With the jet stream heading straight
at the UK last winter, it brought with
it warm, wet tropical air, resulting in
torrential rain and widespread floodingBrian Hoskins, director of the Grantham
Institute for Climate Change at Imperial
College London.
The perfect storm
Clearly something was cockeyed with
the global weather system to produce
such weird patterns, and serious detective
work by meteorologists at the UK’s Met
Office finally unravelled the mystery: a
perfect storm as the Pacific Ocean and the
stratosphere drove a fast and buckled jet
stream around the globe.
The seas in the western Pacific were
unusually warm, billowing up warm
air into beefy rain clouds that unleashed
flooding rains over Indonesia. That warm
wet rising air also sent ripples out through
the atmosphere. “It’s like dropping a rock
into a pond, sending waves rippling out
from the tropics into the higher latitudes,”
explains Adam Scaife at the Met Office
Hadley Centre. “Those waves helped to
buckle the path of the jet stream towards
the Aleutians off the west coast of America.
Everything downstream of that was then
locked into a weather pattern all winter.”
HOW THE JET
STREAM CHANGED
THE COURSE OF
HISTORY
The jet stream is a river of wind circling the globe
eastwards at speeds of around 320km/h (200mph)- which is why aircraft flying from New York to
London can go much faster and save fuel if a pilot
rides the jet stream over the Atlantic. If the jet
stream travels directly over the UK, that usually
brings mild wet winters and cool damp summers;
but if the jet stream passes to the north or south it
generally delivers cold, dry winters. These winters
can be exceptionally cold, like that recently experi-
enced in the United States.
So powerful is the jet stream’s influence it can
even help change the course of history. In the
1940s, the jet stream swung much further south
and created brutal winters during World War II. In
the winter of 1939-1940, Russia invaded Finland
but was totally unprepared for an exceptionally cold
winter and suffered massive casualties at the
hands of the tiny Finnish army, which was well
equipped for winter warfare. But when Germany
invaded Russia in 1941, the Germans were also
unprepared for another intensely cold winter,
leading to huge casualties that arguably helped the
Russians defeat them.
And there was also trouble in the
stratosphere, 32km (20 miles) high.
Winds in the stratosphere race around
the tropics, but every 14 months or so
they suddenly switch direction and this
winter they blew eastwards, the same
direction as the Atlantic jet stream. They
reached double their usual speed and
supercharged the jet stream lower down
in the atmosphere. It reached record
speeds, around 400km/h (250mph)
over the North Atlantic, making storms
explode into a frenzy as they tore across
the UK and Western Europe.
But the dual attacks of the Pacific
Ocean and stratosphere can’t explain the
crazy weather Britain has suffered over
the last few years, lurching from floods
to droughts, freezes to heatwaves, storms
and tornadoes. Hardly a month goes
by without a record broken: December
2010 was the coldest for over 100 years,
England had its wettest year on record in
2012, the coldest March for 51 years in
2013, and so it goes on.
The weather has also been extreme
across the globe. In the summer ofExtreme weather proved
decisive in World War II
Finnish troops patrol their borders during the bitterly
cold winter of 1939, conditions that would help them
defeat the Red Army