Effects of the solar wind electric field on heavy-ion precipitations onto the Martian upper atmosphere
Mr. Takuya Hara
Nagoya Univ.
Japan
Abstract:
We study effects of the solar wind magnetic field orientations on
precipitating planetary-origin ions onto the Martian upper atmosphere
using ion distribution functions observed by Ion Mass Analyzer (IMA)
onboard Mars Express (MEX). In order to compensate the absence of
magnetometer onboard MEX, we newly develop a method to estimate
interplanetary magnetic field (IMF) orientations from characteristic
partial-ring distributions in the phase space formed by picked-up
protons tracing a cycloid trajectory in the real space. We then
conduct statistical trajectory tracings of exospheric protons under
static and uniform solar wind conditions in order to verify that
estimated IMF orientations are reasonable and to determine the IMF
polarity. We confirm that the results of the statistical trajectory
tracings can reproduce the ring velocity distribution function similar
to that of observations. For two events, we can successfully determine
the IMF polarity from the gradation in the ring distributions. The
results show that the locations of precipitating planetary-origin ion
events are distributed around the polar region of anti-E-field
hemisphere determined by the solar wind electric field. The observed
asymmetry with respect to the solar wind electric field is consistent
with results of previous numerical simulations. This agreement
indicates that precipitating planetary-origin ions have undergone
picked-up acceleration in the magnetosheath region, and the energy of
precipitating heavy ions less than a few keV might reflect the short
distance from a picked-up region in the magnetosheath than in the
solar wind.
Created 2012-08-30 11:48:01 by Mats Holmström Last changed 2012-10-04 08:50:39 by Mats Holmström
