Air near the surface flows down and also away in a high pressure system (left) and also air flows up and together in ~ a short pressure system (right).Credit: NESTA


Standing top top the ground and also looking up, you room looking v the atmosphere. It could not look prefer anything is there, specifically if there room no clouds in the sky. Yet what friend don’t check out is air – lots of it. Us live at the bottom of the atmosphere, and also the weight of all the air over us is called air pressure. Over every square customs on the surface ar of the planet is 14.7 pounds of air. That way air exerts 14.7 pounds per square customs (psi) of press at earth surface. High in the atmosphere, air press decreases. V fewer air molecules above, there is much less pressure native the weight of the wait above.

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Pressure varies from day to day at the Earth’s surface - the bottom that the atmosphere. This is, in part, due to the fact that the earth is no equally heated by the Sun. Areas where the air is warmed often have lower pressure because the heat air rises. These areas are called low pressure systems. Areas where the air press is high, are dubbed high push systems.

A low pressure system has actually lower pressure at its center than the areas around it. Winds blow towards the short pressure, and the wait rises in the atmosphere where lock meet. Together the waiting rises, the water vapor within it condenses, developing clouds and also often precipitation. Since of earth spin and also the Coriolis Effect, winds of a low pressure device swirl counterclockwise phibìc of the equator and clockwise south of the equator. This is dubbed cyclonic flow. ~ above weather maps, a short pressure mechanism is labeled v red L.

A high press system has greater pressure at its facility than the areas about it. Winds punch away indigenous high pressure. Swirling in the contrary direction indigenous a low pressure system, the winds that a high pressure system rotate clockwise north of the equator and counterclockwise southern of the equator. This is called anticyclonic flow. Wait from higher in the atmosphere sinks down to fill the space left as air is blown outward. On a weather map, girlfriend may notification a blue H, denoting the ar of a high push system.

How do we recognize what the press is? just how do us know how it alters over time? Today, digital sensors in weather stations measure up air pressure. This sensors are able come make consistent measurements of push over time. In the past, barometers were used and measured just how much air thrust on a fluid, such as mercury. Historically, measurements of air press were described as “inches that mercury.” Today, meteorologists usage millibars (mb) to explain air pressure.

Air push depends ~ above temperature and also density.

When friend inflate a balloon, the wait molecules inside the balloon get packed much more closely with each other than air molecules external the balloon. This method the density of wait is high inside the balloon. As soon as the density of air is high, the air push is high. The press of the waiting pushes top top the balloon indigenous the inside, resulting in it come inflate. If you warmth the balloon, the air press gets also higher.

Air pressure depends ~ above the temperature that the air and also the density of the wait molecules.

Atmospheric scientists use math equations to describe how pressure, temperature, density, and also volume are related to each other. They speak to these equations the Ideal Gas Law. In these equations, temperature is measure up in Kelvin.

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This equation help us define how weather works, such as what wake up in the atmosphere to produce warm and cold fronts and also storms, such together thunderstorms. For example, if air press increases, the temperature must increase. If air press decreases, the temperature decreases. It likewise explains why waiting gets cooler at higher altitudes, where push is lower.