Martian crustal magnetic fields and their control of ionospheric plasma densities and temperatures

Mars Express and 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. However, quantifying this control remains challenging given the generally dynamic and spatially varied nature of the Mars solar wind interaction, and the therefore naturally varying densities and temperatures of the upper ionosphere in particular. In this study we examine MAVEN Langmuir Probe and Waves data, finding a very clear correspondence between the structure of the crustal fields and both the measured electron temperatures and densities, by first constructing a robust “average” profile from which departures can be quantified. Electron temperatures are shown to be systematically lower in regions of strong crustal fields over a wide altitude range, as has been previously reported. Here, we additionally 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 IMF.  We also attempt to quantitatively determine the altitude range over which this coupling between plasma density and temperature and crustal fields is effective.