A Multiannual Record of Convective Instability in Mars’s Middle Atmosphere from the Mars Climate Sounder

Abstract

Gravity waves (GW) transfer energy and momentum from the lower to the middle and upper atmospheres of Earth and Mars. Momentum transfer can occur through the wave dissipative process of saturation associated with convective or shear instability. GW saturation both impacts the atmospheric circulation where saturation occurs and also mediates the GW flux above the level of saturation. It was previously demonstrated that convective instabilities are observable in Mars’s middle atmosphere. Here we characterize the seasonal, interannual, and dust event-driven variability in convective instability in Mars’s atmosphere using retrieved temperature profiles from more than 7 Martian yr of observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. The mean probability of convective instability in the middle atmosphere is <1%, except in the upper portions of the winter westerly jets (≈70 km altitude, 60°–75° N/S), near 30°–40° S and ≈60 km altitude on the dayside in southern summer, and in the tropics at 40–50 km altitude around northern fall equinox. Probabilities of convective instability in or near these three regions can increase by an order of magnitude during planetary-scale dust events and some regional-scale dust events. GW-driven drag on both the equatorial easterly jet and winter westerly jet therefore could increase by an order of magnitude during these dust events, as long as changes in GW properties and the local winds do not provide a compensating reduction of the drag.

Keywords

• Mars
• Planetary atmospheres
• Atmospheric variability