Understanding Connections of Tropics–Arctic Is Necessary to Explain ENSO Diversity

Decline of sea ice extent (SIE) in the Arctic, which is mainly due to anthropogenic forcing, has large impacts on climate variability in the mid-latitudes by modulating atmosphere circulation. We further hypothesize that a SIE loss has a potential to influence the condition of sea surface temperature in the tropical Pacific through atmosphere-ocean coupled processes in the North Pacific. To test this hypothesis, we conduct 15 ensembles of idealized experiments in which historical SST for 1951-2016 is restored over the Arctic north of 65N only with different initial condition using coupled global climate model. We found that the North Pacific Oscillation (NPO)-like atmospheric circulation, which is modulated by the reduction of SIE, acts to trigger El Nino-like warming in the tropical Pacific through seasonal footprinting mechanism (SFM). SIE loss in the Pacific Arctic sector (140ºE-130ºW, 65-82ºN) including Chukchi sea and East Siberian sea in boreal springtime can induce El Nino-like warming in the following winter via SFM. This result implies that connections of tropics-Arctic should be considered to understand the changes in El Nino property