Surface current variability east of Okinawa Island obtained from remotely sensed and in situ observational data

Abstract

We investigated ocean surface current variability in the region east of Okinawa Island in the spring of 1998 using in situ and remotely sensed data including surface velocity estimates inferred from HF ocean radars. Most previous studies utilizing HF ocean radars were limited to shallow continental shelves. In contrast, most of the observation area in this study was in the open ocean. During the observation period the HF ocean radars sampled a region where anticyclonic and cyclonic mesoscale eddies were adjacent to each other. The HF‐radar‐derived ocean currents agree with those measured by a current meter. The surface currents were highly variable in both time and space and were affected by the eddy field in the offshore region. The current field was related to the near‐surface water temperature. For example, a local temperature rise was often associated with northeastward flows. The surface currents in regions shallower than about 1000 m had a significant correlation with local wind forcing. Our HF ocean radars often detected a strongly convergent zone, which was different in character from those described in previous studies in that it was in the deep ocean. From other data such as National Oceanic and Atmospheric Administration advanced very high resolution radiometer imagery, we concluded that the convergent zone was due to mesoscale eddy fronts.