P24     Two moment coupled microphysics on Mars.

Lee, Christopher, University of Toronto, Canada

Dust and water ice aerosol significantly enhance the variability of the Martian climate by providing a nucleation source for condensational ice growth and through scattering and absorption of visible and thermal radiation. The combination of strong forcing feedback and coupling has led to various problems in understanding and modeling of the Martian climate: in reconciling cloud abundances at different locations in the atmosphere, in generating a stable dust cycle, and in preventing numerical instability within models.

The terrestrial two-moments Morrison and Gettelman (2008) scheme has been modified for use in MarsWRF, including the simulation of transport and microphysics of coupled dust and water ice particles. Dust is tracked using a single two-moment tracer with fixed effective variance, and water ice is tracked using a three-moment tracer allowing the dust cores of the ice particles to be tracked along with the ice mass in the particles. This novel method allows dust to be scavenged from the atmosphere by ice nucleation and provides preferential scavenging of larger particles because of their increased nucleation efficiency. Nucleation and condensation microphysics use a finite bin scheme with dynamically chosen bin edges to resolve all particles sizes better. Nucleation and condensation are implemented to maintain numerical stability during the fast microphysical processes, and the microphysics can be used at the dynamical timesteps of the parent atmospheric model.

In the coupled simulations, we show that climate variability has been increased over seasonal and annual timescales, strong 'solstitial pause' features are produced in both winter high latitude regions, and dust storm seasons are more varied, with early southern summer (Ls 180) dust storms and/or more than one storm occurring in some seasons.