Articles | Volume 31, issue 4
Ann. Geophys., 31, 647–663, 2013
Ann. Geophys., 31, 647–663, 2013

Regular paper 11 Apr 2013

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 S. K. Das et al.
  • 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.