How to interpret WRF variables

Grid

Grids in WRF are logically rectilinear. Variables for WRF cell indexed (i,j,k) can be located at one of 4 possible point. You can tell where by looking at the WRF registry or the attributes of NetCDF files, which WRF uses as I/O format. You can also tell by the fact that staggered variables have the staggered dimension larger by one, since there needs to be variable at the last boundary face.

• at the center of the cell - theta points, not staggered
• at the center of the left face - U point, staggered in X
• at the center of the front face - V point, staggered in Y
• at the center of the bottom face - W point, staggered in Z

Scalar variables (such thermodynamical variables, hence the theta: temperature, pressure,...) generally live at theta-points. One exception is the geopotential, which lives at W-points. Components of the wind velocity vector U, V, W live at the corresponding points, hence the point names.

Footnotes

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See also

• WRF output fields from the WRF-ARW user's guide
• A Description of the Advanced Research WRF Version 3 (June 2008) Fig 7.3 page 59

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