Re: Tutorial script question; hyam and hybm

What Dave says is correct.

Whoever donated the sample script (arbitrarily) chose
the name "eta". This has nothing to do with thw WRF model
vertical coordinate.

I would suggest writing wrfhelp_at_ucar.edu.

I am sure they will be able to help you.

Good Luck

David Brown wrote:
> Hi Erik,
> I will try to answer this as best I can, but you should probably talk to
> someone knowledgeable about WRF for a "real" answer.
>
> hyam and hybm stand for hybrid level coefficients "a" and "b" at the the
> midlevel of the vertical layer.
> P0 is the reference pressure.
>
> The usual formula for converting from hybrid levels to pressure levels
> is the following for a field with dimensions (time, lev, lat, lon):
>
> pressure (time, lev, lat, lon) = hyam(lev) * P0 + hybm(lev) *
> surface_pressure(time,lat,lon)
>
> As an apparent simplification this example script assumes the surface
> pressure is everywhere equal to the reference pressure, making the
> pressure levels constant,
> This reduces the equation to
>
> pressure(lev) = (hyam(lev) + hybm(lev)) * P0.
>
> Hope this helps.
> -dave
>
>
> On Dec 17, 2008, at 3:43 PM, Erik Noble wrote:
>
>> In the NCL application example for zonal averages:
>> http://www.ncl.ucar.edu/Applications/Scripts/zonal_cn_4.ncl
>>
>> What are the 2 variables “hyam” and “hybm” representing?
>> I am to plot the exact same type of plot for WRF data.
>> -Erik
>>
>> ;************************************************
>> a=in->hyam ; select hyam
>> b=in->hybm ; select hybm
>> p=in->P0 ; select P0
>> eta = (a+b)*p ; calc eta
>> eta = eta/100 ; scale eta by 100
>> ;************************************************
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Received on Wed Dec 17 2008 - 17:34:55 MST