Examining the Sensitivity of Regional Scale Cloud Properties to Convective Microphysics

A two-moment microphysics scheme for deep convection was implemented in the NCAR Community Atmosphere Model version 5 (CAM5) by Song et al. (2012). The new scheme improved hydrometeor profiles in deep convective clouds and increased deep convective detrainment, reducing the negative biases in low and mid-level cloud fraction and liquid water path compared to observations. Here, we examine in more detail the impacts of this improved microphysical representation on regional scale water and radiation budgets.

As the primary source of cloud water for stratus clouds is detrainment from deep and shallow convection, the enhanced convective activity leads to larger stratus cloud fractions, higher cloud water content, and more stratiform precipitation in all oceanic regions examined, particularly in the subtropics. This can be seen also in increased values of net cloud radiative forcing. Over land regions, cloud amounts are reduced, leading to weaker cloud forcing and increased OLR. The magnitude and, occasionally, the sign of the changes in cloud properties can differ if scaled by the precipitation produced in a region, and much of the changes occur in the mixed phase region of the atmosphere. This indicates that the complex interactions between liquid and ice phase microphysics can effect changes in regional scale circulations.

We will present details of the large scale water and radiation budgets and the microphysical budgets of cloud liquid and ice for several regions. Results will be compared to cloud resolving model simulations.