[Met_help] [rt.rap.ucar.edu #68926] History for copygb and precipitation analysis

[John Halley Gotway via RT]

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  Initial Request
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Hello, my name is Andrew and I am trying to make precipitation comparisons with models of different resolutions using the METv4.0 framework.  In order to do this, I am using 'copygb' to copy precipitation fields for all models onto a common grid, so that the skill scores will be comparable.

One of my models is on a latlon grid, the other is mercator projected.  I would ideally like to define new grid boxes in km rather than degrees.  Therefore, I have tried to convert the latlon projection to a mercator using the following command.

./copygb.exe -xg"255 1 400 400 42441 -511 128 55620 23407 45000 128 0 12000 12000"

Fields 3 and 4 of this command are the number of grid points that exist between the start and end lat/lon.
The last two fields typically specify the grid spacing in km (when converting to mercator).

These field must correspond, correct?  I.e. what is specified as grid spacing MUST have the correct corresponding number of grid points (fields 3 and 4) in the domain.  For my evaluations, I would like the models to retain their original domain sizes while only changing the horizontal resolution.  So my question is: is there a way to input a desired resolution (in km) and have the number of points (fields 3 and 4) be calculated on the fly instead of explicity entering them?  

Thank you in advance for your help,

Andrew

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  Complete Ticket History
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Subject: copygb and precipitation analysis
From: John Halley Gotway
Time: Wed Sep 10 13:53:26 2014

Andrew,

Let me say that this question should probably go to wrf-help.  copygb
is
distributed as part of the UPP package which is supported via WRF.

I did look around and see that there aren't many good examples of
specifying a Mercator grid for copygb out there.  I did find the
following
w3fi63 grid definition info:
   http://www.nco.ncep.noaa.gov/pmb/docs/libs/w3lib/w3fi63.html

I too have found that the grid definition is some-times over-
specified.
For example, for a lat/lon grid, specifying the beginning and ending
points, and the grid spacing, and the number of grid points is one too
many
pieces of info.  Sounds like the same thing is true of specifying a
mercator grid.

The only thing to do would be to write a wrapper script for copygb
that
does the math to compute and pass in the required copygb grid
definition -
or modify the copygb source code to that computation.  But I'd just
recommend figuring out the numbers yourself.

Hope that helps.

Thanks,
John Halley Gotway
met_help at ucar.edu




On Wed, Sep 10, 2014 at 10:13 AM, Andrew J. via RT <met_help at ucar.edu>
wrote:

>
> Wed Sep 10 10:13:11 2014: Request 68926 was acted upon.
> Transaction: Ticket created by andrewwx at yahoo.com
>        Queue: met_help
>      Subject: copygb and precipitation analysis
>        Owner: Nobody
>   Requestors: andrewwx at yahoo.com
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=68926 >
>
>
> Hello, my name is Andrew and I am trying to make precipitation
comparisons
> with models of different resolutions using the METv4.0 framework.
In order
> to do this, I am using 'copygb' to copy precipitation fields for all
models
> onto a common grid, so that the skill scores will be comparable.
>
> One of my models is on a latlon grid, the other is mercator
projected.  I
> would ideally like to define new grid boxes in km rather than
degrees.
> Therefore, I have tried to convert the latlon projection to a
mercator
> using the following command.
>
> ./copygb.exe -xg"255 1 400 400 42441 -511 128 55620 23407 45000 128
0
> 12000 12000"
>
> Fields 3 and 4 of this command are the number of grid points that
exist
> between the start and end lat/lon.
> The last two fields typically specify the grid spacing in km (when
> converting to mercator).
>
> These field must correspond, correct?  I.e. what is specified as
grid
> spacing MUST have the correct corresponding number of grid points
(fields 3
> and 4) in the domain.  For my evaluations, I would like the models
to
> retain their original domain sizes while only changing the
horizontal
> resolution.  So my question is: is there a way to input a desired
> resolution (in km) and have the number of points (fields 3 and 4) be
> calculated on the fly instead of explicity entering them?
>
> Thank you in advance for your help,
>
> Andrew
>

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