Day-To-Night Ionosphere Transport by Neutral Winds

Abstract:

Nightside low altitude nightside ionosphere production sources for the terrestrial planets are either transport from the dayside and production due to energetic particle impacts. The transport can be driven by ion coupling to the neutral atmosphere motions as part of the general atmospheric global circulation patterns and/or by ionosphere density gradients near the terminators produced as a result of a dayside source of ionization (photoionization) and a nightside sink (chemical losses). The day to night transport of ionization at high altitudes on Venus (during solar max and at Earth maintains the ionosphere throughout the night. This is not the case for Mars, where the dense ionosphere carried from the day does not extend much further than ~120 degrees solar zenith angle. Although predicted neutral wind speeds in the lower thermosphere of Mars are comparable to those on Earth and Venus, the winds at Mars can have larger impacts on horizontal transport since the planet’s circumference is much smaller. One prominent effect of the winds is indicated by the observed rapid global dispersal of long-lived metal ions associated following the short, localized impact of the meteor storm associated with Comet Siding Spring . This paper will explore wind control of the low altitude Mars ionosphere ion composition measurements across the terminator from day into night, using the Neutral Gas Ion Mass Spectrometer instrument on MAVEN with the wind patterns predicted by the Mars Global Ionosphere-Thermosphere Model (M-GITM).