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What is the NAO?

What is the NAO?. Geoffrey Vallis 1 and Adam Scaife 2 April 2004 C20C workshop, ICTP. 1 - GFDL, Princeton, USA . 2 - Hadley Centre, Met Office, Exeter, UK. Observed NAO +. Observed NAO -. NAO timescales. Hemispheric Modes. NAO+ => Double jet structure. Models.

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What is the NAO?

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  1. What is the NAO? Geoffrey Vallis1 and Adam Scaife2 April 2004 C20C workshop, ICTP. 1 - GFDL, Princeton, USA. 2 - Hadley Centre, Met Office, Exeter, UK.

  2. Observed NAO +

  3. Observed NAO -

  4. NAO timescales

  5. Hemispheric Modes

  6. NAO+ => Double jet structure

  7. Models

  8. Symmetric EOFs from asymmetric events. +ve events 1st EOF from symmetric GCM -ve events

  9. The mid-latitude jet is an eddy driven jet

  10. Stirring and Momentum fluxes

  11. 1st EOF – statistically symmetric barotropic model. 1st EOF – asymmetric models. Barotropic model G.C.M.

  12. Conclusions • The NAO (and AO) is produced by the forcing from weather. • Dipole patterns are a natural consequence of meridionally localised stirring by baroclinic eddies. • Stirring produces eddy momentum fluxes which drive the midlatitude westerly jet. • Zonally localised forcing/stirring produces zonally localised response (the NAO). • The same mechanism drives the NAO and AO.

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