Abstract:
Data from the Coastal Ocean Processes Inner Shelf Study are analyzed to determine
atmospheric forcing characteristics and the heat balance of the inner shelf, and are
used as motivation for a numerical study of inner shelf circulation during upwelling
and downwelling. Variation in meteorological forcing on the North Carolina Inner
shelf is shown to be dominated by synoptic weather systems. The structure of cold
fronts, which are the dominant synoptic feature, and the local meteorological conditions
they produce result in a strong correlation between the surface heat flux
and the wind orientation. This has implications for the heat balance of the inner
shelf, which is considered next. During stratified conditions (observed during August
1994), cross-shelf heat fluxes due to Ekman dynamics dominate variation in
heat content of the inner shelf, while during weakly-stratified conditions (observed
during October 1994), the surface heat flux dominated variation in heat content.
Both processes are correlated with the alongshelf wind, implying that the heat balance
of the inner shelf can be modeled largely in terms of the alongshelf wind. The
dominance of cross-shelf processes during stratified conditions motivated numerical
studies of upwelling and downwelling. It was found that the feedback between
mixing and stratification played a role in determining the strength of the circulation
on the inner shelf, which differed between upwelling and downwelling. During
upwelling, dense water is brought onto the inner shelf from below the pycnocline,
producing vertical stratification, lowering eddy viscosities, and enhancing the inner
shelf circulation. In contrast, during downwelling, circulation was weakened by the
presence of stratification. These circulation patterns are discussed in the context
of coastal observations, and the implications for cross-shelf transport and exchange
processes are considered.
