19.1 Understanding Air Pressure What is Air Pressure? The force exerted by the weight of a column of air above a given point Exerted in all directions The air pressure pushing down on an object exactly balances the air pressure pushing up on the object Barometer – used for measure air pressure Air pressure rises, mercury in the tube rises (and opposite) Factors Affecting Wind Wind is the result of differences in pressure Air flows from areas of higher pressure to areas of lower pressure The unequal heating of Earth’s surface generates pressure differences Solar radiation is the ultimate energy source for most wind Named based off what direction it comes from Continued… 3 Factors combine to control wind Pressure Differences - Pressure Gradient - Closely spaced isobars indicate a steep pressure gradient & high winds. - Widely spaced isobars indicate a weak pressure gradient & light winds Coriolis Effect Friction - Slow air movement (changes wind direction) - Most prominent features of airflow high above the friction layer is the jet streams In a high pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds CANNOT form. In a low pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds are LIKELY to form. low pressure warm or cold air air rising or sinking clouds or no clouds clockwise or counterclockwise wind direction winds toward or away from the center high pressure Review Questions What is the ultimate energy source for most wind? Why do jet streams flow parallel to isobars? How does the Coriolis effect influence motion of freemoving objects?