On Tuesday, August 11, 2015 at 11:46:00 AM UTC+1, Graham P Davis wrote:
On Tue, 11 Aug 2015 02:35:01 -0700 (PDT)
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.

There have been several suggestions that the differential warming of
the Arctic and the Tropics will weaken the Jet Stream due to a
reduction in thermal contrast. This weakening of the Jet would then
lead to large meanders in the Stream and long spells of severe
weather, either cold or hot. This idea seems to have been accepted
though it bothered me a bit when I actually started to think about it.

I recall being taught (which I accept does not necessarily mean I was
taught) that slow-moving or stationary upper waves are associated with
a strong Jet; small, transitory waves are associated with weak Jet
Streams.

Then I found an article by CEP Brooks in an online 1950 issue of
Weather which said more or less the same thing. It also said that
they'd expected a weakening of upper winds due to the differential
warming that had occurred before WWII and had been surprised to find
that they'd strengthened instead.

At lower levels in the atmosphere, the number of Atlantic gales affecting the UK has dropped significantly this century compared to much of the last century. THe winter of 2013/14 was exceptional, but even then not for the number of gales, more for the quite exceptional sea conditions in the SW largely, due to the unusual track of the depressions. (We got the seas normally reserved for western Ireland.)

At my site in Penzance there were an average of 14 gales per annum 19993-2002 - broadly in line with Lambs observations. The following 10 years saw an exceptionally low average of 5.5 per annum


One thing that has an effect on the atmospheric circulation, as I've
said before, is the pattern of SST anomalies, particularly in the Grand
Banks region.

--
Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer]

I think that it's an easy option for the media to go back 1 step and blame everything on the Jet Stream. I agree that the SST anomalies have an influence, but this years N Atlantic SST anomalies can be blamed on the winds in that area over the late winter period. But what caused that anomalous set up? It's all about how far back you want to go.

Interesting area though

Graham
Penzance