Publications: paper No 14

Atmospheric effects of proton precipitation in the Martian atmosphere and its connection to
the Mars-solar wind interaction

Esa Kallio and Pekka Janhunen
Finnish Meteorological Institute, Helsinki, Finland

Journal of Geophysical Research, 106, NO. A1, pp. 5617 - 5634, January 1, 2001

Atmospheric effects of precipitating solar wind protons in the Martian atmosphere are studied. The proton flux to the atmosphere
is derived from a newly developed global quasineutral hybrid simulation which includes solar wind H+ ions and planetary
O+ ions. The motion of the precipitating particles in the atmosphere is followed and the effects of collisions to
atmospheric neutrals are studied by a collision-to-collision Monte Carlo algorithm. Maximum atmospheric effects are estimated by
using a fully absorbing boundary condition in the hybrid model where all solar wind protons are allowed to precipitate into the atmosphere without reflection.

The developed mass-loaded hybrid code is found to reproduce many of the observed plasma and field features near Mars. When the
vertical profiles of the energy deposition rates, CO2+ ionization rates, and Lyman alpha emission rates are calculated at
different solar zenith angles (SZAs), the maximum atmospheric effects on the dayside under average solar wind conditions are
found to be typically a few percent of the effects of extreme ultraviolet (EUV) radiation. On the nightside the proton
precipitation is estimated to be intensive enough to be able to produce the measured ionospheric electron densities. The analysis
illustrates that the atmospheric effects are strongly coupled with the global plasma interaction process between Mars and the solar wind.

Article (3.7 MB pdf file)