Spatial heterogeneity of stratiform precipitation response to aerosol fast adjustments over India: A general circulation model study with ECHAM6-HAM2

Abstract:

The response of precipitation changes to aerosol emissions can be decomposed into stratiform and convective components which can be understood using an atmospheric energy budget framework. This work focusses on the fast timescale of rapid adjustments of the atmosphere to aerosol changes using a chemistry coupled atmospheric general circulation model, ECHAM6-HAM2. These effects are extracted from two simulations, using prescribed SST with different aerosol emission levels at 1971 and 2010 levels. The precipitation response to increased aerosol emissions during peak monsoon shows a large spatial variability with increases over the Northern Indian region and decreases over the Southern Indian region. The spatial heterogeneity is associated with the spatial variability in the dynamic component of divergence of the dry static energy linked to rapid regional circulation changes, along with increase in lower tropospheric stability, leading to simulated increases in moisture content over the North Indian region. However, this spatial variability is shown only in stratiform precipitation responses, through aerosol induced changes in cloud liquid water path. Aerosol-cloud interactions play an important role in the stratiform rainfall response with the precipitation formation processes, autoconversion and accretion showing large increases over the Northern Indian region. The findings in this work suggests that precipitation response over the short timescale can behave differently in stratiform and convective clouds, under the influence of distinct processes.