| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 99 === The development of ENSO and its impacts on climate are well-known from the literatures, however, the origin of ENSO indeed remains unknown. Recently, two types of ENSO are further defined; Eastern-Pacific ENSO (EP ENSO) and Central-Pacific ENSO (CP ENSO), respectively. Recent studies indicate that they are driven by different driving mechanisms which require better understanding. Here, we discussed these driving mechanisms and how ENSO is generated resulting from the southern hemisphere extra-tropical influences. It is found that CP ENSO becomes more prominent since 1977 and leads EP ENSO for about 12 months with increasing correlation during the recent decades. Around two to three years before the occurrence of EP ENSO, warm Sea Surface Temperature anomaly (SSTa) and negative Sea Level Pressure anomaly (SLPa) propagate eastward from the Southern Pacific toward South America through the ocean-atmosphere coupled Antarctic Circumpolar Wave (ACW). In the tropic, the warm SSTa and negative SLPa also propagate eastward through the low-frequency component of Global ENSO Waves (GEW) and enhances the occurrence of EP ENSO. The evolving of ENSO after 1977 could be due to the large pattern changes of ACW and GEW after the 1976/1977 region shift. Further coupled model results show that the ACW indeed affects the occurrence of EP ENSO while there is no direct link with CP ENSO.
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