Evaluation of HYCOM in the Kuroshio Extension region using new metrics

A high resolution (0.08° at equator) HYbrid Coordinate Ocean Model (HYCOM) simulation is evaluated using observations for the period 1993–2003 for a western Pacific region containing the Kuroshio Extension (KE) (25–45°N and 135–180°E). Comparisons are made for the KE path and strength and for the upper ocean heat budget. The mean strength and path agree well with observations, except near the KE separation point, where the jet is as much as 2° of latitude too far south. However, the model path variations are considerably more energetic than observed, and this likely obscures the observed tendency for weaker meandering when the KE is strong. The model accurately reproduces seasonal variations of upper ocean heat content, but the long‐period (about 10‐yr) variations of heat content and KE strength clearly differ in the region upstream of 150°E. The long‐period variations in model SSH do not show the same relationship to wind forcing that is seen in the observations and in a low‐resolution ocean model simulation. The HYCOM upper ocean heat budget is similar to a diagnostic heat budget inferred from observations in that the dominant contribution is from lateral fluxes (advection); however, advection fluctuations (again primarily in the upstream region) are much larger in the model. This evaluation of HYCOM shows realistic mean quantities and realistic variations away from the separation region. However, an overly energetic jet upstream of 150°E can obscure the longer period variability and its contribution to the upper ocean heat budget.