Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 31, 647-663, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
11 Apr 2013
Investigation of radiative effects of the optically thick dust layer over the Indian tropical region
S. K. Das1, J.-P. Chen1, M. Venkat Ratnam2, and A. Jayaraman2 1Department of Atmospheric Sciences, National Taiwan University, Taiwan
2National Atmospheric Research Laboratory, Gadanki, Tirupati - 517 502, India
Abstract. Optical and physical properties of aerosols derived from multi-satellite observations (MODIS-Aqua, OMI-Aura, MISR-Terra, CALIOP-CALIPSO) have been used to estimate radiative effects of the dust layer over southern India. The vertical distribution of aerosol radiative forcing and heating rates are calculated with 100 m resolution in the lower atmosphere, using temperature and relative humidity data from balloon-borne radiosonde observations. The present study investigates the optically thick dust layer of optical thickness 0.18 ± 0.06 at an altitude of 2.5 ± 0.7 km over Gadanki, transported from the Thar Desert, producing radiative forcing and heating rate of 11.5 ± 3.3 W m−2 and 0.6 ± 0.26 K day−1, respectively, with a forcing efficiency of 43 W m−2 and an effective heating rate of 4 K day−1 per unit dust optical depth. Presence of the dust layer increases radiative forcing by 60% and heating rate by 60 times at that altitude compared to non-dusty cloud-free days. Calculation shows that the radiative effects of the dust layer strongly depend on the boundary layer aerosol type and mass loading. An increase of 25% of heating by the dust layer is found over relatively cleaner regions than urban regions in southern India and further 15% of heating increases over the marine region. Such heating differences in free troposphere may have significant consequences in the atmospheric circulation and hydrological cycle over the tropical Indian region.

Citation: Das, S. K., Chen, J.-P., Venkat Ratnam, M., and Jayaraman, A.: Investigation of radiative effects of the optically thick dust layer over the Indian tropical region, Ann. Geophys., 31, 647-663,, 2013.
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