MAVEN ROSE Observations of the Response of the Martian Ionosphere to Dust Storms

During a Martian dust storm, the lower atmosphere is heated locally. Due to dynamical effects, the upper atmosphere and ionosphere can be lifted upward on a global scale by approximately 10 km. The connections between lower atmospheric dust events and associated ionospheric responses are poorly understood due to limited observations. Here, we present MAVEN Radio Occultation Science Experiment (ROSE) observations of ionospheric peak altitude during dust events in 2018 and 2016. In June 2018, a planet-encircling dust event arose from the Acidalia storm track in the northern hemisphere. Ionospheric peak altitudes at around 20 degrees S were normal in ROSE egress observations on 19 June and 22 June and then 10-15 km higher on 26 June and thereafter. Ionospheric peak altitudes at around 50 degrees N were also elevated in ROSE ingress observations, which began on 17 June. This suggests that the ionospheric peak altitude was affected by the dust event in the northern hemisphere before the southern hemisphere. We also observe evidence that smaller dust storms can trigger ionospheric responses: In July-October 2016, ionospheric peak altitudes at solar zenith angles of 54-70 degrees and latitudes of 50-80 degrees S were 20 km higher than expected. These observations were acquired during a modest "A storm" during a year without a global dust storm.