[ncl-talk] A request for data file and problem on "bw_bandpass_filter" function

[Dennis Shea]

[1] DATA: The years have changed but the files are available at:


ftp ftp.cgd.ucar.edu
anonymous
your_email
cd pub/shea/MJO
mget *                            .
quit
==========

Note: The file names have changed slightly from those used in the examples.
For example:

olr.day.anomalies.1980-2005.nc  ==> olr.day.anomalies.1980-2011.nc

Perhaps, some minor changes in the graphic resources will be needed.
==========
/ftp/pub/shea/MJO
-rw-r--r-- 1 shea cgdcas 458055500 Jan 11 10:08
MODEL.SST.HAD187001-198110.OI198111-201703.nc
-rw-r--r-- 1 shea cgdcas  30699392 Jan 11 10:18 OLR.12hr_2yrs.wheeler.nc
-rw-r--r-- 1 shea cgdcas 858482293 Jan 11 09:40
olr.day.anomalies.1979-2011.nc.gz
-rw-r--r-- 1 shea cgdcas 304335976 Jan 11 10:10 olr.day.mean.nc
-rw-r--r-- 1 shea cgdcas 615513004 Jan 11 10:24 pregpcp19962008.daily.nc
-rw-r--r-- 1 shea cgdcas 350655700 Jan 11 10:23 TRMM.200006-200109.thin.nc
-rw-r--r-- 1 shea cgdcas 929887809 Jan 11 09:41
uwnd.day.anomalies.1979-2011.200.nc.gz
-rw-r--r-- 1 shea cgdcas 934253770 Jan 11 09:41
uwnd.day.anomalies.1979-2011.850.nc.gz
-rw-r--r-- 1 shea cgdcas 939714739 Jan 11 09:41
vwnd.day.anomalies.1979-2011.200.nc.gz
-rw-r--r-- 1 shea cgdcas 939092767 Jan 11 09:41
vwnd.day.anomalies.1979-2011.850.nc.gz
====
The *gz files will have to be unpacked:
   %>  gzip -d *nc.gz
====

FILTERS:
  *http://www.ncl.ucar.edu/Applications/filter.shtml*
<http://www.ncl.ucar.edu/Applications/filter.shtml>

There are several examples of Butterworth filters.
These included comaprison with Lanczos filters.

I do not know why: ".. exchange values of ca and cb .." does not change the
results.
I don't have time to look right now.
Perhaps the interface between NCL and the ubderlying fortran code does an
exvhange.

re: making the band pass into a low-pass filter. Pergform xome comparisons
withe a Lanczos low pass filter.

Good Luck


On Sat, Jan 12, 2019 at 8:27 PM 15295538792 <15295538792 at 163.com> wrote:

> Dear NCL experts,
>
> I'm writing to ask if you could send me the data file named "
> uwnd.day.850.anomalies.1980-2005.nc" which is used in the script
> "bfband_2.ncl". I can't find it in the online data files. In addition, I'd
> like to consult you about the function "bw_bandpass_filter" which applies a
> Butterworth bandpass filter to time series. The online documentation says
> that the cut-off paramaters ca and cb of this function should meet a
> condition of ca>cb (fcb>fca). However, when I exchanged the values of ca
> and cb, the results remained the same. How could this happen? In fact, I
> want to use this bandpass filter as a low pass filter which need only one
> cut-off frequency. So which parameter should I set to arbitrarily large (ca
> or cb)? Is there anything wrong in my script?  Please help. Thanking in
> anticipation. (PS: Input and output data files as well as ncl script I used
> has been attached to this email.)
>
>
> Sincerely,
> Shouli Xuan
> Email:15295538792 at 163.com
>
> 2019-01-13
> ------------------------------
> 15295538792
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