[gradsusr] Meridional gradient?

[sushant puranik]

Jeff
I tried with making changes asper your suggestion.
I got results as Constant field value =333533 for
dy=6.37e6*cdiff(lat,y)*(3.1416/180) command

and also tried dx=6.37e6*cos(lat*(3.1416/180))*cdiff(lon,x)*(3.1416/180) in
this case it shows simply parallel lines on the plot.
Results are attached with this mail.

Thank you

Sushant

On Sat, Jun 25, 2011 at 8:58 PM, Jeffrey Duda <jdduda at iastate.edu> wrote:

> Put the literal argument "lat" in place of "19.5" in the cdiff command for
> dy and put "lon" for "30" in the cdiff for the dx definition.  There's
> nothing wrong with setting your dimensions first, as that will only affect
> the horizontal scope of the subsequent fields you define.
>
> Jeff
>
>
> On Sat, Jun 25, 2011 at 12:11 AM, sushant puranik <
> sushantpuranik at gmail.com> wrote:
>
>> Thanks Jeff.
>> But i am not able to plot the output. It gives error with the latitudinal
>> command
>>
>> ga-> define dy=6.37e6*cdiff(19.5,y)*(3.1416/180)
>> Error from CDIFF:  Specified dimension non varying
>> Operation Error:  Error from cdiff function
>>   Error ocurred at column 8
>> DEFINE error:  Invalid expression.
>>
>> and also tried with the longitudinal command
>>
>> ga-> define dx=6.37e6*cos(10*(3.1416/180))*cdiff(30,x)*(3.1416/180)
>> Error from CDIFF:  Specified dimension non varying
>> Operation Error:  Error from cdiff function
>>   Error ocurred at column 29
>> DEFINE error:  Invalid expression.
>> Segmentation fault
>>
>> i think i am have to set dimensions first?
>>
>> Thank you
>>
>> Sushant
>>
>>
>> On Fri, Jun 24, 2011 at 10:14 PM, Jeffrey Duda <jdduda at iastate.edu>wrote:
>>
>>> Sushant,
>>> Unfortunately, no.  Getting the longitudinal gradient is not as simple
>>> since the distance between longitude lines is a function of the latitude.
>>> However, the formula is
>>>
>>> dx = Re*cos(lat*(pi/180))*cdiff(lon,x)*(pi/180).
>>>
>>> The cos(lat*(pi/180)) term is the adjustment for dependence of longitude
>>> space on latitude.
>>>
>>> Jeff
>>>
>>>
>>> On Fri, Jun 24, 2011 at 12:55 AM, sushant puranik <
>>> sushantpuranik at gmail.com> wrote:
>>>
>>>> Hi Jeff
>>>> Can i use same command for longitudinal gradient computation by
>>>> replacing lat --> lon in the command
>>>> dy = Re*cdiff(lat,y)*(3.14159/180)
>>>>
>>>> thanks
>>>>
>>>> Sushant
>>>>
>>>>
>>>> On Tue, May 4, 2010 at 2:33 AM, Jeffrey Duda <jdduda at iastate.edu>wrote:
>>>>
>>>>> Li,
>>>>> If you want to find a temperature gradient, why not just use cdiff?
>>>>> Just realize that you'll have to use the following expression for dy (the
>>>>> incremental change in meridional distance between grid points, in meters):
>>>>>
>>>>> dy = Re*cdiff(lat,y)*(3.14159/180)
>>>>>
>>>>> where Re is the radius of the Earth (about 6.371e6 meters, I
>>>>> believe).   This is to account for the projection Grads uses to display your
>>>>> data.  Hope this helps.
>>>>>
>>>>> Jeff Duda
>>>>>
>>>>>
>>>>> On Mon, May 3, 2010 at 3:20 PM, Li Dong <ldong at unm.edu> wrote:
>>>>>
>>>>>> Hello list,
>>>>>>
>>>>>> I need to calculate the meridional temperature gradient across 20
>>>>>> degree
>>>>>> latitude belt using global gridded data. Below is what I did:
>>>>>>
>>>>>> 'open ta.ctl'
>>>>>> 'set t 1'
>>>>>> 'set lev 1000'
>>>>>> 'set lon 0 360'
>>>>>> 'set lat -80 80'
>>>>>> 'define Tgrad=ta(lat+10)-ta(lat-10)'
>>>>>>
>>>>>> However, Grads complained "Cannot use an offset value with a varying
>>>>>> dimension". If I set 'lat' at a fixed value, such as 'set lat 40', the
>>>>>> above script did work, but the downside is that this only gives
>>>>>> temperature meridional gradient at the specified latitude instead of
>>>>>> over the entire latitude range. Any inputs would be highly
>>>>>> appreciated!
>>>>>>
>>>>>> Best,
>>>>>>
>>>>>> Li
>>>>>>
>>>>>> _______________________________________________
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>>>>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Jeff Duda
>>>>> Iowa State University
>>>>> Meteorology Graduate Student
>>>>> 3134 Agronomy Hall
>>>>> www.meteor.iastate.edu/~jdduda<http://www.meteor.iastate.edu/%7Ejdduda>
>>>>>
>>>>> _______________________________________________
>>>>> gradsusr mailing list
>>>>> gradsusr at gradsusr.org
>>>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>>
>>>
>>>
>>> --
>>> Jeff Duda
>>> Iowa State University
>>> Meteorology Graduate Student
>>> 3134 Agronomy Hall
>>> www.meteor.iastate.edu/~jdduda <http://www.meteor.iastate.edu/%7Ejdduda>
>>>
>>> _______________________________________________
>>> gradsusr mailing list
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>>>
>>>
>>
>>
>> --
>>
>>
>>
>>
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>
>
> --
> Jeff Duda
> Iowa State University
> Meteorology Graduate Student
> 3134 Agronomy Hall
> www.meteor.iastate.edu/~jdduda <http://www.meteor.iastate.edu/%7Ejdduda>
>
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