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# chapter6 - Chapter 6 Air Pressure and Winds Air Pressure at...

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Chapter 6 Air Pressure and Winds Air Pressure at a point is the pressure (force/area) exerted by the weight of the air above that point. -It's the same in all directions around that point. -Avg. air pressure = 101,325 N/m^2 1mb = 100 pascals 1013.25mb Measuring Air pressure 1. Measured by mercury barometers and aneroid barometers 2. Air pressure measurements are converted to sea level equivalents 3. Horizontal variations in pressure are small 4. Pressure ranges between 30 and 60 millibars above or below average sea-level pressure Factors affecting air pressure- ideal gas law pv=nrt p-pressure v-volume n-# of mols in v R- constant T- Temperature 1. n and T are constant then the pressure is inversely proportional to the volume 2. n and v are constant then an increase in temperature means an increase in pressure 3. In atmosphere, n does not remain constant. In the atmosphere, a decrease in temperature leads to an increase in density, which usually leads to an increase in pressure. Temp and Pressure- Air pressure is high if temp is low, because there is more air in the column above you. Air pressure is low if temp is high Water content and pressure Water has a molecular weight of 18 Nitrogen = 28 Oxygen = 32 Water vapor is lighter than air humid air is lighter than dry air humid air exerts lower pressure Pressure changes with altitude 1. Altitude increase, air decreases, pressure decreases 2. Pressure drops about ½ every 5.6km 3. aircraft follow surfaces of constant pressure Air Flow and Pressure Convergence-happens when wind blows into a region, if it can't move horizontally, it piles up and the

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pressure rises. Divergence- wind blows air away from a region and so the pressure lowers.
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chapter6 - Chapter 6 Air Pressure and Winds Air Pressure at...

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