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Re: [ExternalEmail] [ferret_users] RE: How to calculate seasonal rainfall totals from daily gridded rainfall?


You will need to create a time grid which encompasses the seasons. The best way would be to use a variation of the usual method to create a monthly axis using the DAYS1900 function and DEFINE AXIS/EDGES


A slight modification to the definition of the variable indices in the example makes the step 3 months rather than 1 month.

yes? LET start_year = 1950
yes? LET nyears = 20
yes? LET indices = L[L=1:`nyears*12`:3]*3
yes? LET month = MOD(indices-1,12)+1
yes? LET year = start_year + INT((indices-1)/12)
yes? DEFINE AXIS/UNITS=days/T0=1-jan-1900/EDGES truemonth = DAYS1900(year,month,1)

yes? show axis truemonth
 name       axis              # pts   start                end
 TRUEMONTH TIME                79 i   16-APR-1950 00:00    16-OCT-1969 12:00
T0 = 1-JAN-1900

We see that the start of the seasons (DMJS) are correct.

yes? SHOW AXIS/T=1-jan-1958:1-jan-1959 truemonth
 name       axis              # pts   start                end
 TRUEMONTH TIME                79 i   16-APR-1950 00:00 16-OCT-1969 12:00
T0 = 1-JAN-1900
   Axis span (to cell edges) = 7215

       L     T                   TBOX      TBOXLO TSTEP (DAYS)
      32>  15-JAN-1958 00:00:00  90         01-DEC-1957 00:00:00    21198
      33>  16-APR-1958 00:00:00  92         01-MAR-1958 00:00:00    21289
      34>  17-JUL-1958 00:00:00  92         01-JUN-1958 00:00:00    21381
      35>  16-OCT-1958 12:00:00  91         01-SEP-1958 00:00:00    21472.5
      36>  15-JAN-1959 00:00:00  90         01-DEC-1958 00:00:00    21563

The appropriate averages for the seasons  can be easily done

let pr_seas=pr[gt=truemonth@ave]


On 29/07/14 15:03, Yun.Li@xxxxxxxx wrote:
Dear Colleague,

I am trying to calculate seasonal (DJF, MAM, JJA and SON) rainfall totals from daily gridded rainfall.  As an example, the information of gridded daily rainfall data is as follows.

yes? show data
      currently SET data sets:
     1> ./pr_AWAP_day_native_2010.nc  (default)
  name     title                             I         J         K         L
  PR       Precipitation                    1:886     1:691     ...       1:365

Could you please let me know how to get these seasonal rainfall totals?

Many thanks,



Dr Yun Li
Principal Research Scientist
Data Analytics Program
CSIRO Digital Productivity and Services Flagship
Leeuwin Centre, 65 Brockway Road
Floreat, WA 6014, Australia
Phone: +61-8-9333-6388 Fax: +61-8-9333-6121
E-mail: Yun.Li@xxxxxxxx
Web: http://www.csiro.au/people/Yun.Li.html

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