Potential modulations of pre-monsoon aerosols during El Niño: impact on Indian summer monsoon

The potential role of aerosol loading on the Indian summer monsoon rainfall during the El Nino years are examined using satellite-derived observations and a state of the art fully interactive aerosol-chemistry-climate model. The Aerosol Index (AI) from TOMS (1978–2005) and Aerosol Optical Depth (AOD) from MISR spectroradiometer (2000–2010) indicate a higher-than-normal aerosol loading over the Indo-Gangetic plain (IGP) during the pre-monsoon season with a concurrent El Nino. Sensitivity experiments using ECHAM5-HAMMOZ climate model suggests that this enhanced loading of pre-monsoon absorbing aerosols over the Indo-Gangetic plain can reduce the drought during El Nino years by invoking the ‘Elevated-Heat-Pump’ mechanism through an anomalous aerosol-induced warm core in the atmospheric column. This anomalous heating upshot the relative strengthening of the cross-equatorial moisture inflow associated with the monsoon and eventually reduces the severity of drought during El Nino years. The findings are subject to the usual limitations such as the uncertainties in observations, and limited number of El Nino years (during the study period).