Occurrence and Distribution of High Altitude Plasma Clouds at Mars

Mars Global Surveyor (MGS) Electron Reflectometer (ER) detected signatures of ionospheric plasma via a peak in the electron energy spectrum consistent with the presence of ~500 eV Auger electrons (Mitchell et al., 2000). Some of these were observed above the nominal ionopause of Mars, potentially analogous to parcels of ionospheric plasma above the nominal ionosphere of Venus, dubbed plasma clouds (Brace et al., 1982). These were envisioned as instabilities on the ionopause that evolved to escaping parcels of ionospheric plasma. We determine the distribution of plasma clouds in the near-Mars environment using MAVEN Solar Wind Electron Analyzer (SWEA) data. Martian plasma clouds are observed near the terminator like at Venus. They move to higher altitude as solar zenith angle increases, consistent with the escaping plasma hypothesis. The presentation also examines the occurrence of high altitude plasma clouds as a function of environmental drivers.