Circulation and Dust Dynamics at Gale Crater on Mars: Comparisons of MarsWRF and REMS data

The Martian implementation of the Planet Weather Research and Forecasting (PlanetWRF) model, MarsWRF, is used to simulate the atmospheric conditions at Gale Crater for the four seasons (L_s 0º, 90º, 180º, 270º) and different atmospheric opacities. A comparison with the Rover Environmental Monitoring System (REMS) measurements revealed that the model is capable of reproducing the observed weather conditions provided that the atmospheric dust distribution is properly simulated. In addition of capturing the observed annual variability in the winds due to the interaction of the local circulations with the global mean meridional circulation, for all seasons the model predicts rather high wind speeds at night typically in excess of 15 ms^-1. These stronger near surface winds, which are missed by REMS due to the wind sensor cadency, are consistent with the suppressed boundary layer and associated reduction in vertical mixing and explain the higher nighttime dust loadings predicted by the model. Experimentation has also shown that even though the maximum daytime boundary layer depth does not change much with seasons, the time during which it exceeds the height of the crater rim shows a large variability: for L_s 90º it is about 2.9 h whereas for L_s 270º this figure more than doubles to about 6.7 h. This has important implications for the mixing of the air at the bottom of the crater with the outside air. Sensitivity experiments are performed in which the dust lifted in the model is decreased. They reveal that as less dust is suspended in the atmosphere the amplitude of the air and ground temperature diurnal cycle is increased, the surface pressure fluctuations are reduced and the depth of the boundary layer and temporal extension of the daytime convective boundary layer are expanded. The horizontal wind direction and speed are found to be largely insensitive to domain-wide changes in the atmospheric opacity. Given the widespread presence of dust in the Martian atmosphere, these findings have important implications for the simulation of the weather conditions elsewhere on the planet.