Dust lifting on Mars: towards better representations of reality

To date, no numerical model of the global martian atmosphere has been able to fully capture the range and variability of martian dust storms. One major difficulty is that the largest (sometimes planet-encompassing) dust storms are global manifestations of what begin as local scale processes, and it is not feasible to run a global model at high enough resolution everywhere to capture both localized dust lifting events and regional storm expansion. We will present results showing the wind stresses, dust lifting and dust storms generated in the MarsWRF model [Richardson et al., JGR 2007] run at different global resolutions, and discuss why the threshold wind stress chosen (with dust lifted only when this value is exceeded) has a major impact on results. A partial solution is to run at higher resolution in areas thought to be major dust injection centers, but this risks biasing results towards the regions selected. We will present some results from MarsWRF simulations with high resolution 'nests' over regions such as the Hellas basin to look at this effect.

Another problem common to many global dust cycle modeling efforts is the assumption of an unlimited supply of surface dust. This precludes any region running out of dust, and so prevents the possibility of increased variability and range of storm types as primary lifting centers become depleted of dust and then refill over several years. We will present results showing the impact of allowing the MarsWRF model to determine the surface dust distribution in a self-consistent manner (i.e., as predicted over time due to its own lifting and deposition parameterizations) and will discuss how this affects the realism of dust cycles and storms predicted by the model.