Spatial gradients in aerosol characteristics over the Arabian Sea and Indian Ocean

Abstract

Aerosol spectral optical depths (τ_pλ) estimated at 10 wavelengths in the visible and near infrared range over oceanic regions covering near and far coastal regions of the Arabian Sea and remote areas of the equatorial Indian Ocean adjoining the Indian peninsula have been used to study the spatial variation of aerosol optical depths over the ocean. Size parameters and concentrations of aerosols along the downwind direction have been derived with a view to studying the effect of the continent on aerosol properties over the ocean. The studies showed a gradual decrease in τ_pλ with fetch distance D with an e^−l scaling distance in the range of 1700 to 2400 km under calm to moderate wind conditions. The scaling distance increases with increase in wind speed. A significant increase in the relative concentration of small (accumulation size range) particles is seen as the continent is approached from deeper oceanic regions downwind, indicating increased influence of anthropogenic activities. The coarse-particle concentration appears to be of oceanic origin and remains nearly steady over the entire region when the winds are low to moderate.