Latitudinal variation of aerosol optical depths from Northern Arabian Sea to Antarctica

Abstract

Measurements of the spectral aerosol optical depths (AODs) were made over the Arabian Sea, Indian Ocean, Southern Ocean, and Antarctica during a trans-continental cruise experiment conducted during January to April 2006. Our investigations show that AODs (at 500 nm) remain low (≤0.1) and steady in the Southern Indian Ocean (20°S to 40°S). In contrast, large latitudinal gradients exist north of 20°S. The AODs increase nearly exponentially from ∼0.1 near Antarctica to reach a value as high as 0.7 in the northern Arabian Sea (∼15°N). The latitudinal gradients were larger in summer than in winter. The comparison of measured daily optical depths with those retrieved from MODIS satellite sensor showed good agreement (within ∼0.02) for regions north of 40°S. The AODs were higher over remote oceans between 40°S to 60°S (MODIS observations) latitudes as a result of enhanced sea-salt production due to high winds associated with the ‘Roaring Forties'.