Southern hemisphere extra-tropical forcing on ENSO -observation and model comparisons

The mechanisms of ENSO and its patterns and impacts to climate are well-known from the literatures, however, the origin of ENSO still remains unknown. It has been confirmed that there are two types of ENSO; namely East Pacific ENSO (EP ENSO) and central pacific ENSO (CP ENSO). Both are driven by different driving mechanisms which require better understanding currently. We will discuss these driving mechanisms and how the ENSO is generated here. We first analyzed the observational data for both ENSO and their driven mechanisms. Further, we tried to construct the relationship between ENSO and Antarctic forcing. Several climate model simulations are performed to verify these driven mechanisms. Radon Transform (RT) will be used to determine the direction and phase speed of Arctic Circumpolar Wave (ACW) and Global ENSO Wave (GEW) to clarify the relationship among ACW, GEW, and ENSO. To distinguish the significance of CP ENSO and EP ENSO, we used combined regression EOF (CREOF). The EOF analysis for the whole Pacific Ocean and the tropics shows that ENSO is not only limited in the tropics but is a dominant pattern of the Pacific Ocean. The CP ENSO also strengthened and had a higher frequency after the climate regime shift in the 1970s. The analysis of ACW shows that the negative anomaly of zonal surface wind (ZSW) propagates eastward in the mid-latitude in the south hemisphere before the occurrence of EP ENSO. This is shown in both observation and ECHAM model, which indicates that ACW does impact EP ENSO and is driven by the ocean forcing.