| Summary: | Approved for public release; distribution is unlimited === Performance of the Navys latest operational ocean forecast model (the Hybrid Coordinate Model, HYCOM, which became operational in March 2013) is systematically evaluated by comparing its velocity fields with actual ADCP velocities collected during a two-week cruise in the Agulhas Return Current region in 2012 (ARC 12). This chaotic region is complex and highly variable, with velocities sometimes exceeding 200 cm/s. Assessment using in-situ velocity measurements is very rare. This analysis characterizes the uncertainty in the model output and its predictions that Undersea Warfare operators, as well as other warfighters, obtain from the HYCOM output, and use in real world operations. Qualitative comparisons show good placement by HYCOM of persistent and energetic ocean current and eddy features, but difficulty (as expected, because HYCOM cannot resolve features finer than eddy scale) resolving the finer-scale variability present in the chaotic ARC region. Quantitative comparisons showed that the overall Root Mean Squared Error (RSME) is 35 cm/s and 47 near-surface, and 17 cm/s and 32 at 500 m depth, showing a general decrease of RMSE with depth.
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