ENSO事件中次表层海温距平在10°N附近向西传播的机理

THE MECHANISM OF SUBSURFACE SEA TEMPERATURE ANOMALY TRANSMITTED WESTWARD ABOUT 10°N IN ENSO EVENTS

在最大温度距平的极值曲面上,对观测资料的分析表明,在这个曲面上的次表层海温距平,一般从西太平洋暖池附近沿赤道向东传播,然后在东太平洋95°W附近向两极传播,并在10°N附近(北半球比南半球清楚)向西传播,再在140°E暖池海域传向赤道,形成一个信号传播的回路。文章试图研究东太平洋次表层海温距平信号在10°N附近向西传播的可能机制。低空850 hPa风场的资料分析表明,当ENSO处在暖(冷)位相时,东太平洋沿岸附近将出现经向风,首先在经向风的吹引下,将产生沿岸的Kelvin波,进而在经向风的辐散(辐合)作用下,通过沿岸的上升(下沉)流在各个纬度激发出向西的Rossby波,但理论表明在与观测接近的周期性经向风作用下由Kelvin波产生的沿岸上升(下沉)流在10°N附近最大,因此在那个纬度附近Rossby波的振幅最大,更易将距平意义下的冷(暖)水传向西太平洋。

The data show that the temperature anomaly core of vertical Maximal Sea Temperature Anomaly （MSTA） level moves eastward from “warm pool” in Equatorial Western Pacific Ocean to 95°W in Equatorial Eastern Pa- cific Ocean and turns to northward and southward to 10°N, 10°S respectively and then turns to westward to 140°E and returns to “warm pool” in Equatorial Western Pacific Ocean. They make up a pairs of cycles. The north cycle is stronger than the south one. This study focus on the possible mechanism of the temperature anomaly core turning westward near eastern Pacific Ocean 10°N, 10°S. The wind fields in 850 hPa show that there is meridian wind near eastern Pacific Ocean coast when ENSO growing （fizzling）. It rouses Kelvin wave and upwelling （down welling） along the coast. The Rossby waves of west propagating in various latitudes are triggered by upwelling （down welling） along the coast. The theoretic analysis shows that the upwelling （down welling） and Kelvin wave along the coast triggered by periodic meridian wind which is similar to the observation are biggest about 10°N, 10°S. So the amplitude of the Rossby wave reaches maximum at that location. It makes the anomaly cool （warm） water easily transport to western Pacific Ocean.