Winter coastal upwelling off northwest Borneo in the South China Sea
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摘要: 通过分析卫星数据、气候态温盐资料和再分析数据研究了冬季婆罗洲岛西北沿岸上升流. 该上升流十二月份形成, 一月份达到最强, 二月份开始减弱, 三月份基本消失不见. 进一步分析表明沿岸东北季风引起的艾克曼输运和由于山脉阻挡形成的正的风应力旋度导致的艾克曼抽吸是该上升流形成的主要原因, 两者输运量显示艾克曼输运对上升流的贡献更大. 受ENSO(厄尔尼诺/南方涛动)的影响, 上升流还表现出明显的年际变化: 厄尔尼诺年冬季, 南海出现反气旋式异常风场, 在婆罗洲岛西北沿岸表现为东北风异常和正的风应力旋度异常, 两者都可以加强上升流, 导致海表温度降低、叶绿素浓度增高;而在拉尼娜年, 情况正好相反. 在ENSO的调控下, 冬季婆罗洲岛西北沿岸海表温度异常与越南东南外海的刚好相反, 在南海南部东西方向出现海温异常变化的 "跷跷板"现象.Abstract: Winter coastal upwelling off northwest Borneo in the South China Sea (SCS) is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in december, matures in January, starts to decay in February and almost disappears in March. Both Ekman transport induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ekman transport is two times larger than Ekman pumping in January and February. Under the influence of El Niño-Southern Oscillation (ENSO), the upwelling shows remarkable interannual variability: during winter of El Niño (La Niña) years, an anticyclonic (a cyclonic) wind anomaly is established in the SCS, which behaves a northeasterly (southwesterly) anomaly and a positive (negative) wind stress curl anomaly off the northwest Borneo coast, enhancing (reducing) the upwelling and causing anomalous surface cooling (warming) and higher (lower) chlorophyll concentration. The sea surface temperature anomaly (SSTA) associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter.
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Key words:
- coastal upwelling /
- northwest Borneo /
- South China Sea /
- Ekman transport /
- Ekman pumping
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