INVESTIGATIONS OF MARINE AEROSOLS OVER THE TROPICAL INDIAN-OCEAN

Results of the studies on the characteristics of marine aerosol optica l depths made in remote regions of the tropical Indian Ocean using a m ultiwavelength solar radiometer, taken on a scientific cruise, are pre sented. The dependence of the aerosol optical depths on prevailing win ds in marine boundary layer and on deck level relative humidity (RH) a le examined. Aerosol optical depths (tau(p)) in far oceanic regions wi th marine air mass prevailing, in general, are found to increase nearl y exponentially with average wind speed (U-a) as tau(p) = tau(0) exp(a U-a), where a = 0.16 +/- 0.04. No association is seen with deck level relative humidity, as the effects of wind appear to offset the effect s due to RH. The columnar size distributions retrieved from aerosol sp ectral optical depths reveal two modes, one at similar to 0.04 mu m an d a secondary mode at similar to 0.8 mu m. The columnar mass loading e stimated from the size distributions increases exponentially with wind speed and has a wind independent value of similar to 28 mg m(2).