# Re: hydro function 'zsfc' argument

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Tue Jan 15 2013 - 13:09:13 MST

re: clarity on exactly what the surface GPH argument
is providing the hydro function

```---
zsfc provides the base 'elevation' to which layer thicknesses
c calculate geopotential height if initial z available [hydrostatic eq]
zh(1)  = zsfc
do nl=2,nlvl
tvbar  = (tkv(nl)*alog(p(nl)) + tkv(nl-1)*alog(p(nl-1)))
*             /  alog(p(nl)*p(nl-1))
zh(nl) = zh(nl-1)+rdag*tvbar*alog(p(nl-1)/p(nl))
enddo
On 1/14/13 3:39 PM, jonathan meyer wrote:
>
> Hello to the community,
> My question is regarding ncl's 'hydro' function which calculates geopotential height using Pres (mb), Virtual Temperature (K) and surface GPH (gpm).
> For a quick background of what I am doing, I am needing to compare the method our group is using to calculate GPH using the hydrostatic equation with ncl's hydro function to ensure that our method is working correctly.
> If at all possible, I'd like some clarity on exactly what the surface GPH argument is providing the hydro function. I've never run across an actual surface GPH variable in model data, and I'm wondering if this represents something as easy as surface elevation (easy to get from NARR data), or the actual geopotential height at the surface calculated by using surface pressure and the hydrostatic equation to derive GPH at the surface?
> As the units for the argument are gpm, I'm guessing the latter is the correct assumption, but didn't want to assume incorrectly.
> Any thoughts are much appreciated, and as always, thanks in advance!
> Jon
>
>
>
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```
Received on Tue Jan 15 13:09:24 2013

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