Compressive Low Frequency Waves At The Martian Magnetic Pileup Boundary: Mgs Observations

BERTUCCI, C.; MAZELLE, C.; CRIDER, D.; MITCHELL, D.; SAUER, K.; ACUÑA, M.; CONNERNEY, J.; RÈME, H.; LIN, R.; CLOUTIER, P.; NESS, N.; WINTERHALTER, D.

Congreso; EGS XXVII General Assembly; 2002

We use magnetic field and electron plasma measurements from the MAG/ER exper- iment onboard the Mars Global Surveyor spacecraft to study the properties of com- pressive, low frequency waves, which are frequently observed on both sides of the magnetic pileup boundary (MPB). This thin, sharp and permanent plasma boundary marks the end of the Martian magnetosheath where wave activity is high, and the entry in a region where the magnetic field is less disturbed, more intense, and draped around the ionospheric obstacle. On both sides of the MPB, the waves are linearly polarized with respect to a very steady background magnetic field. Cross-correlation analyses of the magnetic field and electron data reveal that on the upstream side these are mir- ror mode waves, while downstream, large amplitude, quasi-monocromatic fast mode waves are observed. Interestingly, this feature was also reported around the MPB of active comets. Following a characterization of the MPB, we present detailed analyses of the properties of these LF waves for some particular events as well as the results of a statistical study on their occurrence and properties, from a large set of orbits. The source mechanism and the role on the plasma dynamics of these compressive LF waves at the MPB of both comets and Mars are also discussed.