P21A-2076
Characterization of low frequency plasma waves and their energy deposition in the Martian magnetosphere with MAVEN
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Suranga Ruhunusiri1, Jasper S Halekas1, John E P Connerney2, Jared R Espley2, James P McFadden3, Davin E Larson3, David L Mitchell3, Christian Xavier Mazelle4,5, Bruce Martin Jakosky6, Dave A Brain7, Yuki Harada8 and Roberto Livi3, (1)University of Iowa, Iowa City, IA, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)University of California Berkeley, Berkeley, CA, United States, (4)Universite Paul Sabatier, TOULOUSE, France, (5)IRAP CNRS, Toulouse, France, (6)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (7)University of Colorado at Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (8)Space Sciences Laboratory, Berkeley, CA, United States
Abstract:
Mars has one of the unique environments in the solar system for the exploration of plasma waves. Mars does not have an intrinsic magnetosphere, but it has an induced magnetosphere due to the interaction of the solar wind with its ionosphere. Mars also possesses an extended exosphere, which spans beyond its bow shock. The interaction of the solar wind with the magnetosphere and the exosphere leads to excitation of low frequency waves that have frequencies near or below the proton gyro-frequency. MAVEN has been orbiting Mars since the late September of 2014, traversing through various regions of the Martian magnetosphere and the upstream region. MAVEN has a number of particle and field instruments for performing plasma diagnostics. Thus, for the first time at Mars, we have a complete set of plasma instruments for characterizing these low frequency plasma waves. The goal of this work is to distinguish the observed waves as one of the four low frequency wave modes (Alfven, fast, slow, and mirror) and to characterize their occurrence ratios and energy deposition in the various regions of the Martian magnetosphere and in the upstream region. To identify these waves, we use ratios and phase differences among the ion moment fluctuations and magnetic field fluctuations. To measure the ion moment fluctuations, in particular, we use two of the MAVEN ion instruments, solar wind ion analyzer (SWIA) and suprathermal and thermal ion composition instrument (STATIC). We use the MAVEN magnetometer for obtaining the magnetic field fluctuations. SWIA and STATIC have sampling cadence of 4s, much higher than that of their predecessors flown to Mars, and this is often adequate to detect the low frequency waves at Mars. We find that the Alfven waves are the most dominant waves in the upstream region and in the Martian magnetosphere. Fast waves, on the other hand, have the second highest occurrence ratio and they are found frequently near the bow shock and near the magnetic pileup boundary. To characterize the energy deposition from these waves to the magnetosphere, we compute the Poynting vector using the ion and magnetic field data. The variability of the low frequency waves and their energy deposition to upstream conditions such as the solar wind dynamic pressure and IMF direction is studied in this work.
