[ncl-talk] bandpass filter olr data expressed as pentads

[Lyndon Mark Olaguera]

Dear all,

I have daily interpolated olr data from NOAA (
https://www.esrl.noaa.gov/psd/data/gridded/). I already expressed these
data by pentads (73 timesteps). I wanted to do a 20-72 days bandpass filter
(butterworth).

I am confused as to the correct cutoff frequencies should I use and the
idea behind this.

The time step of the data sets is 1 (1 to 73). Is this the correct way of
doing this?


*fca = dt/t1 = 1./72.   (low frequency cutoff)
fcb = dt/t2 = 1./20.   (high frequency cutoff)*


Or this:


*fca = dt/t1 = 5./72. (low frequency cutoff)*

*fcb = dt/t2 = 5./20. (high frequency cutoff)*

I hope anyone can help me.


Many thanks in advance,

Lyndon
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