Evaluation of forecasted southeast Pacific stratocumulus in the NCAR, GFDL, and ECMWF models

Forecasts of southeast Pacific stratocumulus at 20°S and 85°W during the East Pacific Investigation of Climate (EPIC) cruise of October 2001 are examined with the ECMWF model, the Atmospheric Model (AM) from GFDL, the Community Atmosphere Model (CAM) from NCAR, and the CAM with a revised atmospheric boundary layer formulation from the University of Washington (CAM-UW). The forecasts are initialized from ECMWF analyses and each model is run for 3-5 days to determine the differences with the EPIC field observations. Observations during the EPIC cruise show a well-mixed boundary layer under a sharp inversion. The inversion height and the cloud layer have a strong and regular diurnal cycle. A key problem common to the models is that the planetary boundary layer (PBL) depth is too shallow when compared to EPIC observations. However, it is suggested that improved PBL depths are achieved with more physically realistic PBL schemes: at one end, CAM uses a dry and surface-driven PBL scheme and produces a very shallow PBL, while the ECWMF model uses an eddy-diffusivity/mass-flux approach and produces a deeper and better-mixed PBL. All the models produce a strong diurnal cycle in the liquid water path (LWP), but there are large differences in the amplitude and phase when compared to the EPIC observations. This, in turn, affects the radiative fluxes at the surface and the surface energy budget. This is particularly relevant for coupled simulations as this can lead to a large SST bias.

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Author Hannay, Cécile
Williamson, David
Hack, James
Kiehl, Jeffrey
Olson, Jerry
Klein, Stephen
Bretherton, Christopher
Köhler, Martin
Publisher UCAR/NCAR - Library
Publication Date 2009-06-01T00:00:00
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Topic Category geoscientificInformation
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Metadata Date 2023-08-18T18:57:38.539635
Metadata Record Identifier edu.ucar.opensky::articles:15497
Metadata Language eng; USA
Suggested Citation Hannay, Cécile, Williamson, David, Hack, James, Kiehl, Jeffrey, Olson, Jerry, Klein, Stephen, Bretherton, Christopher, Köhler, Martin. (2009). Evaluation of forecasted southeast Pacific stratocumulus in the NCAR, GFDL, and ECMWF models. UCAR/NCAR - Library. http://n2t.net/ark:/85065/d7668f7m. Accessed 11 February 2025.

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