Bao Xianwen

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  • Article
    Observational and model studies of the circulation in the Gulf of Tonkin, South China Sea
    (John Wiley & Sons, 2013-12-03) Ding, Yang ; Chen, Changsheng ; Beardsley, Robert C. ; Bao, Xianwen ; Shi, Maochong ; Zhang, Yu ; Lai, Zhigang ; Li, Ruixiang ; Lin, Huichan ; Viet, Nguyen Trung
    Moored current measurements were made at one mooring site in the northern Gulf of Tonkin for about 1 year during 1988–1989. Analyses were performed to examine characteristics and variability of tidal and subtidal flows. Rotary spectra showed two peaks at diurnal and semidiurnal periods, with higher diurnal energy. Complex demodulations of diurnal and semidiurnal tidal currents indicated that the tidal current magnitudes varied significantly with seasons: more energetic in the stratified summer than in the vertically well-mixed winter. The observed subtidal currents were highly correlated with the surface wind in winter but not in summer; challenging the conceptual summertime anticyclonic circulation pattern derived using wind-driven homogenous circulation theory. The computed currents from a global ocean model were in good agreement with the observed currents. Similar to the current observations, the model-computed flow patterns were consistent with the conceptual wind-driven circulation pattern in winter but opposite in summer. Process-oriented experiments suggest that the summertime cyclonic circulation in the northern Gulf of Tonkin forms as a result of the combination of stratified wind-driven circulation and tidal-rectified inflow from Qiongzhou Strait. The interaction between the southwest monsoon and buoyancy-driven flow from Hong River can significantly intensify the cyclonic circulation near the surface, but its contribution to the vertically averaged flow of the cyclonic circulation is limited.
  • Article
    Unusual cross-shelf transport driven by the changes of wind pattern in a marginal sea
    (American Geophysical Union, 2021-11-01) Yao, Zhigang ; Chen, Ke ; Ding, Yang ; Lin, Xiaopei ; Bao, Xianwen ; Qiao, Lulu
    The traditional understanding of the regional circulation in the Northwest Pacific marginal seas is that the Korean Coastal Current flows southward, following the isobaths of 20–50 m. However, an unusual tongue-shaped structure of cold water is observed in satellite SST data in January 2017, indicating a possible offshore spread of cold coastal water into the middle Southern Yellow Sea (SYS). Additional observations, including in situ hydrographic data as well as direct current measurement, also suggest this cross-shelf transport of the Korean Coastal Water in January 2017. Our analysis shows that this flow breaks through the isobaths at ∼37°N, moves southward between 50–75 m, and eventually veers anti-cyclonically at ∼35°N to join the western slope of the SYS. This circulation pattern is further supported by heat budget analysis. Diagnosis of potential vorticity (PV) reveals that the elevated negative PV anomaly imposed by surface wind stress favors this unusual cross-shelf transport. The change of wind pattern, although under a deceasing wind speed condition, plays an important role. This work provides an alternative view of the wintertime circulation pattern and motivates future studies of the variability of the coastal currents over interannual and longer time scales in the SYS.