Local and global properties of plasma waves at the proton cyclotron frequency upstream from Mars

ROMANELLI, NORBERTO; BERTUCCI, CESAR; GOMEZ, DANIEL; MAZELLE, CHRISTIAN

San Francisco

Congreso; AGU Fall Meeting 2011; 2011

American Geophysical Union (AGU)

A comprehensive study on the properties of electromagnetic ULF plasma waves upstreamfrom Mars is presented. This study is based on reliable upstream measurements provided by the magnetometerand electron reflectometer (MAG/ER) onboard the Mars Global Surveyor (MGS) spacecraft during the SciencePhasing Orbit period.We find that a large majority of these waves is characterized - in the spacecraft frame - by a left-hand circularpolarization and a frequency which coincides with the local proton cyclotron frequency. Minimum varianceanalysis of the magnetic field indicates that these waves propagate almost parallel to the background magneticfield and comparison with suprathermal electron fluxes measured by ER suggests a small degree ofcompressibility.A survey based on more than 300 MGS elliptical orbits indicates that these waves are almost permanent andtheir spatial distribution does not seem to depend on the orientation of the solar wind convective electric fieldassuming a flow along the Sun-Mars line. Also, we find that their amplitude decreases with radial distance fromthe planet, supporting the idea that their source is Mars.Theoretical (analytical and numerical) approaches suggest that these properties are compatible with plasmawaves originating in the pick-up of ionized exospheric hydrogen. We discuss these theoretical results and theirimplications for Mars and other atmospheric unmagnetized objects such as Venus.