Earth Planets Space, Vol. 64 (No. 2), pp. 121-134, 2012
Catherine Diéval1, Esa Kallio2, Gabriella Stenberg1, Stas Barabash1, and Riku Jarvinen2
1Swedish Institute of Space Physics, SE-98128,
2Finnish Meteorological Institute, FIN-00101, Helsinki, Finland
(Received February 16, 2011; Revised June 11, 2011; Accepted August 20, 2011; Online published March 8, 2012)
We study the dependence of proton precipitation patterns onto the Martian upper atmosphere on altitude, proton energy, proton origin, and in a lesser extent, solar zenith angle, using the HYB-Mars model, a 3D quasi-neutral hybrid model. We find that the flux of precipitating protons has a strong altitude dependence: on the dayside, the flux of precipitating protons decreases substantially when the altitude over Mars decreases. We also find that the contribution of exospheric protons to the deposition is significant and its spatial distribution is not identical to that of the solar wind protons. In addition, the low energy proton population comes mainly from the newborn planetary protons. The energized pick-up protons and solar wind protons contribute to the higher energy proton population. The study also confirms that the proton precipitation is highly asymmetric with respect to the direction of the convection electric field in the solar wind. The study implies that the Martian induced magnetosphere protects the upper atmosphere effectively against proton precipitation.
Key words: Solar wind, Mars, proton precipitation, Martian atmosphere, magnetospheres.