[ncl-talk] mjoclivar_5.ncl

[Dennis Shea]

FYI:  You might find the following WWW URL of interest:
         NOAA: Earth System Research Laboratory: Physical Sciences Division
produces

               https://www.esrl.noaa.gov/psd/map/clim/olr.shtml

         These may be adequate for your needs.
==============

"My input daily OLR data file contains data from  1-1-2002 to 14-7-2018"
"I am trying to make time-longitude (Hovmueller)  plot for the period 10
June 2018 to 25 June 2018."
"I am using NCL script  ”mjoclivar_5.ncl” from “MJO clivar."

[1]
If you want the values for 25 June 2018 to be included in the Hovmueller
and your data ends in 14 July 2018, you have a only *19 days after* 25 June
2018. As noted in the


http://www.ncl.ucar.edu/Document/Functions/Diagnostics/band_pass_hovmueller.shtml

documentation, a *Lanczos band-pass* filter is used to filter the values :


http://www.ncl.ucar.edu/Document/Functions/Built-in/filwgts_lanczos.shtml

The MJO-Clivar committee suggested using a Lanczos filter  of 20-100 days
with the half-power points at 20 and 100 days

  spd     = 1               ; sample per day
  bpf     = (/20,100,201/)  ; 20 is the low cutoff and 100 is the high cutoff

bpf(2)=201 weights are used. So, after the Lanczos filter is performed, 100
days at the beginning and 100 days at the end are returned as missing
(_FillValue). You do not have enogh data after 25 June 2018 to uses these
settings.

[2]
What band-pass period do you want: bpf(0) and bpf(1) ? The maximum number
of weights  would be *bpf(2)=37*. Hence, it can not be a sharp band-pass
period.

[3] As a matter of implementation, I suggest passing the filter over the
entire time span, then plot the 10 June 2018 to 25 June 2018 period.

[4] My suggestion is that you play with the lanczos function.

Good luck

On Mon, Jul 23, 2018 at 6:30 AM, Sujata Mandke <amin at tropmet.res.in> wrote:

>
> Dear NCL community,
> Greetings!
>
>  I am using NCL script  ”mjoclivar_5.ncl” from “MJO clivar”
>  application examples on NCL website.
>
> I am trying to make time-longitude (Hovmueller)  plot for the
> period 10 June 2018 to 25 June 2018.
>
> My input daily OLR data file contains data from
> 1-1-2002 to 14-7-2018.
> I have question on time setting (for buffer) in this NCL script
>
>
> (i) In the sample script -”mjoclivar_5.ncl” enough buffer
>       (1 year buffer) is included by setting
>     twStrt  = 19950101 and twLast  = 19981231
>      and Hovmueller start and end time are set as follows
>       thStrt  = 19960101        ; Hov start time
>      thLast  = 19971231        ; Hov last  time
>
> (ii)Last day in the daily OLR data file (which i am using)
>     is 14-7-2018. In order to set enough buffer what should
> be set for  “twLast”?
> As ip data ends on 14-7-2018, buffer time of
> 1 year in case of  “twLast” is not possible.
>
> I am using NCL version 6.4.0 on linux machine.
> Please help in this regard.
> Any suggestion would be of great help.
>  Many thanks in advance.
> With best regards
> Sujata
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