On Saturday, January 24, 2015 at 8:43:43 PM UTC, Dave wrote:
For those wondering what causes a Sudden Stratospheric Warming (Small, Medium or Intermediate, and Large) the possible source & knock on effects to global circulations, you may wish to read the following link.

http://neven1.typepad.com/blog/2013/...s-effects.html

Here is an extract, but please read the whole article that indicates that the source of most Sudden Stratospheric Warmings in the Northern Hemisphere can be traced back to the The Taklamakan Desert, Kunlun Shan & Altun Mountains in Asia.

When a large SSW event occurs such as we had in 2013, warm and descending air over the pole compresses even more, warms even more, disrupts the vortex (as shown above) and turns the AO Index negative. What needs to be clear however is that the AO Index is of course a tropospheric reading, and the SSW begins in the stratosphere and the pressure effects can work their way down into the troposphere and last over a period of many weeks.

Thanks Dave. I'd already read it - a google search takes you there on the first page. Might not go down well with some, mind, because the writer, even though his work is detailed and accurate, is not a meteorologist. He's a television producer.