The Martian ionosphere at solar minimum: Empirical model validation using MAVEN ROSE data

The Radio Occultation Science Experiment (ROSE; Withers et al., 2018, 2020) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite has produced over 400 electron density profiles from July 2016 to November 2019. These N-e(h) profiles occurred over a large range of solar zenith angles (54 degrees - 130 degrees) and solar flux conditions (24-54 solar flux units at Mars). One of the goals of the MAVEN mission is to characterize the status of the topside ionosphere at Mars as a reservoir of possible escaping plasma. Here we evaluate how ROSE topside ionospheric measurements, made predominantly under solar minimum conditions, compare with the only empirical model of the topside ionosphere (Nemec et al., 2019). To assess congruence between the model and the observations, a deviation factor (DF) is calculated for each predicted versus observed N-e(h) profile. Diurnally, low DFs (and thus higher agreement) occur for occultations with solar zenith angles (SZA) < 82 degrees. On a longer time scale, lower solar fluxes tend to have higher DF values. Correlations of the maximum electron density (N-max) of each profile (predicted and observed) have an overall correlation coefficient (CC) of 0.96. Similarly, the observed total electron content of the topside ionosphere (TTEC) agrees with predictions (CC = 0.86). The model and the predictions differ most for the altitude of peak density (CC = 0.62 for SZA < 90 degrees).