Download Ch 19 Wind

Ch 19: Atmosphere in Motion (aka: the Wind Chapter)
• Wind: horizontal movement of air.
– moderates surface temps
– distributes moisture
– cleans the air
• Air pressure: weight of atmosphere
– Decreases with elevation, 50% drop/5km increase
in elevation.
– 14.7 lbs/in2 at sea level
– 12.1 lbs/in2 in Albuquerque
• Barometer: instrument used to measure air
pressure (inches or millimeters of mercury)
– Millibars used on US weather maps.
Measurements must be adjusted to account for
elevation when creating weather maps.
• Sea level: 1013 mb Hg
• Albuquerque: 835 mb Hg
• Changes in air pressure also caused by temp
and humidity.
– Warm air weighs less
– Moist air weighs less (H2O is a lighter molecule
than both O2 and N2).
• Decrease in pressure (“Low”) typically
signals change in weather.
– Warmer, humid, frequently precipitation.
• Increase in pressure (“High”) brings clear skies
and fair weather.
Why, oh why does the wind blow?
• Greater the difference in air pressure between
two points, the stronger the wind blows.
• Press differences & winds caused by unequal
heating of Earth’s surfaces.
• Anemometer: instrument that measures wind
speed & direction.
The Coriolis Effect: the tendency of an object
moving freely over Earth’s surface to curve away
from its path of travel.
• N. Hem: deflects objects to
right (when looking down
over N.
from over the pole.)
• Most visible with long. motion
• Effect increases as object
speed increases.
• Not dependent on an objects direction of
movement.
• Most noticeable over long distances.
Jet stream: fast winds near
top of troposphere.
• Speeds 140-240 km/hr
• Thousands km long
• May split into two parts
• Big effect on US weather
Global Wind Patterns are affected by temp
differences between polar & equatorial regions,
the rotation of Earth, locations of continents,
time of year & local topography.
3-Cell Circulation Model
• Equator – 30° latitude
• 30° – 60° latitude
• 60° latitude – poles
• Alternating bands of
high & low pressure.
• Both weaknesses and
strengths to this model.
Create a weaknesses and strengths
chart in your notes for this model.
ITCZ: Intertropical Convergence Zone is the area
where the winds meet between the two
hemispheres.
• Hot, humid air with little wind & lots of rain,
referred to as the doldrums.
• Horse latitudes: 20°-35° is area of subtropical
Highs. Calm wind zone with deserts on land.
• Trade winds: area between doldrums and
horse latitudes.
Global winds change with seasons.
• Highest temps not found at equator.
• Continents hotter than surrounding oceans
creating low pressure areas.
• Winds spiral out of high-pressure areas into
low-pressure areas, altering wind patterns.
– Monsoons: winds that change direction with
seasons
• Local winds: extend for 100 km or less.