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Monday, April 30, 2012

Chapter 6:

Air Pressure and Winds

• Factors Affecting Air Pressure

• Altitude and Air Pressure

• Factors Affecting Wind

• Pressure-Gradient Force

• Coriolis Effect

• Friction

• Various Kinds of Winds

• Surface Winds

• Winds Aloft & Geostrophic Flow

• Curved Flow & Gradient Wind

• Winds & Vertical Motion

• Cyclones

• Anticyclones

• Wind Measurements

• Direction & Speed

Chapter 6: Air Pressure & Winds

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Air Pressure

• Air pressure is the weight that air molecules exert onto a surface

• The air pressure is HIGHEST at the ground level and DECREASES as you move up in the atmosphere

• We experience about 15 psi (pounds per square inch) at sea level… That is about 11,000 pounds on a surface the size of your desktop!

• But we experience this ALL AROUND us, in all directions at once… so we don’t feel it.

• Also, people have evolved to live within this pressure.

Air Pressure

Because the

Earth’s gravity is

pulling these air

molecules toward

the surface, we have

the majority of the

atmospheric gasses

concentrated near

the surface.

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Air Pressure Ranges

• Differential heating of the earth’s surface makes different pressures

• These pressure differences affect all scales: local, regional, national, worldwide

• Consider a parking lot and a field… ~~Example drawn on board~~

• Wind always moves from High to Low pressure

• Winds are named from where they come FROM!

Air Pressure Basics

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Local

Regional

National

Worldwide

Scales of Winds

Local

Regional

National

Worldwide

Scales of Winds

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Local

Regional

National

Worldwide

Scales of Winds

Local

Regional

National

Worldwide

Scales of Winds

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• Temperature

• Colder air has higher pressure Cold air Sinks The molecules are more compact

• Warmer air has lower pressure Warm air Rises The ‘activity’ of the molecules causes them to ‘push’ out more

• Density

• Higher Density = Higher Pressure

Factors Affecting Air Pressure

Cold vs. Warm Air

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Higher Density = Higher Pressure

• Altitude and Air Pressure

• Vertical change in pressure Lower Pressure = Higher Altitude Higher Pressure = Lower Altitude

• Standard atmospheric pressure Change in Altitude is main factor in calculation

• Measuring Air Pressure

• Barometer

Altitude & Measurement

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Air Pressure

Percent Miles

100% 300 miles

99% 31 miles

90% 10 miles

75% 7 miles

50% 4 miles

Standard Atmospheric Pressure

Lapse Rate ≠ 0 Lapse Rate = 0

Formula(s) for determining the Standard Atmospheric Pressure (>11 miles)

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Barometers

Three Factors Affecting Wind

• Pressure-Gradient Force

• Air moves from HIGH to LOW Pressure

• Isobars

• Coriolis Effect

• Increases with Increasing Speed

• Increases with Increasing Latitude

• Friction

• Surface roughness

• Surface winds = more friction

• Winds aloft (high above ground) = less friction

Factors Affecting Wind

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Pressure-Gradient Force Air moves (always)

from High to Low pressure

H L

Coriolis Effect Wind appears to move in a curved path when moving over a rotating earth.

Turn RIGHT in NH

Turn LEFT in SH

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• Winds & Vertical Motion

• Cyclones LOW Pressure Counter-Clockwise Movement Spin INTO the Low Pressure

• Anticyclones HIGH Pressure Clockwise Movement Spin OUT of the High Pressure

• Factors Promoting Vertical Flow

• Convergence

• Divergence

• Friction

Wind & Vertical Motion

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• Various Kinds of Winds

• Surface Winds

• Winds Aloft & Geostrophic Flow

• Flow parallel to isobars

• Idealized model

• Curved Flow & Gradient Wind

• Isobars are generally curved

• Ridges (surface highs)

• Troughs (surface lows)

Kinds of Winds

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• Wind Measurements

• Direction

• Prevailing Wind (Wind Rose)

• Speed

• Plotting Wind Symbols

Wind Measurement

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1)

2)

3)

4)

Direction:

Speed:

Direction:

Speed:

Direction:

Speed:

Direction:

Speed:

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