Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) Forum
question on RAP terrain - native model vs.130 grid
Posted By: Stan Benjamin
Date: 10-January-12 1554Z
Q: A Rapid Refresh was wondering if the sfc height value in the 13 km files represents the topography. I think that the value of sfc height on the native grid reflects the topography, but it's interpolated to the 130 grid, so it's not a true representation of the topography on any output grid. Correct?
A: Yes, only the native RAP 83 grid (or a subset of it covering the area of the 130 grid) would exactly show the model terrain. Of course, the 83 grid data cannot be distributed due to bandwidth issues.
Q: She also noted that the sfc height values differ quite a bit at some points on the RAP 130 grid compared to the RUC 130 grid. I know that the models are using different topography data sets - can you briefly elaborate on that?
A: Sure, of course there are differences in the topography between RUC (native 130 grid data) and RAP (interpolated to 130 grid). The procedure for obtaining the 13km terrain for RUC was through a RUC-specific terrain program, whereas the WRF uses the WPS code. The amount of smoothing is similar, but between those differences and more importantly, the interpolation to the 130 grid, there are a few dozen gridpoints with >200m terrain elevation differences over mountainous areas.
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