Lanczos-Filter

Low pass filtering a time-series by applying a weighted running mean over the time dimension.
Details of Lanczos Filter could be found here

Core Code:

lanczosbp.py:
Use two low pass lanczos filters to get 3 to 10 days bandpass 850 hPa vorticity, the variance of which could be thought of the pre-TC synoptic disturbance, i.e. TC seed index.

Data:

I used EAR5 reanalysis hourly 850hPa vorticity.
Results are presented for Jul–Oct although data in June and November are also needed because the time filter requires extra data at the beginning and end of each year’s time series.