Comparisons of different ensemble schemes for glider data assimilation on West Florida Shelf

An Ensemble Optimal Interpolation (EnOI) system is built to assimilate underwater profiling glider observations into a West Florida Shelf (WFS) coastal ocean model. The Floating Temporal Window (FTW) technique is incorporated into the EnOI scheme to generate and update associated ensemble members, which are directly extracted from the model output states from previous output cycles. The model performance is validated against independent observations from moorings located near the glider tracks. The EnKF, traditional EnOI and the FTW-EnOI schemes are compared in terms of error covariance evolution and model performance at mooring locations. It is found that all three assimilation schemes provide significant (2-3 times) better fit to the mooring data compared with the free model run. Although the EnKF scheme produces the best results, the FTW-EnOI should be considered as an alternative method given the low computational cost and the flow-dependent information embedded in the algorithm.