An evaluation of a hybrid, terrain-following vertical coordinate in the WRF-based RAP and HRRR models

A new hybrid, sigma-pressure vertical coordinate was recently added to the Weather Research and Forecasting (WRF) Model in an effort to reduce numerical noise in the model equations near complex terrain. Testing of this hybrid, terrain-following coordinate was undertaken in the WRF-based Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) models to assess impacts on retrospective and real-time simulations. Initial cold-start simulations indicated that the majority of differences between the hybrid and traditional sigma coordinate were confined to regions downstream of mountainous terrain and focused in the upper levels. Week-long retrospective simulations generally resulted in small improvements for the RAP, and a neutral impact in the HRRR when the hybrid coordinate was used. However, one possibility is that the inclusion of data assimilation in the experiments may have minimized differences between the vertical coordinates. Finally, analysis of turbulence forecasts with the new hybrid coordinate indicate a significant reduction in spurious vertical motion over the full length of the Rocky Mountains. Overall, the results indicate a potential to improve forecast metrics through implementation of the hybrid coordinate, particularly at upper levels, and downstream of complex terrain.

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Author Beck, Jeffrey
Brown, John
Dudhia, Jimy
Gill, David
Hertneky, Tracy
Klemp, Joseph
Wang, Wei
Williams, Christopher
Hu, Ming
James, Eric
Kenyon, Jaymes
Smirnova, Tanya
Kim, Jung-Hoon
Publisher UCAR/NCAR - Library
Publication Date 2020-05-15T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2023-08-18T18:31:33.937265
Metadata Record Identifier edu.ucar.opensky::articles:23449
Metadata Language eng; USA
Suggested Citation Beck, Jeffrey, Brown, John, Dudhia, Jimy, Gill, David, Hertneky, Tracy, Klemp, Joseph, Wang, Wei, Williams, Christopher, Hu, Ming, James, Eric, Kenyon, Jaymes, Smirnova, Tanya, Kim, Jung-Hoon. (2020). An evaluation of a hybrid, terrain-following vertical coordinate in the WRF-based RAP and HRRR models. UCAR/NCAR - Library. http://n2t.net/ark:/85065/d7c82dhr. Accessed 11 February 2025.

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