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.
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