Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Abstract

<p><strong>Abstract.</strong> Thermodynamic soundings for premonsoon and monsoon seasons from the Indian subcontinent are analyzed to document differences between convective environments. Pre-monsoon environment features more variability for both near surface moisture and free-tropospheric temperature and moisture profiles. As a result, level of neutral buoyancy (LNB) and pseudo-adiabatic Convective Available Potential Energy (CAPE) vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher Lifting Condensation Levels (LCLs). LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCL and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.</p>

Microphysical Origin of Raindrop Size Distributions During the Indian Monsoon

“…Most intense storms occur over semiarid regions (Zipser et al., 2006), and hence the decreasing reflectivities are usually associated with the intensity of the convective rain (C. Liu & Zipser, 2013). However, the active monsoon phase is characterized by the humid lower troposphere and low convective cloud bases (Thomas et al., 2018). Supercooled water and ice processes above the freezing level produce large raindrops and the moist boundary layer preserves the tiny raindrops for the efficient warm rain processes thus producing a sharp downward increase in reflectivity for deep convection.…”