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“Station pressure” is the air pressure at a reporting location, measured using a barometer. Altitude and temperature affect readings, and weather patterns can be predicted by changes in pressure. Readings are reported in inches of mercury or hectopascals.
“Station pressure” is a term used in meteorology that describes the air pressure at the reporting location. In effect, it measures the relationship between the weight of air extending in a column directly above the measurement area and the size of the area being measured. Air pressure measurements depend on the altitude and air temperature in the station, so very different pressure readings can be given at the same time depending on where the station is located.
Although it cannot be seen or held, the air that makes up the earth’s atmosphere is very heavy. The weight of this air puts pressure on the earth’s surface, which is what is really measured to get an air pressure reading. An instrument known as a barometer is used to measure this pressure. Most barometers use liquids, mercury, or an accordion-like metal framework to contract as pressure increases and to expand as it decreases. The measurement read directly from a barometer is known as station pressure.
Station pressure can vary based on the altitude of the station. Since pressure measures the weight of air in a column above the station, the higher the station, the shorter the column of air. A station that is several thousand feet up a mountain will generally have much lower pressure readings than one at sea level, simply because there is less air above it.
Temperature is another factor that can affect station pressure readings. As the temperature drops, the air becomes slower and denser, causing the weight of the air to increase. As the weight increases, the pressure also increases, causing a higher station pressure reading. Air pressure is also usually higher at sea than on land, as water is heated more slowly than land, thus keeping the surface temperature generally lower. It is important to note that these relationships are often complicated by factors such as winds and the Earth’s rotation, however, and are usually more complex than the station’s basic concept of pressure would indicate.
Weather also plays a large part in shifting air pressure; thermometer and barometer readings are often used to predict weather patterns. A significant drop in the barometer usually indicates that the air mixture is being invaded by lighter water vapors associated with storms, hurricanes and tornadoes. If a station’s pressure drops suddenly, it can indicate a storm on the horizon. Sudden rises, on the contrary, indicate dry weather or frosts.
Station pressure numbers are usually reported in inches (or centimeters) of mercury or hectopascals. This measurement refers to how far the mercury level is pushed on a liquid-based barometer. Hectopascals, also sometimes called millibars, give a more direct reading of air pressure.
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