The shallow marine boundary layer adjacent to the steep topography of the California coast gives rise to a number of coastal mesoscale phenomena including (among other things) coastally trapped wind reversals (CTWR), coastal eddies, and hydraulic effects (expansion fans and compression jumps). In the present study, we investigate an event in which two coastal cyclonic eddies formed at the leading edge of a region of southerly flow associated with a CTWR in the presence of an expansion fan and a compression jump. This remarkable event was captured in satellite imagery as it occurred on 28 August 2002 in the vicinity of Point Arena, California. The eddies are clearly visible as “swirls” in the coastal fog and stratus and undulations associated with the compression jump appear as a series of fine-scale, linear features in the cloud field.

The Naval Research Laboratory’s nonhydrostatic COAMPS model is used to simulate this event. The model reproduces all of the aforementioned features, albeit with a 2-4 h time lag. Model results also compare favorably with available data from buoys and coastal stations. Using the model fields, we can delineate the vertical structure of the compression jump and cloud and wind fields. The dynamical aspects of the event are currently under investigation. Sensitivity studies have also been performed to investigate the roles of surface friction and topography.