[ncl-talk] month_to_season() how does it work?

Thu Feb 19 11:31:10 MST 2015

It won't work. The routine expects the input to have  full years, so the
time dimension has to be divisible by 12. I haven't played around with the
routine enough to know if it would work if you give it full years, but
starting in December. So for example:

1979-Dec 1980-Jan .... 2001-Oct 2001-Nov

How about you just try that and see if it works? If it does, I would make
sure that the result is what you expect by also computing the averages by
index (since you know which months correspond to which indices).

Maria

On Thu, Feb 19, 2015 at 11:05 AM, Erik Jan Schaffernicht <
eschaffe at uni-koeln.de> wrote:

>  Ok, usually 3, single month seasons are dropped, and at the start a two
> month season is possible.
>
> Now imagine I select from a long time covering netcdf a sub-time-range and
> create a new netcdf based on that range.
> This new one has as a first entry 1979-Dec and goes on like you can in the
> next line below. Last entry of my sub-time-file will be 2001-Feb:
>
> 1979-Dec   1980-Jan  1980-Feb  1980-Mar...2000-Nov   2000-Dec   2001-Jan
> 2001-Feb
>
> If I now run ncl, ask to read in the slp for   YYYY.ge.1979  to
> YYYY.ge.2001   of this file and  execute then:
>
> slpSeason=  month_to_season(slp, "DJF")
>
> do I get then my seasonal field based on three months always? Even for the
> first season 1979/80 which starts in Dec-1979  (as I deleted all
> 1979AD-months before 1979-Dec beforehand)?
>
>
>
>
>
>
>
>
> On 19.02.2015 17:55, Maria Gehne - NOAA Affiliate wrote:
>
> It should really do that, only the first year average for DJF is JF and
> only the last year NDJ is ND. It doesn't really make sense to talk about
> seasonal averages when you only use 2 month averages for one of the season
> options. And it's not necessary to only use 2 months for DJF in the middle
> of the data where you have DJFs in a row. The reason the documentation
> mentions the 2 month averages for the first DJF and last NDJ average is so
> that people know those values are only based on 2 months and not 3 like the
> rest of the DJF and NDJ values.
>
>  You can easily test the DJF averages by computing the averages for a few
> years yourself and comparing that to the result from month_to_season.
>
>  Maria
>
> On Thu, Feb 19, 2015 at 9:18 AM, Daniel Barandiaran <
> dbarandiaran at gmail.com> wrote:
>
>> does it really do that? my reading of the documentation suggests that DJF
>> is just JF for all years, and similarly NDJ is just ND.
>>  On Feb 19, 2015 8:30 AM, "Maria Gehne - NOAA Affiliate" <
>> maria.gehne at noaa.gov> wrote:
>>
>>> Hi Erik,
>>>
>>>  month_to_season gives you as many seasons as you have full years in
>>> your data. So if your data has 13 years then you will end up with 13 values
>>> for DJF with the first one only being computed for JF in the first year.
>>> The last december value will be ignored, because that would be the 14th
>>> season.
>>>
>>>  Does that help?
>>>
>>>  Maria
>>>
>>> On Thu, Feb 19, 2015 at 12:56 AM, Erik Jan Schaffernicht <
>>> eschaffe at uni-koeln.de> wrote:
>>>
>>>> I am not sure how month_to_season() function works for   DJF   (and NDJ
>>>> is probably similar).
>>>>
>>>> Say, I select "DJF"
>>>>
>>>> I take the years like this:
>>>> [snip]
>>>> iYYYY=  ind(YYYY.ge.1979 .and. YYYY.le.2003)
>>>> slp= ifle->slp(iYYYY,:,:)   + ...   (further steps, input from ncep slp
>>>> data.nc, and I flip some dimension to make it fitting to formal
>>>> requirements)
>>>> slpSeason=  month_to_season(slp, "DJF")
>>>> [snip]
>>>>
>>>> What does the month_to_season() exactly do?
>>>>
>>>> My understanding of 'what belongs to a season' written down looks like
>>>> this, if I group it by DJFseason:
>>>>
>>>> 1979-Jan and 1979-Feb
>>>> 1979-Dec and 1980-Jan and 1980-Feb
>>>> ...
>>>> 2002-Dec and 2003-Jan and 2003-Feb
>>>> 2003-Dec
>>>>
>>>> How does  month_to_season() process this?
>>>> It says that DJF takes only  two months?   Does it mean only two for
>>>> the first entry of this list, i.e. 1979-Jan 1979-Feb     but thereafter it
>>>> takes always three, so 1979-Dec + 1980-Jan+1980-Feb, so three months in
>>>> general except for one exception at the beginning?
>>>> Or is it always
>>>> 1979-Jan-Feb
>>>> 1980-Jan-Feb
>>>> 1981-Jan-Feb,   so December is skipped completely?  Then the "*D*JF" is
>>>> confusing!?
>>>>
>>>> And what happens to the 'lonely'  2003-Dec? It has no neighbouring
>>>> DJFmonths due to time range selection by years AD.  Is it skipped? Or is
>>>> it: "take this month and define it as a season"?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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