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

[1] 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.’