Characteristics of Dust Devils in Two Pre-Selected Landing Regions of the Tianwen-1 Mission - Comparing Observations and Predictions Using Numerical Model.

The spatial and temporal distribution of dust devils (DDs) in the two pre-selected landing regions (ZA and ZB) of the Tianwen-1 mission in southern Utopia Planitia have been investigated by using images from the Context Camera (CTX) of the Mars Reconnaissance Orbiter (MRO). From the images of the regions in 8 Martian years, no DD was found in ZA, while 77 DDs were found in ZB. The observed DDs are mainly distributed in the northeastern part of ZB. The temporal variation in the observed DDs shows a prominent two-peak pattern in their local early spring and late summer. The size and height of the observed DDs have also been evaluated from the images, and they show a similar temporal variation as the occurrence. To investigate the possible conditions pertinent to these observed patterns of DD distribution, some analysis based on the thermodynamic theory of heat engines was performed using the output of the Mars climate model, MarsWRF. The spatial and temporal distribution of the simulated DDs are generally consistent with the observation, with significantly more DDs in ZB. Analysis of the model results suggests that the spatial distributions of the predicted DDs are mainly related to the distribution of sensible heat flux, which, in turn, is mainly determined by the surface-to-air temperature difference. The difference in DDs between ZA and ZB (more DDs in ZB) is dominated by the difference in sensible heat flux, which, in turn, is mainly related to the spatial variation of surface albedo.