Pressure is defined as force per unit area applied to a surface in a direction perpendicular to the surface. Barometric sensor pressure is the force per unit area exerted on Earth’s surface by the mass of air overlying the surface. High pressure indicates more atmospheric air mass over a given area, whereas, low pressure indicates less atmospheric air mass. Barometric pressure is strongly dependent on elevation, and decreases as elevation increases, due to the less overlying air above the surface (shorter column of air) at higher elevations.
- Aeroid barometer- Capacitive element to sense pressure.
- Water-based Barometer- Water is poured into the spout.
- Mercury barometer- Mercury is poured in a glass
- Vacuum pump- Vacuum oil is poured
Barometric pressure and the pressure tendency (the change of pressure over time) have been used in weather forecasting since the late 19th century. When used in combination with wind observations, reasonably accurate short-term forecasts can be made. Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced, which were the first form of the modern weather map when created in the 19th century. Isobars, lines of equal pressure, when drawn on such a map, give a contour map showing areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Atmospheric lift caused by low-level wind convergence into the surface brings clouds and sometimes precipitation. The larger the change in pressure, especially if more than 3.5 hPa (0.1 inHg), the greater the change in weather that can be expected. If the pressure drop is rapid, a low pressure is approaching, and there is a greater chance of rain. Rapid pressure raises, such as in the wake of a cold front.