Estimate of bottom and surface stress during a spring‐neap tide cycle by dynamical assimilation of tide gauge observations in the Chesapeake Bay

Abstract

Abstract.Dynamical assimilation of surface elevation from tide gauges is investigated to estimate the bottom drag coefficient and surface stress as a first step in improving modeled tidal and wind-driven circulation in the Chesapeake Bay. A two-dimensional shallow water model and an adjoint variational method with a limited memory quasi-Newton optimization algorithm are used to achieve this goal. Assimilation of tide gauge observations from 10 permanent stations in the Bay and use of a two-dimensional model adequately estimate the bottom drag coefficient, wind stress, and surface elevation at the Bay mouth. Subsequent use of these estimates in the circulation model considerably improves the modeled surface elevation in the entire Bay. Assimilation of predicted tidal elevations yields a drag coefficient, defined in the hydraulic way, varying between 2.5 x 10 -4 and 3.1 x 10 -3.The bottom drag coefficient displays a periodicity corresponding to the spring-neap tide cycle with a maximum value during neap tide and a minimum value during spring tide. From assimilation of actual tide gauge observations, it is found that the fortnightly modulation is altered during frontal passage. Furthermore, the response of the sea surface to the wind forcing is found to be more impbrtant in the lower Bay than in the upper Bay, where the barometric pressure effect seems to be more important.

Sea-Level Slopes and Volume Fluxes Produced by Atmospheric Forcing in Estuaries: Chesapeake Bay Case Study

“…Results show that its relative effect, compared to total subtidal variability, was smaller in the upper bay than in the middle and lower bay. These results are different from those found by SPITZ and KLINCK (1998). At Tolchester Beach station, in the upper bay, the inverse barometric effect accounted for less than 14% of the subtidal variability, whereas at Kiptopeke station, in the lower bay, it accounted for 32% of the subtidal variability ( Figure 3).…”

“…In the Chesapeake Bay, the inverse barometric effect on sea level has been found to be smaller than the wind stress effects but not negligible (PARASO and VALLE-LEVINSON, 1996). This effect may be as important as the wind-forcing effect in the upper bay (SPITZ and KLINCK, 1998). However, observational studies of estuaries and bays regarding the inverse barometric effect are scarce (KIM et al, 1996).…”

Hydrometeorological controls on water level in a vegetated Chesapeake Bay tidal freshwater delta

“…Barometric pressure changes apparently add to the effect of wind stress in causing water level variations (Paraso and Valle-Levinson, 1996), with the effect possibly greater in the upper bay (Spitz and Klinck, 1998). Sanford (1994) found that in upper Chesapeake Bay wave-forced resuspension of bed sediment driven by winds dominated tidal resuspension, confirming the significance of winds and water level variation in broader estuarine processes, especially near the head of the bay.…”

Comparison of statistical and model‐based hindcasts of subtidal water levels in Chesapeake Bay

“…Numerical circulation models of Chesapeake Bay have been designed for general or environmental hindcasting [Blumberg, 1977; and for process studies [Spitz and Klink, 1998]. Here we used the barotropic version of a three-dimensional model [Hess, 1989 Hess, 1990; Brooks, 1994] which has been set up specifically for hindcasting and forecasting tidal and subtidal water levels in Chesapeake Bay [Bosley and Hess, 1998].…”