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Abstract

Mean field and annual variation of surface flow in the East China Sea as revealed by combining satellite altimeter and drifter data

Dr Daisuke TAKAHASHI(1), Dr Akihiko MORIMOTO(2)

(1) Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Japan
(2) Hydrospheric Atmospheric Research Center, Nagoya University, Japan

Session theme: Others (Posters only)

  • poster

    Abstract

    A surface flow field in the East China Sea (ECS) has been studied by many oceanographers using various approaches such as hydrographic observation, geomagnetic electrokinetopraphs data, current meter, satellite tracked drifters, ocean Radar, and numerical models. Accumulation of findings from those studies has gradually made us understand mean field and seasonal variation in surface flow in the ECS. Although main features of the mean field and seasonal variation in surface flow in the ECS have been roughly clarified, there is still a matter of discussion about its persistency and seasonal variation. Therefore, we made monthly mean absolute sea surface current data in the ECS from 1995 to 2009 combining satellite altimetry data with buoy trajectory data to see surface flow variation. Using the data set, we investigated seasonal variation in sea surface current in the ECS. Especially, we focused on the variation with an annual cycle because the signal is a dominant component in seasonal variation. Contribution of the annual cycle to seasonal variation was estimated as 50 % over the ECS, and the percentage was greater than 70 % in the Kuroshio, Taiwan Warm Current, and northeastward Kuroshio branch west of Kyushu, Japan. The annual variation was characterized by propagation of vorticity anomalies from northeast of the Taiwan Strait and in the Tsushima Strait. The vorticity anomaly from northeast of Taiwan Strait propagates downstream in the northeastward Kuroshio branch along isobaths of about 100 m on the shelf edge. On the contrary, the vorticity anomaly in the Tsushima Strait propagates upstream in the Tsushima Warm Current along isobaths of 100-200 m. The propagations of the vorticity anomaly could be well explained by a dispersion relation of a quasigeostrophic topographic Rossby wave in a mean flow for a first approximation. Generation of the vorticity anomalies from northeast of the Taiwan Strait and in the Tsushima Strait appears to be closely related to annual variation in current speed of the Kuroshio northeast of Taiwan and in volume transports through the Tsushima Strait, respectively.

     
    Corresponding author:

      Dr Akihiko Morimoto
      Hydrospheric Atmospheric Research Center, Nagoya University
      Furo-Cho, Chikusa-Ku
      464-8601 Nagoya
      Japan
      E-mail:
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