How do barometers work? Atmospheric pressure and weather forecast.

The aneroid barometer, designed by the French scientist Lucien Vidie in 1843, consists of a small, sealed, flexible metal case. Small changes in air pressure outside the box cause the box walls to deform, because the pressure inside the box is unchanged. The deformation of the box walls activates a mechanical device that translates into the movement of a needle on a graduated scale. In this way, the movement of the needle represents the variations of atmospheric pressure.

The mercury barometer and the aneroid barometer

The mercury barometer has the disadvantage that it uses mercury, a toxic heavy metal. And, due to the characteristics of its design, it is bulky and fragile. Aneroid barometers are a very common alternative to liquid barometers. They are accurate and practical, more compact than mercury barometers, and better suited for many uses. Aneroid barometers are most commonly used in homes and on small aircraft.

Barometers on mobile phones

Even if you don’t have a barometer at home, at the office, on a boat, or on an airplane, your smartphone probably has a built-in digital barometer. Digital barometers work like an aneroid, except that the mechanical parts are replaced by a pressure sensor. So why do phones have an atmospheric pressure sensor associated with weather data ? Many mobile phone manufacturers incorporate it to improve the altitude measurements provided by GPS services on phones, since atmospheric pressure is directly related to elevation.

Millibars, millimeters of mercury and pascals

Barometric pressure can be measured in any of the following units.

• Millimeters of Mercury (mm Hg) . They are the most common units associated with the operation of mercury barometers. They record the height of the mercury column in millimeters.
• Millibars (mb) . Units of atmospheric pressure used by meteorologists. It is one thousandth of a bar, which is a unit of measurement for gas pressure.
• Pascals (Pa) . SI internal system pressure units. 1 mb is equivalent to 100 pascals.
• Atmospheres (Atm) . It is the atmospheric pressure at sea level at a temperature of 15°C.

To convert the values ​​of atmospheric pressure between the different units, the following equivalences can be used.

760 mm Hg = 1 Atm = 101325 Pa = 1013.25 mb

Fountain

Dominguez, Hector. Our atmosphere: how to understand climate change. LD Books. ISBN 9707320524.