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Re: How to get multi-year seasonal or annual mean from a multi-yearmonthly mean time series

Hi Yang,

Sorry, it looks like I misunderstood your question.

The very simplest approach is to refer to TEMP[L=1:480:3@AVE]. This will average the months in
groups of 3. You can use the SHADE (or LIST, or SHOW GRID) command to see where the boundaries are
between the 3-month grid cells. You can shift the start point to have some control over this as in

For more precise control over where the seasons start and end, define a new seasonal calendar axis
with something like

    yes? define axis/edges/t=1-jan-1950:1-jan-1990/npoints=`40*4` tseasonal

(/EDGES available in Ferret V5). Then

    yes? let TEMP_SEASONAL = TEMP[GT=tseasonal@ave]

to obtain the result you are after.

    - steve


Yang Haijun wrote:

> Hi all,
> I am working on a data with 40 years x 12 months. I want to get a new data with 40 year x 4
> seasons from the old one. How should I do?
> The original data is like below:
>  name     title                             I         J         K         L
>  TEMP     TEMPERATURE ANOMALY FROM XBT     1:73      1:61      1:11      1:480
> Mr.Hankin suggested me see the gt=@MOD syntax at
> http://ferret.wrc.noaa.gov/Ferret/Documentation/Users_Guide/v50/chapter4.html#modulo$regridding
> and define a seasonal modulo axis with DEFINE GRID.
> http://ferret.wrc.noaa.gov/Ferret/Documentation/Users_Guide/v50/partII.html#V5.0_DEFINE
> But I still have no idea to do it. Does anyone give me more detail suggestions?
> And does anyone give a explanation to the following fifth line?
> yes? define axis/t=1-jan-0001:1-jan-0002:1/unit=days/t0=1-jan-0000 tencoding
> yes? let tstep = t[gt=tencoding]
> yes? let start_date = tstep[t=15-mar-0001]
> yes? let end_date = tstep[t=27-may-0001]
> yes? define axis/from_data/T/units=days/name=tax/t0=1-jan-0000/edges/modulo
>      {`start_date,p=7`,`end_date,p=7`,`start_date+365.2425,p=7`}
> Thank you very much.
> Haijun Yang

Steve Hankin
NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-0070
ph. (206) 526-6080 -- FAX (206) 526-6744

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