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

In Mars Year 35 a large-scale regional dust event started at Ls ~ 35° and lasted until Ls ~ 50°. This was during northern spring whose climate is generally very repeatable from year to year with only local and small regional dust events typically occurring. We designate the event as the MY 35 E (for early) event to distinguish it from the traditional perihelion season A, B and C events. Like all large-scale regional dust events, dust was lofted well above the boundary layer and temperatures in the lower atmosphere (< 50 km) were affected nearly globally. We use a combination of observations by the Mars Color Imager (MARCI) and the Mars Climate Sounder (MCS) onboard Mars Reconnaissance Orbiter to examine the context, development and evolution of this unusual dust event.

MARCI daily images indicate that the MY 35 E event initiated as a textured local dust storm northwest of Olympus Mons and west of Alba Patera. While this is a common location for textured local dust storms, they have not been seen before during this season. It became a regional dust event spreading east, and unusual for the season, began interacting with Alba Patera's mountain flows. This lofted significant dust into the lower atmosphere, spread it well onto the Tharsis plateau and encircled Olympus Mons. Also, water ice clouds above the volcanoes disappeared or were much thinner than usual for the aphelion season.

The MY 35 E event is similar in character to C events that occur after the solstice in the perihelion season, with an expected north/south swap due to the location of the sub-solar point and the direction of the overturning circulation. There is direct heating in the spring or summer hemisphere with a strong dynamical response in the opposite hemisphere. However, the E event warming was less pronounced than warming in most C events as expected due to differences in insolation. Our results suggest that similar dynamical forcings and responses are triggered by these events despite the large seasonal differences in the atmosphere.

Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Government support acknowledged.