Variability in ionospheric total electron content at Mars

Abstract

The Mars Express (MEX) mission includes a multi-purpose radio instrument called the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). When used in its ionospheric-penetrating subsurface sounder (SS) radar mode, a by-product of the MARSIS observations is the ray-path-integral of electron densities, called the total electron content (TEC). We have used the initial TEC database of approximately 1.2 million TEC values spanning the period June 2005 to September 2007 to study the basic characteristics of TEC morphology and variability. We find quantitative agreement between the TEC values measured and those computed from model simulations of global diurnal behavior. With the basic photo-chemistry of the martian ionosphere a well understood process, it is the departures from average conditions that need specification and modeling. Here we use MARSIS TEC to do this quantitatively. We explore the specification of variability using different ways to define it: standard deviations from sample averages versus departures from control curves.