Re: DJF averaging

Hi Adam,

This is exactly what I needed! Thank you so much!
Kindest regards,

Michel

Quoting Adam Phillips <asphilli_at_ucar.edu>:

> Hi Michel,
> The answer depends on the time coordinate coordinate variable that's
> attached to the data that you want to use. I prefer to work in time
> units of YYYYMM, as I find it the easiest format to quickly subset:
> sst = b->sst({190001:200012},:,:)
>
> If however, your data comes in with units of "months-since ..." or
> some other format, there are two easy options: 1) Convert the time
> coordinate variable to something that would be easier to subset, as I
> show below. or 2) Use regular subscripting to grab what you want, which
> is the method I used in the example I previously sent you.
>
> In many cases, using ut_calendar is the way to go. Here's an example
> where I read in a file, and use ut_calendar to switch the time from
> units of "hours since 1-1-1 00:00:0.0" to YYYYMM, and then select only
> the data I want using coordinate subscripting:
>
> a = addfile("hadsst2_1x1.185001-200812.nc","r")
> sstT = a->sst
> sstT&time = ut_calendar(sstT&time,1)
> sst = sstT({197901:200712},:,:)
> delete(sstT)
>
> Adam
>
>
> Michel.Mesquita_at_bjerknes.uib.no wrote:
>> Hi Adam,
>>
>> Thank you so much for helping me!
>> You're right, I meant the function 'month_to_season'. :-)
>> I was actually slicing the data first and then applying
>> month_to_season. So, I see that the correct way would be the other
>> way around!
>> There's something else I'd like to ask you. You said:
>>> You can make that more generic instead of coding in the 31:60 if you
>>> wish, and that would probably be recommended.
>>
>> I am not sure how to refer to the exact timesteps I want in NCL.
>> So, what I do is to use 'ut_calendar' to find out the indexes to
>> the period I want. Is there a more generic way? (for example, in
>> Grads you can specific the time directly, 'set time 12JAN79' - or
>> something like that)
>>
>> Thank you and have a great day!
>>
>> Kindest regards,
>>
>> Michel
>>
>>
>> Quoting Adam Phillips <asphilli_at_ucar.edu>:
>>
>>> Hi Michel,
>>> When you say you are using the function month_to_month, do you mean you
>>> are using the function month_to_seasonN?
>>> http://www.ncl.ucar.edu/Document/Functions/Contributed/month_to_seasonN.shtml As the documentation states, the time dimension must be divisible
>>> by
>>> 12, and must start in January. Also, the first average (DJF year 0) is
>>> actually the average of January and February year 0.
>>>
>>> So, taking all of that into account, you want to compute the DJF
>>> average from 1979-2008, and you want to take into account December
>>> 1978...
>>>
>>> d = addfile("data.nc","r")
>>> data = d->slp ; data will be dimensioned time x lat x lon
>>>
>>> data_temp = month_to_seasonN(data,"DJF")
>>> data_djf = data_temp(0,31:60,:,:) ; 31:60 = 1979-2007
>>>
>>> You can make that more generic instead of coding in the 31:60 if you
>>> wish, and that would probably be recommended.
>>>
>>> Finally, if you want an overall DJF 1979-2007 mean, use dim_avg_Wrap to
>>> average over the time dimension of data_djf.
>>> http://www.ncl.ucar.edu/Document/Functions/Contributed/dim_avg_Wrap.shtml
>>> Good luck,
>>> Adam
>>>
>>>
>>>
>>> Michel.Mesquita_at_bjerknes.uib.no wrote:
>>>> Hi everyone,
>>>>
>>>> I have a netcdf file with data from 1948 - 2009(march). I want to
>>>> calculate the DJF average from 1978(9) to 2007.
>>>>
>>>> First, I need to slice the data for the period I am working with.
>>>> But where should I start this slice if I use the function
>>>> month_to_month in NCL? I know this function has to start from
>>>> January.
>>>>
>>>> If I start from January 1978 do these values (January and
>>>> February 1978) enter in the average calculation? And if I end
>>>> the data in December 2008, does that December enter in the
>>>> calculation? I assume they don't.
>>>>
>>>> I really appreciate your help!
>>>>
>>>> Kindest regards,
>>>>
>>>> Michel
>>>>
>>>>
>>>> _______________________________________________
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>>>
>>> --
>>> --------------------------------------------------------------
>>> Adam Phillips asphilli_at_ucar.edu
>>> National Center for Atmospheric Research tel: (303) 497-1726
>>> ESSL/CGD/CAS fax: (303) 497-1333
>>> P.O. Box 3000
>>> Boulder, CO 80307-3000 http://www.cgd.ucar.edu/cas/asphilli
>>
>
> --
> --------------------------------------------------------------
> Adam Phillips asphilli_at_ucar.edu
> National Center for Atmospheric Research tel: (303) 497-1726
> ESSL/CGD/CAS fax: (303) 497-1333
> P.O. Box 3000
> Boulder, CO 80307-3000 http://www.cgd.ucar.edu/cas/asphilli

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Received on Thu Jun 11 2009 - 15:35:58 MDT