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Evaluating Model Physics in the Unified Forecast System (UFS) Medium-Range Weather Application
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  • LIGIA BERNARDET,
  • Weiwei Li,
  • Michelle Harrold,
  • Xia Sun,
  • Judy Henderson,
  • Lulin Xue,
  • Dan D'Amico,
  • Jimy Dudhia,
  • Michael Ek
LIGIA BERNARDET
NOAA Global Systems Laboratory

Corresponding Author:[email protected]

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Weiwei Li
NCAR
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Michelle Harrold
NCAR
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Xia Sun
NOAA GSL
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Judy Henderson
NOAA GSL
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Lulin Xue
NCAR
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Dan D'Amico
NCAR
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Jimy Dudhia
NCAR
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Michael Ek
NCAR
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Abstract

To support the development of the Global Forecast System (GFS) physics suite and identify opportunities for improving the model physics in the UFS, the Developmental Testbed Center (DTC) conducted an array of analyses for evaluating the operational GFSv15 forecasts and the experimental forecasts using the GFSv16beta physics suite distributed with the UFS Medium-Range Weather Application v1.0 public release. Five-day GFSv16beta forecasts for one boreal winter season were generated using the operational GFS analyses as initial conditions. The evaluation metrics included tools from Model Evaluation Tools (MET) and in-house process-oriented diagnostics. The evaluations focused on the perpetuating GFS forecast errors pertaining to the planetary boundary layer (PBL), land-surface, cumulus, radiation, and cloud processes. The runs using GFSv16beta outperformed the operational GFSv15 with respect to the root-mean-square errors of large-scale environmental variables and the anomaly correlation coefficient for 500 hPa geopotential height. Nevertheless, larger biases associated with key physical processes were identified in the GFSv16beta forecasts. For example, the global precipitation forecast skill degrades and a dry bias remains in the tropics, suggesting a persistent problem in the cumulus scheme. The near-surface and boundary-layer cold biases are larger over most continents and polar regions, which is partly related to the systematic negative temperature errors in the GFS analysis. The overestimated near-surface wind speed particularly at night in the northeastern U.S. implies that the surface drag may be underrepresented. Excessive short-wave radiation reaching the ground in the high-latitudes of the summer hemisphere appears to be related to low cloud liquid and ice water path. These and other results will be described in this presentation.