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南海季風實驗(SCSMEX)期間海氣通量和海洋上層混合層之變化

Air-Sea Eddy Fluxes and Upper Oceanic Mixing Layer over the South China Sea during SCSMEX Field Experiment in 1998

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摘要


本文利用1998年南海季風實驗(SCSMEX)期間,海洋觀測平台在13°N、114°E附近的海氣觀測資料,研究南海地區季風爆發前和爆發時,海氣通量及海洋上層混合層的變化。南海季風爆發前,海面氣象場和海氣通量的日夜變化相當清楚;南海季風爆發時,日夜變化的現象也消失。比較季風爆發前和爆發時海面淨能量通量差異時可發現,在季風爆發前平均海面淨熱通量為181.7W/平方公尺,有加熱海洋的效應;在季風爆發時則變為-47.5W/平方公尺,有冷卻海洋的作用。 海洋混合層的發展明顯受到海氣動量通量的影響,其日夜變化則受控於海面淨熱通量的變化。南海季風爆發前,觀測海洋混合層的厚度具有明顯日夜變化的現象。當白天海面受熱時,近表面海溫升高,形成穩定層,使紊流強度減弱、海洋混合層不易發展,平均白天混合層的厚度約為6m;反之夜間表面冷卻時,近表面海溫降低形成不穩定層,使渦流強度增強、海洋混合層容易發展,夜間平均海洋混合層的厚度約在22m。在季風爆發前,整個平均海洋混合層的厚度約為15.6m。當南海季風爆發時,受海面風應力的混合作用和海面淨熱通量的冷卻作用,使得海洋混合層厚度日夜變化的現象消失,平均海洋混合層的深度亦比季風爆發前深,約為23.3m。

並列摘要


The Observation data of the South China Sea Monsoon Experiment (SCSMEX) of the Autonomous Temperature Line Acquisition System(ATLAS) mooring, near 13°N、114°E, are used to study the variability both air-sea eddy fluxes and upper oceanic mixing layer. The diurnal cycle is significant before the on set of the south China sea monsoon in the air-sea eddy fluxes and upper oceanic mixing layer. Then diurnal cycle is vanished after on set. It's shown that the average sea surface net heat flux before on set is about 181.7W/m^2, which heating ocean. However, the sea surface net heat flux during on set is about -47.5W/m^2, which cooling ocean. It is showed that the development of the oceanic mixing layer is influenced by the sea surface momentum flux. The diurnal cycle is controlled by the sea surface net heat flux. The oceanic mixing layer showed a clear diurnal cycle before on set. When the ocean is heating during daytime, the sea surface temperature increases and a stable layer is formed near surface. Therefore the turbulent mixing effect is weak that the oceanic mixing layer became shallow. The oceanic mixing layer depth is about 6 meters during the daytime. Conversely, the ocean is cooling during nighttime, the sea surface temperature decreases and an unstable layer is established near surface, so the turbulent mixing effect is increases that the oceanic mixing layer is deep. The mixing layer depth is about 22 meters during the nighttime. Averagely, the oceanic mixing layer depth is about 15.6m before on set. During the activity of the monsoon, the depth is about 23.3 meters, which is deeper than before on set. Due to the wind stress mixing and cooling effect of the net sea surface heat flux, the diurnal variability of the oceanic mixing layer depth vanished during the activity of the monsoon.

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