WIND NOTES I. What is Wind?: • Wind: the horizontal movement of air from an area of high pressure to an area of lower pressure. • The movement of air is caused by differences in air pressure. • The greater the pressure difference, the faster the wind moves. Measuring Wind • Winds are described by their direction and speed. • Wind Vanes are used to determine wind direction. • Wind Speed is measured with an anemometer. • Wind Chill Factor measures cooling that combines temperature and wind speed. Local winds • Are winds that blow over short distances. • Are caused by the unequal heating of Earth’s surface within a small area. 1. Sea Breezes • Occurs along the shore of a large body of water like an ocean or lake. • Are created during the day when solar radiation warms land faster than water. • Air over land is heated by conduction. • The heated air is less dense and is forced upward by cooler, denser air moving in from the water. • Draw the sea breeze picture that is on the next slide. 2. Land Breezes • Land breezes are created at night when land cools faster than water. • Air over land becomes cooler and denser. • The cool air over land pushes out over water and forces the warm air over water upward. • Draw the land breeze picture that is on the next slide. 3. Mountain Breezes • In the evening, the mountain slopes cool the surrounding air more quickly than the air found lower in the atmosphere. This creates a high pressure as air becomes more densely packed. The resulting high pressure causes winds to blow down the mountain towards the valley floor. 4. Valley Breezes • During the day, the surface of the mountain heats the air high up in the atmosphere, quicker than the valley floor can. • As the warmer air expands a low pressure is created near the top of the mountain. This attracts the air from the valley, creating a breeze that blows from the valley floor up towards the top of the mountain. • eagles, hawks, condors, and vultures float on these breezes to preserve their energy. Mountain and Valley Breezes •In the daytime we typically see valley breezes, as winds blow from the valley up towards the mountains. •In the night we often see mountain breezes, as winds travel from the mountains, down towards the valleys. 5. Seasonal Winds • Seasonal winds change with the seasons. a. Monsoons • Monsoons occur in tropical areas. • 1. In Winter: land is cooler than the ocean causing the air to flow away from land bringing dry weather. • 2. In Summer: land is warmer than the ocean and the air blows toward land bringing extremely heavy rain. (wet) III. Global Winds • Are winds that blow steadily from specific directions over long distances. • Are created by the unequal heating of earth’s surface. • Occur over large areas • Why does Earth and Atmosphere heat unevenly? • The uneven heating is due to Earth’s curved surface. Since it isn’t flat, different areas receive different amounts of solar radiation. The equator receives the most and the poles receive much less. • Differences in air pressure are created by temperature differences. • Heated air is less dense (lighter) than cold air, which is more dense (heavier). • The warmer air gets pushed upward by the cold air creating the general circulation of air around Earth. • Giant convection currents are produced in the atmosphere by the temperature differences between the equator and the poles. • Air pressure is greater at the poles and lower near the equator. • At the surface, the winds blow from the poles towards the equator. • Higher in the atmosphere, the air flows away from the equator toward the poles. Coriolis Effect • The apparent curving of the path of a moving object from an otherwise straight path due to earth’s rotation. IV. Global Wind Belts The major global wind belts are the trade winds, the polar easterlies, and the prevailing westerlies. 1. Doldrums • Areas where the air seems motionless because it is moving almost straight up. • Located along each side of the Equator. • Ships avoid these areas since there is no wind to fill their sails. • Have you ever had the doldrums? 2. Horse Latitudes • At about 30° north and 30° south latitude, sinking air creates an area of high pressure. • Weak winds form as a result of the sinking air making it difficult for ships to sail. • Sailing ships that carried horses in this area would throw the horses overboard to save drinking water for the sailors. 3. Trade Winds • provided a dependable route for trade in the days of the great sailing ships. • Located between the equator and 30 latitude North or South • Blow to the southwest in the Northern Hemisphere and to the northwest in the Southern Hemisphere. 4. Prevailing Westerlies • Responsible for the movement of weather systems across the US and Canada • In the Southern Hemisphere, they blow from the northwest to the southeast. • In the Northern Hemisphere, from the southwest to the northeast. Westerlies, contd. • blow in the opposite direction from the trade winds. • Used by sailors to sail from the Americas to Europe. • Located between 30 and 60 latitude North and South of the Equator. 5. Polar Easterlies • Located from 60 to 90 latitude North and South • Blow from northeast to southwest near the North Pole and from southeast to northwest near the South Pole. 6 . Jet Streams • Are high altitude winds. • Narrow belts of strong winds that blow near the top of the troposphere. • 2 jet streams in each hemisphere that blow from W to E at the upper boundaries of the prevailing westerlies. • Resemble fast moving rivers. • Position changes daily and seasonally in latitude and altitude. How do the jet streams help/hinder air travel? Wind Observation Homework • Make 3 wind observations between now and Monday. • Your observations must include the time of day, the temperature, weather conditions and evidence of wind. Try to make observations at different times during the day. • Your evidence can be things feeling it, seeing it, hearing it, etc. Be sure to describe your evidence. THE END!
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