Mars interannual variability during the dusty southern spring and summer season using Radio Occultation data

Abstract

Dust is one of the major factors influencing the meteorology and climatology of the Martian atmosphere. Southern spring and summer on the planet Mars correspond to periods with increased dust activity.  These periods include pre-, near- and post-  perihelion regional dust storms [Kass et al., 2016]. The exact timing, size, location, and number of dust storms varies from year to year.  Increased dust content can affect a broad region by changing the atmospheric temperature as well as the water propagation from the lower to the upper atmosphere [Karatekin et al., 2023].Here, we use the Radio Occultation profiles to study the interannual variability during the dusty southern spring and summer seasons. Radio occultation is a remote sensing method for vertical profiling of both lower and upper atmosphere providing the variations in tropospheric temperatures as well as electron densities. The data sets we use are publicly available Mars Express (MEX) [Pätzold et al., 2004] and Mars Atmosphere and Volatile EvolutioN (MAVEN) [Withers et al., 2020] radio occultation experiments. Both conduct experiments with spacecraft components consisting of a radio transceiver and a High Gain Antenna (HGA). At the ground, the radio signals are transmitted and received using ESA’s Estrack and/or NASA’s Deep Space Network (DSN) radio antennas (34 m and 70 m). MEX uses simultaneous and coherent dual-frequency downlinks at X-band and S-band, whereas MAVEN uses a single frequency (X-band) to conduct RO experiments. Both MEX and MAVEN are in elliptical orbit. MAVEN makes observations in both ingress (spacecraft disappearing behind the planet as seen from Earth) and in egress (spacecraft reappearing from behind the planet as seen from Earth) with occultation opportunities occurring once per orbital period of approximately 4.5 hours [Withers et al., 2020]. Whereas MEX primarily makes ingress observations with 1–2 occultations per sol. The publicly available MEX and MAVEN residual Doppler measurements are analyzed with the ROB - RO data analysis code [Krishnan et al., 2023].The interannual changes and the variability of the upper atmosphere as well as the neutral atmosphere is investigated. The results are further compared with other observations like MCS and NOMAD and with numerical models as well.