What is atmospheric pressure?
Atmospheric pressure, the force per unit area of the atmosphere
It is common to hear about air pressure, for example, on the television weather programme. The problem is that few people understand what it is all about. Did you know that sailors and aviation enthusiasts use a barometer to measure the atmospheric pressure and thus receive reliable forecasts of the weather, which is closely linked to the conditions in which they carry out their activities?
Let's take things in order, starting from the origin of atmospheric pressure. The mass of the atmosphere exerts an average pressure of 1013 hectopascals (hPa) on the Earth's surface.
Note that the air pressure decreases with altitude, as the higher you go, the thinner the atmosphere becomes. From 0 to 1,000 metres above sea level, this pressure decreases on average by 1 hPa for every 10 metres. At an altitude of 5.5 kilometres, the atmospheric pressure is only about 500 hPa (twice as low as at the lowest point on Earth).
These pressure variations are the source of winds, which, through a complex mechanism also involving air temperature, determine the weather.
Measuring air pressure is therefore useful for weather forecasting, but it is not a complete substitute for measuring temperature or humidity.
The hPa, a unit of measurement for atmospheric pressure
Previously, the millibar (mb) was used as the unit of measurement for atmospheric pressure. But nowadays, this air pressure is measured in pascal or hPa (hectopascal). A short history lesson will help us understand where hPa comes from.
Indeed, Pascal was a great 17th-century scientist who worked on the subject of atmospheric pressure. According to him, 1 pascal = 1 N/m2. In this case, N stands for Newton, the unit of measurement for force. The atmospheric pressure and the pascal, therefore, define the force per unit area.
The first instrument for measuring atmospheric pressure was created in 1647: the first barometer.
Note that atmospheric pressure is most often expressed in hPa or hectopascal, as the pascal is too small: 1 hPa = 100 pascals.
How to measure air pressure accurately, without forgetting other weather data? It's easy with the Netatmo Smart Weather Station ! Find all your weather data (but also your indoor air quality or noise pollution level) on your smartphone.
Why measure air pressure at home?
When you hear about the weather, can you imagine measuring temperature, humidity (the amount of water vapour in the air), sunshine forecasts, and the likelihood of rain? This is not completely wrong… but it is incomplete.
Any weather forecast is based on the measurement of atmospheric pressure (in hPa). This measurement, taken with a device that has a barometer function, is a valuable indicator for anticipating the weather and especially the wind.
The pressure of the atmosphere on the Earth is an important indicator and you will soon see why. The first thing to know is that in the temperate zones of the Earth, the pressure varies on average from 950 hPa to 1050 hPa. However, it can change very quickly, indicating bad weather ahead if it drops quickly and rather pleasant weather if it rises.
In terms of numbers, consider 1010 hPa and 1020 hPa. If the air pressure falls below the first threshold of 1010 hPa, we are talking about a low-pressure system (or just low-pressure conditions). When it rises above 1020 hPa, on the other hand, there is an anticyclone (or anticyclonic conditions).
Atmospheric pressure, therefore, has a direct (though still poorly explained) influence on temperature, weather, and weather in general on Earth.
Measuring the pressure in the atmosphere in front of your home allows you to accurately anticipate the weather in the coming hours.
Temperature, humidity, air quality, weather… and especially atmospheric pressure, the Netatmo Smart Weather Station allows you to measure all the data that matters: the data right in front of your house and inside your house! So you never have to miss out on the sunshine! Easily view historical variations to better predict and anticipate changes.
How to measure air pressure?
Mercury barometer, aneroid barometer, weather station… what are the instruments for measuring atmospheric pressure?
Temperature has a thermometer, humidity has a hygrometer, wind speed is measured with an anemometer… and air pressure has a barometer (or other devices with this function, like a weather station).
Today, the aneroid barometer is the most widely used device for measuring atmospheric pressure.
The barometer, therefore, measures the pressure of the atmosphere on the Earth's surface and expresses it in hPa. Knowing how to interpret this measurement as explained above allows you to anticipate a change in the weather: is it likely to rain? Should the weather be good? Nothing is ever certain, of course, but the predictions remain likely. It is by combining temperature, pressure, wind, and other indicators that meteorologists produce the weather forecasts you see on your smartphone or TV.
One last remark: why place a sensor inside the house (barometer or weather station) to measure the outside pressure? Simply because it is identical inside and outside: no dwelling is sealed off from the outside atmosphere.
Anticipating the weather, the sun, and its sunshine, and the rain with precision is not magic! But to do this accurately, it is ideal to have a barometer, thermometer, hygrometer, anemometer, or a weather station that combines these functions. They will all help you to know why the weather is so bad at times. Measuring air pressure, temperature, humidity, and wind speed is the key to realistic weather forecasts!