Abstract
East Asia experienced a record-breaking cold event during the 2015/16 boreal winter, with pronounced impacts on livelihood in the region. We find that this large-scale cold spell can be attributed to the concurrent super El Niño event in the tropical Pacific. Our analysis reveals that all super El Niño winters (1982/83, 1997/98, and 2015/16) were accompanied by a rapid sub-seasonal North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) phase reversal from a positive to a negative state during early January, which was largely caused by the interaction of these super El Niño events with the subtropical jet annual cycle. The NAO/AO phase transition leads to a rapidly strengthened Siberian High, which favors southward intrusions of cold air to East Asia and thus causes severe local cooling. Similar cold spells can also be detected over Northern Europe associated with the fast sub-seasonal NAO/AO phase reversal. Due to the weaker amplitude of the ENSO forcing, these sub-seasonal atmospheric responses cannot be detected for moderate El Niño events. The super El Niño associated sub-seasonal signal of the East Asian and Northern Europe wintertime temperature responses carries important implications for future predictability of regional extreme events.
Highlights
During the 2015/16 boreal winter, we witnessed a super El Niño event in the tropical Pacific, with comparable amplitude to the well-known 1982/83 and 1997/98 extreme El Niño events[6]
During the 2015/16 winter, while a pronounced warming occurred during the early winter season, it was followed by a rapid reversal towards an extreme cold surge event (Fig. 1a,b)
The present study demonstrates that super El Niño events tend to be accompanied by a pronounced wintertime SAT warming to cooling transition in East Asia and Northern Europe through a sub-seasonal modulation of the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO)-associated atmospheric circulation
Summary
During the 2015/16 boreal winter, we witnessed a super El Niño event (by the Niño 3.4 measure) in the tropical Pacific, with comparable amplitude to the well-known 1982/83 and 1997/98 extreme El Niño events[6]. El Niño tends to cause a negative NAO phase, which results in a colder and drier than normal climate during the late winter season in Europe[8]. The question whether the concurrent super El Niño was responsible for the strong cooling event during the 2015/16 winter is not answered. We explore a possible dynamical linkage between El Niño and strong wintertime SAT cold surge events over East Asia and Northern Europe. Our main finding is that super El Niño winters are generally accompanied by a pronounced North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) phase reversal from a positive to a negative state in early January (not observed during moderate El Niño winters) that gives rise to the severe cooling in both East Asia and Northern Europe in the subsequent mid-to-end January period
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