[gradsusr] Diagnostics in Ctl File?

Mon Nov 14 16:50:59 EST 2011

On Mon, Nov 14, 2011 at 4:28 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:

> 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.
>
>
If would like to double check the formulas, compare it to the opengrads
advection functions, e.g.,

      tadv = muadv(ugrdprs,tmpprs) + mvadv(vgrdprs,tmpprs)

(all the metric terms are computed internally, no need to mess with dx,
dy). The computation uses a formula described in:

Bott, A., 1989a: A positive definite advection scheme obtained by nonlinear
renormalization of the advection flux. *Mon. Wea. Rev.*, *117*, 1006-1015.

Bott, A., 1989b: Notes and correspondance. *Mon. Wea. Rev.*, *117*,
2633-2636.
This is usually a more accurate algorithm than using cdiff, particularly
for tracers.

    Arlindo

> 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
>>> >
>>>
>>> _______________________________________________
>>> 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
>>>
>>>
>>>
>>>
>>> --
>>> 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
>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>
>>> _______________________________________________
>>> gradsusr mailing list
>>> gradsusr at gradsusr.org
>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>> _______________________________________________
>>> 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
>
>

-- 
Arlindo da Silva
dasilva at alum.mit.edu
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