Toward Satellite Inference of the Decoupling Degree and Cloud-Base Updrafts of Marine Stratocumulus

To what extent the surface-originated aerosols impact boundary layer warm clouds is influenced by the degree of cloud-surface coupling and the cloud-base updrafts. Neither of these two variables, however, is retrievable from satellite. This study concerns itself with developing satellite-based methods of inferring the decoupling degree and the cloud-base updrafts for marine stratocumulus (Sc) over subtropical oceans. The estimation concept of the coupling state is that decoupled Sc clouds under cold-advection conditions, which are typical in subtropical oceans, are fed by spreading of the tops of cumulus clouds that are coupled. The cumulus clouds constitute a much larger liquid water path (LWP) over small areas, which is identified by a positive skewness of the LWP, a quantity measurable from high-resolution satellite data. We estimate the cloud-base updrafts by quantifying the cloud-top radiative cooling rate that, in combination with the decoupling degree, determines the turbulence level at the cloud bases. These concepts and the satellite-based estimations are supported by ship measurements over the northeast Pacific. Preliminary results of applying these new techniques to studying aerosol-cloud interactions will be shown.