The Mesoscale Structure of Drizzling Stratocumulus Clouds: Perspectives from Observations and Large Eddy Simulations

The deployment of the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) at Cape Cod, MA during the Two-Column Aerosol Project (T-CAP) afforded a unique opportunity to observe the properties of a number of cloud regimes, including stratocumulus clouds. Stratocumulus clouds were observed for a 48-hour period beginning 15 November 2012, when northeast winds brought stratocumulus off the ocean across the AMF site in the wake of a cold-frontal passage. This case is of particular interest because it fits into an intermediate type between continental post-frontal stratocumulus and the marine stratocumulus found in subtropical regions. In this case, boundary-layer air parcels originating over Eastern Canada passed over the Gulf of St. Lawrence and Gulf of Maine before again encountering land at the AMF site. In addition to the land-sea contrasts, this case is further enriched by the fact that the stratocumulus began to drizzle as the event progressed.

Using the AMF instrumentation, including vertically pointing and scanning cloud radars, we document the observed structure of the stratocumulus event in this study, including the boundary layer turbulence and mesoscale variability of the cloud and drizzle structure. In addition, we have used the Weather Research and Forecasting model in large-eddy simulation mode not only to assess the model's ability to capture the mesoscale structure but also to study the effect of topography on the cloud and precipitation structure.