On Tuesday, August 11, 2015 at 5:35:02 AM UTC-4, xmetman wrote:
After listening to Carole Kirkwood talking about what a wet and cold summer its been over Scotland this year on this mornings Breakfast Weather, it does seem to me that as far as the media are concerned most of today's weather woes in this country today, including this one can be blamed on the jet stream, or lack of jet stream, or the position of the jet stream. So if the answer to most of the world's climate problems is the ubiquitous "jet stream", what about its part in global warming? I haven't seen any research that looks into the role jet streams play in global warming, but I'm sure it won't be long before there is a slew of scientific papers about it.

If this is true, just what controls the position and strength of the jet stream, and the answer to that must be the general atmospheric circulation, but of course that's not half as catchy, dynamic or sexy as the phrase "jet stream". I just can't imagine John Hammond for instance spending an hour in a BBC Horizon program to explain the intricacies of the Hadley cell and the northeast trade winds, when he can talk over a 3D animation and fly through of a North Atlantic super jet blowing at 250 knots.

I'm sure that the phrase "jet stream" will be cropping in many conversations about the weather in the coming years, you can easily picture one old dear saying to another in a bus queue "I know Enid the weather has been simply terrible, and you know it's all down to the orientation of the Jet stream over Iceland you know".

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It's not so much what affect a fundamentally changed jet stream would have on global warming, although feedback mechanisms are no doubt set in train. The effect of a weaker and meridionally exaggerated jet stream would be in the distribution of heat and cold rather than net warming or cooling. Contrarily, it's the warming that might impact the jet stream. Arctic warming being more rapid than elsewhere, the argument goes that the thermal gradient north to south would lessen and thus reduce atmospheric zonality.

As others have pointed out, it is posited that this could result in greater-amplitude Rossby waves and a greater frequency of blocked patterns - thus also of extended periods of weather types, or more severe local or regional conditions. Jennifer Francis at Rutgers has done a lot of research in this area and there was a 2013 workshop that explored this: The Committee on Linkages Between Arctic Sea Ice Loss and Mid-Latitude Weather.

I'm not yet thoroughly convinced, and there are many inter-annual and inter- and intra-seasonal forcings to consider - no doubt including some "unknown unknowns".

Stephen.