Coastal Meteorology A Review of the State of the Science (1992) / Chapter Skim
Currently Skimming:
6. The Influence of the Atmospheric Boundary Layer on the Coastal Ocean
6. The Influence of the Atmospheric Boundary Layer on the Coastal Ocean
Pages 51-62
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 51... ...
The presence of a lateral boundary can substantially modify the wind field that drives currents, upwelling, and surface waves, creating highly variable fields. As a consequence, the processes that drive the air-sea exchange of heat, mass, momentum, and trace gases over the continental shelf are highly variable; they are dominated by spatial scales on the order of tens to hundreds of kilometers.
|
From page 52... ...
Recent atmospheric measurements in the vicinity of a weak ocean front in the open ocean have revealed complex wind stress, cloud cover, and boundary layer depth patterns (Friehe et al., 1991~. More dramatic effects are likely in the coastal ocean where fronts are persistent and strong (Charnock and Businger, 1991~.
|
From page 53... ...
The local wind velocity consists of two components, one part driven by the pressure gradients and another part driven by the stress divergence, which is confined to a shallow layer called the Ekman layer. Along the west coast of North America, the response of sea level to fluctuations in along-shore wind stress at large scales accounts for a substantial fraction of the total sea-level variance.
|
From page 54... ...
This problem, however, has hitherto not been addressed. Ocean Fronts In a wind-driven upwelling environment, a sharp discontinuity in density typically develops between the less dense surface water offshore and the denser upwelled water near shore.
|
From page 55... ...
This large temperature or salinity discontinuity is maintained by momentum and buoyancy fluxes across the air-sea interface and by changes in the path of the boundary current. Rapid cooling of the sea surface may intensify the frontal structure because the shallow shelf water cools at a faster rate than the water offshore, which, in any case, is resupplied with heat by the poleward advection of warmer water.
|
From page 56... ...
This pattern, which occurs with generally northerly winds, is characterized by a strong low-level temperature inversion at the top of the marine atmospheric boundary layer, and the spatial structure of the surface wind is correlated with the coastal topography. There have been extensive studies of topographic effects on the development of internal waves in a stable stratified fluid; however, the effect of topographically forced gravity waves on the coastal marine atmospheric boundary layer and sea surface layer has received relatively little attention (Dorman, 1987; Gossard and Munk, 1954; Wald and Georgopolous, 1984~.
|
From page 57... ...
The land-sea boundary, ocean temperature fronts, surface wave field, variations in water depth, and biological activity play an important role in determining the magnitude and variability of air-sea fluxes over the coastal ocean. Wind Stress, Heat Fluxes, and Trace Gas and Particulate Exchange Momentum flux is particularly important in determining the effect of the atmosphere on coastal circulation.
|
From page 58... ...
Recent advances in chemical flux estimates using conditional sampling techniques that combine estimates of the variance of the vertical velocity and the mean concentration of the trace gas may reduce much of the uncertainty in atmospheric measurements of tracer fluxes across the air-sea interface (Businger and Delany, 1990; Businger and Oncley, 1990~. Coupled Interactions with the Planetary Boundary Layer Coupled air-sea interactions occur when, for example, the atmosphere is forced by the ocean, resulting in a feedback to the ocean that modifies
|
From page 59... ...
For the case of cold air flowing over a warm surface, an unstable IBL develops, rapidly replacing the existing boundary layer; for the case of warm air flowing over a cold surface, a stable IBL develops that may persist as a shallow layer until either the air is cooled by radiation or the surface temperature increases to reverse the stability of the air. This stable boundary layer accounts for many of the more important effects that occur in the interaction of the marine boundary layer with topography (Dorman, 1987; Winant et al., 1988~.
|
From page 60... ...
The relative effect of topographically forced flows and thermally driven circulation on the coastal ocean circulation has not been explored. There is compelling evidence for both topographically forced and sea-breeze-driven wind stress variations along the west coast of the United States, although little is known about the effect of the thermally driven circulation on the structure of the marine layer that controls the hydraulically driven flow near the ocean surface.
|
From page 61... ...
In conclusion, the panel recommends the following: · Studies should be conducted to determine the relative effects of topographically forced flows and thermally driven circulation on coastal ocean circulation. · Further research should be conducted to understand the coupled oceanatmosphere processes that control the interactions between the wind field, atmospheric boundary layer structure, and upper ocean.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.