Re: [ferret_users] monthly averages

[Neil Swart <ncswart@xxxxxxx>]

Okay, I see why you are confused now. Your time axis does indeed have 12 points (as you can see in the #pts column, for the month_reg time row). 

Because the time axis is now modulo, it 'wraps around'. Thus saying 

yes? shade uwnd_climatology[l=13]  

 ...is equivalent to saying... 

yes? shade uwnd_climatology[l=1]

 in this case.

You can explicitly test this by plotting both of them if you like. (or shade l=13 minus l=1, which should give you zero everywhere)

 In the same way, l=14 is equivalent to l=2 or so on. An easy example of why a modulo axis makes sense is the case of longitudes. For a modulo axis of longitude, x=361 is the same as x=1. For a climatology a modulo axis is also sensible. For example, imagine forcing a model

with the climatology, in year two, we want January (l=13) to be the same as in year one (l=1). and so on.

Neil

 

---------------------------------------------------

Neil Swart

Climate Modelling Group

School of Earth and Ocean Sciences

University of Victoria

Victoria, BC

Canada

http://climate.uvic.ca/

On Jul 11, 2011, at 12:26 AM, Izidine Pinto wrote:

Hi,
The result of show grid is:

yes? show grid uwnd_climatology
    GRID (G002)
 name       axis              # pts   start                end
 FNOCX     LONGITUDE          144mr   20E                  17.5E(377.5)
 FNOCY     LATITUDE            73 r   90S                  90N
 normal    Z
 MONTH_REG TIME                12mr   16-JAN 06:00         16-DEC 01:20

My problem is when I do:
yes?  shade uwnd_climatology[l=13]

I was expecting an error instead of a  graph.

Thanks

On 9 July 2011 18:09, <ncswart@xxxxxxx> wrote:

Hi Izidine,
That's strange, when I do it, there result is 12 time steps as expected.
Can you give some more info (like the result of show grid
uwnd_climatology):

SET DATA monthly_navy_winds
yes? USE climatological_axes

 *** NOTE: regarding
/net/mer/home5/nswart/ferret/go/climatological_axes.cdf ...
 *** NOTE: Climatological axes SEASONAL_REG, MONTH_REG, MONTH_IRREG,
MONTH_GREGORIAN, MONTH_NOLEAP, MONTH_360_DAY  defined

yes? CANCEL DATA climatological_axes
yes? LET uwnd_climatology = uwnd[GT=month_reg@MOD]

yes? show grid uwnd_climatology
   GRID (G002)
 name       axis              # pts   start                end
 FNOCX     LONGITUDE          144mr   20E                  17.5E(377.5)
 FNOCY     LATITUDE            73 r   90S                  90N
 normal    Z
 MONTH_REG TIME                12mr   16-JAN 06:00         16-DEC 01:20

> Hi
> Thank you for the replies.
> I was using the modulo regrinding, but was not sure about the results.
> When
> I used the
>
> yes? SET DATA monthly_navy_winds
> yes? USE climatological_axes
> yes? CANCEL DATA climatological_axes
> yes? LET uwnd_climatology = uwnd[GT=month_reg@MOD]
>
> the variable uwnd_climatology has more than 12 time steps (l>12). This was
> confusing me.
>
>
>
> On 8 July 2011 20:25, <ncswart@xxxxxxx> wrote:
>
>> Hi Izidine,
>>
>> It sounds like you want to create a monthly climatology. You can do this
>> by regridding on the time axis using the @mod transformation. The
>> climatological_axes command (below) gives you several calendar options
>> to
>> choose from for your climatology (e.g. month_noleap, month_gregorian,
>> month_reg).
>>
>> E.G.:
>>
>> yes? SET DATA monthly_navy_winds
>> yes? USE climatological_axes
>> yes? CANCEL DATA climatological_axes
>> yes? LET uwnd_climatology = uwnd[GT=month_reg@MOD]
>>
>>
>>
>>  This is explained in detail in the FAQ here:
>>
>>
>> http://ferret.pmel.noaa.gov/Ferret/faq/how-do-i-calculate-climatologies-and-climatological-anomalies/?searchterm=climatology
>>
>> Neil
>>
>>
>> > Dear ferreters
>> >
>> > I have gridded monthly data (CRU) for 18 years and I am having
>> problems
>> to
>> > calculate the averages of all jan, feb....,dec.
>> > Any hint?
>> >
>> > Thanks
>> > --
>> >
>> > Izidine S. Pinto
>> >
>> >  <izidinep@xxxxxxxxxxxxxx>
>> >
>>
>>
>>
>
> Thanks
> --
>
> Izidine S. Pinto
>