Assimilation of HF Radar Observations in the Chesapeake-Delaware Bay Region Using the Navy Coastal Ocean Model (NCOM) and the Four-Dimensional Variational (4DVAR) Method

The impact of HF radar observations on constraining and improving model forecasts of the coastal ocean circulation is examined using a very high resolution model and a 4DVAR data assimilation system. The latter can propagate the influence of these surface velocity measurements through all the model variables in space and time. Assimilation experiments with a high-resolution model show that, although the analysis is able to significantly reduce the model\u27s discrepancy to the observed surface velocities, the main challenge remains in providing more reliable atmospheric forcing fields to the coastal ocean model. However, using a very high resolution in the model can become a liability for the assimilation as the model would resolve small-scale circulation features that cannot be constrained by the available observations. An additional assimilation experiment with a reduced horizontal resolution with the same atmospheric forcing shows significant improvements in both the analysis and the forecast