>Does NCL have a function to run a specific filter on time series data
>(ex: Butterworth)? For example, if I want to keep all low-frequencies
>of 10 years or greater, how could I do that? Previously I have only used
NCL does not have a Butterworth filter. NCL does have a function
That will allow the user to specify low/high/band-pass frequencies
and generate a user specified number of weights.
The more weights ... the better the filter characteristics.
The response functio is returned as an attribute which
you may wish to plot.
The returned weights may then be input to wgt_runave for application.
An alternative is to perform and fft on the data and set the desired frequencies to 0.0
This can create problems [Gibbs phenomena] due to the abrupt cut-off.
See "Digital Filters" by Hamming
--- Butterworth filter routine written in fortran are available and could be included in future NCL releases.
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