Simultaneous Atlantic-Pacific blocking and the Northern Annular Mode
Quarterly Journal of the Royal Meteorological Society 134:636 (2008) 1635-1646
Abstract:
A synoptic situation termed 'high-latitude blocking' (HLB) is shown to occur frequently in both the Atlantic and Pacific sectors, and to result in flow anomalies very similar to those associated with the negative phase of the Northern Annular Mode (NAM) in the respective sector. There is a weak but significant link between the occurrence of HLB in the two sectors, with Atlantic HLB tending to lead Pacific HLB by 1-3 days. This link arises from rare events in which both sectors are almost simultaneously affected by a large-scale wave-breaking event which distorts the polar trough over Northern Canada. In several cases the tropospheric wave-breaking occurs in tandem with a large-scale disturbance of the stratospheric polar vortex. There is, therefore, a physical link between the Atlantic and Pacific sectors, but analysis suggests that this does not contribute to determining the pattern of the NAM, as conventionally defined from monthly mean data. However, an alternative version of the NAM, derived directly from daily data, does appear to reflect this physical link. These conflicting results highlight the sensitivity of the NAM to the period over which data are averaged. Copyright © 2008 Royal Meteorological Society.A new Rossby wave-breaking interpretation of the North Atlantic Oscillation
Journal of the Atmospheric Sciences 65:2 (2008) 609-626
Abstract:
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. © 2008 American Meteorological Society.Atmospheric blocking and patterns of low-frequency variability arising from the breaking of upper level rossby waves
87th AMS Annual Meeting (2007)
The answer is blowing in the wind
Planet Earth (2007) 28-29
Abstract:
The North Atlantic Oscillation (NAO) is a natural climate variability and can be attributed to the UK warming in average winter temperature. Being responsible for both the strength and orientation of the Atlantic jetstream, the NAO is associated with the storm track beneath the jetstream. Changes in NAO is associated with large-scale waves that break in the upper atmosphere. The air waves which stretch for a few thousand kilometers, have some peaks and troughs and when distorted, becomes distorted and collapses into a very turbulent flow.Entropy sources in a dynamical core atmosphere model
Quarterly Journal of the Royal Meteorological Society Wiley 132:614 (2006) 43-59