Sea-level slopes and volume fluxes produced by atmospheric forcing in estuaries: Chesapeake Bay case study

Time series at eight locations in Chesapeake Bay and the adjacent inner shelf were used to determine the relative influence of the wind and barometric pressure effects on subtidal sea-level variability and slopes in the estuary. Special emphasis was placed on the lower Chesapeake Bay, where inverse barometric effects accounted for up to 32% of the subtidal sea-level variations, and wind forcing accounted for more than 67% of the variance. The wind frequency from any given direction varied from one station to another due to the nonsynoptic characteristics of atmospheric pressure in Chesapeake Bay. In the northern bay, northwesterly winds were most frequent in winter, and southerly winds were most frequent in summer. In the southern bay, northeasterly winds were most frequent in fall and winter, and southwesterly winds dominated in the summer. These winds produced sea-level responses as follows: northeasterly winds caused water to pile up in the southwestern corner of the bay, whereas southwesterly winds produced water-level depressions in the same area. This study is one of the few to document the influence of atmospheric pressure gradients on estuarine sea-level slopes. It was found that atmospheric pressure gradients produced sea-level slopes of the same order of magnitude (10(-7)) as those induced by westerly-easterly winds. In contrast to previous studies, the volume fluxes calculated here, with geostrophy, geostrophy plus wind stress, and the continuity constraint, showed drainage of the bay with northerly and northwesterly winds and filling of the bay with southeasterly winds.