Study of fog dissipation in an internal boundary layer on Sable Island

An interesting fog dissipation event was observed during the Fog and Turbulence Interactions in the Marine Atmosphere (FATIMA) Grand Banks field campaign, where a fog-free region appeared immediately downstream of Sable Island as fog advected past it. This fog-free region was predicted a priori by a high-resolution numerical model that guided intensive operational periods of the FATIMA campaign, and its presence was adumbrated by GOES satellite observations. A comprehensive set of field observations shows that this fog-free layer was due to the development of a (daytime) thermal internal boundary layer (IBL) that grew with distance from the leading shore line. The net incoming radiation following sunrise led to an increased air temperature and decreased relative humidity close to the ground, thus dissipating fog over the island. The height of the thermal IBL, as identified by the thickness of the superadiabatic layer, was found to be consistent with several available theoretical IBL formulae.