Abstract
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.
Highlights
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A comparative study on the retrieved vertical distribution of dust radiative heating rate over western Africa from aircraft lidar observations and CALIPSO revealed that the dust radiative heating rate derived from CALIPSO is in fair agreement with that derived from lidar observations (Lemaıtre et al, 2010)
In the present study we investigate the vertical distribution of radiative forcing and heating rate with a high resolution of 100 m due to a layer of transported dust (LTD) over Gadanki (13.5◦ N, 79.2◦ E), a tropical station in southern India during May, the period just before the arrival of the Indian southwest monsoon
Summary
Optical and physical properties of aerosols, such as AOD, the Angstrom exponent, Aerosol Index (AI) and SSA are obtained from the MODIS onboard Aqua (Remer et al, 2002), the Ozone Monitoring Instrument (OMI) onboard Aura (Torres et al, 2007), and the Multi-angle Imaging SpectroRadiometer (MISR) onboard Terra (Diner et al, 2008). MISR onboard the NASA-EOS Terra spacecraft, which is in a sun-synchronous orbit and crosses the equator at 10:30 local solar time, provides aerosol optical and physical properties It is a push broom imaging instrument operating at four spectral bands centered at 0.446, 0.558, 0.672, and 0.867 μm in each of its nine separate cameras oriented along the orbital track with surface viewing zenith angles in the range ±70.5◦ (Diner et al, 2008). Dust layer Dust layer Dust layer Depolarization Radiative Heating height thickness optical thickness ratio forcing rate (km)
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