Delayed impacts of NPO on wintertime surface air temperature in East Asia

Observations show that anticyclonic circulation anomalies over the subtropics associated with North Pacific Oscillation (NPO) in December are responsible for surface warming in East Asia of the following January, a 1-month lag. We demonstrate that the lagged impacts of December NPO anomalies on the East Asian surface warming in January are attributable to two possible pathways by way of the 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), leading the intensified negative precipitation anomalies from December to January. This results in a Rossby wave propagation forced by upper-tropospheric divergence in the WNP, and thus affects the persistence of 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 oppose 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 (CMIP6) models reasonably simulate the delayed impacts of December NPO anomalies on the East Asian climate in January supporting observations.