[ncl-talk] ncl-talk Digest, Vol 202, Issue 19

[Michael Toy - NOAA Affiliate]

Joe,

Sorry for the 101st e-mail of the day.  Would you have time after our EPAD coffee ends at ~2pm for a short chat?

— Mike




> On Sep 16, 2020, at 12:00 PM, ncl-talk-request at mailman.ucar.edu wrote:
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> Today's Topics:
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>   1. Re: power spectrum of filtered dataset (Dennis Shea)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 15 Sep 2020 20:13:11 -0600
> From: Dennis Shea <shea at ucar.edu>
> To: Edwin Marco <eigenge at gmail.com>
> Cc: ncl-talk <ncl-talk at mailman.ucar.edu>
> Subject: Re: [ncl-talk] power spectrum of filtered dataset
> Message-ID:
> 	<CAOF1d_6k4VNmieYn8Y3keCMO_tUm_5+i_evq8FnNngPyRgPOqQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> 
> ncl-talk has no idea what you have done. The series has * *pentad** [5-day]
> temporal sampling. The plots have the frequency axis labeled
> 'cycles/month'.
> 
> ncl 0> f = addfile("rainfall_pc_00000.nc","r")
> ncl 1> ymd = cd_calendar(f->time,-2)
> ncl 2> print(ymd)
> 
> (0)     19810303
> (1)     19810308
> (2)     19810313
> (3)     19810318
> (4)     19810323
> (5)     19810328
> (6)     19810402
> (7)     19810407
> (8)     19810412
> (9)     19810417
> (10)    19810422
> (11)    19810427
> (12)    19810502
> (13)    19810507
> .
> .
> It is *your responsibility *[**not ncl-talk's**]  to design a filter that
> addresses the pentad time sampling to create a (say) 20-60 day filter.
> ncl-talk's experience is that dealing with this type of issue leads to many
> emails. We can no longer do that.
> 
> Good Luck
> 
> On Tue, Sep 15, 2020 at 6:43 AM Edwin Marco via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
> 
>> Dear ncl users,
>> 
>> I am trying to prove whether I have correctly filtered my dataset by
>> plotting the power spectrum of the filtered data set.
>> 
>> My approach:
>> firstly I have plotted the spectrum of the unfiltered data set (
>> rainfall_pc_00000.nc) using attached script
>> (plot_spectrum_unfiltered_data.ncl).
>> 
>> Secondly, I decided to filter my dataset at 20-60 days.
>> 
>> Thirdly; Using the Butterworth filtering technique, filtered the dataset (
>> rainfall_pc_00000.nc) at 20-60 days, and plot the spectrum of the
>> filtered dataset.
>> 
>> Problem: After plotting the spectrum of the filtered dataset, I intended
>> to see all peaks out of 60-20days bandpass to disappear however it came the
>> opposite way.
>> 
>> I have attached scripts, plots, and datasets for easy follow-up.
>> 
>> Please help me know if my approach to proof whether I have correctly
>> filtered the datasets is correctly and then where I am getting wrong and
>> plot opposite results, contrary to the theory.
>> 
>> Thanks
>> 
>> Edwin
>> 
>> 
>> 
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> End of ncl-talk Digest, Vol 202, Issue 19
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