Thursday, 6 June 2002: 9:30 AM
Solar Absorption Feedbacks in Simulated Stratocumulus
Previous work using simple, parametric models of the cloud-topped boundary layer have suggested that solar absorption may produce important feedbacks to the well-known Twomey effect. This work has suggested that increases in drop concentration may lead to alterations in cloud reflectivity due to the fact that solar absorption is enhanced. Hence, stratus clouds may thin causing a reduction in cloud reflectivity. We examine the aforementioned hypothesis using an LES model of the cloud-topped boundary layer coupled with sophisticated microphysics and radiation parameterizations. We show that absorption feedbacks that occur under modest perturbations in drop concentrations can cause significant modifications to boundary layer dynamics and thermodynamics. In certain cloud regimes, this leads to a major reduction in cloud reflectivity (up to 20%) primarily through reduced cloud depth.