P21A-2078
Ion cyclotron waves near Mars: Solar wind control of pickup ion instability
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Frank J Crary1, Vincent J Dols2, Peter A Delamere3, Jared R Espley4, Jasper S Halekas5 and John E P Connerney4, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (3)University of Alaska Fairbanks, Fairbanks, AK, United States, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)University of Iowa, Physics and Astronomy, Iowa City, IA, United States
Abstract:
Ion cyclotron waves near the proton gyrofrequency have been observed near Mars by the MAVEN spacecraft. These waves are generated by photo-ionized protons from the Martian corona and reflect the density of the exosphere. However, the amplitude of these waves is highly variable. Despite direct observations of pickup protons, the associated ion cyclotron waves may be absent. We show that this typically occurs when the solar wind magnetic field and velocity are perpendicular. Theoretical calculations and numerical modeling show that the thermal solar wind may damp ion cyclotron waves and suppress the ion cyclotron wave generation. When pickup ions have a significant velocity parallel to the magnetic field, the Doppler shift between the core and pickup protons allows wave growth. Future work, relating ion cyclotron wave amplitude to the ionization of the exosphere, will need to account for this necessary condition for the wave generation process.
