Re: calculating 1000 hPa heights below ground level

I forwarded your email to " wrfhelp@ucar.edu "

If you get a response, please post to ncl-talk@ucar.

===
That said ....

This issue is is similar to the CAM situation.
Really, unless you have some physics to 'guide' you,
extrapolation is *always* dangerous!!!!

For temperature and geopotential height, you can use the standard
lapse rate as a 1st order approximation. This is what is done
for the following:

http://www.ncl.ucar.edu/Document/Functions/Built-in/vinth2p_ecmwf.shtml

The underlying code was extract exactly from the CCM processor. What
about wind, humidity, ...? The above just sets all levels to the last
valid report. So over the Himalaya, the winds at 500hPa would be
set for all levels below the surface.

===

A possible alternative approach can be seen at the "Grid_fill"
section of NCL's Application page:

http://www.ncl.ucar.edu/Applications/grid_fill.shtml

These examples use:

http://www.ncl.ucar.edu/Document/Functions/Built-in/poisson_grid_fill.shtml

[1] get the 1000 and 500 H
[2] use 'poisson_grid_fill" to fill below ground areas
[3] subtract the H500-H1000

Good luck
D

On 04/01/2010 01:58 PM, Joe Grim wrote:
> Hello!
>
> I am trying to get the 1000-500 hPa Thickness from WRF ARW model output.
> For this, I need, of course, 1000 hPa and 500 hPa heights. I have
> tried to use both wrf_interp_3d_z and wrf_user_intrp3d to do this, but
> both give me "missing" heights for much of the 1000 hPa level, because
> most of this is below ground level.
> z1000 = wrf_interp_3d_z(z,pf,1000.)
> z500 = wrf_interp_3d_z(z,pf,500.)
> z1000 = wrf_user_intrp3d(z,pf,"h",1000.,0.,False)
> z500 = wrf_user_intrp3d(z,pf,"h",500.,0.,False)
> I assume there is a relatively easy function to calculate "heights"
> below ground level, but I haven't been able to find it searching through
> the NCL-Talk database.
>
> Does anyone know how to do this, please?
>
> Thanks!
>
> Joe Grim

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Dennis J. Shea                  tel: 303-497-1361    |
P.O. Box 3000                   fax: 303-497-1333    |
Climate Analysis Section                             |
Climate & Global Dynamics Div.                       |
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