Wednesday, 16 January 2002: 1:45 PM
Radiative Forcing of Tropical Anvil Clouds
Lindzen et al. (2001) suggested that tropical anvil clouds act as a
strong negative feedback in the global climate system because the higher
the surface temperature, the lower the cloud amount and the stronger
the thermal emission to space. This study evaluates that hypothesis by using
CERES TRMM satellite measurements over tropical oceans and perturbation analysis
of the 3.5-box model used by Lindzen et al. The modeled radiative fluxes
of Lindzen et al. are replaced by CERES directly observed broadband
radiation fields. Perturbation analysis shows that model simulated climate feedback
is determined by the radiative forcing differences of the anvil clouds and other
climatological regions. CERES TRMM observations show that the
anvil clouds have much higher albedos and moderately larger longwave
fluxes than those assumed by Lindzen et al. As a result, for 22%
reduction in the anvil clouds, the net radiative forcing obtained by the
current study is small and positive. It changes from about 0.02 to 0.44
W/m**2 depending on the relationship between anvil clouds and
other tropical regions, compared to the strong negative net radiative
forcing of Lindzen et al. (varying from -1.7 to -3.9 W/m**2).
Supplementary URL: