Trade wind cumuli statistics in clean and polluted air over the Indian Ocean...

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McFarquhar, G., S. Platnick, L. Di Girolamo, H. Wang, G. Wind, and G. Zhao (2004), Trade wind cumuli statistics in clean and polluted air over the Indian Ocean from in situ and remote sensing measurements, Geophys. Res. Lett., 31, L21105, doi:10.1029/2004GL020412.

Relationships between trade wind cumuli coverage and aerosol concentration Na, and between cloud optical thickness tc and Na are examined using in situ and remote sensing observations acquired on 4 days within and downwind of the Indo-Asian haze. Cloud top height and cloud coverage decrease as Na increases, whereas tc increases, which could be due to aerosol or meteorological effects. Clouds with horizontal sizes less than 2 km, neglected in prior studies, contribute up to 40% to cloud area, and must be considered in studies of aerosol indirect and semi-direct effects. When radiative transfer models are applied to the observations, a regional change in top of the atmosphere TOA (surface) 0.64 mm radiative forcing of approximately +6 (+7) W m-2 mm-1 associated with changes in cloud properties is found. To the degree that synoptic-scale forcings do not vary systematically as air flows south, the results may be interpreted as the dominance of semi-direct over indirect forcing within the Indo-Asian haze for the times sampled. I NDEX T ERMS : 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1610 Global Change: Atmosphere (0315, 0325); 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes.

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