Meteorological and Satellite Analysis of Eddies in the Marine Stratocumulus Photographed by Pilots Over the California Coast

Mechanical atmospheric eddies on the order of 10-20 km across produced by strong northwesterly marine boundary layer flow are often seen in satellite imagery near the California coast. Yet relatively little is known about the details of their structure and wind fields, since they occur at space scales that may only sporadically be observed by conventional coastal surface observation networks or meteorological buoys. For example, it is not clear whether they are mainly features of the marine inversion as indicated by their cloud-free eyes, or whether their circulations penetrate the depth of the boundary layer all the way to the surface. These eddies have implications for mixing and air pollution dispersion as well as predictability at the coastal margin. For example, they have been implicated in cross-inversion transport, yet it is an open question as to whether specific occurrences can be simulated by very high resolution regional models. Routine forecast models almost certainly do not currently operate at the small scales necessary to explicitly predict their existence. This submission presents a satellite and meteorological analysis of two such meso-gamma scale (2-20 km) eddies in the marine stratocumulus that were photographed by commercial pilots flying coastal routes between Santa Ana and San Francisco, California. One of the eddies formed in the wake of Santa Cruz Island, embedded in the southeasterly flow portion of a larger scale Catalina eddy circulation. The other formed over a headland west of San Luis Obispo and passed near several wind monitoring stations owned by PG&E supporting operations of the Diablo Canyon Nuclear Power Plant, before being photographed by the pilots near Grover Beach. Satellite imagery tracking the motions of the eddies prior to, during, and after the snapshots by the pilots, and eddy signatures in the Diablo Canyon wind data will be presented. Satellite imagery revealing the propensity for similar eddies to form near the headland containing the Diablo Canyon Nuclear Power Plant have been collected, and will help define common meteorological threads that apparently contribute to eddy formation in this region. Finally, very fine resolution WRF (Weather Research and Forecasting) model simulations will be presented to explore the degree to which these eddies can be explicitly predicted given the background flow initialization.