IRFP-01
Metro Review
E. Jet stream 21.1.1.3.5
Fig 9: Polar and
Subtropical Jet
1. Forms in tropopause - the boundary between the troposphere and
Streams
the stratosphere
a. Height varies from 65,000 ft at the equator to 25,000 ft or less
at the poles
b. Tropopause drops by steps between arctic and polar
airmasses and another drop between the polar and tropical air
masses
c.
Between the polar and arctic “layers,” the Polar Front Jet
Stream forms; between the polar and tropical “layers,” the
Subtropical Jet Stream is formed
(1) Polar jet stream is the primary North American jet stream
(2) Subtropical jet stream found between 25 degrees and 30
degrees North latitude
NOTE: From the Hawaiian Islands eastward to southern
Florida, the Subtropical Jet Stream sometimes drifts north
and merges with the Polar Jet Stream.
Fig 10: Jet Stream
2. Jet stream characteristics
Profile
a. They are a narrow, shallow band of strong westerly winds of 50
kts or more
(1) Strength of the jet stream is stronger in the winter than in
the summer
(2) Wind speeds up to 300 kts have been recorded
(a) Summer: average 75-100 kts
(b) Winter: average 150-225 kts
Fig 11: Polar Jet
b. Jet streams wander vertically and horizontally around the
Stream
hemisphere in wavelike patterns
(1) Jet streams in northern hemisphere are matched in
southern hemisphere
(2) They are stronger in some areas than others
(3) They rarely encircle entire globe as a continuous river of
wind
(a) Most frequently found in 1,000- to 3,000-mile
segments
(b) 100- to 400-mile width
(8-97) Original
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