Soya Warm Current Effectively Weakened by Easterly Wind

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  • 東風時に弱化され易い宗谷暖流
  • トウフウジ ニ ジャッカ サレ ヤスイ ソウヤ ダンリュウ

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The subinertial variation of the Soya Warm Current(SWC) is investigated through the analysis of current records obtained from the moored meters settled at three sites along the east coast of Hokkaido, during a period from April to October 2011. We found that the rapid decreases of southeastward SWC were frequently observed due to the strong easterly wind blowing, but the inverse(westerly) wind with the similar amplitude never grew the strong SWC. To understand such asymmetrical response of the SWC to the wind forcing, the numerical model experiments including the nonlinear drag law of bottom friction were carried out. In the circumstances combined with the SWC generated by sea level difference across the Soya Strait and wind-induced current, the model result suggests that the asymmetrial action of bottom friction term causes the different dynamic response. When the momentum balance between easterly wind stress and sea level gradient across the atrait is just realized, the SWC effectively is weakened, and hence such dynamic responce becomes the frictional free. In the case of westerly wind forcing, the SWC is superimposed by the eastward wind-induced current so that the southeastward flow speed tends to increase. However, its increase rate is gradually suppressed, because the bottom friction term on the momentum balance dominants in proportional as the square of flow speed.

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