Nonlinear model of short-scale electrodynamics in the auroral ionosphere

International audienceThe optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work). We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions)</p

Solar cycle variations in the ionosphere of Mars

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

IPIM Modeling of the Ionospheric F-2 Layer Depletion at High Latitudes During a High-Speed Stream Event

Our aim is to understand the effect of high-speed stream events on the high-latitude ionosphere and more specifically the decrease of the f(o)F(2) frequency during the entire day following the impact. First, we have selected one summertime event, for which a large data set was available: Super Dual Auroral Radar Network (SuperDARN) and European Incoherent SCATter (EISCAT) radars, Tromso and Sodankyla ionosondes, and the CHAllenging Minisatellite Payload (CHAMP) satellite. We modeled with the IPIM model (IRAP Plasmasphere Ionosphere Model) the dynamics of the ionosphere at Tromso and Sodankyla using inputs derived from the data. The simulations nicely match the measurements made by the EISCAT radar and the ionosondes, and we showed that the decrease of f(o)F(2) is associated with a transition from F-2 to F-1 layer resulting from a decrease of neutral atomic oxygen concentration. Modeling showed that electrodynamics can explain short-term behavior on the scale of a few hours, but long-term behavior on the scale of a few days results from the perturbation induced in the atmosphere. Enhancement of convection is responsible for a sharp increase of the ion temperature by Joule heating, leading through chemistry to an immediate reduction of the F-2 layer. Then, ion drag on neutrals is responsible for a rapid heating and expansion of the thermosphere. This expansion affects atomic oxygen through nonthermal upward flow, which results in a decrease of its concentration and amplifies the decrease of [O]/[N-2] ratio. This thermospheric change explains long-term extinction of the F-2 layer.Peer reviewe

A parametric study of solar wind properties and composition using fluid and kinetic solar wind models

The physical processes in the solar corona that shape the solar wind remain an active research topic. Modeling efforts have shown that energy and plasma exchanges near the transition region play a crucial role in modulating solar wind properties. Although these regions cannot be measured in situ, plasma parameters can be inferred from coronal spectroscopy and ionization states of heavy ions, which remain unchanged as they escape the corona. We introduce a new solar wind model extending from the chromosphere to the inner heliosphere, capturing thermodynamic coupling across atmospheric layers. By including neutral and charged particle interactions, we model the transport and ionization processes of the gas through the transition region and corona and into the solar wind. Instead of explicitly modeling coronal heating, we link its spatial distribution to large-scale magnetic field properties. Our results confirm that energy deposition strongly affects wind properties through key mechanisms involving chromospheric evaporation, thermal expansion, and magnetic flux expansion. For sources near active regions, the model predicts significant solar wind acceleration, with plasma outflows comparable to those inferred from coronal spectroscopy. For winds from large coronal holes, the model reproduces the observed anticorrelation between charge state and wind speed. However, the predicted charge state ratios are overall lower than observed. Inclusion of a population of energetic electrons enhances both heavy ion charge states and solar wind acceleration, improving agreement with observations

Equatorial Ionosphere Characterization for Sub-Saharan Africa SBAS

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