Enhanced ionization of the Martian nightside ionosphere during solar energetic particle events

Electron densities in the Martian nightside ionosphere are more than 90% of time too low to be detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft. However, the relative number of ionograms with peak electron density high enough to be detected represents a good statistical proxy of the ionospheric density. We focus on solar energetic particle (SEP) events, and we analyze their effects on ionospheric formation. SEP time intervals were identified in situ using the background counts recorded by the ion sensor of the ASPERA-3 instrument on board Mars Express. We show that peak electron densities during the SEP events are large enough to be detected in more than 30% of measurements, and, moreover, the reflections of the sounding signal from the ground almost entirely disappear. Nightside electron densities during SEP events are thus substantially increased as compared to normal nightside conditions

Modeling of Planetary Wave Influences on the Pre‐reversal Enhancement of the Equatorial F Region Vertical Plasma Drift

Temporal and longitudinal variations of the pre‐reversal enhancement (PRE) in the equatorial F region vertical plasma drift are examined based on idealized simulations by the thermosphere‐ionosphere‐electrodynamics general circulation model performed under geomagnetically quiet (Kp = 1) and high solar‐flux (F10.7 = 200) conditions. The model takes into account forcing by large‐scale waves from the middle and lower atmosphere, which leads to day‐to‐day variations of PRE. Simulations are performed under different wave forcing in order to separate contributions of various types of waves. It is shown that the simulated day‐to‐day variability of the PRE intensity is predominantly due to forcing by waves with periods less than 2 days, that is, tides and their modulation. Planetary‐wave forcing (periods of 2–20 days) makes contributions to periodic oscillations in the PRE intensity. Especially, the westward‐propagating quasi‐6‐day wave (Q6DW) with zonal wavenumber 1 is found to be an important source of ∼6‐day oscillations of PRE. Not only the Q6DW from below but also the Q6DW generated within the thermosphere, as well as the secondary waves due to the nonlinear interaction between the Q6DW and migrating tides, is at play. The zonal wavenumber 1 nature of the ∼6‐day oscillations could contribute to longitudinal differences in the appearance of equatorial spread F and plasma bubbles, which are strongly controlled by PRE.Key Points: Quiet‐time day‐to‐day and longitudinal variability of the pre‐reversal enhancement (PRE) in the equatorial vertical plasma drift is examined. Planetary‐wave influences on PRE are evaluated for the first time using global simulations. Quasi‐6‐day wave can lead to ∼6‐day oscillations in the PRE intensity with zonal wavenumber 1.Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/50110000165

The Martian ionosphere: comparison of a global climate model with MARSIS data

International audienceWe present here the comparison of the electron den- sity profiles predicted by a 3D global climate model (GCM), the Mars GCM developed at the Laboratoire de Météorologie Dynamique (LMD-MGCM) [4], with the measurements from the instrument MARSIS on board Mars Express [5]. The observations were ob- tained during 5 Martian Years (MY), from MY27 to MY31 (mid 2005-end of 2013). The model was run using the observed day-to-day variability of the UV solar flux and of the dust load during that period. We focus the comparison on two parameters: the electron density at the main peak, and the altitude of the peak. Special attention will be paid to the variability of these two parameters with different geophysical parameters (latitude, SZA, ...), which can provide interesting in- formation about the neutral upper atmosphere of Mars and its interaction with the UV solar radiation