Northern Hemisphere winter circulation associated with the North Atlantic Oscillation and stratospheric polar-night jet

The interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hPa and temperature at 850 hPa, associated with the North Atlantic Oscillation (NAO) and stratospheric polar night jet (PNJ) is examined. It is suggested that the wintertime atmospheric circulation related to the NAO index can be separated into two different modes of variability. One is a regional mode, characterized by a meridional dipole type pattern in the 500 hPa geopotential height anomaly field over the Atlantic region. The other, having more zonal structure, extends over wider region of the northern hemisphere; this is also related to the lower stratospheric polar night jet. Air temperature near the surface over the eastern part of the Eurasian continent is more closely correlated with the above-mentioned hemispheric mode of variability than the regional NAO.