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.