| Popis: |
A series of daily atmospheric flow over the British Isles (the Lamb weather types, LWT) is used to detect possible relationship in winters of the 20th century with the aa index, a proxy of solar activity, and the quasi-biennial oscillation of stratospheric winds (QBO). Our aim is to address different methodological flawns impairing the conclusions of previous studies. We find statistically significant changes in the occurrence of LWT when grouped according to synoptic situations defined by their succession. Combined high aa index and westerly QBO conditions are found to favour the group of LWT which corresponds to more northern location of storm tracks in the north Atlantic. Easterly QBO conditions are found to favour the group of LWT which corresponds to more southern location of storm tracks, or to a blocked circulation over Europe. This latter group of LWT is also favoured in the month following sudden stratospheric warmings of the polar vortex, and this is consistent with a contribution of the polar vortex to these solar and QBO associations with LWT. For a large part these results compare well with previous studies; they are slightly more statistically significant and are not impaired by the methodological problem of time resolution. However, our results are not consistent throughout the 20th century, and it is not possible to decipher whether this is due to shortcomings of the data or to a non-stationary relationship due to the marked secular trend in the solar activity. |
