Evaluating the performance of the immersed boundary method within the grey zone for improved weather forecasts in the HRRR model
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of California, Berkeley, CA (United States)
Improved performance of the High Resolution Rapid Refresh (HRRR) weather forecast in regions of complex terrain is a primary goal of the second Wind Forecasting Improvement Project (WFIP2). The HRRR forecast uses the Weather Research and Forecasting (WRF) model at a horizontal resolution of 3 km and includes an experimental nest over the WFIP2 study area with 750 m horizontal resolution. At these resolutions the complex terrain of the WFIP2 study area, the Columbia River Gorge, is well resolved and can include steep terrain slopes. The terrain-following coordinate system used by the WRF model is susceptible to numerical instabilities as model resolution and resolved terrain slopes increase. The immersed boundary method (IBM) has been shown to reduce these instabilities at very high resolutions (roughly 10 m or less), and thus use of IBM is desirable for high resolution simulations over the WFIP2 study area. However, accuracy of the IBM appears to degrade with coarser grid resolution and the sensitivities of IBMs to grid resolution are not well understood. In this report, we work to understand the accuracy and performance of the IBM at coarser resolutions with the goal of developing an IBM for use in the grey zone, or the intermediate scales between mesoscale and large-eddy simulation. Here, several existing immersed boundary algorithms from the literature are implemented into WRF, along with a new implementation developed during this project. The IBM algorithms for the atmospheric boundary layer are evaluated within the WRF model for a range of grid resolutions. While the strong performance of IBMs at high-resolution is confirmed, important model sensitivities are also revealed. Particular focus is placed on IBM performance at intermediate grid resolutions, which to this point has not been studied in the atmospheric modeling literature.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1544937
- Report Number(s):
- LLNL-TR-763586; 953414
- Country of Publication:
- United States
- Language:
- English
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