Reduction of tropical cloudiness by soot
Measurements and models show that enhanced aerosol concentrations can augment cloud albedo not only by increasing total droplet cross-sectional area, but also by reducing precipitation and thereby increasing cloud water content and cloud coverage. Aerosol pollution is expected to exert a net cooling influence on the global climate through these conventional mechanisms. Here, we demonstrate an opposite mechanism through which aerosols can reduce cloud cover and thus significantly offset aerosol-induced radiative cooling at the top of the atmosphere on a regional scale. In model simulations, the daytime clearing of trade cumulus is hastened and intensified by solar heating in dark haze (as found over much of the northern Indian Ocean during the northeast monsoon).
Ackerman
AS
NASA Ames Research Center, Moffett Field, CA 94035, USA. University of Colorado, Boulder, CO 80309, USA. Lawrence Livermore National Laboratory, Livermore, CA 94551, USA. National Center for Atmospheric Research, Boulder, CO 80301, USA.
Toon
OB
Stevens
DE
Heymsfield
AJ
Ramanathan
V
Welton
EJ