Parallel comparison of the 1982/83, 1997/98 and 2015/16 super El Niños and their effects on the extratropical stratosphere

Abstract

This study uses multiple sea surface temperature (SST) datasets to perform a parallel comparison of three super El Ninos and their effects on the stratosphere. The results show that, different from ordinary El Ninos, warm SST anomalies appear earliest in the western tropical Pacific and precede the super El Nino peak by more than 18 months. In the previous winter, relative to the mature phase of El Nino, as a precursor, North Pacific Oscillation-like circulation anomalies are observed. A Pacific–North America (PNA) teleconnection appears in the extratropical troposphere during the mature phase, in spite of the subtle differences between the intensities, as well as the zonal position, of the PNA lobes. Related to the negative rainfall response over the tropical Indian Ocean, the PNA teleconnection in the winter of 1997/98 is the strongest among the three super El Ninos. The northern winter stratosphere shows large anomalies in the polar cap temperature and the circumpolar westerly, if the interferences from other factors are linearly filtered from the circulation data. Associated with the positive PNA response in a super El Nino winter, positive polar cap temperature anomalies and circumpolar easterly anomalies, though different in timing, are also observed in the mature winters of the three super El Ninos. The stratospheric polar vortex in the next winter relative to the 1982/83 and 1997/98 events is also anomalously weaker and warmer, and the stratospheric circulation conditions remain to be seen in the coming winter following the mature phase of the 2015/16 event.