Long-term variation of stratospheric temperature at the North Pole

The (30 mb) stratospheric temperatures at the North Pole during the winter months (November–February) showed large QBO (Quasibiennial Oscillations) but of an intermittent nature, different for different months and not matching in phase with the QBO of the tropical zonal wind. When the QBO was minimized by moving averages over two successive (yearly winter) values and then further over three successive values, the resultant series showed clear solar cycle variations with lags or leads of ~ (0–2) yr for temperature maxima with respect to sunspot maxima. However, in solar cycle 21 from 1978 onwards, temperatures seem to be more depressed, indicating enhanced stratospheric cooling in recent years, probably due to an increase of greenhouse gases. No relationship with El Nino events is indicated.