Simulation of the 2018 Global Dust Storm on Mars Using the NASA Ames Mars GCM: A Multi-Tracer Approach

Global dust storms are the largest, longest-lasting, most dramatic and thermodynamically significant dust events on Mars. They are produced from the combination of multiple local and regional lifting events, and maintained by positive-radiative feedbacks between dust lifting, atmospheric heating and the strengthening circulation leading to further dust lifting. While the most recent of these events, which occurred in June-September 2018, has been monitored by several spacecraft in orbit and on the surface of Mars, many questions remain regarding the mechanisms controlling its onset, expansion and decay. Here we model the 2018 global dust storm with the NASA Ames Mars Global Climate Model, and we analyze the dust pathways, sources and sinks in order to understand the impact of the general circulation, thermal tides and finite dust reservoirs on the evolution of the storm. Our results show that the global dust storm is characterized by a rapid eastward transport of dust in the equatorial regions, and the subsequent triggering of further lifting, which was a key aspect of the development of the MY25 equinoctial season storm as well. In particular, we highlight the rapid back and forth transfers of dust between western and eastern reservoirs, which may play an important role in the storm development, as they allow for the fast replenishment of the surface with available dust. We also find that dust is efficiently transported upward by the Hadley cell circulation and the diurnal cycle of atmospheric heating, which both increase in intensity as more dust is injected into the atmosphere. In particular, the model predicts large plumes of dust during the mature stage of the storm, resembling planet-scale rocket dust storms, and injecting dust up to 80 km. As a result of atmospheric warming in response to dust heating, we find that the water ice cloud condensation level migrates to higher altitudes, leading to enrichment of the upper atmosphere in water vapor. In our simulations of the storm, the intensity of the Hadley cell is significantly stronger than that in non-dusty conditions.