Contributions from extratropical North Pacific to Arctic summer atmospheric temperature and circulation

A fascinating character of the Arctic summer atmospheric circulation is the anomalous anticyclone circulation centered over the Arctic Ocean. Previous studies have related the underlying mechanisms to the atmospheric internal variability, the earlier spring Eurasian snowmelt, and the tropical Pacific forcing. Here we show that the Arctic summer anomalous anticyclone circulation is strongly associated with positive sea surface temperature anomalies (SSTAs) at midlatitudes of the extratropical North Pacific which are surrounded by significant negative SSTAs, resembling the negative phase of the Pacific Decadal Oscillation (PDO) but without significant signals in the tropics. The numerical experiments from the Whole Atmosphere Community Climate Model, prescribed with negative PDO-like SSTAs from May to August with the influence of El Niño-Southern Oscillation being reduced in advance, have simulated the observed positive air temperature and geopotential height anomalies over the Arctic and the circumpolar easterly anomaly at high latitudes in summer. The observational and simulated results strongly suggest that the extratropical SSTAs can influence the Arctic atmospheric temperature and circulation in summer.