相模湾中央部で観測された内部潮汐の鉛直構造と間欠性  [in Japanese] Vertical Structure and Intermittency of Internal Tides Observed at the Center of Sagami Bay  [in Japanese]

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Abstract

相模湾中央部における内部潮汐の鉛直構造と間欠性を解明するために,科学技術振興機構の戦略的創造研究推進事業(CREST)において2002年冬季から初夏に実施された流速・水温記録を解析した。ADCPで得られた流速記録には,200m深付近の主温度躍層を中心として顕著な半日周期,100m以浅には一日周期の変動が認められた。4月7日に北向きの強い流れとともに水温が急激に上昇し,成層が大きく変化したため,その前後に分けて解析した。表層混合層の発達した観測前半には,半日周期内部波の振幅は主温度躍層で大きく,位相は下層に向かい遅れる傾向が見られた。しかし,半日周期(M_2成分)の変動は,潮流楕円の形状が円に近いことから,単一波によるものではなく,複数点で発生した波あるいは入射波と反射波の合成によるものと考えられた。次に,半日・一日周期帯の運動エネルギー密度の時間変化を追求した。半日周期帯のエネルギーは,観測前半ではほぼ大潮小潮周期で変動し,250m深付近で比較的大きかったが,成層が変化した後の4月下旬以降では200m以浅で大きくなっていた。一方,一日周期帯のエネルギーは,基本場の流れが強くなった時に200m以浅で大きくなる傾向が認められた。この基本場の流れは,相模湾へのイベント的な黒潮系暖水の進入や黒潮流軸の接近に伴い強められていたことが判明した。さらに,基本場の流れが強かった観測後半には一日周期帯のピークが28.8時間周期に現れていたが,これは基本場の流れによって一日周期内部波の周期が変調したものと推察された。Mooring observations using an acoustic Doppler current profiler and a conductivity-temper ature-depth meter were carried out at the center of Sagami Bay from February 22 to May 17 in 2002 for the CREST of Japan Science and Technology Agency. Current and temperature data were analyzed to clarify the vertical structure and intermittency of internal tides in the bay. Semidiurnal period fluctuations were dominant in the middle layer throughout the observation period, while diurnal period fluctuations were predominant at depths shallower than 100 m. Basic stratification for the internal tides changed greatly after a sudden temperature increase associated with a strong northward current on April 7. Vertical structures of tidal ellipses for the M_2 constituent were estimated by using the current data before and after the temperature increase. Current amplitude of the semidiurnal internal tide was larger in the thermocline, and its phase delays greater with depth, in the first half of observation period. However, the tidal current ellipses for the M_2 constituent were almost circular over the observed depth range. This may result from the superimposition of the semidiurnal internal waves, which propagate in different directions. In the first half of the observation period, kinetic energy densities for the semidiurnal internal tide fluctuated with the spring-neap tidal cycle, whereas the energy densities for the diurnal internal tide in the last half of the period were amplified as increases of the low-pass filtered current; i.e., the background current in the bay. The background current was strengthened by the approach and intrusion of the Kuroshio water into the bay. Furthermore, the spectral peak of the diurnal period band appeared at 28.8 h during the period of the strong background current. It was speculated that frequency modulation of the spectral peak was to be due to the Doppler shift of the diurnal internal tide by the background current.

Journal

  • Oceanography in Japan

    Oceanography in Japan 13(5), 461-474, 2004-09-05

    日本海洋学会

References:  18

Cited by:  1

  • Characteristics of temperature and current variations in the intermediate-deep layer of Oshima East Channel, Sagami Bay  [in Japanese]

    WANG Qi , KITADE Yujiro , NEMOTO Masao , Qi Wang , Yujiro Kitade , Masao Nemoto , 東京海洋大学大学院海洋科学技術研究科 , 東京海洋大学大学院海洋科学技術研究科 , 東京海洋大学大学院海洋科学技術研究科 , Graduate School of Marine Science and Technology Tokyo University of Marine Science and Technology , Graduate School of Marine Science and Technology Tokyo University of Marine Science and Technology , Graduate School of Marine Science and Technology Tokyo University of Marine Science and Technology

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

    J-STAGE  References (27)

Codes

  • NII Article ID (NAID)
    110003353450
  • NII NACSIS-CAT ID (NCID)
    AN10382760
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    09168362
  • NDL Article ID
    7084594
  • 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  CJPref  NDL  NII-ELS 
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