Transcript Wind: Global Systems

Chapter 10
General Circulation of the Atmosphere
General refers to the average air flow,
actual winds will vary considerably.
 Average conditions help identify driving
forces.
 The basic cause of the general circulation
is unequal heating of the Earth’s surface

 Warm air is transferred from the Tropics to the
Poles
 Cool air is transferred from the Poles to the
Tropics
General Circulation of the Atmosphere
Single Cell Model


Assume
uniform water surface
Sun always directly overhead the Equator
Earth does not rotate
Result: huge thermally direct convection cell rising
at equator and sinking at poles(Hadley)
1.
2.
3.
Three Cell Model




Allow earth to spin = three cells (Hadley,
Ferrell, Polar)
Alternating belts of pressure starting with L at
Equator (L H L H) (Eq, Sub Trop, Sub Polar,
Polar)
Alternating belts of wind with NE just North of
Equator
General Circulation of the Atmosphere

Average Surface Wind and Pressure:
The Real World
 Semi-permanent high and lows
 Northern vs. Southern Hemisphere
 Major features shift seasonally with the high
sun
○ North in July
○ South in December
General Circulation of the Atmosphere

General Circulation and Precipitation
Patterns
 Rain where air rises (low pressure)
 Less rain where air sinks (high pressure)

Average Wind Flow and Pressure
Patterns Aloft
 North-South temperature and pressure
gradient at high altitudes creates West-East
winds, particularly at mid to high latitudes.
Jet Streams
100-200 kt winds at 10-15km, thousands
of km long, several 100 km wide and a
few km thick (polar and subtropical)
 Observations: Dishpan Experiment

 Illustrates waves, with trough and ridge,
develops in a rotating pan with heat on the
exterior and cold at the center.
Jet Streams

Polar and Subtropical Jet
 Established by steep temperature and pressure
gradients between circulation cells.
 Between tropical-mid-latitude cell (subtropical)
and mid-latitude-polar cell (polar)
 Gradients greatest at polar jet

Topic: Momentum
 Low-latitudes: atmosphere gains momentum
 High-latitudes: atmosphere losses momentum
 Conservation of Momentum
Jet Streams

Other Jet Streams
 Tropical easterly jet stream
 Low-level jet (nocturnal)
 Polar night jet streams