Changes to atmospheric pressure due to changes in temperature

The below article talks about atmospheric pressure, how temperature affects atmospheric pressure, along with some frequently asked questions about the same. 

What is atmospheric pressure?

Atmospheric pressure, a.k.a. Barometric pressures refer to the amount of force exerted per unit area in a specified atmospheric column. It is measured using a mercury barometer, a.k.a. Barometric pressure, or an aneroid barometer. There are several factors that determine the changes to atmospheric pressure including the earth rotation, gravitational force, temperature, altitude, humidity, etc. The below article talks in detail about atmospheric pressure. 

Atmospheric Pressure 

When we look up into the sky, there is one thing we never see- air, lots of it. We live at the very bottom of the atmospheric layers and the weight of the air above us can be referred to as the atmospheric pressure. It is estimated that there are 14.7 pounds of air per square inch of the Earth; which means that the air exerts 14.7 pounds per sq. inch (psi) of pressure on the surface of the Earth (UCAR, n.d.). As we move higher up into the atmospheric layers, the atmospheric pressure decreases; and this can be explained by the fact that as we move higher there are lesser air molecules present to exert the same kind of force we see in the lower atmospheric levels. 

Since the surface of the Earth receives unequal amounts of heating, air pressure over the surface of the Earth is prone to constant change. When air is warmed by the Sun, the pressure decreases as warm air rises, and these areas are called low-pressure systems, and areas with higher air pressure are referred to as high-pressure systems 

Source: UCAR, n.d.

A high-pressure system is characterized by higher pressure at the center in comparison to other areas around it. Therefore, winds tend to move away from the center into lower pressure areas in the surroundings, and thus rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. This is called an anti-cyclonic flow, and due to this phenomenon, air from the higher atmospheric levels tends to move downwards as air from the center of the system moves outwards into lower pressure areas. On maps, a high-pressure system is labeled with an “H”. A low-pressure system is characterized by lower pressure at the center in comparison to other areas around it. Wind tends to move towards areas of lower pressure, and air rises. As the air rises, water vapor condenses to form clouds and eventually causes rainfall. Due to the Earth’s spin and the Coriolis effect, a low-pressure wind system that moves counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. This phenomenon is also called the cyclonic flow and on maps are labeled with an “L”. 

Factors that influence Atmospheric Pressure

There are several factors that contribute towards determining a high or low-pressure system. Some of these factors include temperature, altitude changes, humidity, earth’s gravity, and rotational force. Below is an explanation of how the changes in temperature lead to changes in air pressure. 

Air expands on heating, which causes a decrease in density and thus lowers pressure. Similarly, the density of the air increases as temperatures decrease, thus creating high-pressure systems. Areas towards the equator, therefore, are low-pressure systems, and areas towards the polar regions are high-pressure systems. Due to which it is said that these two elements are inversely proportional, and their relationship is captured in the below sentence:

“When the mercury of the thermometer rises, the mercury of the barometer falls.”

Frequently Asked Questions (FAQs): Are there changes to air pressure due to changes in temperature? 

What causes high pressure in air masses?

High-pressure air masses are usually formed by sudden cooling of the air masses, either from the regions below the air mass such as being cooled by the ocean waters or from above the air mass which happens via infrared cooling of masses over land where cooling of the air mass would precede any condition that may cause its warming. High-pressure air masses at a ground level are caused by air that is moving downwards, and in a high-pressure area, i.e., where the atmospheric pressure at the surface is higher than that of the environment leads to an anticyclone. This is when winds from the high-pressure area move outwards from the center into low-pressure areas. 

What causes a low-pressure air mass? 

Low pressure refers to pressure put downwards onto the surface of the earth. A low-pressure system is when the center of the system has lower pressure than its surrounding environments. Winds would blow inwards from high-pressure areas, and the air in the center of the mass would rise up, causing a cyclone. As air rises, water vapor condenses, forms clouds, and gives precipitation. Usually, tropical and warm air masses have lower pressure.

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References

Jensen D. (2017, April 03). What causes an air mass to have low pressure. Viewed on Quora on 02-14-2022. https://www.quora.com/What-causes-an-air-mass-to-have-low-pressure 

UCAR Center for Science Education (UCAR). (n.d.). The highs and lows of air pressure. How Weather Works. Viewed on 02-14-2022. https://scied.ucar.edu/learning-zone/how-weather-works/highs-and-lows-air-pressure 

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