Patterns of Jet Stream Wintertime Variability and their Relation to the Storm Tracks

In this work we introduce an alternative approach for defining extratropical teleconnection patterns. The zonal wind field at 250 hPa is analyzed separately in the N. Atlantic and the N. Pacific sectors during the winter season December-March. Teleconnectivity of this field is found to be particularly strong. EOF analysis of the zonal wind field yields patterns that: (i) are robust with respect to the range of frequencies included in the data, (ii) relate clearly to the position of the climatological-mean jets, and (iii) are broadly consistent with their traditionally defined counterparts in terms of climatic impacts. These patterns are referred to as jet variability patterns and according to sector and rank they are named: A1, A2, P1 and P2. They are characterized by a north-south shifting or an extension/retraction of the eddy-driven jet in its exit region, and similar changes can be seen at the entrance region of the subtropical jet. The patterns also affect the degree of separation between the subtropical and eddy-driven jets. The leading Atlantic (A1) and Pacific (P1) patterns correspond quite well to the NAO and the PNA, respectively, while A2 is seen as a representation of the Eastern Atlantic pattern. P2 has no counterpart in the literature as far as we are aware, yet it was found to have a pronounced influence on the jet configuration and precipitation distribution over the west coast of N. America. For the leading patterns A1 and P1, the autocorrelation functions of the PC time series exhibit an e-folding decorrelation time of about 10 days. The relation between these jet variability patterns and the storm tracks variability is also examined, including the dynamical interaction between baroclinic waves and the jets. In each sector, the eddy forcing is found to maintain the respective jet anomalies. As suggested by Maximum Covariance Analysis between the jet anomalies and a measure of baroclinic wave activity, these anomalies can be considered as coupled (jet and storm track) patterns. Figure 1: Regressions of zonal wind at 250 hPa onto the standardized Atlantic and Pacific PC-1 and PC-2 as derived for the same variable in the respective sector. Contour interval: 2 m s^{-1}.