[gradsusr] Standard deviation of an area

Thu Nov 20 08:00:46 EST 2014

Julio,

The way you suggested still returned a gridded result, not a number
representig the area. Then I tried averaging the result over the same area
(everything for each t-value):

   define var1 = sqrt( pow( aave( sst, lat=..., lon=...)))
   define var2 = aave( var1, lat=..., lon=...)

Does it make any sense to you?

Thanks again!

Sourabh,

So just checked, you can do:

while (count < 22)
   'set t' count
   'define area = aave (variable-name, lon=120, lon=180, lat=-90, lat-90)
   'd area'
   count = count +1
endwhile

Works as fine as defining the area with x and y. Very small numerical
difference though, don't know why.

On 20 November 2014 10:23, David Nielsen <davidnielsen at id.uff.br> wrote:

> Sourabh,
>
> You can try:
>
> while (count < 22)
>    'set t 'count
>    'define average=ave("variable-name", x and y limits)'
>    'd average'
>    count=count+1
> endwhile
>
> You have to express lat and lon in terms of x and y in the "ave" formula.
> For that, open the file in Grads and:
>
> set lat -90 90
> q dim
>
> And it will tell you the equivalente x limits, for example.
>
> Not sure about this must, though. You can check it here:
> http://www.iges.org/grads/gadoc/gradfuncave.html
>
> Hope it helps!
>
> Julio, I will try your suggestion now! Thanks again!
>
>
> On 20 November 2014 09:39, Sourabh Bal <sourabhbal at gmail.com> wrote:
>
>> Hello David and Julio,
>>
>> if I want to plot time-latitude cross section (Y and T varying), with the
>> data being averaged over longitude (120 to 180), where shall I fix the
>> longitude.
>>
>> set lat -90 90
>> set lon ??????
>> set t 1 21
>> d tloop(ave(aprl,lon=120,lon=180))
>>
>>
>> Sourabh
>>
>>
>>
>> On Thu, Nov 20, 2014 at 1:35 AM, Julio Martinez <julioms24 at hotmail.com>
>> wrote:
>>
>>> *David,*
>>>
>>> *Maybe you could try with*
>>>
>>> *d tloop(sqrt(pow(aave(uwnd,lon=200,lon=300,lat=0,lat=30),-uwnd,2)))*
>>>
>>>
>>>
>>>
>>> Julio N. Martínez Sánchez
>>> M.C. en Oceanografía Física
>>> Consultor en Sitio
>>> Subgerencia de Pronóstico a Mediano y Largo Plazo
>>> Gerencia de Meteorología y Climatología
>>> Servicio Meteorológico Nacional
>>> Ext. 3156
>>>
>>>
>>> ------------------------------
>>> From: davidnielsen at id.uff.br
>>> Date: Wed, 19 Nov 2014 21:13:14 -0200
>>> To: gradsusr at gradsusr.org
>>> Subject: Re: [gradsusr] Standard deviation of an area
>>>
>>>
>>> Hi, Julio,
>>>
>>> My problem is not with the loop in time. I am using a "While" sintax to
>>> execute the average along the series:
>>>
>>> while (count < "number of t-values +1")
>>>    'set t 'count
>>>    'define average=aave(sst,x=127.8,x=128.6,y=27.6,y=28.6)'
>>>    'd average'
>>>    average=subwrd(result,4)
>>>    rc = write ("c:\path\file.txt",average)
>>>    count=count+1
>>> endwhile
>>>
>>> This is working fine. What I need now, is a way to calculate the
>>> standard deviation of SST in the area of interest, also for each value of
>>> t, like something independent of time, for me to insert inside the loop.
>>>
>>> Everything Ive seen before is a standard deviation of the whole series
>>> (like below), and not for each time-value.
>>>
>>> 'define sdsst=sqrt(ave(pow(ave(sst,t=1,t=12)-sst,2),t=1,t=12))' ->
>>> calculates std of the series between t=1 and t=2. What I'd like to do is,
>>> for each t, an std of the area.
>>>
>>> Any suggestions?
>>>
>>> Thanks!
>>>
>>>
>>> On 19 November 2014 13:38, Julio Martinez <julioms24 at hotmail.com> wrote:
>>>
>>> *Hi David,*
>>>
>>>
>>> *I think you could try with tloop command...*
>>>
>>> Julio N. Martínez Sánchez
>>> M.C. en Oceanografía Física
>>> Consultor en Sitio
>>> Subgerencia de Pronóstico a Mediano y Largo Plazo
>>> Gerencia de Meteorología y Climatología
>>> Servicio Meteorológico Nacional
>>> Ext. 3156
>>>
>>>
>>> ------------------------------
>>> From: davidnielsen at id.uff.br
>>> Date: Wed, 19 Nov 2014 13:12:34 -0200
>>> To: gradsusr at gradsusr.org
>>> Subject: [gradsusr] Standard deviation of an area
>>>
>>>
>>> Dear all grads users,
>>>
>>> I would like to calculate the standard deviation of an area in Grads.
>>>
>>> I have a NetCDF wekly time series of SST (attached), and I am able to
>>> calculate the average of a certain area (defining LAT and LON) value using
>>> the "aave" formula, for each value of time, and generate a new series - ok.
>>> In addition to this seires, I would like to generate a series of standard
>>> deviations of this average, also for each time in the series. In other
>>> words, I need to to know, for a given area and time, what is the standard
>>> deviation of my variable?
>>>
>>> Please find attached an example of a NetCDF file I want to treat this
>>> way:
>>> 1. Calculate average of SST in a certain area (lat, lon) using aave, for
>>> each time value
>>> 2. Calculate standard deviation of SST in a certain area (lat, lon), for
>>> each time value
>>>
>>> Would anybody have any kind suggestions on how to address this #2 task?
>>>
>>> Many thanks in advance,
>>>
>>>
>>>
>>> --
>>> David Marcolino Nielsen
>>> Engenharia de Recursos Hídricos e do Meio Ambiente
>>> Universidade Federal Fluminense
>>> davidnielsen at id.uff.br
>>>
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>>>
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>>>
>>>
>>>
>>> --
>>> David Marcolino Nielsen
>>> Engenharia de Recursos Hídricos e do Meio Ambiente
>>> Universidade Federal Fluminense
>>> davidnielsen at id.uff.br
>>>
>>> _______________________________________________ gradsusr mailing list
>>> gradsusr at gradsusr.org http://gradsusr.org/mailman/listinfo/gradsusr
>>>
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>>>
>>
>>
>> --
>> Dr. Sourabh Bal
>> Post-Doc Fellow
>> Institute of Meteorology, Freie Universitat, Berlin
>>
>>
>>
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>
>
> --
> David Marcolino Nielsen
> Engenharia de Recursos Hídricos e do Meio Ambiente
> Universidade Federal Fluminense
> davidnielsen at id.uff.br
>

-- 
David Marcolino Nielsen
Engenharia de Recursos Hídricos e do Meio Ambiente
Universidade Federal Fluminense
davidnielsen at id.uff.br
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