Dear All,
Thanks to Ansley and Jaison for their help
on this thread.
Ansley’s script is for producing the
JJA time series without averaging them (i.e. 3 points in each year), and Jaison’s
script is for the averaged JJA time series (i.e. one point in each year).
Please note a minor problem in Define a calendar axis in Ansley’s script as follows.
! Define a calendar axis containing these months.
def
axis/t0="`uwnd,return=t0`"/units="months" tsummer =
just_summer[l=1:`nja`]
yes? def
axis/t0="`uwnd,return=t0`"/units="months" tsummer =
just_summer[l=1:`nja`]
!-> def axis/t0="14-JAN-1980
14:00:00"/units="months" tsummer = just_summer[l=1:33]
But the t0 should start from “15-JUN-1982”
in this example (I am not sure why t0="`uwnd,return=t0`"
pick up t0="14-JAN-1980 14:00:00").
There is a way to fix this problem using
the following line to redefine the calendar axis, though it is not automatically
choose t0.
def axis/t0="14-DEC-1981
14:00:00"/units="months" tsummer = just_summer[l=1:33]
Any suggestion to the automatically choose
t0 correctly?
Regards,
Yun
From: Ansley Manke
[mailto:Ansley.B.Manke@noaa.gov]
Sent: Thursday, 21 September 2006
2:03 AM
To: Li, Yun (CMIS, Floreat)
Cc: jaison@caos.iisc.ernet.in;
oar.pmel.ferret_users@noaa.gov
Subject: Re: [ferret_users] How
can I produce a time series of JJA averages (or other intervals) from a monthly
time series?
Hi all,
The examples in the Users List archives work fine, but here's another script,
which does not depend on building up a variable with a REPEAT loop and writing
an intermediate file. Just adding to the archives to close this thread...
! Create a time series containing only June,July,
Augst data
! from a monthly data set.
use monthly_navy_winds
! Get a list of the month numbers representing
June ,July, August
! This is correct since the data start in January,
otherwise we
! would need an offset
let nmon = `uwnd,return=Lend`
let tt = t[t=1:`nmon`]
let june = if mod(tt,12) ge 6 then tt
let june_aug = if mod(june,12) le 8 then june
list june_aug
! The number of summer months.
let nja =
`june_aug[t=@ngd]`
let just_summer = compressl(june_aug)
list just_summer[L=1:`nja`]
! Now sample the Lth point of uwnd for the summer
months
let uwnd_jja =
samplel(uwnd,just_summer[l=1:`nja`])
! Define a calendar axis containing these months.
def
axis/t0="`uwnd,return=t0`"/units="months" tsummer =
just_summer[l=1:`nja`]
! Put the sampled summer data on the calendar axis
let uwnd_summer = uwnd_jja[gt=tsummer@asn]
list/x=180/y=0 uwnd_summer
Yun.Li@csiro.au wrote:
Hi
Jaison,
Thanks for your help. The example is very useful. I
have obtained a solution to my problem following the lines of the example.
A minor question is why the extra item
"(X=18.8E:18.8E(378.8), Y=91.3S:91.3N)" appears in the title of new
variable UWND_JJA (see following lines).
yes? use uwnd_jja_mean.nc
yes? show data
currently SET data sets:
1> .\uwnd_jja_mean.nc
(default)
name
title
I
J
K L
UWND_JJA JJA Seasonal Mean
UWND 1:144
1:73 ... 1:11
(X=18.8E:18.8E(378.8), Y=91.3S:91.3N)
This extra item "(X=18.8E:18.8E(378.8),
Y=91.3S:91.3N)" also appeared in my SLP_JJA case. How can I remove it?
Best regards,
Yun
-----Original Message-----
From: Jaison Kurian [mailto:jaison@caos.iisc.ernet.in]
Sent: Wednesday, 20 September 2006 4:16 PM
To: Li, Yun (CMIS, Floreat)
Cc: Ansley.B.Manke@noaa.gov; oar.pmel.ferret_users@noaa.gov
Subject: RE: [ferret_users] How can I produce a time series of JJA averages (or
other intervals) from a monthly time series?
Hi Yun,
Here is an
example using monthly_navy_winds dataset.
Also see these two mails, which deals with somewhat
similar
questions :
http://ferret.pmel.noaa.gov/Ferret/Mail_Archives/fu_2004/msg00575.html
http://www.ferret.noaa.gov/Ferret/Mail_Archives/fu_2005/msg00018.html
Hope this helps...
Jaison
!-------Example : JJA seasonal mean from monthly
data-----------
!
\ cancel mode verify
! Drawbacks : Data should start at January of a year.
Otherwise
!
"yr_months" variable should be modified accordingly.
!
! monthly navy winds : 16-JAN-1982 to 17-DEC-1992
!-----------------------------------------------------------
use monthly_navy_winds
! create a mask such that
only JJA is valid and all other months
! are set
to missing value
let L_indx
= L[GT=uwnd]
let yr_months = L_indx-
12*INT((L_indx-1)/12)
list yr_months
! JJA --> L is 6-8
let mask_other_months = IF
yr_months GT 5 AND yr_months LT 9 THEN 1
list yr_months,
mask_other_months
! Apply the mask
let uwnd_masked = uwnd[d=1] *
mask_other_months
list/x=60/y=10 uwnd_masked
! Club the JJA values together
let uwnd_compr =
COMPRESSL(uwnd_masked)
list/x=60/y=10 uwnd_compr
! 1982-1992 --> 11 years
--> 11*3=33 data points
! we need to average this
data points in pairs of 3 to find the
! seasonal mean. Easy
way is to use two abstract axes, one
! with 33 points
(ranging from 1-33) and another one with
! 11 points (ranging
from 2-32) and regrid using @AVE.
define axis/t=1:33:1 t33
let uwnd_jja_all =
uwnd_compr[gt=t33@ASN]
list/x=60/y=10 uwnd_jja_all
define axis/t=2:32:3
t11 ! for the exact seasonal mean
let uwnd_jja_av =
uwnd_jja_all[gt=t11@AVE]
! now assign a proper yearly
time axis defined over 1982-1992
! here we dont need any
interpolation but the grid change
! ..so use @ASN
regridding
define
axis/t=1982:1992:1/units=years tyear
let uwnd_jja =
uwnd_jja_av[gt=tyear@ASN]
list/x=60/y=10 uwnd_jja !
6.36 7.99 7.12 8.51 9.46 9.32
set var/title="JJA
Seasonal Mean UWND"/units="m/s" uwnd_jja
! save to a NetCDF file for
future use
! sp rm -f uwnd_jja_mean.nc
!
save/file=uwnd_jja_mean.nc/APPEND uwnd_jja
!-------------end of
example-------------------------------------
On Wed, 20 Sep 2006 Yun.Li@csiro.au
wrote:
> Hi Ansley,
>
>
>
> I am trying to do "Leaving only JJA SLP
data" from a monthly NCEP SLP
> data "slp.mon.mean.nc". I have looked at
> http://ferret.pmel.noaa.gov/Ferret/FAQ/analysis/seasonal_masking.html.
> But I could not get a solution because of my poor
ferret skills. Could
> you please give me a help here?
>
>
>
> Thanks,
>
>
>
>
>
> Yun
>
>
>
>
>
>
>
> _____
>
> From: Ansley Manke [mailto:Ansley.B.Manke@noaa.gov]
> Sent: Wednesday, 20 September 2006 3:02 AM
> To: Li, Yun (CMIS, Floreat)
> Cc: oar.pmel.ferret_users@noaa.gov
> Subject: Re: [ferret_users] How can I produce a
time series of JJA
> averages (or other intervals) from a monthly time
series?
>
>
>
> Hi Yun,
> Here are a couple of FAQ's for you to look at -
if one of these is the
> kind of thing you want to do. If you need help
applying the ideas,
> please write back to the users list.
>
> This FAQ makes a "seasonal mask" to
pick out data from part of each
> year. It does the problem with units of
time in days; but if you're
> starting with monthly data you could do a similar
thing with months,
> with JJA being months 6,7,8. You could
combine this with the COMPRESS
> functions to remove the missing data and leave
only the JJA data.
> http://ferret.pmel.noaa.gov/Ferret/FAQ/analysis/seasonal_masking.html
>
> Or, did you have in mind a climatology, averaging
all of the JJA data
> for all years, and returning just one
point? In that case, see
> "climatology, creating" in the Users
Guide, and this FAQ for more
> examples
> http://ferret.pmel.noaa.gov/Ferret/FAQ/analysis/climatologies.html
>
> Ansley
>
> Yun.Li@csiro.au
wrote:
>
> Dear Ferreters,
>
>
>
> I am trying to produce a seasonal time series
(such as JJA time series)
> from a monthly time series.
>
>
>
> There is an example from the Ferret FAQ on
"How can I produce a time
> series of annual averages (or other intervals)
from a monthly time
> series?"
>
>
>
> http://ferret.wrc.noaa.gov/Ferret/FAQ/analysis/annual_from_monthly.html
>
>
>
> I would be most grateful if you can let me know
how to produce a
> seasonal averaged time series (such as
June-July-August average time
> series) from a monthly time series by modifying
the code used to produce
> annual time series in the above web page, that is,
>
>
>
> yes? SET DATA
monthly_navy_winds
>
> yes? DEFINE
AXIS/EDGES/T0=1-jan-1900/UNITS=days tann82_92 =
> DAYS1900(X[i=1982:1993:1],1,1)
>
> yes?
PLOT/X=180/Y=0 uwnd
>
> yes?
PLOT/X=180/Y=0/over uwnd[gt=tann82_92@ave] ! the above
> plot
>
>
>
>
>
>
>
> Thanks,
>
>
>
> Yun Li
>
> CSIRO, Australia
>
>
>
>
>
>
--
~> ~> ~> ~> ~> ~> ~> ~> ~> ~> ~>
Ansley Manke, NOAA/PMEL ansley.b.manke@noaa.gov
7600 Sand Point Way NE, Seattle WA
Phone 206-526-6246, FAX 206-526-6744