Sensitivity of Mesoscale Convective Cloud Systems to Changes in Microphysics and the Environment

The structure and evolution of tropical mesoscale convective cloud systems are known to depend on the environment, and on the details of cloud microphysical processes. Shear, buoyancy, and environmental humidity affect convective vertical development and organization, while changes in water phase and the associated energy sources and sinks have a direct influence on cloud mass and precipitation, and an indirect effect on cloud system thermodynamic properties and dynamics. Previous work has explored convective system sensitivity to changes in microphysics and the environment; however, these studies have been limited in scope.

This presentation explores multivariate sensitivity of convective cloud properties and dynamics to changes in cloud microphysics and the environment. Ensemble methods and EOF/PC techniques are used to generate a large number of three dimensional cloud resolving model simulations of deep convection, which are then examined to assess sensitivity. We draw the following conclusions from a comparison of convective response to changes in microphysics vs. environmental characteristics:

1. Variability in microphysics leads to changes in not only cloud content and precipitation, but also vertical velocity and environmental temperature and relative humidity.

2. Modifications to microphysical processes produce changes in cloud properties and radiative fluxes that are of the same order of magnitude as changes in the initial conditions.

3. Assimilation of bulk convective properties (precipitation rate, liquid and ice water path, and radiative fluxes) does not place any substantial constraint on model microphysical parameters.

4. However, when DA is used to restrict the range of precipitation rates, liquid and ice water path, and radiative fluxes, the result is improved constraint on convective updrafts and latent heating rates.