I am interested in the WRF solution rather close to sloping terrain (LEVELS=1.000, 0.998, 0.996, 0.994...), and I am unsure how to interpret the velocity components ugrdhy#, vgrdhy# (where # specifies the hybrid level, e.g. ugrdhy1 is "1 hybrid level U-Component Of Wind [m/s]").

The two possible interpretations, I think, are that (A) these velocity components defined relative to unit vectors that are locally tangent to constant eta-coordinate planes (i.e. unit vectors that should be close to being tangent to the topographic surface near ground); or (B) they are truly horizontal velocity components.

Just after their Eq. (2.2) Skamarock et al. (http://www.mmm.ucar.edu/wrf/users/docs/arw_v3.pdf) state "(u, v, w) are the covariant velocities in the two horizontal and vertical directions." Thus maybe (A) is the proper interpretation. Thanks for any pointers, John

## basis vectors for ugrdhy#, vgrdhy#

### Re: basis vectors for ugrdhy#, vgrdhy#

Oops, I should have written, "Thus maybe (B) is the proper interpretation"... J