The electrically conducting Martian ionosphere extends from the upper atmosphere of the planet out into space, where it forms an obstacle to the motion of the solar wind in its flow through and around the near-Mars space environment (see e.g., Witasse et al., 2008). Owing to its formation primarily by ionization by solar ultra violet radiation, Mars's ionosphere varies principally with solar zenith angle (SZA) and altitude, h, (or, more accurately neutral atmospheric density). In contrast to the Venus solar wind interaction, which may well be considered somewhat more straightforward, the Mars-solar wind interaction is complicated by two significant factors. First, the larger extent of the Martian exosphere and subsequent ionization of oxygen and hydrogen well outside the ionosphere gives rise to a pronounced pickup ion plume (e.g., Dong et al., 2015), and moreover reduces the extent to which well-defined plasma boundaries can be said to be present separating the solar wind from the ionosphere Abstract 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.Plain Language Summary Mars's atmosphere is exposed to ultra-violet light from the Sun, forming a layer of plasma at high altitudes around the planet. This plasma layer, termed the ionosphere, is strongly affected in terms of its density and temperature, both by external factors like the solar wind and the interplanetary magnetic field (IMF), and internal factors, like Mars's crustal magnetic field. Here...