PHOTO: PRESS ASSOCIATION, GETTY X2“Clearly something was
cockeyed with the global
weather system to produce
such weird patterns”
Manhattan was blasted with
snow storms last winter due
to a kink in the jet streamthe greater its speed. The spin of the Earth
sends the jet stream eastwards, but it can
also snake north and south in great loops,
and where the jet stream goes it takes lots
of weather with it. Over the UK its course
had locked into position for months,
wreaking havoc.
In Britain, the jet stream has only
recently attracted headline news – which issurprising because it exerts a considerable
stranglehold over our weather. And when
the jet stream shoots across the Atlantic
at speed towards the UK, it drives storms
along like an overhead conveyor belt that
can blast the country with wind and rain.
But in recent years the jet stream has
been buckling into huge
kinks that have become stuck
for weeks and months on
end. This winter was a classic
case, as the jet stream looped
up high over northwest
America around Alaska, then
swung towards Florida. It
then bent north across the
Atlantic towards the UK and
Western Europe, dragging
warm wet tropical air that helped fuel
devastating storms and flooding rains, but
also kept the weather remarkably mild.
That wavy pattern persisted for the entire
winter. “Usually the jet stream shifts over
days or weeks, but the amazing thing
about this winter is that it didn’t shift.
It persisted in the same position, that
was the really striking thing,” says Sirhis winter was terrifying. Britain
was pounded by relentless
storms, torrential rain and
floods of biblical proportions for months.
Nothing quite like it had been seen since
records began. Meanwhile, across the
Atlantic, half the US was frozen in an
Arctic hell, while California suffered
record heat and drought. Alaska’s
weather was so mild it set off floods and
avalanches. The rest of the world suffered
too; Saudi Arabia was flooded, northern
Iran had its worst storms for 50 years and
Tokyo broke its snowfall record.
The culprit is the jet stream, a river of
fast-flowing wind several kilometres high
that swept around the globe delivering
violent weather. Scientists are now piecing
together what drove it to this point and
whether it’s likely to happen again. And
what role, if any, does climate change play
in disrupting it?
The jet stream is fuelled by a massive
collision between cold air from the Arctic
and warm tropical air from the equator.
When these two air masses clash it creates
powerful winds, especially in the upperreaches of the atmosphere where there’s
less friction to hinder their speeds. In
fact, at altitudes of 11km (7 miles), the jet
stream travels at speeds of 160-320km/h
(100-200mph) and is often hundreds of
kilometres wide. And the greater the
contrast between the cold and warm air,T
METEOROLOGY