63 Clouds, Wind, and Storms-High

Clouds, Wind, and Storms Written by Kira Freed

Introduction Somewhere on Earth, almost every type of weather is happening right now. Some places have light, puffy clouds. Heavy rain or snow is falling in other places. Did you ever wonder what causes all these types of weather? Our planet is surrounded by a layer of air called the atmosphere. The atmosphere is made of masses of air that are constantly moving and mixing. Warm air masses mix with cold air masses. Dry air masses mix with wet air masses. The mixing of air masses causes wind, clouds, precipitation, and storms.

Weather happens near Earth's surface. The Sun's energy warms Earth's surface, which warms the air above it. But not all surfaces are heated equally. The parts of Earth closer to the equator get more heat than polar regions. Darker surfaces absorb more energy than lighter surfaces. Also, Earth's tilt makes parts of Earth get more sunlight than other parts during different seasons. When air that has received more heat from Earth's surface mixes with air that has received less energy, the result is weather. Weather is determined by the amount of wind, clouds, and precipitation.

Wind Wind is simply air on the move. We can't see it, but we can feel it. And we can see its effects on plants, flags, wind chimes, and other things. As air near Earth's surface gets warmed by its heat, the air gets lighter. The colder air, which is heavier, pushes down on it, squeezing it upward. As the warm air rises, it cools. As the cold air gets closer to the ground, it warms. Air is always moving, warming, and cooling, which makes wind.

Think about the city of Chicago, which is on Lake Michigan. When the Sun is shining, the air over land heats up more than the air over water. As warm air over the city rises, cooler air over the lake moves toward the land to replace the rising warm air. The movement of air creates a breeze from the lake to the land. This is called a sea breeze. Why is wind strong sometimes and just a light breeze at other times. Wind is stronger when the difference in temperature between the warm air mass and the cool air mass is great. When this happens, the cold air "chases" the warm air faster.

Changes in weather are created when air masses of different temperatures meet each other. The line where a warm air mass and a cold air mass meet is called a front. Changes in weather tend to happen along a front. Have you ever noticed the lines on a weather map? Those lines show the location of fronts. Measuring the Wind We measure the wind with an instrument called an anemometer. People measure the wind for many reasons. Information about wind speeds helps scientists predict the weather. Airplane pilots cannot take off or land if the wind is blowing too hard. Ship captains require safe wind speeds to enter harbors. Machines called wind turbines convert fast- moving wind into electricity. In some locations, the wind is too calm to use wind turbines.