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Re: 20040728: grib output?

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  • Subject: Re: 20040728: grib output?
  • Date: 24 Sep 2004 11:28:48 -0600
Mark,

Mixing ratio is scaled by 1000 for display as g/kg
when plotting the known variables MIXR, MIXS, SMXR, SMXS
since that is a traditional (non-MKS) display quantity,
though in MKS units, it is calculated in g/g.
 
Your computation of MAGGRADSMXR is not interpreted as mixing ratio any
longer (as the resulting name of the computed field is no longer 
a form of mixing ratio).

So, your estimated value of 1.3 g/kg/10km would be 1.3x10^-7 g/g/m
or 130x10^-9 (or around the upper end of the range you mentioned in your
email). If it is more convenient to display, as g/kg, you can add a
mul(x,1000) for g/kg or even scale up to "per 100km" instead of meters
as some publications use.

Steve
--------------------------------------------------------------------------

Dr. Steve Chiswell
Uniadta User Support






On Fri, 2004-09-24 at 10:37, Mark Conder wrote:
> Hi Mr. Chiswell
> 
> I have a question regarding the GRAD function on gridded data in 
> GEMPAK?
> 
> I have a grid of sfc mixing ratios.
> If is use MAG(GRAD(SMXR)) I get values on the order of 10-100 with a 
> 10**9 scale factor.
> 
> My grid spacing is approx. 30 km.
> For my dryline case I can manually see a E-W gradient of say about 4 
> g/kg/30 km or 1.3/10 km (for example on successive E-W grid points the 
> smxr goes from 4 to 8 to 12)
> 
> It looks as though the GRAD function does a d(smxr)/dx and a d
> (smxr)/dy for the gradient. But even with the minimal observed 
> gradient in the y-dir I can't understand the resulting small values.
> 
> I guess I am wondering if the values are scaled down quite a bit. I 
> guess from km to m would scale it down by 1000, but that seems to 
> still leave about a 10^4 or 10^5 unknown factor.
> 
> Thanks,
> Mark
> 
> 
> ________________________________________
> Mark Conder
> National Weather Service Forecast Office
> Lubbock, TX
> 
>