Cloud-scale dynamical and microphysical properties in contrasting monsoon environments from observations and simulations

Abstract

Three distinct environmental regimes (moist-rainy monsoon, dry-intermittent-rainy monsoon and post-monsoon) based on atmospheric moist static energy and surface rainfall measurements over the rain shadow region of the Indian peninsula are investigated with large eddy simulation (LES) model and in situ cloud microphysics observations. Cloud condensation nuclei (CCN) number concentration measurement showed increased values for dry-intermittent-rainy monsoon and post-monsoon seasons and aerosol activation characteristics were distinct.The model simulation showed general features as deeper clouds with higher fractional cloud coverage and rain water formation for the moist-rainy monsoon environment compared to the dry-intermittent-rainy and post-monsoon environments. The highest ice water content in the mixed-phase region was noted for the moist-rainy monsoon case and conversion to rain water occurred through the melting of ice. Dry-intermittent-rainy and post-monsoon clouds have no rainwater in the model due to smaller droplet size and lower cloud depth. Cloud core buoyancy, latent heating and updraft velocity are relatively higher (except at the cloud-top level) for the dry-intermittent-rainy monsoon conditions compared to the moist-rainy monsoon conditions. A higher negative buoyancy (associated with latent cooling) at the cloud top curtails cloud growth in dry conditions. Convective mass flux and lateral entrainment rate have decreased with drier environmental conditions. This indicates that clouds are less diluted and mixed with the environmental air in the dry-intermittent-rainy conditions and thereby maintain higher liquid water content in the cloud core region.