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The Antarctic Atmospheric Energy Budget: Observation and CMIP5 Simulation

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Wednesday, 13 January 2016, 12:00

Wednesday, January 13, 2016. The Antarctic Atmospheric Energy Budget: Observation and CMIP5 Simulation. Michael Previdi, Columbia University. Sponsored by NOAA Geophysical Fluid Dynamics Laboratory. Click here for more information.

In this talk, I will present an evaluation of 23 CMIP5 coupled atmosphere–ocean general circulation models in terms of their ability to simulate the observed climatological mean energy budget of the Antarctic atmosphere. While the models are shown to capture the gross features of the energy budget well (e.g., the observed two-way balance between the top-of-atmosphere (TOA) net radiation and horizontal convergence of atmospheric energy transport), the simulated TOA absorbed shortwave (SW) radiation is too large during austral summer. In the multimodel mean, this excessive absorption reaches approximately 10 W m-2, with even larger biases (up to 25–30 W m-2) in individual models. Previous studies have identified similar climate model biases in the TOA net SW radiation at Southern Hemisphere midlatitudes and have attributed these biases to errors in the simulated cloud cover. Over the Antarctic, though, model cloud errors are of secondary importance, and biases in the simulated TOA net SW flux are instead driven mainly by biases in the clear-sky SW reflection. The latter are likely related in part to the models’ underestimation of the observed annual minimum in Antarctic sea ice extent, thus underscoring the importance of sea ice in the Antarctic energy budget. At the surface, substantial differences in the climatological energy fluxes between existing observational datasets preclude any meaningful assessment of model skill in simulating these fluxes. Finally, using simulations from one of the CMIP5 models (CESM-WACCM), I will also discuss the energy budget response to stratospheric ozone depletion during the late twentieth century.

Location  Smagorinsky Seminar Room, NOAA GFDL, Princeton, NJ