13.5
Cloud-climate feedbacks as a result of solar cloud absorption in the SKYHI General Circulation Model
Carynelisa Erlick, The Hebrew University of Jerusalem, Jerusalem, Israel; and V. Ramaswamy and L. M. Russell
In this study we simulate the effect of solar absorption in clouds due to the presence of continental type absorbing aerosols on cloud amount, surface temperature, precipitation, and surface fluxes during the northern summer season. The response arising from this type of forcing is akin to the "semi-direct" effect of absorbing aerosols, with the forcing in our simulation existing only in low cloud layers. We find that globally, the reduction in low cloud single scattering albedo causes a reduction in low cloud amount, a warming of the surface, stabilization of the lower troposphere, and a reduction in precipitation, soil moisture, evaporation and sublimation, and latent heat flux from the surface. Regional changes in surface temperature and low cloud amount are consistent with the global-mean picture. However, the dynamical response of the system varies from region to region. In the midlatitude regions of the United States and Europe/E. Asia, the diabatic heating perturbation in the low cloud layers leads to the dissipation of low clouds, allowing more solar radiation to reach the surface, accompanied by an increase in horizontal heat advection and increased atmospheric stability. In the tropical region of N. Africa, the diabatic heating perturbation in the low cloud layers translates into an increase in convection, a decrease in stability, an increase in middle and high level clouds, and a reduction in shortwave flux to the surface. These results indicate the importance of absorbing aerosols on cloud-climate interactions, and in particular the distinctive response of the tropical versus midlatitude regions to a moderate forcing by absorbing aerosols in low clouds.
Session 13, Radiative Forcing of the Climate (parallel with Session 12)
Thursday, 13 January 2005, 8:30 AM-9:45 AM
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