Tropical Aerosol Radiative Effects: Observations from INDOEX

As a part of Indian Ocean Experiment (INDOEX), a new observatory was established in Maldives namely Kaashidhoo Climate Observatory (4.965°N, 73.466°E) for making long term observations of aerosol chemical composition, microphysics and radiative fluxes. Extensive measurements of aerosols and radiative fluxes are carried out in the haze plume off the South Asian continent as a part of the first filed phase during 1998 and intensive field phase during 1999. A comparison of the two-year observations shows significant inter-annual variability in aerosol properties. The aerosol optical depths observed during 1999 are quite high ranging from ~0.2 to 0.7 compared to the mean value of ~0.16 during the first field phase, 1998. An aerosol model developed from direct measurements of chemical composition and single scattering albedo at the surface and vertical structure from lidar data, in conjunction with a Monte Carlo radiative transfer model successfully explains the observed radiative forcing. The observed diurnal mean surface aerosol forcing is in the range of -10 to -40 W m^-2 with a mean value of about -29 W m^-2 during 1999 compared to the average value of -15 W m^-2 during 1998. The contribution of anthropogenic influence to the total aerosol abundance is examined. The Angstrom coefficient and effective radius show the presence of significant amounts of sub micron aerosols.