[gradsusr] Freezing Level

Ricardo Hallak ricardo.hallak at iag.usp.br
Sun Nov 5 14:51:26 EST 2017

Hi, Steve.

I've tested the fndlvl function this way:

and it worked very well, as you can see in the display. *Results in hPa*.

I got the same result for:
 define H=fndlvl(tmpprs,const(tmpprs,273.16),lev=1000,lev=400)
d H

With shaded:

As you say you want "to determine the freezing level in meters (or feet)",
my guess is tath your data is in meters (or some other similar linear
vertical grid), while the fndlvl function needs the gridded data in
pressure vertical levels.

P.S.: If you have grid data in pressure levels, after calculating the
freezing level in hPa, you can convert the result from pressure to meters
(for example, using the hypsometric equation).

Hope this helps.

Prof. Ricardo Hallak
Laboratório de Meteorologia de Mesoescala - LMM
Departamento de Ciências Atmosféricas
Instituto de Astronomia, Geofísica e Ciências Atmosféricas
Universidade de São Paulo

Phone: +55(11)3091-4698

2017-11-04 14:37 GMT-02:00 Steve Young <shy9 at earthlink.net>:

> I am trying to use GrADS to determine the freezing level in meters (or
> feet).  I can use the following to determine the upper air surface where
> T=273.16 but am unable to figure out how to calculate/extract/determine
> HGT(LEV=H). This command gives an error of invalid expression. I welcome
> any suggestions.
> 'set gxout shaded'
> 'H=fndlvl(air, const(air, 273.16), Lev=1000, lev=400)'
> 'd H'
> 'run cbar'
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