Research Of ENSO Characteristics Changes During 1900-2015 Under Global Warming Background

The El Nino/Southern Oscillation(ENSO) is Earth's most prominent mode of interannual climate variability, and has a significant affect on global weather and climate. NOAA Extended Reconstructed Sea Surface Temperature V3b data set(ERSST) and Hadley Centre Sea Ice and Sea Surface Temperature data set (HadISST)were used in this paper to analyze the typical change of ENSO characteristics during 1900-2015. And 22 CMIP5 sea surface temperature datasets were also used to systematically analyze the simulated results. The main conclusions are as following:(1) It was demonstrated that ENSO amplitude changed clearly over the past more than 100 years. The weakest ENSO intensity occurred from the 1920s to the 1950s, during which the north- south width of ENSO spatial pattern narrowed and the maximum sea surface temperature anomaly (SSTA) center had a westward shift.In contrast, the width was the widest and the maximum SSTA center had an eastward shift after the late 1970s when ENSO intensity kept a strong magnitude. And then the width and the center had an opposite changing tendency after 2000.(2) Since the 1980s, the correlation coefficient between Nino3 region and Nino4 region had decreased, which means the two areas were becoming more independent.The El Nino Modoki, as the second tropical pacific SST mode, had come into being, and strength of which was becoming larger with time.(3) From the 1900s to the 1930s, the ENSO period was about 2 to 3 years. From the 1930s to 1960s, it demonstrated a longer ENSO cycle of 4 to 6 years. After that,one quasi-two-years cycle of ENSO occurred and another cycle of 3 to 5 years appeared in the 1980s. After 2000, the ENSO cycle became shorter with a 2-3 years period.(4) From the 1910s to the late 1960s, the skewness of ENSO was at a low level,indicating that there was no extreme El Nino event. However, since the 1980s, the ENSO skewness had increased significantly and remained being at a high level.(5) The models had different performances in simulating the ENSO typical characteristics of properties. Models could well simulate the climatological state and the first mode of the tropical Pacific SST. ENSO parttens in models were longer and narrower than that in observation. The model simulated range of ENSO amplitude was quite wide and even larger than the observed ENSO amplitude. The simulated ENSO skewness was very close to zero, which means that distribution of the simulated ENSO intensity was Gaussian-like. Our results also showed that the majority of models could well reproduce the standard 2-7 years period of ENSO in observation, and the variation of ENSO intensity during the past 100 years in some models also had a good simulation.