Processes controlling Southern Ocean Shortwave Climate Feedbacks Jen Kay University of Colorado at...
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Transcript of Processes controlling Southern Ocean Shortwave Climate Feedbacks Jen Kay University of Colorado at...
Processes controlling Southern Ocean Shortwave Climate Feedbacks
Jen KayUniversity of Colorado at Boulder
Why Southern OceanShortwave Feedbacks?
Cloud feedbacks in idealized 2xCO2 experimentsGettelman, Kay, and Shell (2012)
1) Literature focuses on mean state including model biases, not feedbacks2) 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. 2014 Figure 1
21st century Southern Ocean clouds top=early 21st C, bottom=21st 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 shiftsBarnes 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. 2014 Figure 3
RCP8.5 forcing vs. natural jet variability
Adapted from Kay et al. 2014 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 21st 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
EXTRA
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 OceanShortwave Feedbacks?
Cloud feedbacks in idealized 2xCO2 experimentsGettelman, Kay, and Shell (2012)
1) Literature focuses on mean state including model biases, not feedbacks2) 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]
21st Century Zonal Mean Warming
Zonal vertical mean Southern Oceanthis time with the change…
Poleward Stormtrack Shifts
20th C = poleward SH stormtrack shiftO3 (GHG )
Thompson et al. 2011
21st C = poleward SH stormtrack shift
GHG (despite O3 )
“Bonygrams” can separate the dynamic and thermodynamic
components of tropical cloud changes
Bony et al. 2004, Climate Dynamics
Ascent Descent
Ascent Descent
“Bonygrams” for the Southern Ocean?
Thermodynamics in stormtracks explains “juicier clouds”