Processes controlling Southern Ocean Shortwave Climate Feedbacks

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”