Seasonal and inter-annual variability of regional aerosol distribution over the Indian Ocean observed using NOAA-14 AVHRR

The regional distribution of atmospheric aerosols over the Indian Ocean, Bay of Bengal and Arabian Sea during the Asian winter monsoon period of November to April, and its inter annual variability during 1996 to 1999 are studied. During the winter monsoon period, the predominantly northeasterly winds from the Asian continent transport large amount of polluted air mass deep into the otherwise pristine ocean areas. The aerosol optical depth (AOD) is obtained by inverting the observed radiance in channel I of NOAA-14 AVHRR after accounting for multiple scattering and absorption due to aerosols and molecules and the wind dependence of sea surface reflectance. The Scattering phase function and single scattering albedo used for the estimation of AOD are based on the in situ measurements of physical, chemical and optical properties of aerosols in this region during the Indian Ocean experiment (INDOEX). Transport of aerosols from continental areas into the oceanic environments is studied using a combination of regional atmospheric circulation and the aerosol distribution over the oceanic regions. It is observed that the Bay of Bengal region is significantly affected by large-scale transport of aerosols from the Southeast Asia and the Indian subcontinent. Aerosol distribution over the Arabian Sea is mainly controlled by the transport from the Indian subcontinent and the Arabia. Continental aerosols are transported deep into the Indian Ocean up to the Inter Tropical Convergence Zone (ITCZ). The aerosol distribution shows significant monthly and year-to-year variability at the north of ITCZ.