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Journal Club: 05-09-2018

Article: The link between eddy-driven jet variability and weather regimes in the North Atlantic-European sector (Madonna et al, 2017)

This study aims to reconcile the 2 perspectives on wintertime atmospheric variability in the North Atlantic – European sector: 

  1. The zonal-mean framework comprising of 3 preferred locations of the eddy-driven jet.
  2. The weather regime framework comprising of four classical North Atlantic- European regimes.

Questions?

  • Are there common jet structures that do not fit within the three preferred jet locations?
  • Can we reconcile the three preferred jet locations with the four classical weather regimes?

Eddy momentum flux convergence from transient eddies creates a deep barotropic eddy-driven jet in mid latitudes. This is not always clearly separated from the subtropical jet. The leading pattern of variability in eddy driven jet is a latitudinal shifting (30-40% monthly variance) related to phase of the NAO. We would expect jet and weather regimes to be associated but there is a mismatch. Also, flow regimes tend to have characteristic Rossby Wave breaking patterns – pushing the jet polewards/equatorwards. 

The literature on the eddy driven jet stream has identified three preferred jet configurations using a zonally averaged jet latitudinal index method (Woolings et al, 2010).

However, this paper applies a clustering analysis to 10 day low pass filtered low level zonal wind to identify 3, 4 and 5 jet configurations.

 

The 4 cluster analysis identifies a new jet configuration (Mixed) along with the previous identified ones (Southern, Central and Northern). A persistence analysis shows that this new configuration is not merely a transition pattern but a jet regime in its own right.

Comparing new representation of jet regimes to the classical weather regimes, there is a clear match. Most notably the Scandinavian Blocking weather regime matches the new Mixed jet configuration very well.

This paper has identified a new jet configuration (mixed) and reconciled eddy driven jet variability with the four classical weather regimes.

This study uses methods such as filtering and clustering that we may apply to our own research in the future. It ties in well with the work on jet stream interactions and Rossby waves. It would be good to find links between the upper level steering flow and the eddy driven jet stream. We would like to find out if a similar analysis has been carried out of the upper level jet stream and would it yield similar results.