Atmospheric pressure influences the weather because it is related to the movements of air in the atmosphere. High pressure typically brings good weather, as the air descends and warms up, while low pressure is associated with more unstable and rainy weather conditions due to the rising and cooling air, forming clouds and precipitation.
Atmospheric pressure is simply the weight of the air above your head. Yes, even if you don't feel it, air has its own weight and it weighs quite a lot: about 1 kilogram per square centimeter at sea level! The higher you go, the less dense the air is, and thus the pressure drops rapidly. Conversely, at sea level, the column of air above is thicker, resulting in higher pressure. This pressure is generally measured with a device called a barometer. Changes in pressure give us precise clues about upcoming weather conditions: a sudden drop often signals a disturbance, while a rise usually indicates the return of good weather.
Atmospheric pressure is strongly dependent on temperature: warm air is lighter, so it rises, causing the pressure near the ground to drop. Conversely, cold air, being denser, will sink and increase the pressure close to the ground. Humidity also plays an important role in this: humid air contains water vapor that is lighter than dry air, which slightly decreases its density, and thus also decreases its pressure. The result: when the pressure drops, you can often expect humid and cloudy weather, while rising pressure generally promises a rather clear, dry, and cool sky.
The weather systems you often see in the news, like cyclones and anticyclones, mostly come from stories about atmospheric pressure. When warm air rises because it is less dense, it leaves behind a low-pressure area. This then attracts the surrounding air, which rushes in to fill this relative void, much like when you pull the plug from your bathtub: the water rushes toward the opening. This movement creates a whirlwind that, on a large scale, gives a cyclone. Conversely, regions where the air descends from the upper layers form a high-pressure area, which is therefore called an anticyclone. In there, the air is more stable and dry, which explains why an anticyclone is often accompanied by calm and sunny weather. The Earth's rotation adds an extra touch by causing these systems to spin around themselves (this is the Coriolis effect). That’s why cyclones spin one way and anticyclones spin the other, depending on the hemisphere they are in.
Basically, when atmospheric pressure drops somewhere, the warm and humid air present at the surface starts to rise. As it rises, it cools and eventually forms clouds. The result: we often get precipitation (rain, snow). Conversely, when pressure increases, the air descends while warming and drying out, so there is less chance of rain and more nice weather.
Pressure differences also explain how winds work. Air always flows from a high-pressure area (anticyclone) to a low-pressure area (depression), creating wind in the process. The greater the pressure difference between two areas, the stronger the wind will be. This is how we get powerful storms when two opposing systems collide, for example.
To measure atmospheric pressure, the most classic tool remains the barometer. This instrument directly indicates pressure variations and allows meteorologists to predict the weather for the coming days. Today, electronic sensors are primarily used, placed in weather stations or onboard weather balloons and satellites. Thanks to these tools, meteorologists identify high-pressure areas (anticyclones) associated with good weather, or low-pressure areas (depressions) synonymous with rain and wind. Closely monitoring these variations helps anticipate the arrival of a storm or, conversely, a clear sky, which is extremely useful both on a daily basis and in the case of extreme weather events.
The atmospheric pressure at the summit of Everest is about one third of that measured at sea level. This is why climbers must carry oxygen tanks to breathe properly at these extreme altitudes.
In meteorology, a sudden drop in barometric pressure generally indicates the rapid arrival of a disturbance or a severe thunderstorm. Regular readings of the barometer can help anticipate them!
The world record for the highest atmospheric pressure measured at sea level is 1083.8 hPa, recorded in Siberia, Russia, on December 31, 1968, leading to an intense cold wave.
Some animals, such as birds and insects, can sense changes in atmospheric pressure. This particular sensitivity sometimes allows them to anticipate bad weather early enough to seek shelter.
Anticyclones are characterized by high atmospheric pressure, which generally implies stable and sunny weather, whereas depressions have low atmospheric pressure and are often associated with unstable weather conditions, including clouds, strong winds, and precipitation.
Indeed, many animals, including birds, fish, and pets, seem to be very sensitive to fluctuations in atmospheric pressure. These changes can prompt them to seek shelter, alter their activity, or anticipate the arrival of a specific weather event.
A rapidly falling atmospheric pressure generally indicates that the weather will become unsettled, with stronger winds, an increase in cloudiness, and potentially precipitation. A slowly rising pressure often indicates a gradual return to calmer and drier weather.
The differences in atmospheric pressure between regions mainly depend on altitude, temperature, and humidity. For example, at sea level, the pressure is generally higher than at altitude due to the amount of air above the surfaces. Additionally, warm regions tend to have lower pressure compared to cold areas.
Our body continuously adjusts to environmental conditions. A rapid change in atmospheric pressure alters the internal pressures of the body, sometimes causing discomfort, joint pain, or headaches in certain sensitive individuals.
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