It's like this. In the following DiffEq profile, both the periodic impulse (LHS) and the response (RHS) is provided:


If you don't have the impulse and only have the response, one can try to guess what the impulse is. For ENSO, I had to guess what it is because the geniuses at NOAA filtered it out. No matter ... since when I added the filtered impulse back in (found as an analysis artifact in the "ensostuff" directory), it *exactly* matched my guess anyways.

The scientists at NASA JPL warn about doing this kind of thing. [Perigaud et al]( have pointed out how reckless it is to remove what are considered errors (or nuisance parameters) in time-series by assuming that they relate to known tidal or seasonal factors and so can be safely filtered out and ignored.

> " ... real-time Lunisolar tidal noise ... " "... and the tidal noise they are subject to ..."

"One man's noise is another man's signal", which was a [well-known saying from the space program]( LOL