Thursday, June 30, 2016

High Winds - Equatorial crossing jet streams and the Quasi-Biennial Oscillation

Curious things are aloft.

Robert Scribbler, in his blog, brought the world's attention to the fact that over the last few days the jet stream was crossing the Equator in three different regions, over the Pacific, Atlantic and Indian Oceans. He described it as 'unprecedented'. It may have happened but before but it is certainly not normal. Jet streams in the northern and southern hemispheres are separated by the equatorial air masses and don't, as a rule, mix.

Paul Beckwith picked up the story and made this informative video. He used the Earth Map that shows, quite wonderfully, all the planet's winds in real time. Click this link and have a play.  Click on 'EARTH' to pull up the menu. To see the jet stream click the 250 hPA on the row marked Height. Today, Thursday 30th June 2016, the jet stream can clearly be seen crossing the Equator if three places (drag across the map to see different views of the world). By the time you are reading this the patterns will, of course, have changed, but here's a screenshot I took yesterday:
The north to south equatorial jet stream crossing can be seen in the central Pacific Ocean.

Another feature that Paul Beckwith talked about was the Quasi-Biennial Oscillation. The what? Here's a useful short article from the European Centre for Medium-Range Weather Forecasts (ECMWF) that explains this phenomenon and it's importance. Briefly, very high up there are winds that blow consistently east to west or west to east, changing direction about every 28 months.  The pattern has been rather regular for the last 40 years during which it has been observed - until this year.  You can see these winds on the Earth map if you adjust the Height to the for right of the scale by clicking on 10 hPa. These are winds high up in the stratosphere but they have their influence on the atmosphere lower down.

The ECMWF article was written more than a year ago and it concludes with this question: " knows what will happen to the QBO in the decades ahead – will it remain largely unchanged, will its period lengthen, or will it change more radically?" A year on and we can already begin to answer that. There is right now an ongoing radical change.

The data for the QBO has been made available by Markus Kunze of
Institute of Meteorology at the Freie Universität Berlin. Take a look at their accompanying figure showing the past 60 year record and then revisit Paul's video, about 12 minutes in. Here's a screen-shot showing the critical change in the QBO pattern this year.

These high level winds, in the stratosphere and upper troposphere, are important for the redistribution of heat energy from the tropics to the poles. And the temperature difference between tropics and poles influences in turn these winds - and ultimately our weather. As the planet warms because of the greenhouse gasses we have emitted, the poles are warming faster than the tropics, the high winds adopt new patterns and we experience weather we are ill-adapted to cope with.

While a local flood or dry spell may be dismissed as just the vagaries of weather these changes we are seeing up aloft are profound, on a planetary scale, and will gradually show their impacts. The thermal gradient, equator to pole is weakening as poles warm more. This weakens the jet (driven by density, pressure differences and the Coriolis force) letting it move around more, further mixing warm and cold air and reducing seasonality. The the warm wet winters we in the British Isles have experienced recently may be an impact of this phenomenon and we can expect similar in future winters. 

We don't know exactly what will happen but the probability distribution of uncertainty is skewed to the bad side. That's why Paul Beckwith and Robert Scribbler are calling this a 'climate emergency'. 

Since Robert wrote his blog on this subject and since Paul Beckwith made his video some aspects of the story have been criticised by other climate scientist and Robert has revised the original piece, adding a note of explanation at the bottom. That's the way science works. We're working at the frontiers of knowledge and all understanding is provisional, but it's important to understand the significance of the phrase I used earlier, the probability distribution of uncertainty is skewed to the bad side. The other important thing is never, ever bother with that dwindling band of climate change deniers who get excited who jump up and down whenever a real climate scientist, quite properly, pushes at the boundaries of knowledge. 

Further reading:

David Edwards
Gabriel Samuels
Caroline Holmes
Josh Marks

And for facebook users, join the discussions on Climate Geek.

Added note Friday morning 1st July.

The story has gained a lot of attention over the last 24 hours and divided the social media into it's two traditional camps. There are a great many in the "Oh dear, this looks bad" camp. There are also a lot of people, though not quite so many as at Camp 1, muttering "Utter nonsense" and linking to the story in the Washington Post and quoting the long-standing climate change deniers Joe Bastardi, Roy Spencer and Anthony Watts.

There is a third camp, the great majority of climate scientists who just get on with science, very properly publish their work in the peer reviewed journals so that almost nobody reads it when it eventually emerges. They don't get publicly shot down in flames when their work is not perfect and they don't create the public reaction that might influence politicians to act to save human civilisation from its own destruction.  Pity about that.

In the fullness of time we will discover whether the changes in the jet stream and the QBO are real and are significant or not but meanwhile these things are being thought about by non-scientists and questions are being asked. That's no bad thing, so we should sing yo for Robert and Paul.


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