Observations of the Mars Year 35 E (Early) Large-Scale Regional Dust Event

Abstract:

We report on an unusual large-scale regional dust event that started at Ls ~35° of this Mars year (early June 2019). The event occurred in Northern spring during the aphelion season, when the atmosphere of Mars is usually relatively clear. As the event developed, the atmospheric circulation was transitioning from the equinoctial (2-cell) to perihelion (1-cell) circulation. While dust storms, even regional ones, are not unknown at this season, they are generally confined to the boundary layer. The perturbations from the event lasted through Ls ~50°, or around 30 sols. We will examine observations from Mars Climate Sounder (MCS) and Mars Color Imager (MARCI) on MRO over the course of the event.

The MY 35 E event was unique to the record over the last Mars decade in almost all aspects and best resembles the large-scale regional events seen during the dusty season. This is particularly the case for its impact on the atmosphere beyond the boundary layer. The event appears to have initiated to the northwest of Tharsis and migrated East, probably interacting with Alba Patera. Eventually, a dust haze at altitude extended over most of the northern hemisphere, increasing temperatures and significantly reducing ice cloud opacity.

There was significant dust-driven warming of the atmosphere well above the boundary layer. At 50 Pa (~25 km), northern mid-latitude temperatures increased by over 25 K (from ~165 K to over 190 K). There were significant temperature increases at all longitudes as the event evolved and zonal mean temperatures increased by ~20 K at 50 Pa. However, the largest difference from usual events at this season was the significant dynamical response in the southern hemisphere, a feature not previously seen in any dust event between Ls 340° and Ls 150°.