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Unformatted text preview: Geography- OBrian CHAPTER 5 Study Guide Atmospheric Pressure and Wind The Nature of Atmospheric Pressure o Atmospheric pressure is the force exerted by the gas molecules on some area of Earths surface. o At sea level: around 1 kilogram per square centimeter o Drops with increasing altitude o Omni directional o Due to gravity, air pressure decreases as you move away from the surface. Factors Influencing Atmospheric Pressure o Pressure of a gas proportional to its density and temperature. Density and Pressure o Density is the mass of matter in a unit volume. o Solid always the same, gas proportional to the pressure on it. Denser the gas, the greater pressure exerted. Temperature and Pressure o As air is heated, molecules become more agitated and speed increases. o Increase in speed produces a greater force to collisions and results in higher pressure. Thus. . . warm weather = low atmospheric pressure. Increase in temperature>decrease in pressure>caused by decrease in density. Cold>closer, pull in. Of coarse until 4 degrees C, when expands Dynamic Influences on Air Pressure o Descending air associated with high pressure at the surface. o Thus, rising air would be associated with relatively low pressure at the surface. o Dynamic high-strongly descending air often associated with high pressure at the surface o Thermal high- very cold surface conditions are often associated with high pressure at the surface. o Dynamic low- strongly rising air often associated with low pressure at the surface. o Thermal low-very warm surface conditions often associated with relatively low pressure at the surface. Mapping Pressure with Isobars o Barometers measure atmospheric pressure in millibars . Millibar- force per surface area, or 1000 dynes per square centimeter Average sea-level is 1013.25 millibars. o Weather maps Isobars- lines connecting places of equal pressure Ridge-elongated area of relatively high pressure Trough-elongated area of relatively low pressure Pressure gradient-the horizontal rate of pressure change. Steeper the gradient, the stronger the wind. Nature of Wind o Atmosphere is always in motion. o Wind is horizontal air movement. Updrafts and Downdrafts are small-scale vertical movements Ascents and subsidence are large-scale vertical movements Direction of Movement o Insolation is the ultimate cause of wind o Winds generate from unequal heating of different parts of Earths surface Represent natures attempt to even out the uneven distribution of air pressure over Earth.pressure over Earth....
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This note was uploaded on 09/10/2008 for the course GEOG 1111 taught by Professor O'brian during the Spring '08 term at Gainesville State.
- Spring '08