On Sunday, December 16, 2012 11:13:37 PM UTC, wrote:


[...] a bit of understanding of what blocking is (not actually

an entirely surface feature at all)

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Exactly. And although the UK, being peripheral, got just a few days of extremely cold weather, such blocking as there has been has produced a lengthy period of below average (and at times far below average) temperatures over Scandinavia and NE Europe, and indeed Germany and Poland (not just cold but snowy).

Woolings et al 2010 links SSWs and tropospheric blocking for one. And researching into the December 2009 cold, Lin Wang and Wen Chen (Geophysical Research Letters) note this: "Another interesting point is that in previous studies, the downward propagation is usually documented for extreme strong stratospheric anomalies such as major warming or strong vortex intensification [e.g., Baldwin and Dunkerton, 2001; Limpasuvan et al., 2005]. However, the
warmings in this case even do not meet the criteria for minor warming defined by World Meteorological Organization. *It suggests that in addition to extreme strong events, some weaker stratospheric anomalies can also propagate downward and influence the troposphere.*"

("Downward Arctic Oscillation signal associated with moderate weak stratospheric polar vortex and the cold December 2009." Lin Wang and Wen Chen, GRL 11 May 2010.)

It is quite in order to suggest *a greater likelihood* of tropospheric blocking even during a weak stratospheric warming event.

Stephen.