Re: Tutorial script question; hyam and hybm

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
> ;************************************************
> _______________________________________________
> ncl-talk mailing list
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk

_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Wed Dec 17 2008 - 17:27:39 MST