教師著作

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End date: 2013Subject: search.filters.subject.wind stress curl

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    Contrasting the flow patterns in the equatorial Pacific between two types of El Ni隳.
    (Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2012-11-01) Wang, L.-C.; C.-R. Wu
    Outputs based on the National Centers for Environmental Prediction (NCEP) Global Ocean Data Assimilation System (GODAS) are adopted to contrast the current variations in the equatorial Pacific between two types of El Niño. The model fully resolves the equatorial currents. We found that the central Pacific El Niño (CP-El Niño) corresponds well with previous El Niño studies in that both the eastward Equatorial Undercurrent (EUC) and westward South Equatorial Current (SEC) weaken. On the other hand, the eastern Pacific El Niño (EP-El Niño) displays a distinct circulation pattern. The North Equatorial Countercurrent (NECC) strengthens in the developing phase and persists into the peak of the warm event, whereas the northern branch of the SEC (SECn) also intensifies during the mature phase and lasts for about six months. The South Equatorial Countercurrent (SECC) strengthens during the decaying phase of the EP-El Niño. The shifting of the wind stress curl associated with the thermocline variability is chiefly responsible for the unique current performance of the EP-El Niño. It is worth noting that the air–sea interaction plays an important role in the current variability not only during a CP-El Niño but also during an EP-El Niño. RÉSUMÉ [Traduit par la rédaction] Nous adoptons les sorties basées sur le système GODAS (Global Ocean Data Assimilation System) des NCEP (National Centers for Environmental Prediction) pour mettre en évidence les variations de courant dans le Pacifique équatorial entre les deux types d'El Niño. Le modèle représente complètement les courants équatoriaux. Nous trouvons que l'El Niño du centre du Pacifique (CP-El Niño) correspond bien aux études précédentes sur l'El Niño puisque le sous-courant équatorial (EUC) vers l'est et le courant sud-équatorial (SEC) vers l'ouest faiblissent. D'autre part, l'El Niño de l'est du Pacifique (EP- El Niño) affiche une configuration de circulation distincte. Le contre-courant nord-équatorial (NECC) se renforce dans la phase de développement et persiste jusqu'au maximum du réchauffement, tandis que la branche nord du SEC (SECn) s'intensifie aussi durant la phase de maturité et persiste pendant environ six mois. Le contre-courant sud-équatorial se renforce durant la phase de dissipation de l'EP-El Niño. Le changement du rotationnel de la tension du vent lié à la variabilité thermocline est principalement responsable du comportement particulier du courant de l'EP-El Niño. Il est à remarquer que l'interaction air–mer joue un rôle important dans la variabilité du courant, non seulement durant un CP-El Niño mais aussi durant un EP-El Niño.
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    The forcing mechanism leading to the Kuroshio intrusion into the South China Sea
    (American Geophysical Union (AGU), 2012-07-01) Wu, C.-R.; Y.-C. Hsin
    We use a high-resolution numerical model to examine the forcing mechanism responsible for Kuroshio intrusion into the South China Sea (SCS). The collective wisdom is that variations in Kuroshio intrusion are closely related to the wind, inside or outside the SCS. A series of experiments was performed to identify the wind-related forcing regulating the intrusion. The experiments demonstrated that the importance of wind inside the SCS is greater than that outside the SCS. Furthermore, the northwestward Ekman drift due to northeasterly wind in winter intensifies the upstream Kuroshio in the Luzon Strait, enhancing the Kuroshio intrusion into the SCS. In particular, the wind stress curl (WSC) off southwest Taiwan is chiefly responsible for the Kuroshio intrusion. Both the WSC and intrusion show both seasonal and intraseasonal variation. As the negative WSC off southwest Taiwan becomes stronger, it contributes to anticyclonic circulation. The enhanced anticyclonic circulation helps the development of the Kuroshio intrusion. The consistency between WSC variability and the intrusion suggests that the WSC off southwest Taiwan is essential to the Kuroshio intrusion variability.
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    Bimodal Behavior of the Seasonal Upwelling off the northeastern coast of Taiwan
    (American Geophysical Union (AGU), 2009-03-01) Chang Y.-L.; C.-R. Wu; L.-Y. Oey
    Observations over the outer shelf and shelf break off the northeastern coast of Taiwan indicate a curious seasonal variability of upwelling. At deeper levels 100 m below the surface, upwelling is most intense in summer but weaker in winter. Nearer the surface at approximately 30 m below the surface, the opposite is true and the upwelling is stronger in winter than in summer. Results from a high-resolution numerical model together with observations and simple Ekman models are used to explain the phenomenon. It is shown that the upwelling at deeper levels (∼100 m) is primarily induced by offshore (summer) and onshore (winter) migrations of the Kuroshio, while monsoonal change in the wind stress curl, positive in winter and negative in summer, is responsible for the reversal in the seasonal variation of the upwelling near the surface (∼30 m). This mechanism reconciles previous upwelling data.