[gradsusr] Diagnostics in Ctl File?

Mon Nov 14 16:28:05 EST 2011

Mason,
I see an error in what I typed, but it is only syntactic.  The Grads
commands should be

'define dx = 're'*cos(lat*(3.1419/180))*cdiff(lon*(3.14159/180),x)'
'define dy = 're'*cdiff(lon*(3.14159/180),y)'

Note that I forgot to include the second argument in the cdiff function
call.

Jeff

On Mon, Nov 14, 2011 at 3:17 PM, Rowell, Mason D.
<Mason.D.Rowell-1 at ou.edu>wrote:

>  All,
>
>  Okay, but I see one other disparity, surely just a small typo. The
> definition of dy provided by Jeff calls lon for first argument of cdiff,
> but in the cdiff documentation it calls lat. Geometrically, lat seems to be
> correct to me. Also, each usage of cdiff in dx and dy only has one argument.
>
>  Mason
>  ------------------------------
> *From:* gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on
> behalf of Jeff Duda [jeffduda319 at gmail.com]
> *Sent:* Monday, November 14, 2011 3:05 PM
> *To:* GrADS Users Forum
> *Subject:* Re: [gradsusr] Diagnostics in Ctl File?
>
>  Eric is correct.  I forgot that cdiff includes points surrounding a
> given grid point, and thus the "2dx" part is already included in the cdiff
> function.
>
> Jeff
>
> On Mon, Nov 14, 2011 at 3:00 PM, Eric Altshuler <ela at cola.iges.org> wrote:
>
>> Mason,
>>
>> Yes, the expressions for dx and dy are correct.
>>
>> Eric
>>
>> ----- Original Message -----
>> From: "Mason D. Rowell" <Mason.D.Rowell-1 at ou.edu>
>> To: "GrADS Users Forum" <gradsusr at gradsusr.org>
>> Sent: Sunday, November 13, 2011 11:07:24 AM
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>> Eric,
>>
>> You agree that dx and dy are defined right though?
>>
>> Mason
>> ________________________________________
>> From: gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on
>> behalf of Eric Altshuler [ela at cola.iges.org]
>> Sent: Sunday, November 13, 2011 1:33 AM
>> To: GrADS Users Forum
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>> I believe the factor of 2 in the denominator of Jeff's expression for
>> temperature advection should not be there. The expression should be:
>>
>> 'define tadv = -ugrdprs*cdiff(tmpprs,x)/dx - vgrdprs*cdiff(tmpprs,y)/dy'
>>
>> because the cdiff function, when evaluated at a grid point (i,j), gives
>> the difference of its argument between the grid points at (i+1) and (i-1)
>> or (j+1) and (j-1), i.e. the distance the difference is taken across is two
>> grid points. This is also true of dx and dy because they are themselves the
>> results of using cdiff. Thus, if there is a factor of 2 in the denominator,
>> then there must also be one in the numerator, and they would cancel.
>>
>> Eric
>>
>> ----- Original Message -----
>> From: "Mason D. Rowell" <Mason.D.Rowell-1 at ou.edu>
>> To: "GrADS Users Forum" <gradsusr at gradsusr.org>
>> Sent: Saturday, November 12, 2011 8:57:32 PM
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>>
>>
>> Disregard. I am getting the script to use it now. Though I am curious
>> about the discrepancy between Jeff's definition of temp. advection and that
>> suggested by the cdiff documenation....
>>
>> Mason
>>
>>
>>
>> From: gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on
>> behalf of Rowell, Mason D. [Mason.D.Rowell-1 at ou.edu]
>> Sent: Saturday, November 12, 2011 7:03 PM
>> To: GrADS Users Forum
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>>
>>
>>
>> All,
>>
>> Interesting, I get a display when used at the command line, but when run
>> within the script, I get,
>> 'Function not found: cdiff
>> Error occurred on line 15'
>>
>> Why could this be? It is not syntax related..it just doesn't recognize it
>> within the script...the only difference is that it is used in a definition
>> (for defining dx) and not with a display command like when used at the
>> command prompt...
>>
>> Mason
>>
>>
>>
>> From: gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on
>> behalf of Jeff Duda [jeffduda319 at gmail.com]
>> Sent: Friday, November 11, 2011 11:07 PM
>> To: GrADS Users Forum
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>>
>>
>> Mason,
>> What happens when you enter the command
>> 'd cdiff(tmpprs,x)' ?
>>
>> Does it display something that looks like the meridional gradient in
>> temperature?
>>
>> Jeff
>>
>>
>> On Fri, Nov 11, 2011 at 11:00 PM, Rowell, Mason D. <
>> Mason.D.Rowell-1 at ou.edu > wrote:
>>
>>
>>
>>
>> Jeff,
>>
>> My problem comes in using cdiff. Everything else should be fine (it is
>> practically verbatim from the webpage). I have a suspicion it is because it
>> uses x and y as arguments on two different lines but I don't really have
>> much of a way to know without more Grads experience. Could this be causing
>> the problem?
>>
>> Mason
>>
>>
>>
>>
>> From: gradsusr-bounces at gradsusr.org [ gradsusr-bounces at gradsusr.org ] on
>> behalf of Jeff Duda [ jeffduda319 at gmail.com ]
>> Sent: Friday, November 11, 2011 3:17 PM
>>
>>
>>
>> To: GrADS Users Forum
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>>
>>
>>
>>
>>
>> Mason,
>> I preferred to derive the formulas for spacings myself. Simple
>> trigonometry reveals the following that you should use for dx and dy (i.e.,
>> meridional and zonal grid spacing):
>> dx = Re*cos(phi)*d(theta)
>> dy = Re*d(phi)
>>
>> where Re is the radius of the Earth (6371 to 6374 km), phi is latitude,
>> theta is longitude, and the d operator means "change in". To convert this
>> to Grads scripting code, you use the cdiff command. Also note that all
>> angle measures need to be in radians, so you'll have to convert them as you
>> do the operation. Here are the literal Grads command lines I use for this:
>>
>> re = 6.371e3
>> 'define dx = 're'*cos(lat*(3.1419/180))*cdiff(lon*(3.14159/180))'
>> 'define dy = 're'*cdiff(lon*(3.14159/180))'
>>
>> Obviously you can assign the conversion factor pi/180 to a script
>> variable to simplify the symbolism there:
>>
>> conv_factor = 3.14159/180
>> e.g., 'define dy = 're'*cdiff(lon*'conv_factor')'
>>
>> If you try to display dx or dy, you should get a nice little image that
>> contours or colors dx and dy (dx should decrease towards the poles and not
>> change along a line of constant latitude, and dy should only be a function
>> of latitude as well). Now use this to define temperature advection
>> (assuming the temperature variable is tmpprs and wind is ugrdprs/vgrdprs):
>>
>> 'define tadv = -ugrdprs*cdiff(tmpprs,x)/(2*dx) -
>> vgrdprs*cdiff(tmpprs,y)/(2*dy)'
>>
>> The 98cbar.gs is indeed just a script that defines color levels and sets
>> a color scheme for when you plot temperature advection. Changing the color
>> tables is rather easy in Grads. You only need to define a color using 'set
>> rgb # R G B', where # is anything between 16 and 255 (just a reference
>> number) and R, G, and B are between 0 and 255. Then you set the contour
>> intervals manually using 'set clevs , , , , , ...' where you insert
>> literally the levels you want to use (separated by SPACES, not COMMAS).
>> Then set the colors for those levels using 'set ccols , , , , , , ,+1'
>> again using the reference numbers for each color and separating by SPACES.
>> The "+1" is for the fact that you need one additional color for the number
>> of levls you put. You can consult the controlling colors page for full info
>> on what I just said. Also, I have a number of very simple color bar scripts
>> that I've used in the past. I can provide them to all if anyone is
>> interested.
>>
>> You can also create a simple color bar using the cbar.gs script which is
>> provided in the script library .
>>
>> Let me know if you need any more help.
>>
>> Jeff
>>
>>
>> On Fri, Nov 11, 2011 at 2:50 PM, Rowell, Mason D. <
>> Mason.D.Rowell-1 at ou.edu > wrote:
>>
>>
>>
>>
>> Jeff and others,
>>
>> Strange. This is exactly what was suggested in the ctl file near the
>> comments at the bottom (that which I pulled from nomads). The only
>> difference is that they have also the inclusion of a 98cbar.gs script
>> right after the other expressions like that in this link you gave me, whose
>> utility is a mystery since it is not necessary, at least suggested as so by
>> the cdiff documenation given that it is not included. Perhaps it is just
>> some coloring scheme. At any rate, the script fails at the first line
>> (which attempts to define dtx), with each line coded exactly as it is shown
>> (with the appropriate NARR temp as TMPprs and wind as UGRDprs and VGRDprs
>> of course). I assume it will do so again at dty, and so forth. I originally
>> didn't include define with these since I thought they weren't necessary but
>> adding that in didn't solve the problem anyways. I suspect it is because
>> cdiff calls x, and since I define my domain with lat long, it doesn't have
>> a x variable to use? There definitely !
>>  isn't a spacing issue this time...
>>
>> Mason
>>
>>
>>
>> From: gradsusr-bounces at gradsusr.org [ gradsusr-bounces at gradsusr.org ] on
>> behalf of Jeff Duda [ jeffduda319 at gmail.com ]
>> Sent: Thursday, November 10, 2011 11:11 AM
>> To: GrADS Users Forum
>> Subject: Re: [gradsusr] Diagnostics in Ctl File?
>>
>>
>>
>> Mason,
>> There is a good example of how to code temperature advection in the page
>> for the cdiff command: http://www.iges.org/grads/gadoc/gradfunccdiff.html
>> The reason for all of the crazy manipulations is because the data points
>> on your grid are not uniformly spaced on the globe. Thus corrections have
>> to be made to get the correct distance between individual grid points.
>>
>> Jeff
>>
>>
>> On Thu, Nov 10, 2011 at 11:00 AM, Wesley Ebisuzaki <
>> Wesley.Ebisuzaki at noaa.gov > wrote:
>>
>>
>> Mason,
>>
>> I think that you've discovered the "private" commands used by nomads
>> plot software for defining new variables
>> and custom plots. The nomads plot package is a wrapper for GrADS. It
>> has the ability to run grads .gs files that
>> are embedded within the ctl files.
>>
>>
>>
>> http://www.cpc.ncep.noaa.gov/products/wesley/ncep_data/plot_doc.htmlhttp://www.cpc.ncep.noaa.gov/products/wesley/ncep_data/plot_doc.html
>>
>> Ask NCDC for a copy of the .gs files.
>>
>>
>> > Has anyone done this before with grads?
>> How do you expect the developers to debug the scripts?
>>
>> Wesley
>>
>>
>>
>>
>>
>>
>> Rowell, Mason D. wrote:
>> > All,
>> >
>> > I noticed ample comments toward the end of the ctl files available on
>> the nomads servers from the NARR page, with a description of how to
>> implement these in grads scripting. I tried to take this to plot
>> temperature advection but it didn't work, b/c the last line of the comments
>> calls for some function never provided. Has anyone done this before with
>> grads?
>> >
>> > Mason
>> > _______________________________________________
>> > gradsusr mailing list
>> > gradsusr at gradsusr.org
>> > http://gradsusr.org/mailman/listinfo/gradsusr
>> >
>>
>> _______________________________________________
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>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>>
>> --
>> Jeff Duda
>> Grad student - PhD, Meteorology
>> University of Oklahoma School of Meteorology - Center for Analysis and
>> Prediction of Storms
>>
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>>
>>
>> --
>> Jeff Duda
>> Grad student - PhD, Meteorology
>> University of Oklahoma School of Meteorology - Center for Analysis and
>> Prediction of Storms
>>
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>>
>>
>> --
>> Jeff Duda
>> Grad student - PhD, Meteorology
>> University of Oklahoma School of Meteorology - Center for Analysis and
>> Prediction of Storms
>>
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
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>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>> _______________________________________________
>> gradsusr mailing list
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>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>
>
>
> --
> Jeff Duda
> Grad student - PhD, Meteorology
> University of Oklahoma School of Meteorology - Center for Analysis and
> Prediction of Storms
>
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>

-- 
Jeff Duda
Grad student - PhD, Meteorology
University of Oklahoma School of Meteorology - Center for Analysis and
Prediction of Storms
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