Delayed impacts of North Pacific Oscillation on wintertime surface air temperature in East Asia

Observations indicate that anticyclonic circulation anomalies over the midlatitudes, associated with the North Pacific Oscillation (NPO) in December, contribute to surface warming in East Asia of the following January, with a 1-month lag. We demonstrate that the delayed impacts of December NPO anomalies on the East Asian surface warming in January can be attributed to two possible pathways: tropics-extratropics teleconnections and local air-sea interactions. The northeasterly anomalies along the southern edge of the December NPO-related anticyclonic circulation anomalies efficiently advect dry air towards the western North Pacific (WNP), intensifying negative precipitation anomalies from December to January. This process triggers a Rossby wave propagation, driven by upper-tropospheric divergence in the WNP, which subsequently maintains the anticyclonic anomalies over East Asia into January. Over the Kuroshio region, the easterly anomalies along the southern edge of the December NPO anticyclonic circulation anomalies counteract the prevailing westerly winds. The significant weakening of wind speeds, which in turn give rise to sea surface temperature (SST) warming along the Kuroshio region as a result of wind-evaporation-SST feedback, lead to favorable conditions for the East Asian warming in January. Additionally, the Coupled Model Intercomparison Project Phase 6 models (CMIP6) reasonably simulate the delayed impacts of December NPO anomalies on the East Asian climate in January, aligning well with observational evidence.