GENERALIZED INVERSE WITH SHIPBOARD CURRENT MEASUREMENTS - TIDAL AND NONTIDAL FLOWS IN LONG-ISLAND SOUND

A simple linear shallow-water model forced by tidal boundary condition s can capture mast of the tide height variability in Long Island Sound . In this sense, the tides are easy to model. The modeled tidal curren ts can be subtracted from measurements in order to obtain estimates of subtidal circulation. But linear shallow-water dynamics is not accura te enough for this purpose. Allowing for dynamical errors with a gener alized inverse model leads to improved estimates of tidal and nontidal flow. The analysis provides expected errors for the prior (before inv ersion) and posterior (after inversion) tidal velocity field. Estimate s of the flow field in central Long Island Sound are obtained with cur rent measurements from a ship-mounted Acoustic Doppler Current Profile r (ADCP) survey. Inversion of data from a single ten-hour survey impro ves tidal predictions, as verified with independent data. Furthermore, the posterior penalty functional is shown to be an effective test sta tistic for the existence of nontidal flow. The inverse model reduces m odel-data misfit, using interior dynamics and open-boundary conditions as weak constraints. Model-data misfit can also be reduced by tuning the friction parameter in the prior tidal model. However, in contrast with inversion, tuning degrades predictability.