Comparisons of MAVEN/ROSE Results to an Empirical Ionospheric Model

Abstract:

The Radio Occultation Science Experiment (ROSE; Withers et al., 2018) 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^o- 130^o). For this project, 367 cases qualify as useable data, meaning not only is there data available from 100-200km in height, but they also occur at a SZA of 100^o or less. One of the goals of the MAVEN mission is to assess the status of the topside ionosphere at Mars as a reservoir of possible escaping plasma. To evaluate how ionospheric measurements made by ROSE above the height of maximum electron density (h_max) compare to ionospheric models, we compared ROSE data with the Němec et al. (2019) empirical model of the Martian ionosphere above h_max. The input parameters for the empirical model are solar zenith angle (SZA 100^o), Sun-Mars distance, solar radio flux at Mars, and magnetic field at 400km at the latitude and longitude of interest. To assess congruence between the model and the observations, a deviation factor (DF) is calculated for each predicted electron density profile.

Analysis of DF versus the input parameters exhibits low DFs, and thus higher agreement, for occultations with SZA less than 82^o, than for those cases with higher SZAs. Higher DFs at higher SZAs are perhaps expected, as no high-SZA profiles were used for the model development and the extrapolation to those conditions is problematic. It also shows that lower solar fluxes tend to have higher DF values, while the few occultations with high solar flux are characterized by a small deviation factor. Additionally, peak density (N_max) comparisons indicate high accord between model and measurements with a correlation coefficient (CC) of 0.96. Similarly, the predicted total electron content (TEC) aligns with the calculated values with a CC = 0.85. Finally, the model and the predictions differ more with respect to peak altitude (CC= 0.62 for SZA<90^o).

References:

Němec, F. et al (2019). Characterizing average electron densities in the Martian dayside upper ionosphere. JGR: Planets, 124, 76– 93.

Withers, P. et al (2018). First ionospheric results from the MAVEN Radio Occultation Science Experiment (ROSE). JGR: Space Physics, 123, 4171–4180.