A discrepancy remains in the first two leading empirical orthogonal function(EOF) modes of the tropical Pacific sea surface temperature anomaly(SSTA) based on observations since the 1980s. The EOF1 mode, representing ...A discrepancy remains in the first two leading empirical orthogonal function(EOF) modes of the tropical Pacific sea surface temperature anomaly(SSTA) based on observations since the 1980s. The EOF1 mode, representing the El Ni?o-Southern Oscillation(ENSO), is a robust result. However, the EOF2 features either El Ni?o Modoki(EM) or ENSO evolution during different periods, which is probably associated with the impacts of global warming. The underlying question is what the EOF2 mode of the tropical Pacific would be without global warming. Using the CMIP5 preindustrial scenario to exclude the influence of global warming, we find that the EOF1 mode of the tropical Pacific SSTA represents ENSO and that the EOF2 mode is not EM. According to the lead–lag correlation between the ENSO and EOF2 modes, the linkage between these two modes is as follows: …El Ni?o → EOF2 → La Ni?a →–EOF2 → El Ni?o…. By analyzing the evolution of sea surface temperature, surface wind, and subsurface ocean temperature anomalies, we find the mechanism linking the ENSO and EOF2 modes is the air–sea interaction associated with the ENSO cycle. This result suggests that the EOF2 mode represents an aspect of ENSO evolution under preindustrial conditions. Therefore, this study further indicates that the EM is probably due to the influence of global warming.展开更多
基金supported by the National Key Research and Development Program on Monitoring,Early Warning and Prevention of Major Natural Disasters(2018YFC1506006)the National Natural Science Foundation of China Project(41805054,41875108,41805041,41705065)the Scientific Research Fund of the Chengdu University of Information Technology(KYTZ201724,KYTZ201602,KYTZ201727)
文摘A discrepancy remains in the first two leading empirical orthogonal function(EOF) modes of the tropical Pacific sea surface temperature anomaly(SSTA) based on observations since the 1980s. The EOF1 mode, representing the El Ni?o-Southern Oscillation(ENSO), is a robust result. However, the EOF2 features either El Ni?o Modoki(EM) or ENSO evolution during different periods, which is probably associated with the impacts of global warming. The underlying question is what the EOF2 mode of the tropical Pacific would be without global warming. Using the CMIP5 preindustrial scenario to exclude the influence of global warming, we find that the EOF1 mode of the tropical Pacific SSTA represents ENSO and that the EOF2 mode is not EM. According to the lead–lag correlation between the ENSO and EOF2 modes, the linkage between these two modes is as follows: …El Ni?o → EOF2 → La Ni?a →–EOF2 → El Ni?o…. By analyzing the evolution of sea surface temperature, surface wind, and subsurface ocean temperature anomalies, we find the mechanism linking the ENSO and EOF2 modes is the air–sea interaction associated with the ENSO cycle. This result suggests that the EOF2 mode represents an aspect of ENSO evolution under preindustrial conditions. Therefore, this study further indicates that the EM is probably due to the influence of global warming.
