MAVEN and the mars initial reference ionosphere model

Abstract

The Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite measured the distribution of thermal ions (2-150 amu) at ionospheric heights (~130-400 km) under midday conditions during the "Deep-Dip" orbit campaign from 17 to 22 April 2015. Assuming charge neutrality, we use the sum of NGIMS ions as a proxy for electron density (Ne) and compare results with a new version of the Mars Initial Reference Ionosphere (MIRI) developed for this study. At altitudes where the transition between photochemical and dynamical processes occurs (130-200 km), the NGIMS results agree with the shape of the MIRI-predicted Ne(h) profiles, but the model predictions are a factor of 2 higher. Above 200 km, the NGIMS gradients of total ions versus height diverge even more from MIRI's Ne(h) predictions for reasons that may involve crustal-B field effects, ionopause-like boundaries, and horizontal plasma transport away from the noon sector - factors not yet included in MIRI.