相模湾大島東水道の中深層における水温・流速変動の特性  [in Japanese] Characteristics of temperature and current variations in the intermediate-deep layer of Oshima East Channel, Sagami Bay  [in Japanese]

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Abstract

<p>大島東水道における流速変動の特性を調べるため,2007年5月22日から9月11日に布良沖の相模トラフ東斜面と大陸棚上で係留観測を実施した。両地点では3.7日周期を中心とした数日周期帯の流速変動が卓越しており,相模トラフの703 m~1020 m 深の3.7日周期の流速変動は布良の潮位変動とほぼ同位相であった。銚子から御前崎までの潮位記録から,数日周期帯(2日~11日)の潮位変動は,神津島では殆ど見られないが大島や沿岸の潮位では見られ,銚子から伊東まで岸に沿って1.5~2.2 m s<sup>-1</sup>の速さで伝播していた。さらに,数日周期の流速変動は,大島および銚子の風と高いコヒーレンスを示したことから,風により励起された沿岸捕捉波であることが示された。大島東水道での沿岸捕捉波の断面構造を調べるため,Brink and Chapman(1987)に倣って沿岸捕捉波のモードを求めた結果,観測された流速変動は主に沿岸捕捉波の第2モードで説明できることが分かった。一方,8月中旬から下旬に,703 m 深で 15 cm s<sup>-1</sup>に達する流出と流入が続いて生じるイベントが発生しており,8月下旬には相模湾内250~550 mの深度帯に親潮系低塩分水が観測された。このイベント的流速変動の発生要因として,冷水渦の西進に伴う黒潮流軸の離岸が考えられた。</p>

<p>Mooring observations were carried out at the stations on the northeastern slope of Oshima East Channel and the continental shelf off Mera from 22 May to 11 September 2007. Observed velocity was dominantly varied at periods around 3.7days at both the stations. The 3.7days oscillation observed at depths of 703 m-1020 m in Sagami Tough was approximately in phase with the sea-level change at Mera. Sea level was fluctuated dominantly at periods of several days (2-11 days) at all the stations on the coast from Choshi to Omaezaki and in Oshima, whose signal was propagated along the coast from Choshi to Ito with speeds of 1.5-2.2 m s<sup>-1</sup>. In addition, we found significant coherency at periods around 3.7 days between velocity at the depths 703 m-1020 m in the trough and wind at Choshi and Oshima. Accordingly, we suggested the coastal-trapped wave was generated by the windon the coast. Based on Brink and Chapman (1987), we investigated the modal structures of the 3.7-days fluctuationalong the section crossing the channel and then revealed the correspondence of the second mode to the mooring data. Current velocity at the 703 m depth was suddenly strengthened in the direction of outflow from the bay in the middle of August and being reversed at the end of the month with speed reaching as fast as 15 cm s<sup>-1</sup>. Low-salinity water was also observed at depths of 250 m-550 m in the bay at the end of this month being coincided with this event. This may be because water originated from the Oyashio flowed into the bay due to the offward shift of the Kuroshio axis induced by a cold core eddy moving westward.</p>

Journal

  • Oceanography in Japan

    Oceanography in Japan 22(1), 1-18, 2013-01-15

    The Oceanographic Society of Japan

References:  27

Codes

  • NII Article ID (NAID)
    110009579042
  • NII NACSIS-CAT ID (NCID)
    AN10382760
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    09168362
  • NDL Article ID
    024280846
  • NDL Call No.
    Z15-778
  • Data Source
    CJP  NDL  NII-ELS  J-STAGE 
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