Electron Densities and Temperatures in the Martian Ionosphere: MAVEN LPW Observations of Control by Crustal Fields

Mars Express and Mars Atmosphere and Volatile Evolution (MAVEN) observations have demonstrated the influence of Mars's spatially variable crustal magnetic fields upon the configuration of the plasma in the ionosphere. This influence furthermore leads to variations in ionospheric escape, conceivably in part through the modification of the plasma density and electron temperature in the upper ionosphere. In this study, we examine MAVEN Langmuir Probe and Waves data, finding a clear correspondence between the structure of the crustal fields and both the measured electron temperatures and densities, by first constructing an "average " profile from which departures can be quantified. Electron temperatures are shown to be lower in regions of strong crustal fields over a wide altitude range. We extend previous analyses to cover the nightside ionosphere, finding the same effects present to a lesser degree, in contrast to previous studies where the opposite relationship was found between densities and crustal fields. We further determine the altitude range over which this coupling between both plasma density (and temperature) and crustal fields is effective and use measurements made by MAVEN in the solar wind to explore the dependence of this crustal field control on the coupling to the solar wind and the interplanetary magnetic field (IMF). Based on this, there is some suggestion that variations in the solar wind dynamic pressure are associated with modulation of the effects of the crustal fields on plasma density, whereas the strength of the IMF modulates the crustal fields effects on both electron densities and temperatures.