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20030205: P03M in Grids

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  • Subject: 20030205: P03M in Grids
  • Date: Wed, 5 Feb 2003 12:39:21 -0700
Patrick,

The units of kg m**-2  and mm of precipitation are generally equivalent
for water.

Eg, a dimensional analysis:
1kg of water = 1 L of water = 1000 mL = 1000 cc of water = 10^6 mm**3
where 1cc = 1000 mm**3, and 1 m**2 = 10^6 mm**2

so,

kg m**-2 = ( 10^6 mm**3 ) / ( 10^6 mm**2 ) = 1mm.

Steve Chiswell
Unidata User Support

On Wed, 5 Feb 2003, Patrick O'Reilly wrote:

> Hello,
>
> I am aware of the P03M, P03I and similar surface parameters and their units
> (mm, in.), but see P03M in the icwf212 and eta212 grids.  I wanted to plot
> forecast precip, and am a little confused with the units.  From
> wmogrib2.tbl:
>
> 061 Total precipitation               kg m**-2             P--M
> 0     -0.01
>
> Is this telling me that the P03M in these grid files are in units of kgm**-2
> and not millimeters, which is units of mass/area?  I do get a reasonable
> plot when using GDPFUN=P03I, but this doesn't make sense if the units of
> P03M are in kgm**-2 and not mm....unless gempak is converting units of
> mass/area to inches on the fly.  Any light shed on this would be helpful.
>
> Patrick
> _______________________________________
> Patrick O'Reilly
> Meteorological Decision Support Scientist
> The STORM Project - University of Northern Iowa
> address@hidden  ~  ph: 319-273-3789
> http://www.uni.edu/storm
>
> No trees were killed in the making of this e-mail...however,
> a large number of electrons were horribly inconvenienced."
>