'Blocked'
jetstream to blame for freak weather in Russia and
Pakistan, say scientists
By Niall Firth
UPDATED: 05:36 EST, 12 August 2010
A massive heatwave
in Russia and the current devastating floods in Pakistan could be linked by the
unusual behaviour of the jetstream,
scientists believe.
The jetstream is
the high-altitude wind that circles the globe from west to east and normally
pushes a series of wet but mild Atlantic lows across Britain.
But meteorologists who study the phenomenon
say that it is producing unusual holding patterns which keep weather systems in
one place and produce freak conditions.
A satellite map which shows the intense heat
that has built up over Russia after the jetstream has
been held up due to Rossby waves
The jetstream is
being held by the Rossby waves that normally produce
its distinctive wave-like pattern.
These powerful spinning wind currents are
caused by the Earth’s shape and rotation and push the jet stream from east to
west at high altitudes.
Now scientists believe that Rossby waves are acting against the jetstream’s
usual pattern, holding it in place, according to a report in New Scientist.
Since mid-July, when it would normally be
moving eastwards the jetstream has been held in one
place as strong Rossby waves push against it.
When the jet stream is held in one place it
traps the weather systems that are caught between its meanders. Warm air is
sucked north to the ‘peaks’ while cold air travels to the ‘troughs’.
Professor Mike Blackburn of the University of
Reading believes that a blocked jetstream could be
behind a heatwave in Japan which killed 60 and the
sudden end to warm weather in the UK.
A satellite image from this afternoon shows
smoke from wildfires burning in Russia. The red dots indicate active fires.
Scientists believe the jetstream could be to blame
Pakistani flood survivors evacuate a flooded
area in Bssera village near Muzaffargarh
today
In Pakistan, the blocking event took place at
the same time as the summer monsoon, with tragic consequences.
Floods triggered by heavy monsoon rain over
much of Pakistan began nearly two weeks ago and have killed around 1,600 people
and forced more than two million from their homes.
Many survivors from flooded villages have
lost their stores of food as well as crops and livestock and are surviving on
relief handouts.
In Russia, the immobile jetstream
pulled in hot air from Africa creating stifling conditions and horrendous smog
in Moscow.
Hundreds of wildfires have been burning
across three time zones. Prime Minister Vladimir Putin yesterday boarded a
fire-fighting plane to dump water on blazes close to Moscow, where the smoke
has caused thick smog
Scientists are still unclear as to the cause
of ‘blocking events’ although there have been some research that linked them to
low solar activity.
A graph for 24 - 30th July which shows a
succession of meanders along the jet stream, with a northward meander (ridge of
high pressure) over the Atlantic, a southward meander (trough of low pressure)
over Europe. Here the jet splits, around a large 'blocking' anticyclone over
western Russia. On the eastern side of this anticyclone, air moves into the
southward meander (trough) close to Pakistan from quite far north
A graph from the same period over a number of
years shows what scientists would normally expect over this period with calmer
winds and fewer 'trapped' weather patterns