Abstract
Abstract. Electrons with energy of ~40–80 eV measured by the instrument ASPERA-3 on Mars Express and MAG-ER onboard Mars Global Surveyor are used to trace an access of solar wind electrons into the Martian magnetosphere. Crustal magnetic fields create an additional protection from solar wind plasma on the dayside of the Southern Hemisphere by shifting the boundary of the induced magnetosphere (this boundary is often refereed as the magnetic pileup boundary) above strong crustal sources to ~400 km as compared to the Northern Hemisphere. Localized intrusions through cusps are also observed. On the nightside an access into the magnetosphere depends on the IMF orientation. Negative values of the ByIMF component assist the access to the regions with strong crustal magnetizations although electron fluxes are strongly weakened below ~600 km. A precipitation pattern at lower altitudes is formed by intermittent regions with reduced and enhanced electron fluxes. The precipitation sites are longitudinally stretched narrow bands in the regions with a strong vertical component of the crustal field. Fluxes ≥109 cm−2 s−1 of suprathermal electrons necessary to explain the observed aurora emissions are maintained only for the periods with enhanced precipitation. The appearance of another class of electron distributions – inverted V structures, characterized by peaks on energy spectra, is controlled by the IMF. They are clustered in the hemisphere pointed by the interplanetary electric field that implies a constraint on their origin.
Highlights
Mars presents a nonmagnetized, conducting obstacle to solar wind with local magnetizations
We have explored the access of the magnetosheath electrons (40≤Ee≤80 eV) into the Martian magnetosphere, and the role of the IMF and crustal magnetic fields
It is shown that crustal sources in the Southern Hemisphere located in the longitude range of 130◦−240◦ contribute essentially to the pressure of the obstacle deflecting solar wind around Mars on the dayside
Summary
Mars presents a nonmagnetized, conducting (due to the presence of the ionosphere) obstacle to solar wind with local magnetizations. It was shown that the crustal magnetic fields act as an additional screen protecting the lower atmosphere/ionosphere from direct contact with solar wind (Fraenz et al, 2006). Mitchell et al (2007) inferred a magnetic field pattern below 400 km altitude with implications for the formation mechanisms of the dichotomy on Mars from analysis of electron angular distributions. We present further observations made by the electron spectrometer ELS on Mars Express (MEX) to infer a picture of access of solar wind electrons into the Martian magnetosphere based on more than two years of ASPERA-3 measurements. A mechanism of the generation of such electron distribution is discussed
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