Branch Seminar Series: Robin Hogan

Dept. of Meteorology, University of Reading, Reading, UK
The accurate representation of clouds in radiation schemes is crucial for climate prediction, yet substantial biases still remain due to unrepresented cloud structure. I this talk I will first discuss results from radar to characterize cloud vertical overlap and horizontal heterogeneity. I will then present a new method for representing these properties efficiently in a radiation scheme, and use it to estimate the global effect on cloud radiative forcing. Considerable regional structure is found in the change to net forcing; in marine stratocumulus regions the shortwave horizontal inhomogeneity effect is dominant, while in the Pacific Warm Pool region, there is a large degree of cancellation between the effects of inhomogeneity and overlap. Finally the issue of three-dimensional radiative transfer will be addressed, including a new method to represent radiative transport through cloud sides by modifying the two-stream equations of radiative transfer at a fundamental level.