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John M. Bane, Clinton D. Winant, and James E. Overland

A number of observational programs have been carried out on the United States continental shelf to describe coastal-ocean circulation with emphasis on mesoscale processes. In several of these studies the atmosphere was found to play a central role in determining the coastal circulation through either local or remote forcing. Because of these results, the Coastal Physical Oceanography (CoPO) planning effort has designated three coastal air-sea interaction areas to focus on in a national program to study the physical processes on the continental shelf. These areas are shelf frontogenesis, interaction of stable layers with topography, and forcing by severe storms. The long-term objective of the air-sea interaction component of CoPO is to better understand the structure, dynamics, and evolution of the various mesoscale and synoptic-scale processes that significantly affect coastal/shelf circulation through air-sea interactions. Within this body of knowledge will be an improved quantification of the air-sea exchanges of dynamically important quantities set in the framework of mesoscale and synoptic-scale processes.

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Wendell A. Nuss, John ML Bane, William T. Thompson, Teddy Holt, Clive E. Dorman, F. Martin Ralph, Richard Rotunno, Joseph B. Klemp, William C. Skamarock, Roger M. Samelson, Audrey M. Rogerson, Chris Reason, and Peter Jackson

Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of fog or stratus, are an important warm-season forecast problem due to their impact on coastal maritime activities and airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for producing these events, yet observational and modeling limitations at the time left these competing interpretations open for debate. In an effort to improve our physical understanding, and ultimately the prediction, of these events, the Office of Naval Research sponsored an Accelerated Research Initiative in Coastal Meteorology during the years 1993–98 to study these and other related coastal meteorological phenomena. This effort included two field programs to study coastally trapped disturbances as well as numerous modeling studies to explore key dynamic mechanisms. This paper describes the various efforts that occurred under this program to provide an advancement in our understanding of these disturbances. While not all issues have been solved, the synoptic and mesoscale aspects of these events are considerably better understood.

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David P. Rogers, Clive E. Dorman, Kathleen A. Edwards, Ian M. Brooks, W. Kendall Melville, Stephen D. Burk, William T. Thompson, Teddy Holt, Linda M. Ström, Michael Tjernström, Branko Grisogono, John M. Bane, Wendell A. Nuss, Bruce M. Morley, and Allen J. Schanot

Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address several problems, including the cross-shore variability and turbulent structure of the marine boundary layer, the influence of the coast on the development of the marine layer and clouds, the ageostrophy of the flow, the dynamics of trapped events, the parameterization of surface fluxes, and the supercriticality of the marine layer.

Based in Monterey, California, the National Center for Atmospheric Research (NCAR) C-130 Hercules and the University of North Carolina Piper Seneca obtained a comprehensive set of measurements on the structure of the marine layer. The study focused on the effects of prominent topographic features on the wind. Downstream of capes and points, narrow bands of high winds are frequently encountered. The NCAR-designed Scanning Aerosol Backscatter Lidar (SABL) provided a unique opportunity to connect changes in the depth of the boundary layer with specific features in the dynamics of the flow field.

An integral part of the experiment was the use of numerical models as forecast and diagnostic tools. The Naval Research Laboratory's Coupled Ocean Atmosphere Model System (COAMPS) provided high-resolution forecasts of the wind field in the vicinity of capes and points, which aided the deployment of the aircraft. Subsequently, this model and the MIUU (University of Uppsala) numerical model were used to support the analysis of the field data.

These are some of the most comprehensive measurements of the topographically forced marine layer that have been collected. SABL proved to be an exceptionally useful tool to resolve the small-scale structure of the boundary layer and, combined with in situ turbulence measurements, provides new insight into the structure of the marine atmosphere. Measurements were made sufficiently far offshore to distinguish between the coastal and open ocean effects. COAMPS proved to be an excellent forecast tool and both it and the MIUU model are integral parts of the ongoing analysis. The results highlight the large spatial variability that occurs directly in response to topographic effects. Routine measurements are insufficient to resolve this variability. Numerical weather prediction model boundary conditions cannot properly define the forecast system and often underestimate the wind speed and surface wave conditions in the nearshore region.

This study was a collaborative effort between the National Science Foundation, the Office of Naval Research, the Naval Research Laboratory, and the National Oceanographic and Atmospheric Administration.

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