A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIÑO EVENTS

Abstract:

The atmospheric and oceanic conditions before the onset of EP El Niño and CP El Niño in nearly 30 years are compared and analyzed by using 850 hPa wind, 20°C isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Niño is earlier than that of the CP El Niño. Its intensity is far stronger than that of the CP El Niño. Two months before the El Niño, the anomaly westerly winds of the EP El Niño have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Niño can only extend to the west of the dateline three months before the El Niño and later stay there. Unlike the EP El Niño, the CP El Niño is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Niño can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Niño. The strong MJO activity of the EP El Niño in the western and central Pacific is earlier than that of the CP El Niño. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Niño is significantly greater than that of the CP El Niño before the onset of El Niño.