[Thread Prev][Thread Next][Index]
Re: annual average from monthly mean for precise 365-day years.
On Sat, 17 Mar 2001, Steve Hankin wrote:
> Hi Wei,
>
> I'm not sure what problem you are describing. Here is an example of averaging 24
> months of data into 2 annual averages:
>
> /export/home/ja3/hankin/tmp> ferret
> NOAA/PMEL TMAP
> Program FERRET
> Version 5.22 - 07/27/00
> 17-Mar-01 14:03
>
> yes? define axis/t=1-jan-1980:1-jan-1982/npoints=24/edges t24months
> yes? let my_var = T[gt=t24months]
> yes? define axis/t=1-jan-1980:1-jan-1982/npoints=2/edges t2years
> yes? list my_var[gt=t2years@ave]
> T[GT=T24MONTHS]
> regrid: 8772 hour on T@AVE
> JUL-1980 / 1: 696546.
> JUL-1981 / 2: 705318.
>
> Will this approach work for you?
Hi Steve,
Imagine that I have 101 years' monthly means. So the total data points
in month is 101*12 = 1212. If I use:
define axis/edges/t=1:1212:1/npoints=1212/unit=months tax
LET newtaux = stresx[GT=tax@asn]
define axis/edges/t=1:1212:12/UNITS=months tann
let/title="X-component of surface stress (N/m2)" tauxx=newtaux[gt=tann@ave]
list/x=180/y=0 tauxx
Here is part of the output:
7 / 1: 0.02913
19 / 2: 0.02431
31 / 3: 0.03450
43 / 4: 0.02694
55 / 5: 0.02979
67 / 6: 0.02674
79 / 7: 0.02317
91 / 8: 0.02608
... skipped
1171 / 98: 0.02994
1183 / 99: 0.02505
1195 / 100: 0.02370
1207 / 101: ....
Notice that the annual mean variable tauxx is defined at month 7, 19
etc. of the original data and the last data point at month 1207 is a bad
value (I thought it has sth to do with the fact that the total data point
is an even number "1212", not an odd number. Now I am not sure about it).
But, I have 101 years' data; and I should be able to get 101 non-bad
values.
Next, I used "/npoints=101" according to your suggestion:
define axis/edges/t=1:1212:1/npoints=1212/unit=months tax
LET newtaux = stresx[GT=tax@asn]
define axis/edges/t=1:1212:12/npoints=101/UNITS=months tann
let/title="X-component of surface stress (N/m2)" tauxx=newtaux[gt=tann@ave]
list/x=180/y=0 tauxx
And here is part of the output from the above script:
7 / 1: 0.02914
19 / 2: 0.02431
31 / 3: 0.03448
43 / 4: 0.02703
55 / 5: 0.02976
66.9 / 6: 0.02675
78.9 / 7: 0.02321
90.9 / 8: 0.02598
102.9 / 9: 0.03899
114.9 / 10: 0.02785
... skipped
1134.1 / 95: 0.02630
1146.1 / 96: 0.02690
1158 / 97: 0.03507
1170 / 98: 0.03012
1182 / 99: 0.02504
1194 / 100: 0.02452
1206 / 101: 0.02895
Notice that now I do get 101 good values. However, their time
axis is different from the previous method (and therefore the
value of the variable itself). I think I trust the previous
method more.
Any solutions to the above dilemma? Thanks.
Wei
[Thread Prev][Thread Next][Index]
Dept of Commerce /
NOAA /
OAR /
PMEL /
TMAP
Contact Us | Privacy Policy | Disclaimer | Accessibility Statement