Polar vortex controls coupling of North Atlantic Ocean and atmosphere

The structure of the North Atlantic leading atmospheric winter variability mode strongly depends on the state of the polar stratospheric vortex. If the polar vortex is strong, one teleconnection pattern emerges in the upper troposphere, while two mostly independent ones appear when the vortex is weak. The anomaly patterns associated with the different polarities of these modes show strong differences in the wind fields and in the correlation of atmospheric variability with the sea surface temperature of the North Atlantic. Only when the polar vortex is strong, does a basin‐wide tripole correlation pattern exist between tropospheric variability and sea surface temperature. Under weak vortex conditions one of the variability modes correlates with the subtropical, the other with the subpolar gyre. These results suggest that a NAO index based on near surface pressure that fails to account for the state of the polar vortex is a suboptimal representation of the tropospheric circulation variability.