Spatio-temporal variations in aerosol properties over the oceanic regions between coastal India and Antarctica

Measurements of aerosol optical depth (AOD), mass concentrations of black carbon (MB) and composite aerosols (MT) in the marine atmospheric boundary layer (MABL) were made during onward [Dec 2007 to Jan 2008; Northern Hemispheric (NH) winter] and return (Mar-Apr 2008; NH spring) legs of the trans-continental cruise of 27th Indian Scientific Expedition to Antarctica (ISEA) during International Polar Year of 2007-2008. Large latitudinal gradients are seen; with AOD decreasing from coastal India (AOD~0.45) to coastal Antarctica (AOD~0.04) during NH winter. The measurements also evidenced a strong seasonality of AOD over all regions, with a decrease of the values and gradient in NH spring. BC concentration in the MABL decreases exponentially from 3800 ng m−3 (over 10°N) to 624 ng m−3 near equator and much lower values (<100 ng m−3) over southern oceanic region. Seasonality in the latitudinal gradients of AOD, MB and MT exists over regions north of 20°S. Multi campaign [Pilot Expedition to Southern Ocean (2004), Special Expedition to Larsemann Hills (2007) and Tropical Indian Ocean cruise (2010)] analysis over these oceanic regions showed that the pattern over the regions (south of 20°S) remained the same. Seasonality of AOD exists over Atlantic Ocean as well. Temporal variation of AOD at different latitudes derived from AERONET data also showed marked seasonality and latitudinal variation in northern hemisphere than in southern Hemisphere. Satellite retrieved AOD showed good correlation with the ship borne measurements; while GOCART retrieved AOD underestimates but gives a measure of the spatial variations.