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 If
you've travelled to America and back, you may have noticed
that the flight was quicker on your return flight than it
was on your way to the States. This is not because you simply
fell asleep, but due to a fast flow of air called a 'jet stream'.
'Jet streams' were
first discovered during the second world war. Pilots were
regularly flying between Britain and the United States of
America and they noticed that it was quicker to fly to the
United Kingdom and reported tailwinds of over 100 miles per
hour. These winds blew in narrow ribbons and were named 'jet
streams'.
Nowadays jet streams
are closely monitored and forecast. Pilots want to know where
to find them as their added push will save them time and fuel,
and therefore money. But jet streams are not only important
to pilots. When Breitling Orbiter 3 became the first balloon
to fly non-stop around the world it used knowledge of the
position of the jet streams to speed up its flight.
An example
of jet streams across the USA(©SFSU)
Jet streams are formed
by the temperature differences in the upper atmosphere, between
the cold polar air and the warm tropical air. This abrupt
change in temperature causes a large pressure difference,
which forces the air to move. During the winter there is a
greater difference in the temperature, so this is when the
jet streams are at their fastest.
They generally move
in a west to easterly direction due to the rotation of the
earth. They move north and south too, following the boundary
between warmer and colder air. These boundaries are also where
weather fronts generally develop, so when a front passes overhead,
bringing wind and rain, it is quite likely that a jet stream
is passing undetected too.
Jet streams flow approximately
5 to 10 miles above the surface of the earth, with speeds
up to 310 miles per hour. With these kinds of speeds you see
why the aeroplanes are so keen to use them. However, to navigate
in a jet stream is not as easy as you might think, as it is
only a few hundred miles wide, just a few miles thick, and
constantly moving. Entering and leaving a jet stream can be
a turbulent time for any aircraft no matter how big it is,
and most passengers will want to leave the roller coasters
in America
Other features in
the Weather Basics series
Air Pressure
Clouds
Day and Night
Fog and Mist
Fronts
Frost
High Pressure
Humidity
Lightning
Low
Pressure
Mirages
Northern Lights
Rain or Showers?
Thunder
Watercycle
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