On Wed, 12 Aug 2015 13:10:22 -0700 (PDT)
Stephen Davenport wrote:

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".

=============

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".


As I've already pointed out, this theory dates back a long way, perhaps
even to before WWII. It was also found not to work. Not should
it. For one thing, you get larger amplitude waves and more blocking with
stronger jet-stream winds, not weaker ones.

--
Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer]
http://www.scarlet-jade.com/
I wear the cheese. It does not wear me.
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