An extended velocity projection method for estimating the subsurface current and density structure for coastal plume regions: An application to the Chesapeake Bay outflow plume

We describe a method for estimating subsurface current and density structure in a coastal region dominated by a plume from a set of surface observations of velocity and density. A detailed application of the method is shown via a case study of the Chesapeake Bay in November 1997. The proposed technique relies on developing a ‘plume feature model’ from theoretical models and past synoptic observational data sets, and incorporating the feature model into the previously developed velocity projection method [J. Geophys. Res. 106 (2001) 6973] to obtain subsurface current structure within the Ekman layer depth. The primary feature model parameters include the location and extent of the frontal boundary, a simplified gravity current structure, and the spatial gradient of salinity across the frontal head of the plume, which are inferred from remote sensing or minimal strategic in situ observations. e Chesapeake Bay case study, we show how the proposed method, referred to as ‘extended velocity projection’, can produce estimates of plume current structure consistent with available ADCP profiles. We assess the sensitivity of the results to feature model parameters, and identify the resolution of spatial salinity gradient as being particularly important. The difference between the density-stratified estimate and the ADCP data can be used to calibrate and improve the zero-order dynamic feature model parameters. This synergistic approach with the extended velocity projection method should be applicable to other coastal plumes and possibly other shallow water features.