Plasma and magnetic field conditions during radar blackouts at Mars.

Large scale solar wind disturbances such as Interplanetary Coronal Mass Ejections (ICMEs) have a major impact on planetary systems.  At Mars, for example, Solar Energetic Particles released during the process that creates the ICME cause large scale radar blackouts as a result of enhanced ionisation at lower altitudes than normal.  The increased absorption of the radar signals can last for up to 10 – 12 days, depending on the operational frequency of the radar.  These events occur at all latitudes and local times but there does appear to be a peak in occurrence at a solar zenith angle of about 160o, i.e. deep in the tail of the Martian plasma system. Using data from MAVEN, Mars Express and Mars Reconnaissance Orbiter we investigate the background plasma  and magnetic field conditions, which occur at the same time as these events to investigate how the SEP impact on the nightside atmosphere.  This will provide crucial evidence for plasma transport in the Martian system, in particular during the passage of ICMEs.