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Processes Controlling 21 st Century Southern Ocean Climate-Cloud Feedbacks

Processes Controlling 21 st Century Southern Ocean Climate-Cloud Feedbacks. Jen Kay Brian Medeiros, Andrew Gettelman NCAR CGD AMP. Thanks to Lorenzo Polvani and Cecilia Bitz. Zonal annual mean cloud distribution. Southern Ocean 30-70° South.

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Processes Controlling 21 st Century Southern Ocean Climate-Cloud Feedbacks

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  1. Processes Controlling21st Century Southern OceanClimate-Cloud Feedbacks Jen Kay Brian Medeiros, Andrew Gettelman NCAR CGD AMP Thanks to Lorenzo Polvani and Cecilia Bitz

  2. Zonal annual mean cloud distribution Southern Ocean 30-70° South CloudSat+CALIPSO observations, combined as in Kay and Gettelman (2009)

  3. Why study Southern Ocean clouds? Gettelman, Kay, and Shell (2012) Southern ocean research questions … 1) Which processes control climate-cloud feedbacks over the Southern Ocean (30-70° S)? 2) Are the model processes controlling these feedbacks realistic? Are there observational constraints? 3) How do Southern Ocean climate-cloud feedbacks affect the global climate system?

  4. Today – transient CESM-CAM5 21st century runs with RCP8.5 forcing Lamarque et al. 2011 Meinshausen et al. 2011

  5. Zonal Mean Optical Depth Changes Large changes and large gradients. “Juicier” clouds! 21st century cloud changes resemble 2xCO2 cloud feedbacks

  6. OUTLINE: Processes affecting 21st C Southern Ocean cloud-climate changes 1) Antarctic sea ice loss 2) Large-scale atmospheric circulation shifts (“dynamics”) 3) Warming (“thermodynamics”) II. Summary and ongoing work

  7. PROCESS #1: Antarctic sea ice loss

  8. CESM Vertical cloud structure Early 21st century Cloud response to Antarctic sea ice loss Change over 21st century

  9. Distinct 21st century cloud changes where Antarctic sea ice loss occurs

  10. PROCESS #2: Large-scale atmospheric circulation shifts 20th C = poleward SH stormtrack shift O3 (GHG ) 21stC = poleward SH stormtrack shift GHG (despite O3) Thompson et al. 2011

  11. Zonal mean SH CESM Circulationtop=early 21st C, bottom=21st C change Early 21st century Change over 21st century Stronger Westerlies Increased subsidence

  12. CESM clouds respond to increased subsidence over the 21st Century Cloud fraction decreases except near the surface

  13. 21st Century zonal mean total cloud fraction changes by season Cloud decreases (subsidence increases) are larger in winter than in summer.

  14. PROCESS #3: Thermodynamics Zonal mean change shows both a poleward shift and larger maximum cloud liquid water path. How do we separate the influence of “dynamics” and “thermodynamics” on these cloud changes?

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

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

  17. “Bonygrams” with Temperature? Juicier warm clouds, more often “Cold” “Warm”

  18. Is subsidence the best sorting variable to understand cloud changes?

  19. Summary CESM Southern Ocean cloud-climate feedbacks vary in magnitude and sign: cooling near the Antarctic continent, warming on the equatorward flank of the mid-latitude stormtrack. Over the 21st century, projected Antarctic sea ice loss, a polewardstormtrack shift, and thermodynamic changes all contribute to Southern Ocean cloud-climate feedbacks. “Juicier clouds, more often” explained by thermodynamic changes. Work is ongoing. Suggestions very welcome!

  20. Southern Ocean = cloudiest place on Earth Southern Ocean 30-70° South

  21. Zonal mean atmospheric circulation and cloud distribution Southern Ocean 30-70° South CloudSat+CALIPSO observations, combined as in Kay and Gettelman (2009)

  22. Seasonal storm track shifts affect cloud location/amount Southern Hemisphere Winter (JJA) Southern Hemisphere Summer (DJF) CloudSat+CALIPSO observations, combined as in Kay and Gettelman (2009)

  23. Influence of stormtrack variability on the Southern Ocean in a long model control run Hall and Visbeck (2002)

  24. Southern Ocean cloud biases affect tropical precipitation biases!! Observed Precipitation Climate Model Precipitation Hwang and Frierson 2013

  25. Early 21st C Zonal Annual Means Which processes affect 21st century Southern Ocean climate feedbacks?

  26. CESM has too much sea iceand thus likely too much sea ice loss CESM Historical Sea Ice Bias CESM RCP8.5 Sea Ice Loss What is the climate response to Antarctic sea ice loss in CESM?

  27. 21st century Southern Ocean clouds top=early 21st C, bottom=21st C change

  28. OMEGA JJA vs. DJF

  29. CLOUD: JJA vs. DJF

  30. CLDLIQ change and mean T

  31. F(T) CLDLIQ -40 S to -50 S -30 S to -40 S -30 S to -70 S -50 S to -60 S -60 S to -70 S

  32. Subsidence (OMEGA > 0) F(T) CLDLIQ -30 S to -70 S, >650 mb Upsidence (OMEGA < 0)

  33. F(T) CLOUD Subsidence (OMEGA > 0) Upsidence (OMEGA < 0) -30 S to -70 S, >650 mb

  34. F(U) CLOUD, CLDLIQ Subsidence (OMEGA > 0) Upsidence (OMEGA < 0) -30 S to -70 S, >650 mb

  35. Liquid and Ice tendencies

  36. Today – CESM-CAM5 21st century runs with RCP8.5 forcing Lamarque et al. 2011 Meinshausen et al. 2011

  37. CESM-CAM5 RCP8.5 Warming Surface Temperature avg(2080-2099)-avg(2006-2025)

  38. RCP8.5 Zonal Mean Surface Warming How do Southern Ocean cloud feedbacks affect the climate response to increased greenhouse gas forcing?

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