黒潮の非大蛇行離岸流路期における相模湾の50-70日周期の流速変動  [in Japanese] Flow variability with periods of 50-70 days in Sagami Bay, Japan during the offshore non-large-meander path of the Kuroshio  [in Japanese]

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Abstract

相模湾において,2008年に水中設置自動昇降ブイシステムによる係留観測を行い,湾内の流速変動について調べた。日本南岸海域の黒潮流路は,6月3日付近に非大蛇行接岸流路から離岸流路へ遷移し,それにともなって湾内の流動構造が一変した。6月3日以降,黒潮は比較的安定した非大蛇行離岸流路を取り,その間,湾中央部では水深200m付近に最大振幅を持つ50-70日周期の流速変動が卓越した。この流速変動は湾北部の高気圧性の循環の形成に起因し,高気圧性の循環の消長は房総半島沖の黒潮流軸の変動と対応していた。この高気圧性の循環は,26.2-26.6σ_θ層のレンズ構造の内部に形成され,湾北部でこの循環が形成されるとき,水深200m以浅では下層水の湧昇が生じた。一方,房総半島沖の黒潮流軸の変動は,約60日周期で生じるS字の蛇行によって特徴づけられ,この蛇行が解消されるとき,湾北部で高気圧性の循環が形成された。この黒潮流軸の変動は,遠州灘から東進して来る擾乱と関連し,擾乱が相模湾沖に到達するとき,黒潮流軸の蛇行も解消された。以上のことから,非大蛇行離岸流路期には,遠州灘を起源とする擾乱によって房総半島沖で黒潮流軸が変動し,それに付随するように,湾北部では高気圧性の循環が形成されることが明らかになった。さらに,この高気圧性の循環の形成が,湾内に50-70日周期の流速変動を引き起こし,この変動は非大蛇行離岸流路期に生じる典型的なものであると考えられる。Flow variability in Sagami Bay was examined using mooring data obtained by Project on Ocean Productivity Profiling System (POPPS) buoy during the offshore non-large-meander path (oNLM) of the Kuroshio in 2008. Transition from the nearshore non-large-meander path (nNLM) to oNLM occurred around June 3, 2008, and then the flow field dramatically changed in Sagami Bay. After June 3, 2008, the Kuroshio took the relatively stable oNLM, and the flow variability with periods of 50-70 days whose maximum of amplitude was near 200m depth was dominated in Sagami Bay. This flow variability was caused by generation of an anticyclonic circulation at a depth of 200m in the northern part of Sagami Bay, and this generation was associated with the Kuroshio axial variation, which was characterized by S-like shape meander, with periods of about 60 day off the Boso Peninsula. A lense-like structure of 26.2-26.6σ_θ isopycnal surfaces at depths of 120-320m was accompanied by the generation of the anticyclonic circulation, resulting in upwelling of colder lower layer water at depths shallower than 200m in the northern part of Sagami Bay. When the S-like shape meander vanished off the Boso Peninsula, the anticyclonic circulation inside the lense-like isopycnal structure was generated in the northern part of Sagami Bay. Additionally, this Kuroshio axial variation was associated with disturbance with negative sea level anomaly, which was generated around Enshu-nada and propagated eastward. The disturbance arrived off Sagami Bay, and then the S-like shape meander vanished off the Boso Peninsula. Therefore, the anticyclonic circulation in the northern part of Sagami Bay was caused by the Kuroshio axial variation off the Boso Peninsula occurring with the arrival of the disturbance off Sagami Bay, and the generation of the anticyclonic circulation caused the flow variability with periods of 50-70 days in Sagami Bay, which was a typical phenomenon during the oNLM.

Journal

  • Oceanography in Japan

    Oceanography in Japan 20(3), 59-83, 2011-07-15

    日本海洋学会

References:  29

Codes

  • NII Article ID (NAID)
    110008712072
  • NII NACSIS-CAT ID (NCID)
    AN10382760
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    09168362
  • NDL Article ID
    11228421
  • NDL Source Classification
    ZM44(科学技術--地球科学--海洋・陸水・火山)
  • NDL Call No.
    Z15-778
  • Data Source
    CJP  NDL  NII-ELS 
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