Noctilucent clouds caused by meteors/comets?

Noctilucent clouds appear out of season and far to the south – cometary dust from the Russian meteor blast?

From 19-21 February 2013, noctilucent clouds were observed in the UK, Denmark, Norway and the Netherlands. Since these clouds are usually only seen in summer, it is suspected that they may be the result of comet dust deposited in the upper atmosphere by the Chelyabinsk/Chebarkul meteor or comet fragment explosion over Southern Russia on 15 February.

So, if these are caused by the recent Russian meteor/comet explosion, what’s been causing all the others… it’s been noted that such clouds are being seen more often and further south than ever before for the past several years.