Transcript Chapter 6 CIRCULATION PATTERNS

Upper-Air Winds
• Flow of air at altitudes above 5000
meters (16,500 ft)
• Found in the upper troposphere
• A response to the temperature
difference between warm tropical air and
cold polar air
• Affect the formation, movement,
and decay of surface cyclones and
anticyclones
• Far less complex than the surface
wind circulation
• Poleward of 15˚-20˚ there is a
pronounced westward flow of air known as
the upper air westerlies
· a broad circumpolar
flow of westerly winds
· move much more
rapidly than the
surface counterparts
· strongest in winter (the low-sun season)
· much weaker during the summer
(the high-sun season)
Jet streams
• very strong air currents
• embedded within the upper air westerlies
• polar jet stream
· located where the warm tropical
air
meets cold polar air
· ranges from 40 to 160 km (25-100
mi)
wide and…
up to 2 or 3 km (1- 2 mi) deep
• Subtropical jet stream
· flows above the sinking air of
the subtropical highs
· best developed in winter when their is
the steepest pressure gradient
· often the subtropical
jet stream completely
disappears in the
summer
• Usually the upper air westerlies, and polar
jet stream, flow in a fairly smooth pattern
• Oscillations termed Rossby
waves periodically develop
· cold polar air pushes into the
lower latitudes forming troughs of low
pressure
· surface weather
is most influenced
under these
conditions
· the oscillations can become so extreme
that they become cut off
· the cells eventually dissipate, and
the pattern returns to normal
· a complete cycle takes 4 to 8 weeks
· unusually warm
or cold ocean
currents seem to
trigger the
oscillations