Summer 2012 has been a washout. Some places in the UK have seen
a month's rain in one day! We've had the wettest June for over a
century.
Lots of different factors influence the UK's weather. One factor
is the jet stream.
What is the jet stream?
The jet stream is a ribbon of fast-moving air high up in the
atmosphere. It drives weather systems across the Atlantic. There
are four jet streams, two in the northern hemisphere and two in the
southern hemisphere.
Have a look at this video to find out more.
Why does the jet stream affect UK weather?
The jet stream plays a big part in whether we will get rain or
not. In summer, the jet stream is normally north of the UK.
This means that the rainy weather systems will also be to the
north of the UK.
Normal jet stream activity in
summer (c) BBC
In winter, the jet stream is over - or slightly south - of the
UK. This is when we're used to rainy conditions.
So far this summer, the jet stream has been hovering over us.
The longer the jet stream stays over the UK, the more rain we will
get!
Jet stream activity in summer
2012 (c) BBC
The effect of the jet stream has been very different in the
US.
Much of the US lies south of the jet stream, which has led to a
very dry summer. More than half the US is in drought and disasters
have been declared in 26 states.
Why is the jet stream to the south of the
UK?
Scientists aren't sure. Weather patterns show lots of natural
variability, so it could be due to natural fluctuations in weather
patterns. Sometimes natural fluctuations in sea temperatures can
cause the jet stream to move.
Some scientists think that climate change is playing a part.
Reduced Arctic sea ice could affect weather patterns. This year,
Arctic sea ice is at a record low. However, scientists need to do
more research to see if our rainy summer is a result of climate
change.
It's very hard to predict whether short-term weather patterns
are due to natural variability or whether they are due to climate
change. However, most scientists agree that long-term warming of
the Earth and loss of sea ice is due to climate change.
Will we see the sun in 2012?
Weather forecasters say that the jet stream is likely to move
further north soon. This will end the rainy spell and hopefully
bring us some sunshine!