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

Why Southern Ocean Shortwave Feedbacks? Cloud feedbacks in idealized 2xCO 2 experiments 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]

Southern Ocean Feedback Processes? Community Earth System Model (CESM-CAM5)

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

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

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

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

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 Figure 3

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

How do model biases affect your results?

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

1.Sea ice loss (2.6 Wm -2 ) and clouds (1.2 Wm -2 ) explain 21 st century RCP8.5 absorbed shortwave radiation changes. 2.The radiatively important clouds are low-level liquid clouds. 3.Low-level liquid clouds respond primarily to warming and stability changes, not jet variability and jet shifts. Summary: Processes controlling Southern Ocean cloud-climate feedbacks in CESM

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Shallow convection detrainment…

Zonal annual mean Southern Ocean

Too much sea ice to lose

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

Zonal summer mean Southern Ocean

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

Why Southern Ocean Shortwave Feedbacks? Cloud feedbacks in idealized 2xCO 2 experiments 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 st Century Zonal Mean Warming

Zonal vertical mean Southern Ocean this time with the change…

Poleward Stormtrack Shifts 20 th C = poleward SH stormtrack shift O 3  (GHG  ) Thompson et al st C = poleward SH stormtrack shift GHG  (despite O 3  )

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

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