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

Abstract

SUMMARYThis 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 lowpass-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.

Observational constraints on the tropospheric and near-surface winter signature of the Northern Hemisphere stratospheric polar vortex

“…The interaction of tropospheric baroclinic eddies with downward propagating wind anomalies at the edge of the polar vortex (Wittmann et al, 2007;Scaife et al, 2012; see also the discussion in Gerber et al, 2012) seems to be an important factor of amplification of initial disturbances in both simple and complex models. This was also shown by reanalysis data for strong and weak polar vortex episodes in terms of Eady growth rates (Walter and Graf, 2005; for a discussion of the underlying mechanisms see Walter and Graf (2006)). It is therefore plausible that different mechanisms are at work at polar and midlatitudes of the Northern Hemisphere.…”

Bi-decadal variability excited in the coupled ocean–atmosphere system by strong tropical volcanic eruptions

“…While the simulated PNA response is consistent with observations (Christiansen 2008), the negative EA phase seems to be distinctive of this study. However, reanalysis data suggest that under strong polar vortex episodes the North Atlantic teleconnection pattern is typically characterized by only one, NAO-like dipole structure (Walter and Graf 2006), i.e., a weaker EA pattern is to be expected. Also, the reconstructed average winter response to tropical SVEs (Hegerl et al 2011, their Fig.…”

Evolution of Eurasian teleconnection pattern and its relationship to climate anomalies in China

“…We use composite analysis to investigate the surface air temperature and precipitation anomaly fields, followed by the temporal variation of regional averaged temperature and precipitation anomaly with respect to positive and negative phases of EU pattern in NH winter. To better capture the strong impact of EU pattern on the distribution of surface temperature and precipitation anomalies, we choose the days when EU index remains above one standard deviation for at least 5 days for composite analysis (Horel 1985;Mo 1986;Feldstein 2002Feldstein , 2003Feldstein and Dayan 2008;Walter and Graf 2006). The composite patterns of temperature and precipitation anomaly over China for both positive and negative EU phases are shown in Fig.…”