Omega, Vertical Velocity

The post file includes a variable called VVEL Vertical Velocity (Pressure) [Pa/s].
This field is commonly called omega, the vertical velocity when you are using pressure
as a vertical coordinate.

Omega is the wind that is perpendicular to the pressure surface.  For
CORe, the post is calculating omega (VVEL) as w * dp/dz where w is the vertical (geometric)
wind.  Later versions of the model/post define VVEL as omega, the wind perpendicular
to the pressure surfaces.

Which definition of VVEL is right?  It all depends on how you define vertical. In
geometric vertical coordinates, the old defintion of VVEL is correct.  If you are working in
pressure coordinates, then the latter definition is correct.  The model is working
in hybrid sigma-pressure coordinate system, so the model is not the tie breaker.  So
it depend whether you think the horizontal winds are caused by a pressure or height gradient.