Dusty Deep Convection in the Mars Year 34 Planet‐Encircling Dust Event

• Published in: Journal of geophysical research. Planets Vol. 124; no. 11; pp. 2863 - 2892
• Main Authors: Heavens, Nicholas G., Kass, David M., Shirley, James H.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01-11-2019
• Subjects: Atmosphere; Atmospheric water; Cold fronts; Convection; Convection heating; Convective activity; deep convection; Dust; Dust clouds; Dust storms; Earth atmosphere; Equator; global dust storm; Haze; Hurricanes; Mars; Mars climate; Mars dust; Mars volcanoes; Middle atmosphere; Moisture content; Northern Hemisphere; Planetary atmospheres; Planets; Radiative heating; Storm development; Storm tracks; Storms; Thunderstorms; Tides; Towers; Tracks (paths); Trade winds; Tropical environments; vertical mixing; Volcanoes; Water content; Water vapor; Weather
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2019JE006110

Dusty convection, convective activity powered by radiative heating of dust, is a ubiquitous phenomenon in Mars's atmosphere but is especially deep (i.e., impactful on the middle atmosphere) and widespread during planet‐encircling dust events (PEDEs) that occur every few Mars Years (MYs). Yet the relative roles of dusty deep convection and global dynamics, such as the principal meridional overturning cell and the radiative tides, in dust storm development and the vertical transport of dust and water are still unclear. Here, observations from the Mars Climate Sounder on board Mars Reconnaissance Orbiter (MRO‐MCS) are used to study dusty deep convection and its impact on middle atmospheric water content during the MY 34 PEDE (commenced June 2018). Additional context is provided by MRO‐MCS observations of the MY 28 PEDE (commenced June 2007). This investigation establishes that a few, localized centers of dusty deep convection in the tropics formed in the initial phases of both PEDE simultaneously with a substantial increase in middle atmospheric water content. The growth phase of the MY 34 PEDE was defined by episodic outbreaks of deep convection along the Acidalia and Utopia storm tracks as opposed to less episodic, more longitudinally distributed convective activity during the MY 28 PEDE. The most intense convection during both PEDE was observed in southern/eastern Tharsis, where MRO‐MCS observed multiple instances of deep convective clouds transporting dust to altitudes of 70–90 km. These results suggest that Martian PEDE typically contain multiple convectively active mesoscale weather systems.
Plain Language Summary
Just as the heat released by condensing water vapor powers thunderstorms in Earth's atmosphere, very dusty air heated by the Sun in Mars's atmosphere can power dust clouds that tower many tens of kilometers. These dust towers are most common in Mars's rare and impressive planet‐encircling dust events, when dust is rapidly lifted from the surface and the planet's atmosphere fills with a thick haze of dust. But the role of dust towers is unknown. In one view, dust towers randomly form from dust lifted by stronger trade winds in the dust event. In another view, the dust towers organize into a few hurricane‐like storms that spread dust around the planet. Here we study the two most recent planet‐encircling dust events in 2007 and 2018. We find that dust towers first form at the same time as a rapid increase in water at high latitudes observed early in each event. In the 2018 storm, dust tower forming weather systems initially formed near the equator along low elevation pathways along which strong cold fronts in the northern hemisphere may have traveled. Dust towers east of Mars's high Tharsis volcanoes were especially strong.
Key Points
Deep convection during the MY 34 PEDE was more episodic than in the MY 28 PEDE
The tallest convective clouds during the MY 34 PEDE were more than 80 km high
Tropical hygropause altitude increased from 55 km to 65–70 km during the initial convective episode, peaking at 75–80 km during a later one