Jet Stream and Climate Change

This forum is for comments about the weather spanning several days, developing phenomena eg drought, comparisons with previous years, local climatic features eg Cheshire Gap showers, and anything that does not fit any of the other forums.

Jet Stream and Climate Change

Postby greg_gruner » 2014 Jan 06, 10:47

I have been puzzling over how the UK weather has been affected by climate change. The media, of course, are keen to blame any storm or unusual spell of weather on climate change. In many cases the extreme weather has happened before.
The only provable fact is that mean temperatures in the UK have risen over the last 30 years.
How the warming trend affects the jet stream is a source of speculation. On the one hand, greater warmth and more evaporation means more energy in the atmosphere, and therefore a greater potential for a strong jet and deeper depressions. On the other hand, the arctic is warming more quickly than the tropics, so the temperature gradient is decreasing. As the jet is powered by temperature contrast, it should weaken. Then the big unknown is how the reduction in summer sea ice affects the position and intensity of the jet stream...
When I was in my youth in the 70s, it seemed that any depression deeper than 950mb was extremely rare and noteworthy. In the last 3 weeks we must have had 4 or 5 lows deeper than that. Also, apparently Scotland has had its wettest month ever.
I am no scientist, and I may be wrong, but it seems to me that the jet stream can get stuck in the same pattern for longer periods. Over the last 3 weeks, only one storm (Dec 23/24) was exceptional in terms of wind and rain in SE England; most of the problems seem to be caused by the cumulative effect of depression after depression following the same track, steered by a strong jet in the same position.
Another interesting point is the drought and floods of 2012. Neither the drought nor floods were unprecedented; but the sudden switch from drought to flood in the same year was indeed unprecedented, as described in an article in "Weather". Again, the jet stream was in one configuration for a long time, and then in a new configuration for an equally long time.
In November/December last year, the jet stream was in a meridional configuration, with the trough bringing cold weather as far south as Egypt (snow reported in Cairo). Now we have a strong zonal jet that has persisted - though there are signs that it is about to change.
I am reluctant to attribute anything to global warming as our weather is notoriously variable, but it's an interesting subject and I'm sure that scientists will be looking for an any possible links to climate change....
Greg Gruner
Farnborough, Hampshire
Posts: 224
Joined: 2012 Feb 04, 17:28

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