26 December 2014

Processes Controlling Southern Ocean Shortwave Climate Feedbacks in CESM


The Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5) is used to identify processes controlling Southern Ocean absorbed shortwave radiation (ASR). In response to 21st century GHG warming, both sea ice loss (2.6 W m−2) and cloud changes (1.2 W m−2) enhance ASR and amplify the warming. The relative importance of the effects depends on location and season. At higher latitudes, surface albedo reductions and increased cloud liquid water content (LWC) have competing effects on ASR changes. At mid- and low-latitudes (equatorward of ~55°S), decreased LWC enhances ASR. The 21st century cloud LWC changes result from warming and near-surface stability changes but appear unrelated to a small (1°) poleward shift in the eddy-driven jet. In fact, the 21st century ASR changes are 5 times greater than ASR changes resulting from large (5°) naturally occurring variations in jet position. These results suggest the shortwave climate feedbacks with GHG warming in the Southern Ocean region are dominated by changes in the lower troposphere that are governed by local circulations and thermodynamics, and are relatively unaffected by changes in the mean position of the eddy-driven jet.

J E Kay
Kay, JE, B Medeiros, Y- Hwang, A Gettelman, J Perket, and MG Flanner.  2014.  "Processes Controlling Southern Ocean Shortwave Climate Feedbacks in CESM."  Geophysical Research Letters 41: 616-622.  https://doi.org/10.1002/2013GL058315.