IRFP-01
Metro Review
(c) 3,000 to 7,000 ft in depth
(4) Mean position of Polar Jet Stream shifts south in winter
and north in summer with polar front
(5) As polar front moves south, jet stream cores rise to higher
altitudes and average speed increases
NOTE: The Polar Jet Stream appears to have a life cycle
of formation, intensification, movement, and dissipation
related to the polar front. The core of the strongest winds
is generally found between 25,000 ft and 40,000 ft
depending on latitude and season.
c.
There are as many jet stream occurrences in the summer as in
the winter
d. Two jet streams can exist over the continental United States
Fig 12: Multiple Jet
simultaneously
Streams
NOTE: When two are present, the southern one will usually be
higher and have the strongest winds.
3. Flying the jet stream
a. Flying from west to east, speed and range can be greatly increased
b. Flying east to west decreases range and ground speed
(1) If caught in adverse wind flow, climb or descend to a
colder air mass or take a more northerly track
(a) Wind speeds decrease rapidly on the north (polar) side
and slowly on the south
NOTE: The average rate of change in wind speed is
100 kts for every 100 miles to the north of the core and
25 kts for every 100 miles to the south of the core.
(b) A decrease of 30 to 40 kts in 1,000 ft above or below
the core of maximum winds is not uncommon
4. Jet Stream Meteorology
a. 200 (summer) and 300 (winter) millibar constant pressure
charts are analyzed for lines of equal wind speeds (isotachs)
(1) Areas of 70 kts or greater are shaded and are equivalent to
the horizontal limits of the jet stream
(2) Highest winds running through the axis of this area is the
core
(8-97) Original
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