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Barometric Pressure

Barometric Pressure. Air is made up of molecules of gases (nitrogen, oxygen, argon, water vapor, etc.). Because these gases have mass, air is pulled toward the center of Earth by gravity. Barometric pressure is the weight (force) of the air pushing on a unit of surface area of the ground.

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Barometric Pressure

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  1. Barometric Pressure • Air is made up of molecules of gases (nitrogen, oxygen, argon, water vapor, etc.). • Because these gases have mass, air is pulled toward the center of Earth by gravity Barometric pressure is the weight (force) of the air pushing on a unit of surface area of the ground Image from the University of Illinois WW2010 PROJECT

  2. Barometric Pressure • As you go up in altitude, there is less air above you. • Less air means less mass and less weight pushing down the surface. Elevation Pressure (millibars) Image from the University of Illinois WW2010 PROJECT • So, Barometric pressure decreases as you go up in the atmosphere

  3. Barometric Pressure • Pressure is measured in millibars • 1 millibars = 1 hectopascal • All GLOBE measurements should be reported in millibars or hectopascals. • A barometer is a device that can measure Barometric pressure The GLOBE protocol uses an aneroid barometer, which contains an expandable air chamber that changes size as air pressure changes. A needle attached to the air chamber moves across a scale as air pressure changes Aneroid Barometer

  4. Why Measure Barometric Pressure? • Daily observations will help students see how changes in pressure are related to changes in weather, cloud type, and cloud cover • Pressure observations tell us the mass of the atmosphere between us and the sun, which is needed to measure aerosol optical thickness and Barometric water vapor

  5. Significant Values • Standard sea level pressure is 1013 mb • 960 mb is typical for extremely stormy conditions • 1050 mb is typical for strong high pressure systems • Barometric pressure decreases about 10 mb for every 100 meters higher you go in altitude • For example, at 1,000 meters above sea level your normal pressure range would be roughly 860 to 950 mb • For GLOBE, it is recommended that you report the sea level pressure -- the pressure adjusted to sea level • You can also choose to report station pressure -- the real pressure at your altitude, if you wish.

  6. How to Measure Barometric Pressure • The GLOBE protocol uses a standard aneroid barometer or an altimeter mounted on a wall in the classroom • Barometric pressure should be measured daily within one hour of local solar noon or at about the same time as the Haze measurement • The barometer should be calibrated every 6 months

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