Structure and Controls of the Martian Nightside Ionosphere From One Solar Cycle of MAVEN Observations
Journal Article
Overview
abstract
Abstract; This study characterizes the structure and variability of electron density and temperature in the Martian nightside ionosphere using MAVEN measurements spanning one full solar cycle. Our analysis focuses on altitudes between 150 and 400 km within the nightside region, defined by solar zenith angles (SZA) > 120. We statistically investigate the effects of external drivers (solar EUV irradiance, solar wind dynamic pressure , and interplanetary magnetic field (IMF)), ambient crustal magnetic fields, and spatial asymmetries across SZA and local time. A multidimensional distribution‐matched subsampling approach is applied to isolate the effects of individual factors while controlling for all others. The nightside ionosphere is found to exhibit a coherent vertical structure characterized by prominent slope changes near 200 km in and 300 km in . Solar EUV irradiance is the primary controlling factor: High EUV conditions produce enhanced across all altitudes and systematically reduced . Crustal magnetic fields modulate this structure, with strong field regions exhibiting depleted at low altitudes and reduced at higher altitudes. Spatial asymmetries are primarily organized by SZA, with decreasing toward the deep nightside, while a secondary local‐time asymmetry leaves lower on the dawnside than on the duskside. Notably, the nightside ionosphere exhibits little statistical sensitivity to the upstream solar wind state ( and IMF), suggesting that particle precipitation is probably not the primary global ionization source above 150 km and that the nightside ionosphere is instead sustained primarily by plasma transport from the dayside.
