Relationship between the Stratospheric Arctic Vortex and Surface Air Temperature in the Midlatitudes of the Northern Hemisphere

It is known that different relationships exist between the strength and displacement of the stratospheric polar vortex (SPV), and the surface air temperature (SAT) patterns in Eurasia and North America, but the mechanisms behind these relationships remain unclear, especially on an interannual timescale. Based on empirical orthogonal function (EOF) analysis using NCEP reanalysis data over 1958-2018, this study attempts to ascertain the relationship between the SPV intensity and displacement over the Arctic and the SATs in the midlatitudes of the Northern Hemisphere. Our results indicate that a strengthened SPV corresponds to an SAT increase in Eurasia and a decrease in eastern North America and Greenland. When the SPV is shifted towards Eurasia, however, a corresponding SAT increase occurs in both North America and Eurasia, with a larger increase in North America than in Eurasia. Specifically, a strengthened SPV tends to correspond to a positive North Atlantic Oscillation-like circulation in the troposphere with negative geopotential height (GH) anomalies in Greenland and eastern North American continent and positive GH anomalies to the north of 45 degrees N in Eurasia, which corresponds to lower SATs in North America than in Eurasia. However, when the SPV shifted towards Eurasia, it was accompanied by a positive Pacific/North American-like pattern with a deepened Aleutian low, which corresponds to the increasing SATs in North America. These tropospheric circulation changes are related to the response of tropospheric planetary wave activity to the SPV. A strengthened SPV corresponds to the weakening of tropospheric planetary wave-1 waves, which is accompanied by a negative GH in North America but a positive GH in Eurasia. If the SPV shifted towards Eurasia, the tropospheric planetary wave-1 (-2) waves strengthened (weakened), and the combined effects of the planetary wave-1 and wave-2 waves would cause positive GH anomalies in both Eurasia and North America.