Winds and Deserts

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Winds and Deserts
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Eolian

• Aeolus Greek god of winds.
• Eolian Geological processes driven by wind.

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Wind patterns on Earth

• Rules of thumb
• Warm air rises and cool air sinks.
• Where winds converge, air rises.
• At the Equator
• Suns rays strike the Earths surface nearly
  perpendicularly.
• Air warms and rises, traveling toward the poles.
• By about 30 S and N, air has cooled, so it
  sinks.

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Wind patterns on Earth

• Coriolis effect
• North-south motion of wind cells is affected by
  planets rotation.
• In SOUTHERN Hemisphere, currents are deflected to
  the RIGHT.
• In SOUTHERN Hemisphere, currents are deflected to
  the LEFT.

NORTHERN
SOUTHERN
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Sun
Sun
Sun
Fig. 15.1
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Fig. 15.15
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Wind velocity vs particle size
Faster wind
Larger particles carried
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Reynolds Number

• r fluid density, U fluid velocity, H
  length, and m viscosity.
• If Re gt 500, turbulent.
• If Re lt 500, laminar.

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Turbulent or laminar?

• Air has extremely low viscosity.
• TURBULENT!
• Turbulent air flow picks up particles from the
  surface.
• Large particles are entrained for short
  distances. Cannot be held in air because of
  airs low density and viscosity.
• Small particles (lt0.1 mm diameter, dust) carried
  to heights of many km and very long distances
  (across Atlantic).

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Entrainment
Fig. 15.2
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Fig. 15.3
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Fig. 15.4
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Deflation

• Surface particles (dust, silt, sand) become dry
  and loose.
• Winds entrain surface particles.
• This erosional process is called DEFLATION.
• Vegetation inhibits deflation.
• Whats left behind after delation is called
  DESERT PAVEMENT. Coarse, gravelly ground surface.

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Deflation hollow (Co)
Fig. 15.6
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Alternative theory for pavement formation
Fig. 15.7
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Desert pavement
Fig. 15.7
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Fig. 15.9
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Fig. 15.10
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Fig. 15.10
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Fig. 15.11
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Barchan
Blowout
Transverse
Linear
Fig. 15.12
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Fig. 15.17
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Fig. 15.17
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Playa lake
Dont drink me!
Fig. 15.18