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Paulo Ceppi and Dennis Hartmann 21 September 2011

Interactions between the Hadley Circulation and the eddy-driven jet as revealed by dry GCM experiments. Paulo Ceppi and Dennis Hartmann 21 September 2011. Outline. The general circulation of the troposphere Simple GCM experiments: response of the circulation to thermal forcings

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Paulo Ceppi and Dennis Hartmann 21 September 2011

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  1. Interactions between the Hadley Circulation and the eddy-driven jet as revealed by dry GCM experiments Paulo Ceppi and Dennis Hartmann 21 September 2011

  2. Outline • The general circulation of the troposphere • Simple GCM experiments: response of the circulation to thermal forcings • Comparison with reanalyses and CMIP5 models • Discussion and Conclusion

  3. The General Circulation jet streams

  4. Momentum Fluxes and the Jet 0 U eddy-driven jet (or midlatitude jet) Atmospheric & Oceanic Fluid Dynamics, G. K. Vallis

  5. An idealized dry GCM • GFDL FMS dry General Circulation Model (GCM) • Idealized model: no water, no mountains, no asymmetries, no seasons • Circulation driven by meridional temperature gradients and instability of the flow

  6. Model Climatology temperature equilibrium temperature pressure latitude latitude

  7. Model Climatology streamfunction zonal wind pressure eddy-driven jet latitude latitude edge of Hadley circulation

  8. GCM experiments Temperature response stratospheric cooling (-10 K) tropospheric warming (+10 K) pressure latitude latitude

  9. GCM experiments Zonal wind response stratospheric cooling (-10 K) tropospheric warming (+10 K) pressure latitude latitude

  10. GCM experiments Tropical heating (+6 K) temperature response rad. equilibrium temperature pressure latitude latitude

  11. GCM experiments Tropical heating (+6 K) zonal wind response pressure latitude

  12. Circulation Response Stratospheric heating / cooling

  13. Circulation Response Tropospheric heating / cooling

  14. Circulation Response Tropical heating / cooling

  15. “Monthly” variability 1600 days, 50-day averages troposphere -10 K baseline troposphere +10 K eddy-driven jet edge of Hadley Circulation

  16. ERA-40, 1957-2002southern hemisphere see also Kang and Polvani 2011

  17. CMIP5 models, southern hemisphere

  18. Why a poleward shift of the jet? Temperature response in idealized GCM stratospheric cooling (-10 K) tropospheric warming (+10 K) stronger meridional temperature gradient at tropopause latitude latitude latitude

  19. Jet shift theory ? ? Chen and Held 2007

  20. Phase speed spectra Eddy momentum flux convergence at 225 hPa Baseline climatology latitude phase speeds

  21. Phase speed spectra Eddy momentum flux convergence at 225 hPa Tropospheric warming latitude phase speeds

  22. Phase speed spectra Eddy momentum flux convergence at 225 hPa Tropical heating / cooling latitude phase speeds

  23. Relationship between HC edge and jet latitude • Extent of Hadley Circulation in simple GCM may be determined by extratropical eddies  latitude of Rossby wave breaking • Response to “ENSO-like” forcing follows a different mechanism than “global warming” case • True (to some extent) for real atmosphere

  24. Conclusion and Outlook • Extratropical eddies may be important in determining Hadley Circulation extent • Under what circumstances is this true in the real atmosphere? • Need to investigate relationship between HC extent and wave breaking

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