Wrap the forward-backward Butterworth filter from the scipy package so that it can be easily used by xarray.DataArray.
import xarray as xr
import numpy as np
import matplotlib.pyplot as plt
import xfilter
np.random.seed(0)
da = xr.DataArray(np.random.randn(100), dims='day', name='Ta', attrs={'units': 'degC'})
fig, axes = plt.subplots(2, 1)
ax = axes[0]
da.plot(label='raw', color='k', ax=ax)
da.filter.bandpass([1/10, 1/5], dim='day').plot(ax=ax)
ax.legend(loc='lower right')
ax = axes[1]
xfilter.bandpass_response([1/10, 1/5]).plot(label='10-to-5-day bandpass', ax=ax)
ax.axvspan(1/10, 1/5, alpha=0.3, color='C0')
ax.legend()
