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

14. Causality If no relationship between ASR and jet shift in AMIPfuture1
cloud response SST anomalies jet shift 2
jet shift cloud shift SST anomalies
If no relationship between ASR and jet shift in AMIPfuture
If jet shift and ASR changes are related 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) 1
cloud response SST anomalies jet shift 2
jet shift cloud shift ASR/SST anomalies

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) 2
jet shift cloud shift ASR/SST anomalies

21. Conclusions The End Thank you! 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
minus , in W m-2 K-1
ASR change (W m-2)

24. Effect of clouds
minus
ASR change (W m-2)

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

26. jet shift (deg S K-1)

27. jet shift (deg S K-1)