Thx a lot for your kind answer!

I think with the ongoing change caused by warming we should treat every trend that arises the last ~20 years as a long-term trend. Just as a precaution, as it will be the case more likely than not, as climate warming is now overruling natural variability in an ever-increasing number of subsystems. Anyhow your field of study is highly interesting with the stratospheric circulation now also changing big time the last two decades e.g. recent changes in the QBO and the intensifying BDC - at least recent studies provided additional proof...