Confusion about wind_speed_at_surface variants

[svahl991]

I was wondering if we could get some clarity on the meaning of some of the wind names in the standard. The standard contains eastward_wind_at_surface and eastward_wind_at_10m. It does not contain eastward_wind_at_surface_adjacent_layer. (Although other variables have *at_surface_adjacent_layer variants. )

The standard also contains ratio_of_wind_at_surface_adjacent_layer_to_wind_at_10m. Is eastward_wind_at_surface equivalent to eastward_wind_at_surface_adjacent_layer? And thus eastward_wind_at_surface times ratio_of_wind_at_surface_adjacent_layer_to_wind_at_10m is equal to eastward_wind_at_10m?

If this is not correct, then what is the difference between eastward_wind_at_surface and eastward_wind_at_10m?

We had a lot of confusion and discussion about this at a recent JEDI code sprint.

[dudhia]

eastward_wind_at_surface does sound ambiguous, and we would need to see how it is set from the model.
10 meters is the conventional surface for wind, but some observations may be at other levels.

[climbfuji]

My immediate thought is also that eastward_wind_at_surface is legacy and should be replaced with eastward_wind_at_surface_adjacent_layer. The difference between eastward_wind_at_surface_adjacent_layer and eastward_wind_at_10m is that the the former is the value at the lowest model level to the ground (surface), whereas the latter is interpolated to a height of 10m (that can be extrapolated if the lowest model layer is higher than 10m AGL, or interpolated if the lowest model layer is lower than 10m AGL.

[mkavulich]

While not defined here, the traditional fluid dynamics idea would be that the "surface" has no wind by definition. I agree with Dom's assessment that wind_at_surface_adjacent_layer and wind_at_10m are the relevant variables.

Reviewing the CF standard names and the current CCPP, I don't see any use of "surface_wind" or "wind_at_surface", so these can be safely replaced.