[gradsusr] Diagnostics in Ctl File?

Jeff Duda jeffduda319 at gmail.com
Mon Nov 14 17:20:40 EST 2011 

I'm sorry, but I don't see what you're talking about.

Quoted from the page:

   1.
   2. define dtx = cdiff(t,x) define dty = cdiff(t,y) define dx = cdiff(*lon
   *,x)*3.1416/180 define dy = cdiff(lat,y)*3.1416/180 display -1*(
   (u*dtx)/(cos(lat*3.1416/180)*dx) + v*dty/dy )/6.37e6



On Mon, Nov 14, 2011 at 4:14 PM, Rowell, Mason D.
<Mason.D.Rowell-1 at ou.edu>wrote:

>  All,
>
>  So everyone is doubling down on dx using lon in the first argument of
> cdiff, whereas it is lat in the example code provided with the cdiff
> documentation?
>
>  Mason
>  ------------------------------
> *From:* gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on
> behalf of Arlindo da Silva [dasilva at alum.mit.edu]
> *Sent:* Monday, November 14, 2011 3:50 PM
> *To:* GrADS Users Forum
> *Subject:* Re: [gradsusr] Diagnostics in Ctl File?
>
>
>
> 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
>
> _______________________________________________
> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20111114/af738e15/attachment-0003.html

More information about the gradsusr mailing list