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University of Washington Department of Atmospheric Sciences

The Response of the Southern Hemispheric Eddy-Driven Jet to Future Changes in Shortwave Radiation in CMIP5. Paulo Ceppi , Mark D. Zelinka and Dennis L. Hartmann Souther n Ocean Clouds Workshop , 18 March 2014. University of Washington Department of Atmospheric Sciences. Outline.

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University of Washington Department of Atmospheric Sciences

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  1. The Response of the Southern Hemispheric Eddy-Driven Jet to Future Changes in Shortwave Radiation in CMIP5 Paulo Ceppi, Mark D. Zelinka and Dennis L. Hartmann Southern Ocean Clouds Workshop, 18 March 2014 University of Washington Department of Atmospheric Sciences

  2. Outline • Changes in shortwave radiation in RCP8.5 • Impact of SW changes on SSTs and midlatitude jet • Determining causal relationships • Conclusions

  3. Absorbed SW radiation (ASR) 2050-2099 minus 1950-1999, in W m-2 ASR change (W m-2)

  4. ASR changes (in W m-2) ASR change (W m-2)

  5. ASR changes (in W m-2) albedo ASR change (W m-2)

  6. ASR changes (in W m-2) albedo clouds ASR change (W m-2)

  7. Absorbed SW radiation (ASR) • considerable inter-model spread • wide variety of meridional gradients of ASR response

  8. Effect of ASR changes • Atmospheric circulation is very sensitive to meridional SST gradient • Idea: can the different ASR gradient responses explain spread in SST and eddy-driven jet response? • Define simple ASR and SST gradient indices

  9. Change in ASR gradient ASR index = <ASR>20-50– <ASR>50-90 ASR change (W m-2)

  10. ASR index vsTsfc index change in ASR gradient  change in SST gradient

  11. ASR index vs jet shift poleward jet shift increase in ASR/SST gradient  poleward jet shift

  12. ASR index vs jet shift poleward jet shift But wait! What if the jet shifts are causing the different ASR responses?

  13. Causality • To solve this, use AMIP + AMIPfuture experiments (11 models) • AMIP: 1979–2005 SSTs • AMIPfuture: AMIP SSTs + patterned anomaly • prescribed SSTs = SW effects are suppressed cloud response SST anomalies jet shift 1 jet shift cloud shift SST anomalies 2

  14. Causality In AMIPfuture: • If no relationship between ASR and jet shift in AMIPfuture • If jet shift and ASR changes are related cloud response SST anomalies jet shift 1 jet shift cloud shift SST anomalies 2 1 2

  15. jet shift vs ASR index RCP8.5

  16. jet shift vs ASR index RCP8.5

  17. jet shift vs ASR index RCP8.5 RCP8.5 + AMIPfuture  no relationship between jet shift and ASR change in AMIPfuture

  18. ASR changes: AMIP vs RCP8.5 SW changes are the same! (despite different jet shifts) cloud response SST anomalies jet shift 1 jet shift cloud shift ASR/SST anomalies 2

  19. ASR response to natural jet variability (in W m-2) ASR response (W m-2)

  20. ASR response to natural jet variability (in W m-2) ASR response (W m-2) jet shift cloud shift ASR/SST anomalies 2

  21. Conclusions • Large spread in ASR changes in RCP8.5 • ASR changes cause spread in SST gradient change and jet shift • Spread in ASR response due to model-dependent sensitivity to SST warming • Poleward jet shift seems to play a minor role in ASR response The End Thank you!

  22. Extra plots

  23. ASR changes in AMIPfuture 2050-2099 minus 1950-1999, in W m-2 K-1 ASR change (W m-2)

  24. Effect of clouds 2050-2099 minus 1950-1999 ASR change (W m-2)

  25. Effect of surface albedo 2050-2099 minus 1950-1999 sea ice ASR change (W m-2)

  26. jet shift (deg S K-1)

  27. jet shift (deg S K-1)

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