Barometric pressure, also known as atmospheric pressure, refers to the pressure exerted by the air layers that make up the Earth’s atmosphere. Heavy, dense pockets of air result in relatively higher pressure, while the rising of warm, surface-level air causes lower pressure. Atmospheric pressure affects the weather as high and low-pressure systems move around the globe, so it is frequently used by meteorologists for short-term weather forecasts.
Instruments used to measure barometric pressure are called barometers. The standard unit of measurement is simply called atmospheres (atm), equivalent to the average air pressure at sea level at 15°C, but it is frequently expressed in pressure units such as Pascals / hectopascals / kilopascals (Pa / hPa / kPa), bars / millibars (bar / mbar), or millimeters / inches of mercury (mmHg / inHg), depending on application and region.
One atmosphere is equivalent to 1013 mbar or 29.92 inHg. The typical range of barometric pressure is from about 965-1040 mbar (28.5-30.7 inHg). However, extreme cases are known to have produced pressures lower than 900 mbar and higher than 1070 mbar.
Barometric pressure has standard units of atmospheres (atm) but is commonly reported in various units depending on region and application.
At higher altitudes, there is lower atmospheric pressure because air is less dense and “thinner”. A 10m rise in elevation above sea level will typically result in a pressure drop of about 1 hPa (1 mbar). For comparability between measurement locations, pressure readings are sometimes adjusted to equivalent sea level pressure using a formula that takes elevation and air temperature into account.
Why Measure Barometric Pressure?
Barometric pressure is one of the most influential parameters affecting the weather, as it can tell a great deal about the short-term weather forecast.
High-pressure systems are associated with clear skies and dry air as the dense air pushes away clouds and moisture. Falling barometric pressure is likely to bring precipitation and storms as warm, surface-level air rises and forms clouds. Low pressure also allows air to move more freely, so it can lead to stronger winds. When located over warm sea waters, low-pressure systems can lead to the formation of typhoons, hurricanes, and tropical cyclones.
Besides weather forecasting, there are several other reasons that atmospheric pressure may be measured:
- Aviation: Pilots use pressure readings to adjust their altimeters and ensure safe and accurate flight levels.
- Marine Navigation: Barometric pressure readings are used to predict sea conditions, aiding in navigation and safety during maritime activities.
- Health and Comfort: Some people are sensitive to pressure changes, which may affect conditions like arthritis or migraines. Monitoring pressure can help pressure-sensitive individuals anticipate and manage their symptoms.
How Is Barometric Pressure Measured?
The mercury barometer was the first practical instrument type developed for atmospheric pressure measurement. Mercury barometers consist of a tube with closed top and open bottom placed into a pool of mercury. The mercury in the tube rises and falls as the atmospheric pressure changes. This is where the units of millimeters/inches of mercury originate. While mercury barometers are still used today, modern sensors for environmental measurement systems rely on capacitive or piezoresistive pressure sensors.
Capacitive sensors work by using a diaphragm, often silicon-based, that physically deforms as pressure increases, leading to a measurable change in capacitance (the ability to store electrical charge).
Piezoresistive sensors operate similarly with pressure-based deformation of a silicon-based or ceramic membrane, but they produce a change in electrical resistance rather than capacitance.
In both cases, the measured changes are converted into an electrical signal that can be output directly or into a digital format that can be recorded by a data logger.
How to Select a Barometric Pressure Sensor?
When selecting a barometric pressure sensor, the most important considerations include accuracy, resolution, stability, and environmental conditions.
Accuracy and resolution are important to ensure that the sensor meets the required precision for the application. Meteorological agencies or other authorities often specify such requirements. Typical barometric pressure sensors offer accuracies within ±0.5 hPa or better and resolutions up to 0.01 hPa.
Long-term stability is crucial for applications requiring measurement consistency over extended periods. This is important for remote stations that will operate for lengthy periods of time without recalibration.
Consider the environmental conditions to which the barometer will be exposed, including temperature ranges and humidity levels. Some sensors are designed to withstand extreme conditions, making them suitable for harsh environments.
What to Consider When Preparing a Barometric Pressure Sensor?
Calibration, ventilation, and mounting are crucial to acquire high-quality barometric pressure data. Most sensors arrive with a factory calibration and require minimal maintenance, but periodic calibration may be advisable in some applications to maintain long-term measurement accuracy.
Sensor placement and mounting have a great influence on measurement quality. The sensor must be properly ventilated to accurately measure atmospheric pressure and not localized pressure within an enclosed space. However, it should not be directly exposed to winds as air movement can introduce error into the measurements.
Sensors should also be protected from direct sunlight, precipitation, and debris that can affect readings. Most sensors have enclosures or shields that may be used to mitigate these effects.
How to Deploy a Barometric Pressure Measurement System?
Barometric pressure sensors are frequently integrated into multiparameter instruments that simplify setup and data acquisition. These instruments typically include a mounting bracket for placement on a mast and shield for proper protection of the sensing element.
Barometric pressure sensors are often a component of multi-parameter weather station instruments.
Some applications or weather station standards may require a dedicated barometer that is not a part of a multi-parameter instrument. These instruments allow for measurement at a specific height on a mast, which may be different from other meteorological measurements. They will typically include their own pole or mast-mount and shield or enclosure for proper protection and venting.
Barometers in marine applications are frequently mounted on buoy platforms or ships. These are especially humid environments, so the sensor’s protective housing must be particularly robust to avoid interference from splashing, condensation, and physical motion, which can be quite rough during adverse weather conditions.
Conclusion
Barometric pressure measurement is a fundamental aspect of meteorology and environmental monitoring due to its influence on atmospheric phenomena. Accurate barometric pressure data is essential for weather forecasting, climate studies, aviation, and various scientific research applications.
Proper sensor venting and mounting location are essential for obtaining accurate measurements. By implementing these and other best practices, meteorologists, researchers, and environmental scientists can gather high-quality barometric pressure data.
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