[gradsusr] Standard deviation of an area

David Nielsen davidnielsen at id.uff.br
Thu Nov 20 09:22:20 EST 2014 

Sourabh,

First, if you want it to run from t=1 to 21, you should fix the loop to
"while (count < 22)", so that it will run until t=21.

However, it will generate you a single number for each t: an average of the
variable on the rectangle you defined, not a plot as you wish. I'm also
curious to hear suggestions for that now.

Good luck,



On 20 November 2014 11:45, Sourabh Bal <sourabhbal at gmail.com> wrote:

> Hi David,
>
> Thanks for your suggestion. I tried with the following
> 'reinit'
> 'open SSt12.precip.lon-lat.allssws.ctl'
>
> 'x1=1000*24*60*60*(aprl+aprc)'
> while (count<1)
> 'set t' count
> 'define area=aave(x1,lon=120,lon=180,lat=-90,lat=90)
> 'd area'
> 'enable print figure1.zonalpre120-180E.mf'
> 'print'
> 'disable print'
> '!./gxeps -c -i figure1.zonalpre120-180E.mf -o
> SSt12.preci.120-180E.all.ssws.eps'
> count=count+1
> endwhile
>
>
> but does not yield my result.
>
> After running the script there is no error but the eps file produced is
> blank.
>
> Actually I want zonal average over longitude (120 to 180). The plot would
> be X as time ( t=1 to t =21) and Y as latitude (90N to 90S). More over I
> also want calculate statistical significance (t test values) over this plot
> ( may be in shaded).
>
>
> Please help me
>
> Sourabh
>
>
>
>
>
>
>
> On Thu, Nov 20, 2014 at 2:00 PM, David Nielsen <davidnielsen at id.uff.br>
> wrote:
>
>> 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
>>>>>
>>>>> _______________________________________________ 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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
>>>>>
>>>>> _______________________________________________
>>>>> gradsusr mailing list
>>>>> gradsusr at gradsusr.org
>>>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>
>
> --
> Dr. Sourabh Bal
> Post-Doc Fellow
> Institute of Meteorology, Freie Universitat, Berlin
>
>
>
>


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