Processes controlling Southern Ocean Shortwave Climate Feedbacks

1. Processes controlling Southern Ocean Shortwave Climate Feedbacks Jen Kay University of Colorado at Boulder

2. Why Southern OceanShortwave 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. Southern Ocean Feedback Processes? Community Earth System Model (CESM-CAM5)

4. Sea ice and clouds explain CESM-CAM5 absorbed shortwave radiation changes Kay et al. 2014 Figure 1

5. 21st century Southern Ocean clouds top=early 21st C, bottom=21st C change Are the radiatively important clouds “shifting poleward”?

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

7. Maybe the clouds “shift poleward” because the jet shifts poleward? CESM-CAM5: 1° jet shift RCP8.5, 52 °S to 53 °S Small jet shift consistent with more poleward (realistic) mean jet location. CMIP5 jets and jet shifts Barnes and Polvani 2013, Figure 2

8. Jet shifts ≠ cloud “shifts” If not jet shifts then what? Warming and low level stability influence on shallow convection detrainment Adapted from Kay et al. 2014 Figure 3

9. RCP8.5 forcing vs. natural jet variability Adapted from Kay et al. 2014 Figure 3 RCP8.5 forcing dSW >> natural jet variability dSW

10. How do model biases affect your results?

11. Clouds are still not bright enough, especially at high latitudes How are cloud biases related to cloud feedbacks? Kay et al. GRL Figure 1

12. 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 are low-level liquid clouds. Low-level liquid clouds respond primarily to warming and stability changes, not jet variability and jet shifts.

13. EXTRA

14. Shallow convection detrainment…

15. Zonal annual mean Southern Ocean

16. Too much sea ice to lose

17. Similar jets yet different ASR Both show RCP8.5 forcing >> natural jet variability

18. Zonal summer mean Southern Ocean

19. Which clouds matter for shortwave radiation in CESM? Radiatively important clouds = low level liquid clouds

20. Why Southern OceanShortwave 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]

21. 21st Century Zonal Mean Warming

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

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

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

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