HOW DOES JET-STREAMS WORK

1. JET STREAMS

2. DEFINITION
 In the upper westerlies is present a
relatively narrow band of very strong
winds called JET STREAMS

3. BREAKS IN THE STREAMS
Two breaks in the northern hemisphere:
POLAR JET
Located around (30-60) N , 36000 feet
SUB-TROPICAL JET
Located around (20-30)N, 39000 feet

4. SUB-TROPICAL JET
 The subtropical jet stream is found between
the tropical and middle latitude atmospheric
circulations.
 It is an important transporter of atmospheric
moisture into storm systems.

8. TROPICAL JET
 The polar-front jet stream occurs over the
polar front, where relatively cold air at higher
latitudes comes in contact with warm air from
the lower latitudes, and near the tropopause.

9.  The polar-front jet stream encircles the globe
at altitudes between 9 and 13 kilometers
above sea level in segments thousands of
kilometers long, hundreds of kilometers wide,
and several kilometers thick.
 It generally flows from west to east .

10.  Jet streams speed must be 50 knots or
greater.
 Generally their speed range from (100-150)
knots and sometimes 200 knots along the
east coast of North America and Asia in
winter.

11. JET STREAM SEGMENTS
 They are generally (1000-3000) miles
long.
 Width = 400 miles
 Depth = (3000-7000) feet

13. STRENGTH OF JET STREAM
 Their strength increases in winter in mid
and high latitudes when temperature
contrasts are greatest and then they
shift south with the seasonal migration
of the polar front.

14. FLIGHT IMPORTANCE
 Headwind component for westbound
flights.
 Increased fuel consumption
 Needs additional landings.
 Westerlies jets support flight speeds
 Lesser time with increased speed.

15.  The jet stream is also of great importance
to aviation, as the B-29 pilots quickly
found out.
 Westbound, high-altitude flight routes are
planned to avoid the jet-stream head
winds, which would slow the aircraft and
consume precious fuel.

16.  Eastbound flights welcome time-saving tail winds
from the jet stream to increase their speed and thus
save fuel.
 However, the jet stream produces strong wind
shears, large changes in wind speed over short
vertical and horizontal distances, in some locations
that can be very hazardous to aircraft and
passengers.

17. DISCOVERY
 Discovered during world war-II when high
altitude bombers and fighters reached
tropopause for the first time.
 The Japanese put high altitude balloons
with bombs into jet streams that were
supposed to be dropped automatically on
the west coast of USA after several days.

18. POSITION ON CHARTS
 Location of jet streams can easily be found
on the 300 mb and 200 mb C-P charts i.e
(constant –pressure charts).
 Polar jets appears = 300 mb chart
 Sub-tropical jets = 200 mb chart
 WHY??????

19. BECAUSE…….
 As polar jet is at a lower altitude it appears on
low altitude C-P chart.
 In winter CP chart of 300 mb is used.
 In summer CP chart of 200 mb is used.

21. INFLUENCE OF JETSTREAM ON
PAKISTAN
 No influence on most parts of Pakistan but
affects only certain regions.
 In winter jet streams remain near subtropics
and near tropical regions in Northern
hemisphere and affects only the areas high
above the coastal zone i.e Mirpur Khas and
Nawab shah (Interior Sind)

22.  In summer it shifts upwards near (40-50)
degree in latitude but Pakistan is between
(24-38) N latitude and remains unaffected.
 So Pakistan suffers no changes by the
jet streams.

23. INFLUENCE ON GLOBAL WEATHER
 During major cold breaks over USA the jet
stream often dives south, moving quite well
over Gulf of Mexico.
 During unusual mild winter and summer jet
stream moves northward into Canada.

24.  Can play an important role in
precipitation and storm formation that is
formed due to the rising air that lowers
the air pressure.

25. CAUSES OF JET STREAMS
 Jet streams are found 7-8 miles above the
surface of the earth.
 Caused by temperature difference
between adjacent air masses.
 The mean position of the jet stream in the
northern hemisphere is between
(20-50)°N.

27.  A jet stream forms high in the upper
troposphere over the boundary between two
air masses of different temperature.
 The greater the temperature difference
between the air masses, the greater the air
pressure difference, and the faster the wind
blows in the jet stream.

28.  But how does the temperature difference
between two air masses cause the jet
stream?
 To answer this question, it is first helpful to
understand what causes pressure variations
(and thus wind) at the Earth's surface.

29.  The difference in pressure that cause winds at the
surface of the Earth is ultimately due to the
horizontal difference in air temperature summed up
over the entire depth of the atmosphere.
 Because warm air is less dense (it weighs less),
and cold air is more dense (it weighs more), high
and low pressure areas represent, in a vertical
average sense, cooler and warmer air, respectively.

32.  Polar jet streams is between (30-70) °N
latitude.
 Wind speed varies 35 miles per hour in
summer and 75 miles per hour in winter,
although speeds as high as 200 mph have
also been recorded.

36. Why the jet streams are directed from west
to east?????
 Please try to answer yourself