Hi Kevin,
You could well be right. I was looking at the variability the other day, using some from the BAA database and some I had been sent direct.
The spectra are good quality and there is good coverage so it might be possible to characterise the variability. There is some sign of rapid variations, even from day to day though so any period might be rather short. It might be worthwhile doing a run over a full night and looking at the short term variability.
Robin