Modulation of the Wind Speed Response of Marine Stratocumulus Clouds

Abstract:

We explore a possible feedback mechanism of marine boundary layer clouds in response to expected 21^st century changes in large scale wind speed. The mechanism proceeds via the effect of wind speed on the surface fluxes of sensible and latent heat, horizontal momentum (shear), and sea spray aerosol, and associated changes to cloud properties. An increase in wind speed produces, e.g., a higher latent heat flux from the surface, which causes stronger entrainment of free tropospheric air, and an adjustment in cloud properties. We have investigated how free tropospheric humidity and the evolution of the boundary layer modify the response of marine stratocumulus clouds to changes in wind speed. Results of cloud-system-resolving simulations are presented. The response of cloud properties and of radiative forcing to changes in surface wind speed is quantified under different free tropospheric conditions (dry vs. moist) and different boundary layer states (growing vs. steady state).