# Re: JFM averages.

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Thanks a lot Steve, your solution worked very well!

Marcelo

On Mon, 20 Mar 2000, Steve Hankin wrote:

> Hi Marcelo,
>
> I think that the axis you defined with
>     define axis/edges/t="16-jan-1950:12":"16-dec-1994:12"/npoints=`45*4` tsea
> has a problem. SHOW AXIS indicates a "drift" to your seasonal axis. Here we
> examine every 5th year:
>
>      yes? show axis/l=1:180:`4*5` tsea
>      name       axis              # pts   start                end
>      TSEA      TIME               180 r   03-MAR-1950 01:40
>      31-OCT-1994 22:20
>      T0 = 15-JAN-1901
>
>                 L     T                 BOX_SIZE       TIME_STEP (HOURS)
>                 1>  03-MAR-1950 01:40:00  2187.333       430657.7
>                21>  27-FEB-1955 20:20:00  2187.333       474404.3
>                41>  24-FEB-1960 15:00:00  2187.333       518151
>                61>  20-FEB-1965 09:40:00  2187.333       561897.7
>                81>  17-FEB-1970 04:20:00  2187.333       605644.3
>               101>  13-FEB-1975 23:00:00  2187.333       649391
>               121>  10-FEB-1980 17:40:00  2187.333       693137.7
>               141>  06-FEB-1985 12:20:00  2187.333       736884.3
>               161>  03-FEB-1990 07:00:00  2187.333       780631
>
> Here's an off-the-cuff version of the axis -- using 15-FEB as a crude estimate
> for the middle of the J-F_M season. Note there is no drift:
>
>      yes? define axis/t="15-feb-1950":"15-feb-1995"/npoints=`45*4+1` tsea
>
>      yes? show axis/l=1:180:`4*5` tsea
>       name       axis              # pts   start                end
>       TSEA      TIME               181 r   15-FEB-1950 00:00
>      15-FEB-1995 00:00
>      T0 = 15-JAN-1901
>
>                 L     T                 BOX_SIZE       TIME_STEP (HOURS)
>                 1>  15-FEB-1950 00:00:00  2191.467       430272
>                21>  15-FEB-1955 05:20:00  2191.467       474101.3
>                41>  15-FEB-1960 10:40:00  2191.467       517930.7
>                61>  14-FEB-1965 16:00:00  2191.467       561760
>                81>  14-FEB-1970 21:20:00  2191.467       605589.3
>               101>  15-FEB-1975 02:40:00  2191.467       649418.7
>               121>  15-FEB-1980 08:00:00  2191.467       693248
>               141>  14-FEB-1985 13:20:00  2191.467       737077.3
>               161>  14-FEB-1990 18:40:00  2191.467       780906.7
>
> You can use the DAYS1900 function as shown in
>
> http://ferret.wrc.noaa.gov/Ferret/Documentation/Users_Guide/v50/partII.html#V5.0_DEFINE AXIS\$/EDGES
>
> to get really detailed control over the axis definition.
>
>     - steve
>
> ======================================
>
> Marcelo Barreiro wrote:
>
> > Hi ferreters,
> >
> > I am computing JFM averages from monthly data of a time series which spans
> > 45 years (540 months).
> > I did it in two different ways:
> >
> > (1st)
> > define axis/edges/t="16-jan-1950:12":"16-dec-1994:12"/npoints=`45*4` tsea
> > let my_var_seas = my_var[gt=tsea@ave]
> > let/quiet my_var_JFM = my_var_seas[l=1:180:4]
>
> >
> > (2nd)
> > let/quiet my_var_J = my_var[l=1:540:12]
> > let/quiet my_var_F = my_var[l=2:540:12]
> > let/quiet my_var_M = my_var[l=3:540:12]
> > let/quiet my_var_JFM= (my_var_J + my_var_F + my_var_M)/3
> >
> > Results of my_var_JFM are similar but not equal and in cases the
> > correlation between the results of different methods is as low as 0.90.
> >
> > Does anyone know which way is the best?
> > Thanks!
> >
> > Marcelo
> >
> > ================================================
> > Marcelo Barreiro
> > Dept. of Oceanography, Physical Section
> > College of Geosciences and Maritime Studies
> > Texas A&M University
> > College Station, TX 77843-3146
> > Phone: (979) 845-8216
> > Email: marcelo@ocean.tamu.edu
> > URL: http://www-ocean.tamu.edu/~marcelo/
> > ================================================
>
> --
> 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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