An Investigation of the Encirclement of Mars by Dust in the 2018 Global Dust Storm Using EMARS

Determining how global dust storms originate and develop is one of the major challenges of Martian meteorology. We model the 2018 global dust storm using the Ensemble Mars Atmosphere Reanalysis System (EMARS), combining satellite observations with a Mars global climate model via data assimilation. A reanalysis is a valuable data set for this investigation because it is anchored to the real Martian atmosphere by temperature and dust observations, and the model provides full 4D coverage of wind fields, which are not directly observed and are key to assessing advection. Dust was observed to encircle the northern hemisphere early on in the storm's development. This encirclement could be caused by either the formation of new lifting centers along the path of observed encirclement or the advection of dust from active lifting center(s) elsewhere. Results from EMARS, including particle advection from inferred EMARS winds, provide evidence that the aforementioned dust encircling Mars's northern hemisphere may come from the initial lifting center of the storm, near Chryse Planitia. We propose that dust from the initial lifting center of the storm was entrained into the Martian Hadley circulation, with the assistance of the thermal tides, and then entrained into the northern hemisphere westerly jet. Plain Language Summary About once every three Martian years, or about once every five Earth years, a global dust storm envelops most of Mars, lasting for months. The 2018 global dust storm discussed in this paper began near the solar-powered rover Opportunity. The large amount of dust in the air during a global dust storm can reduce sunlight so much that the Opportunity rover lost power during the 2018 storm, resulting in end of mission. Despite the effect dust has on movement of Martian air, little is known about how global dust storms form and grow. Scientists have historically considered two features of growing global dust storms to be important. One is the existence of multiple locations on Mars where dust is lifted high into the air from the surface. The other is the spreading of dust around Mars, forming a dust ring in the Martian air. We investigate the spreading by combining satellite observations with computer simulations using basic physics equations applied to air. Early in this storm's growth, dust spread eastward and formed a ring around Mars's northern hemisphere. Our computer simulations suggest that dust may have been lifted from one region near Opportunity and moved around the planet by wind.