Interannual Variability In The Shortwave Aerosol Direct Radiative Forcing Over The Oceanic Areas Around The Indian Subcontinent During Dry Season

Impact of atmospheric aerosols on the radiation budget of the Earth-atmosphere system and climate is well recognized. The spatial distribution and the properties of atmospheric aerosols over the oceanic areas around the Indian subcontinent during the Asian dry season (November-April period) are significantly governed by the transport of continental air from the adjoining landmass. In the present study, we report the estimated spatial distribution of monthly mean aerosol direct radiative forcing (ADRF) at the top-of-atmosphere (TOA), within the atmosphere, and at the earth's surface over the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean during the Asian dry season, based on the regional distribution of aerosol optical depth (AOD) derived from NOAA14/16-AVHRR data during 1996-2003, and the model estimates of the diurnal mean normalized aerosol radiative forcing (NADRF) which also compares fairly well with the earlier observations reported over this region. The diurnal mean NADRF varies with latitude and Julian day. Its value at TOA (for AOD at 550nm) is in the range -26.5 Wm(-2) AOD(-1) to -29.5 Wm(-2) AOD-1 while the corresponding value at surface is in the range -77 to -95 Wm(-2) AOD-1. In the Northern Hemisphere, ADRF is in the range -4 to -14 Wm(-2) at TOA, -2 to -42 Wm(-2) at the surface and 8 to 28Wm(-2) in the atmosphere. During the Asian dry season highest DMADRF is observed in the northwest Bay of Bengal followed by the southeast Arabian Sea during the March-April period.