Pressure Systems

In the article, we will learn what pressure systems are and the different types of pressure systems that we observe while forecasting the weather and their effects on us.

What are Pressure Systems?

Have you ever wondered why it rains one day and the very next day it is perfect for a trip to the beach? A lot of factors go into this fickle weather system, and the pressure system is one of the major factors.

A pressure system is an area of the Earth’s atmosphere that has a particularly high or low pressure compared to the surrounding air. We live at the bottom of the atmosphere, and the weight of all the air above us is known as air pressure. Pressure varies from day to day at the Earth’s surface because the earth is not equally heated by the sun. Areas that consist of warm air have low pressure because the warm air rises. These areas are known as low-pressure systems. Likewise, places with high air pressure are known as high-pressure systems.

Air always flows from high-pressure areas to low-pressure areas to reduce pressure difference and reach equilibrium. The rotation of the earth generates a force known as the Coriolis effect which stops the air from moving in straight lines. Rather the wind moves spirally: inwards and upwards in low-pressure systems, downwards and outwards in high-pressure systems.

Low-Pressure System

A low-pressure area is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in upper levels of the troposphere.

A low-pressure system is formed due to localized heating caused by greater sunshine over deserts and other landmasses. Since the warm air in localized areas is less dense than the surroundings, the warm air rises, lowering the atmospheric pressure. Large scale thermal lows over continents help create pressure gradients that drive monsoon circulations. Due to Earth’s spin and the Coriolis effect, winds of a low-pressure system swirl counterclockwise. This type of flow is known as cyclonic flow.

Around the world, the low-pressure systems are most frequently located over the Tibetan Plateau and the lee of the Rocky Mountains. In Europe, the recurring low-pressure weather system is known as depressions.

For better understanding

High-Pressure System

High-pressure systems are normally associated with light winds at the surface and subsidence at the lower portion of the troposphere. Subsidence dries out an air mass by adiabatic or compressional heating. Hence, high pressure usually results in clear skies. Since no clouds are present to obstruct the incoming shortwave solar radiation, the temperature rises during the day. At night, due to the absence of clouds, the outgoing longwave radiation is not absorbed and results in cooler low temperatures in all seasons. A high-pressure system swirls in the opposite direction from a low-pressure system. This type of flow is known as anticyclonic flow.

Air Pressure, Temperature, and Density

When you blow a balloon, the air molecules inside the balloon get packed more closely than the air molecules outside the balloon. This implies that the air density is higher inside the balloon. Higher density implies higher pressure. The air pressure from inside the balloon causes it to inflate. Heating the balloon results in higher air pressure. Atmospheric scientists use the following mathematical equation to describe the relationship between temperature, density, and volume. These equations are known as the Ideal Gas Law.

Ideal Gas Laws

The equations help us explain how weather works, such as what causes the atmosphere to create thunderstorms and why the air gets colder at higher altitudes, where the pressure is lower.

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