination of Mars orientation parameters. The horizontal variation of the Total Electron Content (TEC) of the ionosphere will be derived from the so-called “geometric-free” combination of the Doppler shifts which affect radio links at two frequencies (in the UHF and S bands) between the Netlander microstations on the Mars surface and the data-relay orbiter. We describe a new method for retrieving the horizontal profile of the absolute value of the TEC. Simulations have allowed to evaluate the precision in the determination of the TEC using this method. We show that the daytime TEC can be retrieved with a precision of 5×10 13 m −2 for a nominal accuracy of 0,1 mm / s on the orbital pseudo-velocity, which represents a relative precision of a few percent. A preliminary analysis of the sensitivity of the TEC to the physical parameters which control the ionosphere has been performed. For this purpose, we have used a new one-dimensional ionospheric model based on the solution of coupled kinetic, fluid and MHD equations. This model describes the suprathermal electron component, the thermal plasma component as well as the induced horizontal magnetic field. The code which provides the vertical electron density profile has been used to study the variation of the TEC with the solar zenith angle and with the induced magnetic field at the top of the ionosphere. In particular, we show that NEIGE will allow to diagnose the penetration into the daytime ionosphere of an induced magnetic field.

The more common measurements of the ionosphere are the total electron content (TEC) (measured with the positioning systems) and the parameters of the F-region peak, namely its altitude (hmF2) and its density (NmF2). In this paper, we address the question of using these reduced parameters as tracers of the ionosphere and thermosphere. We make use of a 19 h daylight experiment by the EISCAT incoherent scatter radar based in Tromso, Norway. We reduce the full profile measurement of the electron density (between 80 and 425 km ) to the TEC, hmF2 and NmF2. Using a 1-D fluid/kinetic model, we reproduce these parameters. Then, by inversion, we retrieve the ionospheric profiles of the electron density, electron and ion temperature and, to a smaller extent, of the ion velocity. With this method, we show that it is in principle possible to evaluate a correction factor for the atomic oxygen. This factor evolves with time. We study the different uncertainties (heat flow, molecular densities, limitations of the model). Finally, we evaluate the contribution of the upper ionosphere (up to 3000 km) to the calculation of the TEC and show that 90% of the TEC is reached when the integration is made up to 1200 km .

Recent studies of the ion energy balance in the mid-latitude ionosphere have led to the suggestion that hot neutral atomic oxygen may play a significant role; the presence of a population of hot O could explain some of the problems met in balancing the ion energy budget for Incoherent Scatter (IS) observations. The aim of the present study is to look at such effects by using numerical simulation. The TRANSCAR model is a time-dependent, 13-moment ionosphere model developed for high latitude studies. It was first adapted for mid-latitude conditions. In a first step the model was calibrated and cross-checked with St. Santin IS measurements for the winter case of 27 January 1972 around noon using, in particular, the MSIS neutral atmosphere model. This provides a reference diurnal variation of the ionosphere. The second step investigated the influence of a maxwellian population of hot neutral atomic oxygen introduced in addition to the standard neutral atmosphere. The paper describes the initial comparison between the model and St. Santin IS data, and then the effects induced by a hot atomic oxygen population.Key words. Ionosphere (ionosphere-atmosphere interactions; ion chemistry and composition; mid-latitude ionosphere)