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Abstract:
Based on the Mars Atmosphere and Volatile Evolution measurements we have observed cases when the fluxes of oxygen ions escaping the Martian ionosphere exceed their median values by more than a factor of 100. In the Martian tail very high fluxes of the more energetic (E > 30 eV) oxygen ions fill the plasma sheet which then becomes much broader than under conditions with median values of ion fluxes. We have analyzed the occurrence of such events in the upper ionosphere near the terminator plane, which is the main source region of ions in the plasma tail. The maximum values of fluxes of oxygen ions with E > 30 eV were observed mostly in the hemisphere where the motional electric field imposed by the solar wind is directed outward from the planet. Although high values of the solar wind dynamic pressure and (or) the motional electric field are favorable for the observation of the extreme values of ion fluxes with E > 30 eV, there must also be other factors which initiate these events. In particular, we found a close relation of the maximum ion fluxes with the values of the simultaneously measured fluxes of solar wind penetrating into the upper ionosphere. Direct interaction of both plasmas might be a critical factor for the strong growth of the oxygen ion escape. Very high fluxes of the low‐energy oxygen ions (E < 30 eV) are often related with ion “clouds” with anomalously large number density observed in the upper ionosphere.
