Barometric Pressure

Barometric (or atmospheric) pressure is the weight of the column of air above a given point, reported in hectopascals (hPa, numerically equal to the older millibar). At sea level it averages around 1013 hPa, but it varies continuously as weather systems move: high-pressure systems bring settled, dry conditions, while falling pressure signals approaching low-pressure systems, wind, and precipitation. Pressure also falls predictably with altitude, which is why the same instrument doubles as an altimeter once the local sea-level pressure is known. It is one of the oldest quantitative weather measurements and remains fundamental to forecasting.

Modern instruments use a MEMS piezoresistive or capacitive pressure sensor: a tiny silicon diaphragm flexes under atmospheric pressure, and the resulting change in resistance or capacitance is measured and digitized. These sensors are small, low-power, stable, and accurate enough for both weather monitoring and altitude estimation, which is why they are built into phones, drones, and environmental monitors alike. For reference meteorology, higher-grade digital barometers with tighter calibration are used. Readings are usually reported both as station pressure (the raw value at the instrument) and as pressure reduced to mean sea level, so that stations at different altitudes can be compared on the same synoptic chart.