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

Global dust storms are the most thermodynamically significant dust events on Mars. The most recent of these events occurred in 2018. Although it was monitored by several spacecraft in orbit and on the surface, many questions remain regarding its onset, expansion and decay. Here, we model the 2018 event with the National Aeronautics and Space Administration (NASA) Ames Mars Global Climate Model in order to better understand the evolution of the storm. Our results highlight a mechanism for the expansion of the storm: the initial equatorial regional storm creates a zonal atmospheric temperature gradient causing strong equatorial eastward winds and thus rapid eastward transport of dust and subsequent lifting. The model shows rapid back and forth transfer of dust between western and eastern hemispheres reservoirs, which may also play an important role in the storm's development through teleconnections involving replenishment of surface dust. The model also shows that gigantic dust plumes occur during the storm's mature phase, injecting dust up to 80 km. Our analysis shows that their upward motion in the atmosphere is due to the ascending branches of Hadley cells, whose intensity is reinforced during the storm with increasing dustiness. We show that the global atmospheric warming during the storm cause vapor and water ice clouds to migrate to higher altitudes, in line with recent observations. Finally, we find that the choice of effective radius for the lifted dust particle size distribution impacts the intensity of the Hadley circulation and could explain some of the differences obtained between model results and observations. Plain Language Summary Global dust storms are planetary-scale events on Mars but remain difficult to predict with climate models because the mechanisms of their onset and evolution are not well known and involve many subtle positive or negative feedbacks between the circulation and heating. The most recent of these events, which began in June 2018, was monitored by several spacecraft in orbit and on the surface. Here, we model this global dust storm with the NASA Ames Mars Global Climate Model to better understand the evolution of the storm. We find that the global dust storm is characterized by a rapid eastward transport of dust in the equatorial regions and subsequent lifting. We highlight rapid back and forth transfer of dust between western and eastern hemispheres reservoirs, which may play an important role in the storm development through long-distance connections between regions involving replenishment of surface dust. We also investigate large dust plumes occurring during the mature phase of the storm and injecting dust up to 80 km. Finally, we find that the height at which water condenses to form clouds increases during the storm, leading to more water vapor in the upper atmosphere.