Transcript Wind 6.2
What is wind? Air moves from areas of high pressure to areas of low pressure. This movement of air is the wind. Trade Winds Winds that blow between about 30 N latitude and about 30 S latitude are know as trade winds. They became known as trade winds over hundreds of years ago when sailing ships carried trade goods around the world. Global Winds Trade winds are part of a system of winds called global winds. A global wind blows steadily over long distances in a predictable direction. Global winds blow because sunlight heats areas near Earth’s equator more than it heats areas near Earth’s poles. As Earth rotates, places near the poles travel a shorter distance than places near the equator. This causes winds away from the equator to curve. Global Winds Winds curve to the right in the Northern Hemisphere…Clockwise. Winds curve to the left in the Southern Hemisphere…Counterclockwise . Coriolis Effect The coriolis effect describes the change in the direction of something on or above Earth’s surface due to the Earth’s rotation. This causes the winds to curve. Air warms and cools in 3 different bands as it moves north from the equator. Since warm air is less dense than cold air, the direction the winds blow changes. In the middle band, the direction of the cooling air is reversed and the winds blow in the opposite direction. Local Winds What usually causes local winds? Different parts of Earth’s surface are heated by the Sun at different rates. Which heats up faster, land or water? Land Which type of air, warm or cool, has lower air pressure? Warm air has lower air pressure. In what direction does wind blow? It blows from an area of higher pressure to an area of lower pressure. A visit to the Beach! If you have ever visited the beach, you probably noticed a breeze. During the day, you feel the wind blowing from the ocean onto the land. This movement of air from water to the land is called a sea breeze. A visit to the Beach continued… As the day turns to night at the beach, you may notice the wind blowing from the land toward the ocean. This movement of air from the land to the water is called a land breeze. Sea breeze and Land breeze Remembering what a sea breeze and a land breeze are is easy. Just remember that the breezes are named for where they come from. A land breeze comes from land and a sea breeze comes from the sea. In both types of breezes, cool air is the air that is moving. Valley breeze In the morning, as cool air moves up out of the valley towards the top of a mountain it replaces the warm rising air. This is a valley breeze. Mountain breeze As warm air rises in the evening over the valley, cool air from the mountains flows down into the valley and this forms a mountain breeze. Measuring Wind What instruments are used to measure wind direction? Windsocks and weather vanes What instruments measure wind speed? Anemometers Let’s Review!!! In which direction do winds in the Northern and Southern Hemispheres curve? Winds that blow to the south from the North Pole curve to the right. Winds that blow to the north from the South Pole curve to the left. What would happen to the global winds if no more heat energy reached Earth? The global winds would stop blowing. Describe the movement of air during a sea breeze and a land breeze. In a sea breeze, the cooler, higherpressure air over the ocean moves toward the warmer, lower-pressure air over the land. In a land breeze, the cooler, higher-pressure air over the land moves toward the warmer, lower-pressure air over the ocean. How does the Sun’s energy cause local winds? The Sun’s energy heats one area more than another area, decreasing the air pressure in the warmed area and causing cold air to flow toward the area with the lowered air pressure. Describe three devices that are used to measure wind. A weather vane and a windsock are two devices that can show which way the wind is blowing. An anemometer is a device that measures wind speed using three or four cups that rotate when the wind blows. Why might you see devices such as anemometers and windsocks at airports? Pilots need to know important weather variables such as wind directions and wind speed. For example, if it is too windy, pilots will not be allowed to fly. Wind that blows from the sea to the land is called a______? Sea breeze How does heat energy from the Sun cause winds? Heat energy from the Sun causes changes in air pressure. Highpressure air moves towards lowpressure air. Moving air is wind. How is a global wind different from a local wind, such as a sea breeze? Sunlight heats areas near the equator more than it heats areas near the poles, causing global winds. Sunlight changes temperature in a particular area more than a nearby area, causing local winds. How does wind affect weather? Wind is the movement of air particles. Wind can move over long distances (global winds) or within small areas (local winds).