開放型沿岸域における流れに及ぼす風の効果

Wind effect on currents in a thin surface layer of coastal waters faced open-sea

中野 政尚 ; 磯崎 久明; 磯崎 徳重; 根本 正史*; 蓮沼 啓一*; 北村 尚士*

Nakano, Masanao; Isozaki, Hisaaki; Isozaki, Tokuju; Nemoto, Masashi*; Hasunuma, Keiichi*; Kitamura, Takashi*

沿岸域での風と流れの関係を調べるため、2年間に及ぶ風と流れの連続観測を実施した。観測海域は外洋に直接面した茨城県東海村沖である。沿岸水域特有の強い密度躍層の存在を考慮し、躍層以浅に注目した観測を行った。風と流れの変動は1日と数日以上の周期が卓越していた。風の長周期の変動には恒常的に北風成分が存在しており、これが南下流を形成している。また、風と表層0.5mの流れの間には2年間を通じて高い相関(相関係数0.64)が得られた。1日周期の変動は、調和解析の結果、卓越するS1分潮として現れたが、これは海陸風とそれによる吹送流であった。海陸風にはS1以外の太陽潮周期の成分も含まれており、これは対応する分潮流に吹送流成分を加える。その結果、太陽潮周期の分潮流にはあたかも潮流のように振舞う吹送流(擬似潮流)が含まれる。

To investigate the relationship between the wind and the current along the coast, the continuous observation of wind and current carried out for two years. The observed area was off shore Tokai-mura in Ibaraki prefecture, where faces open ocean. Considering the existence of strong pycnocline, the observation was carried out at the shallow depth over the pycnocline. The period of wind and current variation for 1 day and over several days was significant. Although the long period variation is caused from the variation of weather and season, the south current is formed by the permanent north wind component. The high correlation factor (0.64) between wind and surface current at 0.5 m was obtained throughout two years. As the result of harmonic analysis, both wind and current variations of 1 day period were appeared as S1 component tide, and it was confirmed to be land and sea breeze, and wind driven current, respectively. The land and sea breeze, which contains solar component except S1, adds the wind driven current except S1 to the corresponding component tide. From these results, it is considered that the land and sea breeze makes the pseudo S1 tidal current to the sea surface in the open coastal sea.