Impact of carbonaceous aerosols on Indian monsoon rainfall

Aerosols - liquid or solid particles suspended in the air - are important constituents of the global atmosphere. Asia is the region of the great source of global carbon emission and this trend is expected to increase in the near future. There are two kinds of carbonaceous aerosols i.e. organic matter (OM) and black carbon (BC). Black carbon stands after only carbon dioxide (CO2) in the list of climate change contributors. BC can directly absorb solar radiation or mix with other aerosols to form atmospheric brown clouds which absorb incoming solar radiation and prevent it from reaching the surface, thereby warming the atmosphere. Thus, in this study, the Laboratoire de Meteorologie Dynamique model (LMD, version 3.3) is used to investigate the possible effect of carbonaceous aerosols over India for the monsoon periods on the atmospheric radiation transfer and over the precipitation. LMDZ.3.3 is integrated for different years for the Indian southwest monsoon periods (seasonal experiments) over the globe for the resolution 96x72x19 (approx. 300 km). Model simulated aerosol optical depth at 550 nm has been validated with satellite data (MODIS). The simulation results show that BC aerosol induce a positive radiative forcing, while organic matter show negative radiative forcing at the top of the atmosphere and a negative radiative forcing at the surface in this region. However, the impact of BC and OM over rainfall is different and complex for different places. The sensitivity studies for carbonaceous aerosols have been done for 21 years (1987-2007) for the monsoon period, and the rainfall is compared with GPCP (Global Precipitation Climatology Project) with the help of Principal component analysis.

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