Sensitivity of The South Asian Summer Monsoon Circulation to The Cloud Microphysics and Associated Radiative Effects

Previous GCM inter-model comparisons have indicated that cloud feedbacks remain the primary source of uncertainty in determining Earth's equilibrium climate, as cloud processes are pivotal in the coupled land-ocean-atmosphere system through interacting with dynamical, hydrological, radiation, and boundary-layer processes. On the regional scales, biases in cloud-related fields may induce strong control on the the local energy balance and ensuing responses. In this work, we examine the biases associated with the cloud microphysics assumptions with the regional ARW-WRF model simulations in the South Asian summer monsoon region during August 2006. In the first experiment with two-domain 30- and 10-km nested grids, the long- and short-wave radiative effects of the precipitating hydrometeors were nullified. This resembles the common treatment in GCM that does not allow for precipitating forms of liquid or ice to exist at all grid levels between time steps. The major responses took place around the monsoon trough, where enhanced monthly-mean convective activity and meridional overturning circulation were produced. Consequently, the cloud water contents increased by 5% to 25% over India and the Bay of Bengal. Southward shifts of the genesis sites and tracks of the monsoon depressions (MDs) were also seen. In the second and ongoing experiment, the sensitivities of the genesis, track, and intensity of the MDs to various microphysics assumptions are studied with the ARW-WRF model telescoping from 27-, 9-, to 3-km (cloud-system-resolving) grids. Preliminary results suggested strong sensitivities of the MD track, intensity, and frequency of genesis, to the fidelity of the convective and precipitating processes. Further results will be presented and the implicated biases in the regional climate state will be discussed.