[ncl-talk] Calculating Geostrophic Winds in the WRF using NCL

[brianjs @iastate.edu]

Good Evening,

I am attempting to calculate both the u and v components of the geostrophic
winds in the WRF.

The function z2geouv (which calculates both components using the
geopotential height, as well as the latitude and longitude of gridded data)
must utilize the geopotential height on a constant pressure surface. WRF
data however, is on constant eta levels/terrain following coordinates, and
as such, this function applied to WRF data could only work if data is
converted to a constant pressure surface from its original eta coordinate
system.

Attached is the WRF code with issues. I have attempted to calculate the
geostrophic wind components (ug and vg) by using the z2geouv with a height
variable that has been interpolated on to a constant pressure coordinate
(z_const_p). I first attempted to interpolate z_const_p with a geopotential
height variable that was not terrain following (z_model). When I do this, I
get realistic values for the geostrophic wind components, but I obviously
would not get the lower levels (below 1000 generally) to be interpolated. I
also interpolated z_const_p with an original terrain following geostrophic
height or geostrophic height above ground level (AGLheight_model), but then
unrealistic answers followed.

I have also taken a similar approach by calculating the ug and vg
components separately without using z2geouv, but I am still getting
unrealistic answers.

I wish to implement this routine in order to plot the geostrophic winds on
maps of constant height (above ground level) hence the ug/vg interpolations
thereafter to constant height levels

For reference, I sent the used RUC and WRF output to the ncl-talk FTP
account given their large size. I did get the message "451 Failure writing
to local file" so I am not sure if they made it over there successfully.
The wrf file is rather large (approximately 9 GB) so maybe the account
could not hold it?

I was wondering if someone could guide me to improve this code to get
geostrophic winds interpolated on constant height fields from an original
terrain following (eta) coordinate system (i.e. 200-2000 m at 100 m
intervals), or if someone could assist by making a recommendation for an
alternate approach?  I have also attached my RUC code for plotting RUC
Analysis geostrophic winds along with some sample images of what I believe
the WRF profile should look generally like (as the RUC data is already on
constant pressure surface).

Any suggestions would be greatly appreciated!

Brian Squitieri
Graduate Research Assistant
Iowa State University
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