Weather Patterns Permanently Change Jet Stream Split

This is an excerpt from Crystal's blog at Global Disaster Watch.

I have been reading her work for years now, even before she came to blogger. In fact I have passed on interesting weather tidbits from Canada to her. She always links and quotes her posts to reputable news sources and never sensationalizes, judges or predicts. Weather is only a small portion of the news item topics she collects and posts daily. Fascinating reading to be sure.

Thursday, April 22, 2010

UNITED KINGDOM - COLDEST WEATHER IN 30 YEARS marks the start of a series of extreme winters. Scientists are now warning that Britain can expect to endure a series of extreme winters - the like of which have NOT BEEN SEEN FOR MORE THAN 300 YEARS. Researchers have found that low solar activity - marked by a decrease in the sun's magnetic field - influences the weather conditions across northern Europe. The last time the sun showed similar behaviour, between 1650 and 1700, temperatures dropped so low that Londoners were able to skate and hold fairs on the iced-over River Thames. The latest winter marks the start of a Maunder minimum - when solar activity falls for a prolonged time. The sun's magnetic field is thought to influence the jet stream - a fast-moving, high altitude current of air which moves eastwards at 35,000ft over the Atlantic. During the famously cold winters of the late 1600s the mild westerly winds were blocked and replaced by much colder blasts from the north-east - bringing Arctic conditions with them.

Thursday, August 12, 2010

Frozen jet stream links Pakistan floods, Russian fires - Raging wildfires in western Russia have reportedly doubled average daily death rates in Moscow. Diluvial rains over northern Pakistan are surging south – the UN reports that 6 million have been affected by the resulting floods. It now seems that these two apparently disconnected events have a common cause. They are linked to the heatwave that killed more than 60 in Japan, and the end of the warm spell in western Europe. The UNUSUAL WEATHER in the US and Canada last month also has a similar cause.
According to meteorologists monitoring the atmosphere above the northern hemisphere, UNUSUAL HOLDING PATTERNS IN THE JET STREAM are to blame. As a result, weather systems sat still. Temperatures rocketed and rainfall reached extremes. Renowned for its influence on European and Asian weather, the jet stream flows between 7 and 12 kilometres above ground. In its basic form it is a current of fast-moving air that bobs north and south as it rushes around the globe from west to east. Its wave-like shape is caused by Rossby waves – powerful spinning wind currents that push the jet stream alternately north and south like a giant game of pinball.
In recent weeks, meteorologists have noticed a change in the jet stream's normal pattern. It's waves normally shift east, dragging weather systems along with it. But in mid-July they ground to a halt over the UK. There was a similar pattern over the US in late June. Stationary patterns in the jet stream are called "blocking events". They are the consequence of strong Rossby waves, which push westward against the flow of the jet stream. They are normally overpowered by the jet stream's eastward flow, but they can match it if they get strong enough. When this happens, the jet stream's meanders hold steady, creating the perfect conditions for extreme weather.
A static jet stream freezes in place the weather systems that sit inside the peaks and troughs of its meanders. Warm air to the south of the jet stream gets sucked north into the "peaks". The "troughs" on the other hand, draw in cold, low-pressure air from the north. Normally, these systems are constantly on the move – but not during a blocking event. And so it was that Pakistan fell victim to torrents of rain. The blocking event coincided with the summer monsoon, bringing down additional rain on the mountains to the north of the country. It was the final straw for the Indus's congested river bed.
Similarly, as the static jet stream snaked north over Russia, it pulled in a constant stream of hot air from Africa. The resulting heatwave is responsible for extensive drought and nearly 800 wildfires at the latest count. The same effect is probably responsible for the heatwave in Japan, which killed over 60 people in late July. At the same time, the blocking event put an end to unusually warm weather in western Europe.
Blocking events are not the preserve of Europe and Asia. Back in June, a similar pattern developed over the US, allowing a high-pressure system to sit over the eastern seaboard and push up the mercury. Meanwhile, the Midwest was bombarded by air from the north, with chilly effects. Instead of moving on in a matter of days, "the pattern persisted for more than a week".
So what is the root cause of all of this? Meteorologists are unsure. Climate change models predict that rising greenhouse gas concentrations in the atmosphere will drive up the number of extreme heat events. Whether this is because greenhouse gas concentrations are linked to blocking events or because of some other mechanism entirely is impossible to say. The resolution in climate models is too low to reproduce atmospheric patterns like blocking events. So they cannot say anything about whether or not their frequency will change.
There is some tentative evidence that the sun may be involved. Earlier this year an astrophysicist showed that winter blocking events were more likely to happen over Europe when solar activity is low – triggering freezing winters. Now he says he has evidence from 350 years of historical records to show that low solar activity is also associated with summer blocking events. "There's enough evidence to suspect that the jet stream behaviour is being modulated by the sun." Blocking events have been UNUSUALLY COMMON over the last three years, for instance, causing severe floods in the UK and heatwaves in eastern Europe in 2007. Solar activity has been low throughout.

**If money is your hope for independence you will never have it.
The only real security that a man will have in this world is a reserve of knowledge, experience, and ability.**
Henry Ford

Friday, August 13, 2010

Turbo-charged monsoon confounds forecasters - Normally the jet stream is a giant loop of high speed winds that whip round the upper atmosphere. The jet stream isn't involved in day to day weather - it's too high up - but because it pushes the atmosphere around it's very important in steering large scale weather patterns below.
The stream has split in two. One arm has gone north, another south. The patch in the middle is Russia's drought. A circulating pattern of air has been sitting over Russia for far longer than normal, causing the extreme temperatures and wildfires they've had there. But what's happening over Pakistan is even stranger. The southern arm of the Jet stream has looped down so far it has crossed over the Himalayas into north western Pakistan. Experts at the Met Office say this is VERY UNUSUAL. And the result is that the fast moving jets stream winds high up have helped suck the warm, wet, monsoon air even faster and higher into the atmosphere - and that has caused rains like no one can remember. It has turbo charged the monsoon if you like. They're NOT SURE THAT'S EVER HAPPENED BEFORE.

**In my life nothing goes wrong.
When things seem to not meet my expectations,
I let go of how I think things should be.
It’s a matter of not having any attachment to any fixed outcome.
Deepak Chopra