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configuration problem for parameter "config_nfglevels"

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I want to use ungrib.exe to produce the ICs with ERA5 signle-level data and ERA5 pressure-levels(37 levels) data. According to the MPAS User Guide, the parameter "cong_nfglevels" should be set to the number of vertical levels in intermediate file. And I modify cong_nfglevels=37, and then error happens. So I try 38, then it works. I also try 39, it works too, which makes me a little confused. Can someone give more detailed explanation about "cong_nfglevels"?


  • err.png
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If you have 37 isobaric levels of atmospheric data, plus surface fields (u10, v10, t2, etc.), that would give a total of 38 levels from the perspective of the init_atmosphere_model program. As the error message states, config_nfglevels must therefore be set to at least 38 -- so value of 38, 39, 40, 41, etc. should all work.

Internally, the 'config_nfglevels' namelist option is used by the init_atmosphere_model program to allocate 3-d arrays to hold the horizontally interpolated first-guess ("fg" in the config_nfglevels name) fields. Allocating too few vertical levels in these 3-d arrays is problematic, but allocating extra levels -- which will simply go unused -- isn't a problem, though it does waste memory.

As a side note, because screenshots aren't searchable on the forum, please consider including error messages as quoted text in future.