Absorbing aerosol variability over the Indian subcontinent and its increasing dependence on ENSO

• During El Nino the zonal circulation over the Indian subcontinent gains strength.
• Mean air flow at 700 hPa gets intensified from Arabian Peninsula towards India.
• Strong upper level subsidence converges these aerosols over the Indian region.
• Warm SST anomalies at Nino 3.4 region influence this zonal circulation.
• Zonal circulation gets suppressed during La Nina decreasing aerosol concentration.

In this study, the influence of the El Nino Southern Oscillation (ENSO) on the transport, deposition and distribution of absorbing aerosols over the Indian subcontinent during a period of 30 years (1982 to 2011) is investigated. The analysis reveals that the changes in the zonal circulation over the tropics have a significant effect on the aerosol loading over the Indian region. This interannual variability in aerosol concentration arises due to its increasing dependence on the development of sea surface temperature (SST) anomalies over the tropical Pacific Ocean. Significant statistical correlations in SST anomalies confirm this relationship. During El Nino conditions, warm SST anomalies cause the zonal circulation to become pronounced with well-defined areas of rising and sinking motion along a mean air flow driven by convection at the west (the Arabian Peninsula), and subsidence to the east (Indian subcontinent). These intense westerlies at 700 hPa altitude transport large quantities of aerosols from the Arabian Peninsula towards the east and deposit them over the Indian subcontinent. However, a weaker and less organised zonal circulation system associated with cold SST anomalies suppresses the aerosol loading during the La Nina phase.