Improvements of German Bight Coastal Ocean Predictions: Integration of Models and Observations

A nested-grid modelling system is developed to provide continuously state estimates and forecasts of ocean state for the North Sea and Baltic Sea, and their coastal areas, one example addressed here is the German Bight. The coastal prediction system considered here integrates hydrodynamical , wave and sediment models with near-real time measurements. The role of coupling between wave, circulation and sediment models is demonstrated. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales. The uncertainties in most of the presently used models result from the nonlinear feedback between strong tidal currents and wind-waves, which can no longer be ignored, in particular in the coastal zone where its role seems to be dominant. We present analysis of wave and hydrographic observations, as well as results of numerical simulations. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecasting system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and sediment dynamics are investigated considering wave-dependent stress, vortex velocity and wave breaking parameterization, during several extreme events. Also the effects, which the circulation exerts on the wind-waves are tested for the coastal areas using different parameterizations. We address here also the improvements of model performance through data assimilation. Of particular interest is the question how long the information from the measurements persists in the forecasts. The improved skill resulting from the presented new developments in the forecasting system, in particular during extreme events, justifies further wind-wave enhancements of the coastal pre-operational system for the North Sea and German Bight.