Investigation of radiative effects of the optically thick dust layer over the Indian tropical region

• Main Authors: S. K. Das, J.-P. Chen, M. Venkat Ratnam, A. Jayaraman
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-04-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/31/647/2013/angeo-31-647-2013.pdf

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.