The following statements summarize the primary objectives presented in the chapter.
Air pressure is the force exerted by the weight of air above.
With increasing altitude there is less air above to exert a force, and thus air pressure decreases with altitude, rapidly at first, then much more slowly. The unit used by meteorologists to measure atmospheric pressure is the millibar . Standard sea level pressure is expressed as 1013.2 millibars. Isobars are lines on a weather map that connect places of equal air pressure. A mercury barometer measures air pressure using a column of mercury in a glass tube that is sealed at one end and inverted in a dish of mercury.