Lecture 2-26 grg sec2 - Weather 2.26.2008 Introduction to...

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Weather 2.26.2008 Introduction to Air Pressure What is Air Pressure? Air Pressure – the weight of air above a given surface As you climb in elevation, there are fewer air molecules above you, therefore, air pressure ALWAYS decreases with height Inside of aircraft pressurized to about 8000 feet Pressure Gradient Force says air will move from higher to lower pressure – poke a hole in a high pressure tire and it will blow out, not in Low pressure usually characterized by clouds and rain Animals can often sense changes in pressure before humans can Atmospheric Pressure Models Four identical columns of air (fixed width) If we move air into the column (with no temperature change) – surface pressure would increase If we move air out of the column (with no temperature change) – surface pressure would decrease If we warm one column – the molecules move faster and spread farther apart, the air becomes less dense and the column expands in height If we cool the other column – the molecules move more slowly and crowd closer together, the air becomes more dense and the column shrinks in height As a Result: It takes a shorter column of cold, dense air to exert the same surface pressure as a taller column of warm, less dense air ATMOSPHERIC PRESSURE DECREASES MORE RAPIDLY WITH THE ELEVATION OF A COLD COLUMN OF AIR
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Lecture 2-26 grg sec2 - Weather 2.26.2008 Introduction to...

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