geog 地理題 climate 20分

Atmospheric pressure is the pressure at any point in the Earth's atmosphere.

1. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. A column of air 1 square inch in cross section, measured from sea level to the top of the atmosphere, would weigh approximately 14.7 lbf. A 1 m² column of air would weigh about 100 kilonewtons (equivalent to a mass of 10.2 tonnes at the surface).

2.CHANGES IN ATMOSPHERIC PRESSURE


METEOROLOGIST JEFF HABY

One of the earliest forecasting tools was the use of atmospheric pressure. Soon, after the invention of the barometer, it was found that there were natural fluctuations in air pressure even if the barometer was kept at the same elevation. During times of stormy weather the barometric pressure would tend to be lower. During fair weather, the barometric pressure was higher. If the pressure began to lower, that was a sign of approaching inclement weather. If the pressure began to rise, that was a sign of tranquil weather. There is also a small diurnal variation in pressure caused by the atmospheric tides. The barometric pressure can lower by several processes, they are: