MarsWRF Convective Vortex and Dust Devil Predictions for Gale Crater Over 3 Mars Years and Comparison With MSL‐REMS Observations.

Key Points: MarsWRF output combined with thermodynamic theory is used to predict temporal and spatial trends of "dust devil activity" in Gale CraterModeled activity and observed vortex pressure drops are both greatest in local summer, peaking ~13:00‐14:00, and smallest in winterSensible heat flux drives increased activity as MSL climbs, but pressure drop numbers increase faster, unless a threshold activity is used Convective vortices and dust devils have been inferred and observed in Gale Crater, Mars, using Mars Science Laboratory (MSL) meteorological data and camera images. Rennó et al. (1998, https://doi.org/10.1175/1520‐0469(1998)055<3244:asttfd>2.0.co;2) modeled convective vortices as convective heat engines and predicted a "dust devil activity" (DDA) that depends only on local meteorological variables, specifically the sensible heat flux and the vertical thermodynamic efficiency which increases with the pressure thickness of the planetary boundary layer. This work uses output from the MarsWRF General Circulation Model, run with high‐resolution nests over Gale Crater, to predict DDA as a function of location, time of day, and season, and compares these predictions to the record of vortices found in MSL's Rover Environmental Monitoring Station pressure data set. Much of the observed time‐of‐day and seasonal variation of vortex activity is captured, such as maximum (minimum) activity in southern summer (winter), peaking between 11:00 and 14:00. However, while two daily peaks are predicted around both equinoxes, only a late morning peak is observed. An increase in vortex activity is predicted as MSL climbs the northwest slopes of Aeolis Mons, as observed. This is attributed largely to increased sensible heat flux, due to (i) larger daytime surface‐to‐air temperature differences over higher terrain, enhanced by reduced thermal inertia, and (ii) the increase in drag velocity associated with faster daytime upslope winds. However, the observed increase in number of vortex pressure drops is much stronger than the predicted DDA increase, although a better match exists when a threshold DDA is used. Plain Language Summary: The daytime Martian atmosphere produces convective vortices called "dust devils" when they are dust‐filled. Vortices produce rapid pressure drops, which have been detected in Gale Crater by Mars Science Laboratory instruments. Observed vortex pressure drops are compared with vortex activity predicted using a numerical model, MarsWRF. Because vortices are far smaller than MarsWRF's grid spacing, the model can't predict them directly. Instead, the theory of Rennó et al. (1998) is used to calculate "dust devil activity" (DDA) – a measure of vortex activity – based on the large‐scale atmospheric state. Predicted DDA matches the general variation of vortex observations with time of day and season, such as maximum (minimum) activity in southern summer (winter), peaking between 11:00 and 14:00. However, while two daily peaks are predicted around both equinoxes, only a late morning peak is observed. Predicted DDA also increases as Mars Science Laboratory climbs the slopes of Aeolis Mons, as observed. This is attributed to (i) larger daytime surface‐to‐air temperature differences at higher altitudes and (ii) faster daytime upslope winds higher up the slopes. However, the observed increase in number of vortex pressure drops is much stronger than the predicted DDA increase, although they match better when a threshold DDA is used. [ABSTRACT FROM AUTHOR]