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Barometric Pressure

Barometric Pressure. Air pressure is the force exerted by the atmosphere at the earth’s surface. Air has mass. The Earth’s gravitational force pulls the mass downward . ~14.7 pounds per square inch = 1 Atmosphere 29.92 in. Hg 1013.25 mb.

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Barometric Pressure

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  1. Barometric Pressure • Air pressure is the force exerted by the atmosphere at the earth’s surface. • Air has mass. The Earth’s gravitational force pulls the mass downward. • ~14.7 pounds per square inch = 1 Atmosphere • 29.92 in. Hg • 1013.25 mb

  2. Air pressure is measured with a barometer. There are two main types of barometers. • Column of Mercury • Aneroid Barometer

  3. Column of Mercury Air pushes down on a bath of Hg. As the air pressure changes the height of the column changes

  4. Aneroid Barometer No Liquid A thin membrane is placed over a rigid container. The air presses on the membrane and the surface moves with the changes in air pressure. Flexible Membrane Rigid Container

  5. Air Pressure is measured in millibars(mb) or inches of mercury (in Hg) • Normal Air Pressure at Sea Level is 29.9 in Hg or 1013.2 mb • Conversion Chart is on ESRT

  6. Factors That Influence Air Pressure • Temperature: Less dense air exerts less pressure. As temperature increase pressure decreases.

  7. Water Vapor: • Water vapor has less mass than dry air therefore it exerts less pressure • 78% Nitrogen • 21% Oxygen • 1% other • When water vapor enters the atmosphere it displaces molecules of dry air.

  8. Elevation: • As elevation increases the air gets thinner. Less air means less mass therefore it will exert less pressure.

  9. Changes in Air Pressure • Changes in air pressure cause wind. • Pressure differences at the Earth surface are caused by the alternate heating and cooling of the Earth’s surface. • This causes convection currents to develop. Air moves from High to Low pressure.

  10. Air is heated and it rises leaving a void at the Earth’s surface. The more dense air moves in from the higher pressure areas.

  11. Sea Breeze(Day) • Low High • Warm Cool • Heats Quickly Heats Slowly

  12. Land Breeze(night) High Low Cool Warm Quickly Slowly

  13. As air rises in a low pressure system it expands and cools. The water vapor condenses and forms clouds. LowHigh Bad Good Wet Dry Warm Cool Counterclockwise Clockwise Inward Outward Upward Downward Convergent` Divergent

  14. Global Wind Patterns • Winds bend to the right from their point of origin in the Northern Hemisphere. • This is caused by the earth’s rotation. • It is called The Coriolis Effect.

  15. Climate Factors Influencing Weather Patterns

  16. Global Wind Patterns • Storm Tracks • Orographic Effect • Ocean Currents

  17. Global Wind Patterns • Storm Tracks • Weather Patterns move from West to East with a Northeast trend.(between 30°N and 60°N) • Orographic Effect • Ocean Currents

  18. Zones of Precipitation L

  19. http://www.intellicast.com/National/Radar/Yesterday.aspx

  20. Global Wind Patterns • Storm Tracks • Weather Patterns move from West to East with a Northeast trend.(between 30°N and 60°N) • Atlantic Hurricanes move from the East to the West and then turn Northeast • (below 30°N then above 30°N) • Orographic Effect • Ocean Currents

  21. Global Wind Patterns • Storm Tracks • Orographic Effect • Global winds force air upward along mountains causing adiabatic cooling thereby creating a wet climate on the windward side of the mountain. • Ocean Currents

  22. Global Wind Patterns • Storm Tracks • Orographic Effect • Ocean Currents • Global winds cause surface ocean current patterns. This can cause a warm/cold water current to be forced toward a coastline causing it to influence the climate of a region.

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