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Air Pressure & Wind

Air Pressure & Wind. What is Air Pressure? . Air pressure is the weight of the atmosphere as it pushes down on the Earth’s surface. How do we measure air pressure?. Instrument used is called a barometer. mercury barometer. aneroid barometer. What units are used?.

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Air Pressure & Wind

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  1. Air Pressure & Wind

  2. What is Air Pressure? • Air pressure is the weight of the atmosphere as it pushes down on the Earth’s surface.

  3. How do we measure air pressure? • Instrument used is called a barometer. mercury barometer aneroid barometer

  4. What units are used? • INCHES - average (at sea-level) is 30 inches. • MILLIMETERS - average (at sea-level) is 760mm. • MILLIBARS - used by meteorologists average (at sea-level) 1013 mb.

  5. Factors that Affect Air Pressure • Change in Elevation - the higher the altitude, the lower the air pressure.

  6. Factors that Affect Air Pressure • Temperature - as temperature increases the air pressure decreases (at sea-level). Why? Air molecules spread out as they heat up.

  7. Factors that Affect Air Pressure • Humidity - The more water vapor the lighter the air. Why? Water molecules have less mass than nitrogen and oxygen (NO) and pushes the nitrogen and oxygen out of the way. Dry Air 99% nitrogen & oxygen Warm Air 97% nitrogen & oxygen

  8. Changes in Air Pressure Air Pressure changes can be used in forecasting weather (not always accurate). • As air pressure decreases often signals warmer, more humid, along with rain or snow. • As air pressure increase it signals cooler, drier air, and fair weather.

  9. Air Pressure & Wind • Changes in air pressure causes the wind to blow.

  10. What Causes Wind to Blow? • Wind is caused by uneven heating of the Earth’s surface, thus causing changes in air pressure. • Wind moves from an area of high pressure to areas of low pressure. • Winds are named for the direction from which they come.

  11. Analyzing Air Pressure • Isobars - points on a map having the same air pressure. • Close together = fast wind speed. • Far apart = calm wind

  12. High Pressure - Happy • Anti-Cyclone - air moving clockwise away from the pressure center. • Cold air - weighs more • Dry air • Sunny • No precipitation Symbol indicated on a weather is: H

  13. Low Pressure - Lousy • Cyclones - air moving counter clockwise toward the pressure center • Warm air • Humid/moist air • Cloudy • Precipitation Symbol indicated on a weather is: L

  14. Wind blows from Hi to Lo pressure regions

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