Impact of aerosol optical depth on seasonal temperatures in India: A spatio-temporal analysis

Abstract

The third assessment report of the Intergovernmental Panel on Climate Change (IPCC) describes the clear modulating effect of aerosols both directly and indirectly on the prevailing climatic conditions on the Earth's surface. Several studies have noted higher than average concentrations of aerosols over the densely populated Indian subcontinent and adjacent regions. The study focuses on seasonal-level spatial patterns of aerosol optical depth (AOD) concentrations and their relationship with near-surface air temperatures. The period of analysis includes the years 2000 to 2005 for the summer monsoon season, and 2001 to 2005 for the winter season. The overall patterns of AODs show higher concentrations over the densely populated and highly industrialized Gangetic basin for bot9h seasons. The AOD-temperature relationship was predominantly negative, meaning that higher AOD concentrations resulted in lower temperatures for both seasons over northeastern India and the west coast, in the vicinity of Mumbai. Temperatures in the interior northwestern sector of the subcontinent, extending northwards towards Kashmir, experienced positive forcing during the summer season. The winter-season relationship was predominantly negative, whereas during the summer monsoon season it was neutral to positive. The differences in responses may be attributed to the impact of overcast skies and heavy precipitation during the summer monsoon season, leading to longwave radiation being trapped inside the Earth's atmosphere, producing higher minimum temperatures. However, predominantly clear skies during the winter season resulted in a negative forcing by aerosols on the surface temperatures.