UNIT 5: Atmosphere

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UNIT 5 Atmosphere WeatherChapter 19 The
Atmosphere in Motion

• C/S 19.1 Air Pressure and Wind
• C/S 19.2 Factors Affecting Winds
• C/S 19.3 Global Wind Patterns
• C/S 19.4 Continental and Local Winds

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C/S 19.1 Air Pressure and Wind

• Air Pressure
• Air Pressure-The weight of the atmosphere as it
  pushes down upon Earth's surface exerts a force
  per unit of area called air pressure.
• Air pressure decreases by about 50 for each 5 km
  (3 mi) increase in elevation.
• Measuring Air Pressure
• A barometer is used to measure air pressure.
• Two Types Mercury and Aneroid. P.414 415
• Air pressure at sea level is 30 in. (1013
  millibars).
• If air pressure increases the column rises, if it
  decreases it falls.

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C/S 19.1 Air Pressure and Wind (cont)

• Why Does Air Pressure Change?
• Elevation, temperature and Humidity all affect
  air pressure.
• This is a result of air molecules being closer or
  farther apart. Higher elevations mean fewer air
  molecules. Why? Warmer air causes air molecules
  to be spaced farther apart and moist air
  molecules are also spread farther apart.
• A decrease in air pressure usually indicates the
  approach of warm, moist air.
• Isobar-a line that joins points of equal
  pressure.
• What Makes Wind Blow?
• Air moves from areas of high pressure to areas of
  low pressure. The greater the difference the
  quicker it moves. This causes WIND!
• What creates these differences?
• Meteorologists use a wind vane to measure
  direction and an anemometer to measure speed.

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C/S 19.2 Factors Affecting Winds

• If the air were perfectly smooth and did not
  rotate, air would
• flow straight from high-pressure areas to low
  pressure areas.
• The Coriolis Effect
• It is the tendency of an object moving freely
  over the Earth's surface to curve away from its
  path of travel. See page 419.
• In the Northern Hemisphere objects are deflected
  to their right and in the Southern Hemisphere the
  objects are deflected to the left.
• Friction
• The smoother the surface the faster the wind!
• Jet Stream-Bands of swiftly moving winds formed
  in the troposphere.
• Polar Jet Stream-Cool air from polar regions
  combines with warmer air to the south.
• Coriolis Effect
• Coriolis Effect and wind direction.
• ATMOSPHERIC CIRCULATION (Coriolis)

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C/S 19.3 Global Wind Patterns

• Factors that affect winds are Temperature
  differences between equatorial and polar regions,
  the rotation of the earth, locations of the
  continents, the time of year and local
  topography.
• Effects of Earth's Rotation
• Three Celled Circulation Model-The Northern and
  Southern hemispheres each have three circulation
  cells one between the equator and 30( lat., the
  second between 30( and 60( lat., and a third
  between 60( lat. And the pole. See page 423.
• The circulation cells are caused by alternating
  bands of high and low pressure.
• There are weaknesses in the Three-Celled Model.
  These can be attributed to generalizations about
  the earth landscape and seasons.

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C/S 19.3 Global Wind Patterns (cont)

• Description of Wind and Pressure Belts
• Intertropical Convergence Zone-The air is hot and
  humid, there is little wind, and rain is common.
  This area is historically called the doldrums.
• Horse Latitudes-Found between latitudes of
  20(-30(. They are created by dry sinking air,
  which creates little wind and precipitation.
• Trade Winds-Found between the doldrums and the
  horse latitudes. They are warm and relatively
  steady in both direction and speed.
• Prevailing winds-Blow from the same direction.
• Air Currents

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C/S 19.4 Continental and Local Winds

• Winds change with the changing of the seasons
• due to changes in temperatures.
• Effects of Seasons and Continents
• Air pressure on continents is low in the summer
  and high in the winter. The opposite is true for
  the oceans. See page 427.
• Monsoons-Winds that change direction seasonally.
• Summer

moist
moist
H
H
Hot
Warm
Warm
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C/S 19.4 Continental and Local Winds (cont)

• Local Winds
• Land and Sea Breezes

LAND-BREEZE
SEA-BREEZE
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C/S 19.4 Continental and Local Winds (cont)

• Local Winds (cont)
• Mountain and Valley Breezes

MOUNTAIN-BREEZE
VALLEY-BREEZE
L
H
Hot
H
Cold
L
Warm
Cool