What is a Pressure System?

A pressure system is defined as the relative peak in the sea level pressure distribution. The lowest value that is measured is 87 kilopascals and the highest value that is measured is 108.57 kilopascals. In a pressure system, pressure refers to the distance travelled by the air molecules. The pressure is said to be high when the air molecules are squeezed and packed together. The pressure is to be low when the air molecules are spread apart. It is important to understand that the high pressure is denser than the low pressure.

What is Low-Pressure System?

A pressure system is said to be a low-pressure system when the pressure at the centre is low. When the wind blows towards the low pressure, there is a rise in the air such that the water vapour meets the air in this place. When there is an interaction between the air molecules and the water vapour, the water vapour condenses and forms clouds and results in precipitation. At the north of the equator, the low-pressure system always swirls in counterclockwise while at the south of the equator, the low-pressure system swirls clockwise. This is known as the cyclonic flow. The low-pressure system is labelled with red L on the weather maps.

What is High-Pressure System?

A pressure system is said to be a high-pressure system when the pressure at the centre is high. When the place is at high pressure, the wind blows away. The movement of the wind is in the opposite direction from the low-pressure system. In the high-pressure system, the wind swirls in a clockwise direction near the north of the equator and near the south of the equator, the wind swirls in an anticlockwise direction. This is known as anticyclonic flow. The high-pressure system is labelled with blue H on the weather maps.

Measurement of Pressure 

In the olden days, barometers were used for measuring the pressure. This was possible as they used mercury and by studying the change in the level of the mercury in the barometer, one could tell what was the pressure system type. 


These days, electronic sensors are used in weather stations for the measurement of the air pressure. In olden days, when barometers were, the air pressure was expressed as inches of mercury whereas today the air pressure is expressed as millibars.

Factors Affecting Air Pressure

Air pressure is dependent on temperature and density. The temperature of the air molecules and the density of air molecules determine the air pressure. This is explained with the help of a balloon experiment.


Consider an inflated balloon. The air molecules in the balloon are more tightly packed than the air molecules outside the balloon. This means that the density of air inside the balloon is high and therefore, the air pressure is high. 


Also, there is a relationship between pressure, temperature, density, and volume and this is known as an ideal gas equation. According to an ideal gas equation, the pressure is the product of temperature, density, and a constant. Also, the product of pressure and volume is the same as the product of temperature and constant.

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