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 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.