Life cycles of North Atlantic teleconnections under strong and weak polar vortex conditions

This paper investigates the role of the strength of the polar stratospheric winter vortex in the dynamics of the life cycles of North Atlantic teleconnections. A new set of teleconnection patterns was produced from low‐pass‐filtered daily 300 hPa height data of NCEP (National Centers for Environmental Prediction) reanalysis data 1958–1998. All teleconnections are meridional dipoles, which to a certain degree resemble the North Atlantic Oscillation based on surface pressure data. There are two distinct teleconnections (one over the eastern and one over the western North Atlantic) during episodes of weak polar vortex, and only one, over the central North Atlantic, during strong polar vortex episodes. The teleconnections have periods of about two weeks. Stream function tendency analysis of the life cycles shows that the relatively simple resulting teleconnections evolve from very complex structures. During the growth phase of the teleconnection indices there are strong and systematic differences between the two polar vortex regimes. While in the weak vortex regime the anomaly growth is mainly driven by transient eddy vorticity fluxes from the low‐frequency domain, in the strong vortex regime there is also low‐frequency advection of relative vorticity resulting from the interaction of low‐frequency eddies with stationary eddies. Copyright © 2006 Royal Meteorological Society