VERTICAL VARIATIONS IN RESIDUAL CURRENT RESPONSE TO METEOROLOGICAL FORCING IN THE MID-CHESAPEAKE BAY

Abstract : Records of the nontidal current velocity obtained from current meters deployed for 20 days in two cross sections in Chesapeake Bay were used with an interpolation scheme to produce a vertical profile of the laterally-averaged longitudinal velocity component at one meter depth intervals at each section, at 3 h intervals over the 15 day truncated record. Various statistical procedures were used to relate variations in the residual current at each depth to wind variations. Surface layers down to about 8 m responded directly to wind with little time lag. A slope of the water surface was also set up by the wind, with a consequent barotropic pressure force directed opposite to the wind. The current near the bottom responded first to this pressure force, flowing opposite to the wind with a phase lag of about 8 h. This counter response proceeded up the water column, such that in the intermediate layers just below the pycnocline the negative response to the wind had a phase lag of about 20 h. A diagnostic analytical model, based upon a Fourier transform of the linearized equations of motion, was exercised for a four-layered simulation of the vertical response of the currents to inputs of the observed fluctuations in wind and surface slope. The major features of the time variations in the residual currents in the four layers were reproduced by the model.