Solar System Dynamics and the Triggering of the Martian Planet-Encircling Dust Storm of 2018 - Livestream

The Martian planet-encircling dust storm of 2018 began as a vigorous regional storm, localized within the Acidalia storm track, in early June of 2018 (Ls~185°). In typical Martian regional dust storms, dust may be lifted to altitudes of up to about 45 km; however, in the triggering regional storm of 2018, dust was lofted quite rapidly to altitudes above 70 km. Mars Climate Sounder observations of the Martian atmosphere obtained during the earliest days of the storm document the presence of an intensified, regional-scale, meridional overturning circulation at that time. We will review and highlight the MCS observations that support this conclusion.

The strengthened Hadley circulation revealed by the MCS observations is consistent with predictions made in earlier theoretical and modeling studies of orbit-spin coupling. The orbit-spin coupling hypothesis describes and quantifies an exchange of angular momentum between the "reservoirs" of the orbital motion and the rotational motion of a planet. In this process, the angular momentum of a planetary atmosphere may be intermittently augmented, or diminished, by torques arising due to the coupling. We will briefly describe both quantitative and qualitative aspects of the hypothesis. The deterministic nature of solar system dynamics enables the development of forecasts for future Martian dust storm seasons.

Recent work has shown that Martian global-scale dust storms preferentially occur at times when: 1) Mars is gaining orbital angular momentum, during the southern summer dust storm season, and 2) at times when the orbit-spin coupling torques are changing most rapidly. These two triggering modes account for the seasonal timing of all of the known Martian global-scale dust storms of the historic record since 1877. We will briefly review pertinent results of two century-long Martian global circulation model simulations that identify the expected consequences of the torques acting on the large-scale circulation of the Martian atmosphere. A strengthening of atmospheric meridional overturning circulations was noted, prior to simulated GDS events, in both of the prior modeling studies. The inclusion of orbit-spin coupling torques within Martian global circulation models thus clearly brings about an improved correspondence between numerical modeling results and atmospheric observations.

Speaker: Jim Shirley, Jet Propulsion Labs

This meeting will be held using the video conference utility Zoom. The meeting link will be emailed to members. For non-members if you would like to join the meeting, please send an email to the club president asking for the meeting link and telling us a bit about your areas of interest in astronomy.