The Impacts of Using Mixed Physics in the Community Leveraged Unified Ensemble

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2019-08-01
Authors
Gallus, William
Wolff, Jamie
Gotway, John
Harrold, Michelle
Blank, Lindsay
Beck, Jeff
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Gallus, William
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Geological and Atmospheric Sciences

The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).

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The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.

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1898-present

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  • Department of Geology and Mining (1898-1902)
  • Department of Geology (1902-1965)
  • Department of Earth Science (1965-1977)
  • Department of Earth Sciences (1977-1989)

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Geological and Atmospheric SciencesEnvironmental ScienceHuman Computer Interaction
Abstract

A well-known problem in high-resolution ensembles has been a lack of sufficient spread among members. Modelers often have used mixed physics to increase spread, but this can introduce problems including computational expense, clustering of members, and members that are not all equally skillful. Thus, a detailed examination of the impacts of using mixed physics is important. The present study uses two years of Community Leveraged Unified Ensemble (CLUE) output to isolate the impact of mixed physics in 36-h forecasts made using a convection-permitting ensemble with 3-km horizontal grid spacing. One 10-member subset of the CLUE used only perturbed initial conditions (ICs) and lateral boundary conditions (LBCs) while another 10-member ensemble used the same mixed ICs and LBCs but also introduced mixed physics. The cases examined occurred during NOAA’s Hazardous Weather Testbed Spring Forecast Experiments in 2016 and 2017. Traditional gridpoint metrics applied to each member and the ensemble as a whole, along with object-based verification statistics for all members, were computed for composite reflectivity and 1- and 3-h accumulated precipitation using the Model Evaluation Tools (MET) software package. It is found that the mixed physics increases variability substantially among the ensemble members, more so for reflectivity than precipitation, such that the envelope of members is more likely to encompass the observations. However, the increased variability is mostly due to the introduction of both substantial high biases in members using one microphysical scheme, and low biases in other schemes. Overall ensemble skill is not substantially different from the ensemble using a single physics package.

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This article is published as Gallus Jr, William A., Jamie Wolff, John Halley Gotway, Michelle Harrold, Lindsay Blank, and Jeff Beck. "The Impacts of Using Mixed Physics in the Community Leveraged Unified Ensemble." Weather and Forecasting 34, no. 4 (2019): 849-867. DOI: 10.1175/WAF-D-18-0197.1.

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