# Re: Pressure to height and Potential Temp calculation

Date: Wed Apr 27 2011 - 18:18:04 MDT

Hi,

Thanks for the reply. I have one more question which I faced when
calculating potential temperature. It will be really helpful if somebody
can show me some way out of this problem.
When I applied these and after getting potential temperature I calculated
vertical gradient of potential temperature with "center_finite_diff_n" I
ended up with negative values at some points and as it is a CAM output it
could not have negative vertical potential temperature gradient.

Is it possible that this is coming due to interpolation of pressure levels
while converting from sigma levels ? or it may be the differentiation?
I am attaching the script but it is little bit long.

Thanks,
Soumik

Dennis Shea wrote:
>
>
> On 4/27/11 2:41 PM, sbasu@iarc.uaf.edu wrote:
>> Hi,
>>
>> I have two questions. Is there any function to use which will convert
>> the
>> pressure levels like 900mb,850mb etc to height using Hypsometric
>> equation?
>
> http://www.ncl.ucar.edu/Document/Functions/Built-in/hydro.shtml
>
> http://www.ncl.ucar.edu/Document/Functions/Built-in/pslhyp.shtml
>>
>> I have standard CAM3.output. Its in hybrid sigma levels.What is the best
>> way to calculate potential temperature at different pressure levels ? I
>> interpolated my temperatures in hybrid sigma levels to pressure levels
>> like 900mb, 850mb etc using vinth2p.
>
> You do not have to interpolate to constant pressure levels.
> You can calculate potential temperature at each hybrid level
> directly.
>
> Use:
>
> http://www.ncl.ucar.edu/Document/Functions/Built-in/pres_hybrid_ccm.shtml
>
> hyam = f->hyam ; read from a file the mid-layer coef
> hybm = f->hybm ; read from a file
> ps = f->PS ; surface pressure [Pa]
> p0 = 100000. ; since ps is in Pa or [ f->P0]
>
> p = pres_hybrid_ccm(ps,p0,hyam,hybm) ; (ntim,klev,nlat,mlon)
>
> t = f->T ; (ntim,klev,nlat,mlon)
>
> Then use
>
> theta = t*(1000/p)^0.286
>
>
>
>
>
>>
>> Thanks,
>> Soumik
>>
>

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Soumik Basu
International Arctic Research Center
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Received on Wed Apr 27 18:18:38 2011

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