Results will be presented from a computational study in which droplet concentrations in marine stratocumuli are enhanced, in order to assess if such global cooling could be achieved. This involves the use of both a global climate model to investigate changes in the global radiation balance and a cloud resolving model to examine the sensitivity of the stratocumulus cloud microphysics.
The global climate model used is HadGAM (the atmospheric component of the Met Office Unified Model) in which N has been increased in all regions of low-level cloud, as well as in regions of persistent marine stratocumuli. The effect on cloud droplet effective radius will be presented for different values of N, along with computations of the effect on the earth's radiation balance. The results, an extension of those presented in Latham et al., 2008, indicate that by enhancing the properties of these clouds it may be possible to yield a negative radiative forcing of more than twice that required to offset the warming produced by a doubling of carbon dioxide.
Results will also be shown from the Met Office Large Eddy Model (LEM). This is being used on a regional scale to examine the microphysical and radiational effects of altering droplet concentrations in warm stratocumuli, initialized by atmospheric profiles from the recent VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS) program.