How Does Temperature Affect Air Pressure

and Wind?

The earth is surrounded by a layer of air that pressesdown on the earth. This pressing down is called airpressure. Most of the time you don ‘t even notice airpressure. You may have noticed a change in air pressurewhen you rode in an elevator, in an airplane, or up a hillin a car. The sudden changes in air pressure can make your ears pop.

Think about the air temperature as you go higher. Of course,it gets cooler. Near the surface of the earth, the air is warmer.The surface heats the air above it. As you move higher and higher above the earth’s surface, the air gets colder.

Not only does the temperature change as you go higher abovethe surface of the earth. The air pressure changes as well. Thehigher you are the less air is above you. Less air presses downon you. The air pressure is lower. Near the surface of the earth , the air molecules are close to-gether. Higher up the air molecules are spread out more. The molecules keep getting farther and farther apart.

What causes changes in air pressure? Temperaturechange can bring about air pressure change. Sunlight canheat the surface of the earth. As the air becomes warmer,its molecules move farther apart and the air becomes lighter.The warm air rises. As warm air rises, the warm air pushes down on the surface of the earth with less pressure. Thiscauses a low pressure area.

When the warm air rises cooler air moves in to take its place.Cooler air sinks because it is heavier than warm air. The coldair pushes down on the surface of the earth with more pressurethan warm air. This is called a high-pressure area where thecolder air sinks.

Wind is caused by air moving from an area of high pressureto an area of low pressure.

People need to know the air pressure in differentplaces so they can predict the weather. A tool called abarometer is used to measure air pressure.

One kind of barometer is made of a hollow tube that is closed on one end and open on the other. This tube is filledwith mercury. The mercury moves down the tube a little and airpressure pushes down on the mercury in the dish and holds themercury at a certain level. As the air pressure gets higher, it willpress down more. The added pressure in the dish makes themercury go higher. When the air pressure is lower, it pressesless on the mercury on the dish.

Another kind of barometer has a box inside it. The box hasa needle hooked to it. As the higher pressure pushes on thesides of the box, the needle points to a higher number on thefront of the barometer.

A tool called a wind vane shows the direction the windis coming from. The letters on the vane show which way isnorth, south, east, and west. An arrow turns to point into thewind.

A wind sock can also show wind direction.

An anemometer measures the speed of the wind. As thewind blows faster, it spins faster. A dial on the anemometershows how fast it is blowing.