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The instability of density fronts is investigated as a possible generation mechanism for the small-scale, wavelike patterns that are commonly observed along upwelling fronts and filaments. Unstable-wave solutions are obtained in two linearized models' a loe1ayer model, and a continuously stratified model confined to the surface ß 2 region of the ocean. In both systems the thickness of the upper region is held constant for the background state, the front being specified by allowing the temperature field T within the region to vary zonally. The background state in the layer model consists of vertically oriented isotherms associated with a depth-independent current, whereas in the continuously stratified model it consists of steeply tilted isotherms and a vertically sheared current. Solutions are found both when the background velocity field V is zonally uniform and when it is zonally sheared. When V is weak and zonally uniform, approximate solutions are derived analytically for both models that are valid for lowfrequency, low-wavenumber waves. These solutions demonstrate that the unstable waves in the two systems are dynamically related, both being representations of ageostrophic baroclinic instability. Numerical solutions corroborate the analytic results and extend their range of validity. Energetics analyses confirm that the energy source for the waves is the background potential energy associated with the zonally varying T field. When V is a zonally sheared jet, the models still exhibit a band of instability, which is identifiable with ageostrophic baroclinic instability. The most unstable wave in this band has a short wavelength, a frequency near f/2, and a rapid growth rate consistent with observed features. The layer model also has a band of larger-scale waves that is a mixed, baroclinic-barotropic instability; however, for a typical frontal structure this band is weaker than the baroclinic band.

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Estuarine budget studies often suffer from uncertainties of net flux estimates in view of large temporal and spatial variabilities.Optimum spatial measurement density and material flux errors for a reasonably well mixed estuary were estimated by sampling 10 stations from surface to bottom simultaneously every hour for two tidal cycles in a 320-m-wide cross section in North Inlet, South Carolina. Discharge and ATP and NII,+-N fluxes were computed, The analysis method was to form a number of cases, each based on a different number and combination of stations and compare these fluxes to the ideal case using all 10 stations. A percentage error, y, (rms derivation of a given case from the ideal cast compared to the tidal prism) was <15% with only three lateral stations, each located to cover a separate bathymetric regime. In estuaries with dimensions similar to North Inlet, these results should prove useful in selecting an optimum (or minimum) number of required stations.