Effect of seasonal variability of aerosols in radiative forcing and Indian summer monsoon rainfall over south Asia during ENSO events

Abstract

The analysis of seventeen years (2001–2017) of satellite and MERRA-2 model data products demonstrates the influence of seasonal variability of aerosols on Indian summer monsoon rainfall and Aerosol Direct Radiative Forcing (ADRF) at the Top of the Atmosphere (TOA) as well as at the Surface (SFC) during El-Niño/Southern Oscillation (ENSO) events over South Asia. In order to understand the ENSO influence, deviations were quantified from normal years to El-Niño (E_dev) and La-Niña (L_dev) years. This study investigated greater spatial variability of net ADRF at the TOA (−3 to +3 W m⁻²) and at the SFC (−5 to +6 W m⁻²) during the JJAS season during El-Niño years over northwest India, Himalayan region and central India compared to La-Niña years. It is interesting to note that the magnitude of ADRF is highly variable during the post-monsoon season at both the SFC and TOA. The radiative forcing at the SFC varies significantly, more than (±) 10 times the mean during pre-monsoon season. An important observation is the negligible deviation of radiative forcing (L_dev)at the TOA particularly in the post-monsoon season. Moreover, this study also demonstrates and compares the seasonal variability of aerosols with radiative forcing and their effect on summer monsoon rainfall quantification by using a statistical multiple regression model.