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Ramachandran, S, Rajesh, TA (2008). Asymmetry parameters in the lower troposphere derived from aircraft measurements of aerosol scattering coefficients over tropical India. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 113(D16), D16212.

Aerosol scattering coefficients (total beta(sca) and backscatter beta(backsca)) are measured on board an aircraft using an integrating nephelometer at 450, 550, and 700 nm in the 0 to 3000-m region over four locations in India in an air campaign held during March-May 2006. beta(sca) is a factor of two higher in the east (Bhubaneshwar, Chennai) than in the west (Trivandrum, Goa). beta(sca) is about 5-10 x 10(-5) m(-1) over Bhubaneshwar and Chennai. beta(backsca) is about an order of magnitude lower than beta(sca). Seven-day air back trajectory analysis indicate that air masses originating from arid/semiraid regions, continents, and marine regions are found to influence the aerosol characteristics, in addition to local urban sources. No elevated aerosol layers are seen during the campaign. b, the aerosol backscatter fraction, is greater than 0.13 in the lower troposphere. The columnar mean Angstrom exponent (alpha) is > 1.75. Asymmetry parameter g profiles are derived for the first time over India in the lower troposphere, using the relation between b and g. 550-nmg corresponding to 30% RH is in the 0.3-0.6 range over India. Higher b, higher alpha, and lower g values over these locations suggest the dominance of submicron aerosols during the campaign. Scattering aerosols corrected to 30% RH in the 0 to 3000-m altitude region contribute about 20-35% to MODIS aerosol optical depths (AODs). The variation in the contribution of scattering aerosols to AODs highlights the spatial and vertical differences in aerosol properties.



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