[ncl-talk] power spectrum of filtered dataset

[Edwin Marco]

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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