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A new Rossby Wave-breaking interpretation of the North Atlantic Oscillation

Woollings, T. J., Hoskins, B. J., Blackburn, M. and Berrisford, P. (2008) A new Rossby Wave-breaking interpretation of the North Atlantic Oscillation. Journal of the Atmospheric Sciences, 65 (2). pp. 609-626. ISSN 1520-0469

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To link to this item DOI: 10.1175/2007JAS2347.1


This paper proposes the hypothesis that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wave–breaking events over the North Atlantic. These events lead to synoptic situations similar to midlatitude blocking that are referred to as high-latitude blocking episodes. A positive NAO is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic, unblocked situation. A negative NAO is a description of periods in which episodes occur frequently. A similar, but weaker, relationship exists between wave breaking over the Pacific and the west Pacific pattern. Evidence is given to support this hypothesis by using a two-dimensional potential-vorticity-based index to identify wave breaking at various latitudes. This is applied to Northern Hemisphere winter data from the 40-yr ECMWF Re-Analysis (ERA-40), and the events identified are then related to the NAO. Certain dynamical precursors are identified that appear to increase the likelihood of wave breaking. These suggest mechanisms by which variability in the tropical Pacific, and in the stratosphere, could affect the NAO.

Item Type:Article
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:1042
Uncontrolled Keywords:North Atlantic Oscillation, Wave breaking, Rossby waves, Potential vorticity, Teleconnections
Publisher:American Meteorological Society
Publisher Statement:© Copyright 2008 of the American Meteorological Society. The AMS Copyright Policy is available on the AMS web site at


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