Influence of aerosol-cloud interaction on austral summer precipitation over Southern Africa during ENSO events

Abstract

In the present study, we are investigating the role of aerosols-and clouds in modulating the austral summer precipitation (December–February) during ENSO events over southern Africa region for the period from 2002 to2012 by using satellite and complimentary data sets. Aerosol radiative forcing (ARF) and Cloud radiative forcing (CRF) shows distinct patterns for El-Nina and La-Nina years. Further analysis were carried out by selecting the four Southern Africa regions where the precipitation shows remarkable difference during El-Nino and La-Nina years. These regions are R1 (33°S–24°S, 18°E–30°E), R2 (17°S–10°S, 24°E–32°E), R3 (19°S–9°S, 33°E–41°E) and R4 (7°S–0°S, 27°E–36°E). Aerosol Optical depth (AOD) shows considerable differences during these events. In region R1, R2 and R3 AOD shows more abundance in El-Nino years as compared to La-Nina years where as in R4 the AOD shows more abundance in La-Nina years. Cloud Droplet Effective radius (CDER) shows higher values during La-Nina years over R1, R2 and R3 regions but in R4 region CDER shows higher values in El-Nino years. Aerosol indirect effect (AIE) is estimated both for fixed cloud liquid water path (CLWP) and for fixed cloud ice path (CIP) bins, ranging from 1 to 300 gm–2 at 25 gm–2 interval over all the selected regions for El-Nino and La-Nina years. The results indicate more influence of positive indirect effect (Twomey effect) over R1 and R3 region during El-Nino years as compared to La-Nina years. This analysis reveals the important role of aerosol on cloud-precipitation interaction mechanism illustrating the interlinkage between dynamics and microphysics during austral summer season over southern Africa.