| 1. | the pressure exerted by the earth's atmosphere at any given point, being the product of the mass of the atmospheric column of the unit area above the given point and of the gravitational acceleration at the given point. |
| 2. | a value of standard or normal atmospheric pressure, equivalent to the pressure exerted by a column of mercury 29.92 in. (760 mm) high, or 1013 millibars (101.3 kilopascals). |
| atmospheric pressure n. Pressure caused by the weight of the atmosphere. At sea level it has a mean value of one atmosphere but reduces with increasing altitude. |
atmospheric pressure  (āt'mə-sfîr'ĭk) Pronunciation Key
The pressure at any location on the Earth, caused by the weight of the column of air above it. At sea level, atmospheric pressure has an average value of one atmosphere and gradually decreases as altitude increases. Also called barometric pressure. Our Living Language : The weight of the air mass, or atmosphere, that envelopes Earth exerts pressure on all points of the planet's surface. Meteorologists use barometers to measure this atmospheric pressure (also called barometric pressure). At sea level the atmospheric pressure is approximately 1 kilogram per square centimeter (14.7 pounds per square inch), which will cause a column of mercury in a mercury barometer to rise 760 millimeters (30.4 inches). The pressure is frequently expressed in pascals, after the French mathematician and philosopher Blaise Pascal, who studied the transmission of pressure in confined fluids. Subtle variations in atmospheric pressure greatly affect the weather. Low pressure generally brings rain. In areas of low air pressure, the air is less dense and relatively warm, which causes it to rise. The expanding and rising air naturally cools, and the water vapor in the air condenses, forming clouds and the drops that fall as rain. In high pressure areas, conversely, the air is dense and relatively cool, which causes it to sink. The water vapor in the sinking air does not condense, leaving the skies sunny and clear. |
