Fog and low clouds in the coastal zone

We have recently completed a study of fog and low cloud evolution associated with a coastally trapped disturbance (CTD) event along the California Coast. We investigated both the vertically integrated buoyancy flux components and the vertical variation in these quantities, as well as precursors to fog formation and several sensitivity studies. We also validated model results using available observations. Some of the findings from this study are 1) low-level convergence at the leading edge of the CTD lifts and cools the strongly stratified air adjacent to the surface, thereby preconditioning this layer for fog formation and 2) contrary to standard interpretations, advective cooling over colder water plays very little part in the fog formation process of the CTD; in fact the sensible heat flux is upward throughout the bulk of this fog. Currently, we are investigating a fog event along the East Coast using diagnostic tools similar to those used for the California case. While the morphology of fog formation in these two cases is quite different, it is instructive to compare and contrast fog evolution between the east and west coasts.

In the present study, we use the Naval Research Laboratory's COAMPS® mesoscale mode to simulate two fog events: 1) The CBLAST low area 21 August 2003 and 2) a CTD event along the California Coast 15 June 2000. In both cases, the model is run with three nests and forty-five vertical levels distributed so as to yield high vertical resolution in the lowest 1.5 km (twenty-two levels in the lowest 1.5 km).