Concurrent effects of Martian topography on the thermosphere and ionosphere at high northern latitudes

Abstract

Abstract Martian topography modulated non-migrating tides play important roles in the upper atmosphere and thus in the ionosphere through their coupling, especially in their longitude variations. In this study, the neutral scale height (H n ) and ionospheric peak electron density (N m M 2 ) and height (h m M 2 ) retrieved from the MGS radio occultation measurements were used to investigate the coupling between the Martian thermosphere and ionosphere under the forcing of topography modulated tides by investigating their concurrent longitude variations. A segment of the measurements with fixed local time was selected to analyze the relationships between the longitude variations of the parameters in detail. Longitude variations of the thermosphere and ionosphere are significant though topographic fluctuations are not very prominent at high northern latitudes. Longitude fluctuations of H n and N m M 2 are nearly in anti-phase and percentage fluctuation amplitudes of H n are nearly twice as large as those of N m M 2 , which indicate the non-migrating tide forced coupling between the ionosphere and thermosphere conforms to the Chapman theory, and suggests longitude variation of N m M 2 can be used as a quantitative indicator for that of the thermal structure in the lower thermosphere. Longitude variation phases of H n and h m M 2 are also discrepant. That is due to tide vertical propagation since H n and h m M 2 depend on the atmospheric thermal structures at different height levels. The thermosphere and ionosphere show longitude variations due to the topography; however, they are dominated by inconsistent longitude components. This implies discrepant exciting and propagating efficiencies of various topography modulated tides. Graphical Abstract

Keywords

• Martian ionosphere
• Neutral scale height
• Longitude variation