Alternate modulations of ENSO and the Arctic Oscillation on winter extreme cold events in China

Abstract

Station observations and global reanalysis datasets were applied to investigate the dominant modes of winter cold days (CDs) in China and their relationships with the Arctic Oscillation (AO) and El Niño–Southern Oscillation (ENSO). The dominant modes of the CDs exhibited an interdecadal shift around the 1980s. The first mode reflected a nearly coherent interannual variability with a maximum center over central-northeastern China during 1961–1985 (P1), whereas the maximum center shifted to central-southwestern China during 1993–2017 (P2). The second mode represented a north-south dipole variation, with maximum variations over southern China in the P1 but northeastern China in the P2. The first mode was significantly related to the AO in the P1 and ENSO in the P2, whereas the second mode was closely linked to ENSO in the P1 and the AO in the P2. During the P1, an anomalous quasi-barotropic cyclone over northern East Asia was induced by a negative AO, deepening the East Asian trough along the East Asian coast, which was favorable for the occurrence of CDs over central-northeastern China (i.e., the first mode). The El Niño excited an anomalous anticyclonic circulation over the Northwest Pacific, impeding cold air along the coast of southern China, which seemed to produce a pattern of the second mode. During the P2, the AO was weaker (smaller magnitude), and the AO-related anomalous cyclone shifted northwestward compared to that in the P1, limiting its effect to northeastern China and inducing a north-south dipole pattern. On the other hand, ENSO-related anomalous circulation shifted southwestward compared to the P1, modulating CDs over central-southwestern China and producing an anomalous pattern of CDs similar to the first mode.