Application of an improved horizontal diffusion scheme to a WFIP2 cold pool case
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
The public release of WRF has two options for calculating horizontal gradients in the horizontal diffusion scheme. When the default option (diff_opt = 1) is used, horizontal gradients are calculated along coordinate surfaces, which roughly follow the terrain surface due to WRF’s terrain-conforming grid (i.e. along a sloping line in Fig. 1). Over steeply sloping terrain, horizontal gradients calculated in this way become inaccurate because they do not capture horizontal variation correctly. Therefore, another option exists (diff_opt = 2), for which Taylor series are used to approximate the derivative along a truly horizontal line. During WFIP2, HRRR forecasts switched from using diff_opt = 1 to diff_opt =2, and this was shown to improve velocity predictions, especially within observed cold pools (Olson et al., 2019).
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1571373
- Report Number(s):
- LLNL-TR-794458; 994560
- Country of Publication:
- United States
- Language:
- English
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