Assimilation of high-frequency radar surface currents into a coastal ocean model of the Middle Atlantic Bight

The present work is an attempt to quantify the performance of HF radar observations using the difference between surface currents deduced from three different technologies (a coastal ocean model, HF radar and drifter) and to develop a practical, nearly optimal method to assimilate HF radar data into a coastal ocean model, the New York Harbor Observation and Prediction System (NYHOPS). A nudging or Newtonian damping scheme is developed to assimilate HF radar surface currents. The effectiveness of data assimilation (DA) is evaluated by various comparison methods: tidal analyses, statistical methods and Lagrangian particle-tracking simulations.;The quantitative validation of surface currents derived from HF radar, NYNOPS and drifters during four periods in 2010 and 2011 (total 67 days) showed reasonable comparisons among these three technologies. The root-mean-square-difference (RMSD) of the east-west and north-south component of surface currents showed an error within the order of 18cm/s. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. The comparisons of tidal ellipses from NYHOPS and HF radar against multiple current meter observations show both NYHOPS and HF radar perform well and have similar skill in tidal current estimation. An ensemble-based set of particle tracking simulations using drifters suggests that both the NYHOPS and HF radar currents are representing tidal and inertial time scales correctly.;Impact of DA on NYHOPS's ability in capturing surface currents during hindcast (-24 to 0 h) and forecast (0 to 24 h) periods is analyzed quantitatively. The RMSD of the east-west and north-south components of the surface current between the NYHOPS hindcast and the HF radar showed a slight decrease on the order of 3 cm/s. The tidal analysis of NYHOPS after DA shows slight improvement. The accuracy of surface currents derived from the NYHOPS hindcast after DA shows an average 8% improvement when compared with drifter-derived surface currents. The comparison for NYHOPS forecast surface currents also shows an averaged 5% improvement after DA. Ensemble-based sets of particle tracking simulations for a large number of surface drifters show an improvement for the NYHOPS hindcast of 7% and for the forecast 10% after DA.