Validation and error analysis of wave-modified ocean surface currents in the northwestern Pacific Ocean

By incorporating the wave-induced Coriolis-Stokes forcing into the classical Ekman layer, the wave-modified ocean surface currents in the northwestern Pacific Ocean were estimated. Thus, the ocean surface currents are the combination of classical Ekman current from the cross-calibrated multi-platform (CCMP) wind speed, geostrophic current from the mean absolute dynamic topography (MADT), and wave-induced current based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) surface wave datasets. Weight functions are introduced in the Ekman current formulation as well. Comparisons with in-situ data from Lagrangian drifters in the study area and Kuroshio Extension Observatory (KEO) observations at 32.3°N, 144.6°E, and 15-m depth indicate that wave-modified ocean surface currents provide accurate time means of zonal and meridional currents in the northwestern Pacific Ocean. Result shows that the wave-modified currents are quite consistent with the Lagrangian drifter observations for the period 1993–2017 in the deep ocean. The correlation (root mean square error, RMSE) is 0.96 (1.45 cm/s) for the zonal component and 0.90 (1.07 cm/s) for the meridional component. However, wave-modified currents underestimate the Lagrangian drifter velocity in strong current and some offshore regions, especially in the regions along the Japan coast and the southeastern Mindanao. What’s more, the wave-modified currents overestimate the pure Eulerian KEO current which does not consider the impact of waves, and the zonal (meridional) correlation and RMSE are 0.95 (0.90) and 11.25 cm/s (12.05 cm/s) respectively. These comparisons demonstrate that our wave-modified ocean surface currents have high precision and can describe the real-world ocean in the northwestern Pacific Ocean accurately and intuitively, which can provide important routes to calculate ocean surface currents on large spatial scales.