摘要
Anomalous warming occurred in the equatorial central-eastern Pacific in early May 2014, attracting much attention to the possible occurrence of an extreme E1 Nifio event that year because of its similarity to the situation in early 1997. However, the subsequent variation in sea surface temperature anomalies （SSTAs） during summer 2014 in the tropical Pacific was evidently different to that in 1997, but somewhat similar to the situation of the 1990 aborted E1 Nifio event. Based on NCEP （National Centers for Environmental Prediction） oceanic and atmospheric reanalysis data, the physical processes responsible for the strength of E1 Nifio events are examined by comparing the dominant factors in 2014 in terms of the preceding instability of the coupled ocean-atmosphere system and westerly wind bursts （WWBs） with those in 1997 and 1990, separately. Although the unstable ocean-atmosphere system formed over the tropical Pacific in the preceding winter of 2014, the strength of the preceding instability was relatively weak. Weak oceanic eastward-propagating downwelling Kelvin waves were forced by the weak WWBs over the equatorial western Pacific in March 2014, as in February 1990. The consequent positive upper-oceanic heat content anomalies in the spring of 2014 induced only weak positive SSTAs in the central-eastern Pacific-unfavorable for the subsequent generation of summertime WWB sequences. Moreover, the equatorial western Pacific was not cooled, indicating the absence of positive Bjerknes feedback in early summer 2014. Therefore, the development of E1 Nifio was suspended in summer 2014.
Anomalous warming occurred in the equatorial central-eastern Pacific in early May 2014, attracting much attention to the possible occurrence of an extreme E1 Nifio event that year because of its similarity to the situation in early 1997. However, the subsequent variation in sea surface temperature anomalies （SSTAs） during summer 2014 in the tropical Pacific was evidently different to that in 1997, but somewhat similar to the situation of the 1990 aborted E1 Nifio event. Based on NCEP （National Centers for Environmental Prediction） oceanic and atmospheric reanalysis data, the physical processes responsible for the strength of E1 Nifio events are examined by comparing the dominant factors in 2014 in terms of the preceding instability of the coupled ocean-atmosphere system and westerly wind bursts （WWBs） with those in 1997 and 1990, separately. Although the unstable ocean-atmosphere system formed over the tropical Pacific in the preceding winter of 2014, the strength of the preceding instability was relatively weak. Weak oceanic eastward-propagating downwelling Kelvin waves were forced by the weak WWBs over the equatorial western Pacific in March 2014, as in February 1990. The consequent positive upper-oceanic heat content anomalies in the spring of 2014 induced only weak positive SSTAs in the central-eastern Pacific-unfavorable for the subsequent generation of summertime WWB sequences. Moreover, the equatorial western Pacific was not cooled, indicating the absence of positive Bjerknes feedback in early summer 2014. Therefore, the development of E1 Nifio was suspended in summer 2014.
基金
supported by the National Basic Research Program of China (Grant Nos.2014CB953902,2011CB403505,and 2012CB417203)
the Priority Research Program of the Chinese Academy of Sciences (Grant Nos.XDA11010402 and XDA01020302)
the National Natural Science Foundation of China (Grant Nos.41175059 and 41375087)
