P21A-2087
The Dependence of Mars Atmospheric Loss on Crustal Field Location: MAVEN Observation and Comparison with a MHD Model
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Xiaohua Fang1, Yingjuan Ma2, Yaxue Dong1, James P McFadden3, Jasper S Halekas4, John E P Connerney5, David Brain1, Robert J Lillis3 and Bruce Martin Jakosky6, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)University of California Los Angeles, Los Angeles, CA, United States, (3)University of California Berkeley, Berkeley, CA, United States, (4)University of Iowa, Physics and Astronomy, Iowa City, IA, United States, (5)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (6)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
Abstract:
Our recent time-dependent MHD study suggests that the Mars crustal magnetic field acts as the primary internal driving force of variability in total planetary ion escape. In our global numerical simulation, we assume quiet solar wind conditions and consider the continuous local time change of crustal anomalies due to planetary rotation. Significant fluctuations of ~20% and ~50% are obtained during the entire rotation period for O+ and for O2+ and CO2+, respectively. From the MHD perspective, the control is exerted mainly through two processes. First, the crustal magnetic pressure over the subsolar regime controls solar wind penetration and mass loading and therefore the escaping planetary ion source. There is a strong negative correlation between the dayside magnetic pressure and ion loss with a significant time lag. Second, the crustal magnetic pressure near the terminator region controls the cross section area between the induced magnetospheric boundary and 100 km altitude at the terminator. The change in day-night connection regulates the extent to which planetary ions created in the dayside can be ultimately carried away by the solar wind and escape Mars. There is a strong positive correlation between the terminator crustal pressure and ion loss, with a shorter time lag. As the planet rotates, the dayside process and the terminator process work together to control the total amounts of escaping planetary ions. In the present work, we aim to test this theory by analyzing planetary ion escape observed by the SupraThermal and Thermal Ion Composition (STATIC) instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The upstream solar wind plasma observation by the Solar Wind Ion Analyzer (SWIA) and IMF observation by Magnetometer (MAG) are used to provide an estimate of the external driving force of the Mars-solar wind interaction. We will examine the relationship between the MAVEN observed escaping planetary ion flux and Mars orientation to the Sun, and compare our finding with what we learn from the MHD model.
