Processes controlling Southern Ocean Shortwave Climate Feedbacks

1. Processes controlling Southern Ocean Shortwave Climate Feedbacks Jennifer E. Kay National Center for Atmospheric Research (NCAR) University of Colorado at Boulder Brian Medeiros (NCAR), Ting Hwang (Scripps), Andrew Gettelman (NCAR), Justin Perket (U. Michigan), and Mark Flanner (U. Michigan)

2. Why Southern Ocean feedbacks? Cloud feedbacks in idealized 2xCO2experiments Gettelman, Kay, and Shell (2012) 1) Literature focuses on mean state including model biases, not feedbacks 2) Robust feedback pattern [e.g., CMIP5, Zelinka et al. 2013, Vial et al. 2013] 3) Southern Ocean radiation has global impacts [e.g., Hwang et al. 2013]

3. Welcome to model world! Community Earth System Model (CESM-CAM5) [Hurrell et al. 2013]

4. Absorbed shortwave radiation (ASR) 21st century CESM-CAM5 ASR change resembles feedbacks in idealized experiments (and CMIP5) Like most climate models, CESM-CAM5 has excessive Southern Ocean ASRdue in part to insufficiently bright clouds. Kay et al. GRL Figure 1

5. Which processes explain Southern Ocean climate feedbacks (ASR)?

6. Sea ice and clouds explain ASR How do we separate the cloud and ice influence on absorbed shortwave radiation (ASR) changes? Cryosphericradiative effect (CrRE) implemented in CESM [Perket et al. submitted] Residual cloud radiative effect (dASR-dCrRE) Kay et al. GRL Figure 1

7. Radiatively important clouds =low level liquid clouds Are the clouds “shifting poleward”?

8. Why would the radiatively important clouds “shift poleward”?

9. Maybe the clouds shift poleward because the jet shifts poleward? CMIP3 21st century polewardstormtrackshift Yin et al. [2005]

10. CMIP5 Jets and Jet Shifts Barnes and Polvani 2013, Figure 2a CESM-CAM5 jet shift: 52 °S to 53 °S

11. Jet shifts ≠ cloud “shifts” If not jet shifts then what? Warming and low level stability changes Adapted from Kay et al. GRL Figure 3

12. Let’s compare ASR changes:RCP8.5 forcing vs. natural jet variability Adapted from Kay et al. GRL Figure 3

13. How do model biases affect your results?

14. Summary: Processes controlling Southern Ocean cloud-climate feedbacks in CESM Sea ice loss (2.6 Wm-2) and clouds (1.2 Wm-2) explain 21st century RCP8.5 absorbed shortwave radiation changes. The radiativelyimportant clouds (RIC) are low-level liquid clouds. RIC respond primarily to warming and stability changes, not poleward jet shifts.

15. EXTRA

16. Too much Antarctic sea ice to lose

17. Clouds are still not bright enough, especially at high latitudes Smaller bias than CCSM4 (13.7 Wm-2) How are cloud biases related to cloud feedbacks?

18. Which clouds matter for SW feedbacks? Radiatively important clouds = low level liquid clouds

19. 21st Century Zonal Mean Warming

20. Zonal vertical mean Southern Ocean Kay et al. GRL Figure 2

21. Zonal vertical mean Southern Oceanthis time with the change…

22. Shallow convection detrainment tendency changes explain CLDLIQ changes

23. PolewardStormtrack Shifts 20th C = poleward SH stormtrack shift O3 (GHG ) 21stC = poleward SH stormtrack shift GHG (despite O3) Thompson et al. 2011

24. Both jet surprises consistent in CCSM4.While the jet stats are similar – its influence on ASR looks different…

25. “Bonygrams” can separate the dynamic and thermodynamic components of tropical cloud changes Ascent Descent Ascent Descent Bony et al. 2004, Climate Dynamics

26. “Bonygrams” for the Southern Ocean? Thermodynamics in stormtracks explains “juicier clouds”

27. Key findings from CESM:1) Jet shifts ≠ cloud shifts.2) Cloud shifts > Jet shifts for climate feedbacks. Kay et al. GRL Fig 2c