沿岸海洋と外洋との関わり

中規模渦に対する沿岸海洋の応答を数値的に調べた．地衡流調節の過程で励起されたKelvin jetはその非線形性により「急潮」と良く似た現象を引き起こす．又，残された地衡流渦は回転系に拡張された鏡像効果により岸に沿う方向に移動する．沿岸の地形を考慮した実験は観測された暖水の移動を良く再現することが示された．1. はじめに / 2. モデル実験 / 3. 沿岸海岸における短期変動 / 4. まとめ / 5. 謝

CHARACTERISTIC FEATURES OF THE KUROSHIO WITH AND WITHOUT THE COLD WATER MASS SOUTH OF ENSHUNADA

1. Introduction / 2. Data and data analysis / 3. Surface currents of the Kuroshio / 4. Volume transport of the Kuroshio / 5. The Kuroshio meander and the Cold Water Mass / 6. The warm eddy / 7. Concluding remarksThe data of GEK measurements for these eighteen years and serial observations for these fifty years have been analyzed statistically in order to clarify characteristic features of the Kuroshio with and without the Cold Water Mass south of Enshunada. The warm eddy south of the Kuroshio between 133° and 138° E has been delineated clearly. The eddy for the period when the Cold Water Mass is absent is larger in scale and more extensive in the fall of isotherms than that for the period when it is present. It has been found that a remarkable difference in the path of the Kuroshio east of Honshu is seen in a statistical sense between the two modes of the Kuroshio meander: when the Cold Water Mass is absent the path of the Kuroshio broadens and fluctuates to the north and south, while the path is confined in a narrow zone when it is present. The volume transport of the Kuroshio is about 50xl0^6㎥/sec at the region south or southeast of Shikoku, irrespective of whether the Cold Water Mass is present or absent. While the transport decreases gradually toward the east from 50x10^6㎥/sec to 30x10^6㎥/sec when the Cold Water Mass is present, the transport keeps roughly a constant value of 50x10^6㎥/sec when it is absent. Geographical examination of detailed features of the Kuroshio meander and the Cold Water Mass south of Enshunada suggests a close dynamical relationship between the kuroshio and the bottom topography. Vertical structures of temperature fields have been presented in Appendix

Comparison of Sea Surface Dynamic Heights Estimated from Inverted Echo Sounder Data and Satellite Altimeter Data

Sea surface dynamic height (SSDH) anomalies estimated from long-time inverted echo sounder (IES) data using gravest empirical mode method are compared with satellite altimeter data. The IES-derived SSDH anomalies agree well with the altimetric SSDH anomalies, although the IES-derived SSDH variation is slightly underestimated. We calculate power spectra of these SSDH anomalies to discuss time-scale dependency of their differences. The differences between two SSDH anomalies are found mainly caused by components with the periods from 50 days to 100 days, which correspond to meso-scale eddies or small meanders of the Kuroshio. These differences result in smaller variation of the IES-derived SSDH

Comparison of Sea Surface Dynamic Heights Estimated from Inverted Echo Sounder Data and Satellite Altimeter Data

Sea surface dynamic height (SSDH) anomalies estimated from long-time inverted echo sounder (IES) data using gravest empirical mode method are compared with satellite altimeter data. The IES-derived SSDH anomalies agree well with the altimetric SSDH anomalies, although the IES-derived SSDH variation is slightly underestimated. We calculate power spectra of these SSDH anomalies to discuss time-scale dependency of their differences. The differences between two SSDH anomalies are found mainly caused by components with the periods from 50 days to 100 days, which correspond to meso-scale eddies or small meanders of the Kuroshio. These differences result in smaller variation of the IES-derived SSDH

リニアーな鉛直温度分布を有する安定境界層の風洞実験

By using a thermally stratified wind tunnel, we have successfully simulated stably stratified boundary layers (SBL), in which the mean temperature increases upward almost linearly. We have investigated the flow structure and the effects of linear stable stratification on the transfer of momentum and heat fluxes. The vertical profiles of turbulence quantities exhibit different behavior in two distinct stability regimes of the SBL flows with weak and strong stability. For weak stability cases, the transfer of turbulent momentum and heat fluxes is basically similar to those for neutral turbulent boundary layers, although it is weaken with increasing stability. For strong stability cases, on the other hand, the time-mean transfer of turbulent fluxes is almost zero over the whole boundary layer depth. However, the instantaneous transfer of turbulent fluxes frequently occurs in the both gradient and counter-gradient directions in the lower part of boundary layer. This is due to the Kelvin-Helmholtz (K-H) shear instability and the rolling up and breaking of K-H waves. Moreover, the internal gravity waves are observed in the middle and upper parts of all stable boundary layers

直接測定による四国沖の黒潮流速の変動特性

Direct current measurements were carried out along ASUKA(Affiliated Surveys of the Kuroshio off cape Ashizuri) line crossing the Kuroshio from Shikoku coast, Japan to 25 °N, during 1993-1995. The temporally averaged views of the Kuroshio show that most strongly flowing part, the Kuroshio flow axis, at about 700 m depth is located around 32 °N and it spreads down to about 2000 m depth. Weak countercurrents are detected just above the continental slope and strong countercurrents are also detected near the deepest end of the continental slope. At a reference depth of 650 m, the Kuroshio flow axis coincides with 7° C isotherm. The Kuroshio takes two distinct paths: a near-coast path and a far offshore path. For each case, a horizontal velocity profile at 650 m depth is estimated on a stream coordinate that denotes the component parallel to the velocity at the Kuroshio flow axis.1. 緒言 / 2. RIAM-COMPACTの概要 / 3. 壁面せん断乱流場によるRIAM-COMPACTの計算精度の検証 / 4. 実地形上の風況場解析への適用 / 5. まと

日本南方黒潮域における慣性周期近傍の流速変動

Velocity fluctuations having near inertial frequency are studied on the basis of moored current meter data obtained at mid-depths in the Kuroshio and its recirculation regions south of Japan. Spectra of velocities with tidal currents removed show remarkable peaks near the inertial frequency, having mostly the clockwise rotation component. The energy associated with these fluctuations increases toward the offshore side, or southward. There are several peaks on the higher-frequency side, which seem to be associated with harmonics of the inertial oscillation

四国沖の黒潮の流量の評価

日本南岸での黒潮の絶対流量と熱流量を評価するために，四国の足摺岬から南南東に延びる観測線 ASUKAを設け．その測線上で集中した協同海洋観測を行った． 1993~1995年の 2年間の集中観測のうちの最初の 1年間の係留流速計の記録と．その間に繰り返し行った測線沿いのCTD/XBT観測のデータを組み合わせて．黒潮の絶対的な地衡流断面を求め，その面積積分から絶対流量を求めた．それによって，黒潮の流量と水位差の間に非常に高い相関があることが分かった．この関係を使って，人工衛星 TOPEX/POSEIDON海面高度計データから，黒潮の絶対流量の約 3年間にわたる時系列を得た．得られた流量の時系列には，はっきりとした季節変化は見られなかった．1. はじめに / 2. 観測 / 3. 観測結果 / 4. 黒潮の流量 / 5. おわり