Where is the jet stream today
What is the jet stream and how does it affect the weather?
jet streams are another name for fast
flowing currents of air there are many
different jet streams that exist at both
high and low levels in the atmosphere
each has an important role to play in
the weather experienced on earth the
major jet streams that circle the earth
are found just below the tropopause at a
heights ranging from 9 to 16 kilometers
and can reach speeds over 200 miles per
hour they're hundreds of kilometres wide
by only a few kilometers deep so often
described as a ribbon of very strong
winds the major jet streams are the
polar front and subtropical jets these
occur in both the northern and southern
hemispheres and a part of the larger
global circulation the polar front jet
occurs over mid latitudes and strongly
influences the weather over the UK in
Europe the polar front jet is a type of
thermal wind that arises due to the
strong temperature contrasts between
cold polar air and warm tropical air to
explain this further imagine two columns
of air one in the cold air to the north
of the jet and one in the warm air to
the south the top of each column is
bounded by the tropopause a shorter
column of cold air exerts the same
surface pressure as a taller column of
wor air this is because in the cold air
column the air is more dense
this causes atmospheric pressure to
decrease more quickly with Heights in
the warm air column pressure does not
decrease as rapidly with height because
the warmer air is less dense
the tropopause in both columns is at the
same atmospheric pressure so if you were
to climb to the same heights in both
columns you would find that you would be
at a lower atmospheric pressure in the
cold air column and a higher atmospheric
pressure in the warm air column the
pressure difference caused by this
temperature gradient produces a pressure
gradient force the pressure gradient
force acts from high to low pressure so
theoretically in the Northern Hemisphere
air would flow from south to north
but the Coriolis force resulting from
the Earth's rotation causes the air to
move to the right of the direction of
motion in the Northern Hemisphere and to
the left of the direction of motion in
the southern hemisphere in both
hemispheres the jet stream flows
parallel to this temperature gradients
moving from west to east theoretically
this jet encircles the earth in a
continuous line but in reality it is
more broken up as differential heating
of land sea masses lead to west to east
temperature contrasts as well as north
to south as the polar front Jets forms
due to the temperature contrast the
stronger the temperature gradient
the stronger the Jets this means that
the jet is stronger in the winter than
the summer as the poles call during the
winter months increasing the temperature
contrast in the northern hemisphere the
jet tends to be further south in winter
and further north in summer this is due
to the tilt of the earth and that in the
winter the northern hemisphere is tilted
away from the Sun
and in the summer it is tilted towards
the Sun mid latitude low pressure
systems occur on the polar or northern
side of the Jetstream while more settled
warmer conditions are found to the south
this gives us the wet and windy weather
we often see in the UK during the winter
months as low pressure systems are
steered towards us it can also lead to
some disappointingly wet summers with
the Jetstream remains to the south of
the UK a stationary jet stream pattern
will bring frequent low pressure systems
to the same region when warm air moves
further north and normal or cold polar
air moves further south this can change
the prevailing west to east jet stream
pattern
this causes the jet stream to buckle
driving depressions towards different
regions or blocking their movements
altogether
a straight West East flowing jet stream
won't have much impact on the
development of new weather systems or
strengthened pre-existing ones when a
jet stream meanders north and south air
accelerates and decelerates around the
bends and the flow these areas of
changing speeds are our development
areas where the air is accelerating more
air is leaving than entering a certain
point this means that the air is being
depleted at this point to fill the
depletion air from below Rises when air
rises it forms clouds and precipitation
winds at the surface converge to this
rising air column which causes surface
pressure to fall and a low pressure
system may develop or deepen further so
whilst a jet stream is just an area of
fast flowing air it has a fundamental
effect on our weather
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