Water and the Atmosphere - Chapter 3 Lesson 6 Winds Water and the Atmosphere - Chapter 3 Lesson 6

Windsurfing Planet Diary Imagine being able to ride a wave at almost 81 km/h—not in a boat powered by a motor but on a board powered only by the wind. That’s what windsurfing is all about. Windsurfers stand on a sailboard, which is similar to a surfboard. But the sailboard has a mast and a sail that the surfer can control with his or her hands. It uses a sail to capture wind and move the surfer along the surface of the water. Jim Drake, one of the first inventors of windsurfing, points out: “It’s the simplicity of standing up so you can adjust your weight and move quickly, as well as actively participate in transmitting the sail’s forces to the board.” How does wind move the sail? How have you experienced the effects of wind?

How Do Local Winds and Global Winds Differ? Key Concept Summary Winds that blow over short distances are called local winds. They are caused by the unequal heating of Earth's surface within a small area and form only when large-scale winds are weak. Two types of local winds are sea breezes and land breezes. A sea breeze is a local wind that blows from an ocean. During the day land warms faster than water. The air above the land heats and rises, and cool air from the ocean flows in to take its place. At night the process is reversed, land cools faster than the ocean. The flow of air from land to a body of water forms a land breeze.

How Do Local Winds and Global Winds Differ? Key Concept Summary Global winds are winds that blow steadily from specific directions over long distances. Global winds are created by the unequal heating of Earth's surface over a large area. Because of Earth's spherical shape, rays from the sun strike directly at the equator but hit the poles at an angle. As a result, temperatures near the poles are much lower than near the equator. The difference produces giant convection currents in the atmosphere. Surface winds blow from the poles toward the equator. Higher in the atmosphere, winds flow from equator to poles.

How Do Local Winds and Global Winds Differ? Key Concept Summary The way Earth's rotations make winds curve is called the Coriolis effect. Because of the Coriolis effect, global winds in the Northern Hemisphere gradually turn toward the right. The Coriolis effect and other factors combine to produce a pattern of wind belts and calm areas around Earth. These include doldrums, horse latitudes, trade winds, prevailing westerlies, and polar easterlies.

What Causes Winds? Key Concept Summary Differences in air pressure cause the air to move. A wind is the movement of air parallel to Earth’s surface. Winds move from areas of high pressure to areas of lower pressure. Most differences in air pressure are caused by the unequal heating of the atmosphere. As air over heated surfaces expands and becomes less dense, its air pressure decreases. If nearby air is cooler, it will flow under the warmer, less dense air.

What Causes Winds? Key Concept Summary Measuring Wind  Winds are described by their direction, determined with a wind vane, and speed, measured with an anemometer. A wind is named for the direction it blows from.