Answer to Question 1
ANSWER: We might expect to see the surface pressure dropping as the air temperature rises, and vice versa. However, daily (diurnal) fluctuation of pressure actually appear to be due primarily to the absorption of solar energy by ozone in the upper atmosphere and by water vapor in the lower atmosphere. The warming and cooling of the air creates density oscillations known as thermal (or atmospheric) tides that show up as small pressure changes near Earths surface. A good example of daily pressure fluctuations can be observed in the tropics, where pressure rises and falls in a regular pattern twice a day. Maximum pressures occur around 10:00 A.M. and 10:00 P.M., minimum pressures near 4:00 A.M. and 4:00 P.M. The largest pressure difference, about 2.5 mb, occurs near the equator. It also shows up in higher latitudes, but with a much smaller amplitude.
Answer to Question 2
ANSWER: Air does not rush off into space because the upward- directed pressure gradient force is nearly always exactly balanced by the downward force of gravity. When these two forces are in exact balance, the air is said to be in hydrostatic equilibrium. When air is in hydrostatic equilibrium, there is no net vertical force acting on it, and so there is no net vertical acceleration. Most of the time, the atmosphere approximates hydrostatic balance, even when air slowly rises or descends at a constant speed.
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