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Wind Driving Forces 1. Pressure Gradient • Determines magnitude of wind speed and wind direction • Stronger the pressure gradient, higher the wind speed • Moves from an area of HIGH pressure to LOW pressure • Example: vacuum sealed can… • Pressure gradient is the amount of pressure between high and low pressure Pressure Gradient Low pressure/ High pressure gradient Strong wind High pressure, gentle pressure gradient Isobars • Isobars connect places of equal pressure • The space between bars indicates change in pressure and pressure gradient. • Isobars close together means greater pressure gradient (over distance). REFER TO YOUR MAP 2. Coriolis Effect • The pull of the magnetic force of the coriolis effect can change the WIND DIRECTION only. It does NOT affect the wind speed. 3. Friction at Earth’s Surface • *Friction slows surface wind speed and diverts direction of wind • Hills and mountains have a major influence on wind • Wind speed increases with height • Over ocean less friction Ex. Airplane flying over mountainous area will climb higher to reach more stable air; avoid turbulence Geostrophic Winds Upper air winds unaffected by friction, faster than surface wind EX. Jet streams, winds moving in upper level at 120-240km/hr (75-150 miles/hr Jet streams form between cold and warm air masses RECAP QUESTIONS • 1. Pressure Gradient affects the ______ and ______ of wind. • 2. Wind moves from an area of _____ to _____ pressure. • 3. Isobars close together indicate what about the pressure gradient? • 4. The greater the pressure gradient, than the ______ the wind speed. • 5. The __________ of the wind is effected by the rotation of the earth. Know as the _____________. • 6. The deflection of wind is strongest at the _______. • 7. What influence do hills and mountains have on wind? • 8. Wind speed ______ with height. 9. • 10. Upper air winds unaffected by friction are called what? Cyclones • Areas of LOW pressure • In the N. Hemisphere winds blow inward and counter clockwise • Associated with warm humid conditions Anticyclones • Areas of HIGH pressure • Winds blow outward and clockwise in Northern Hemisphere Compare… Cyclones and Anticyclones • RECAP QUESTIONS…. • 1. Cyclones are associated with areas of _____ pressure. • 2. Anticyclones in the Northern Hemisphere wind moves in which direction ? • 3. T/F Cyclones wind direction is counter clockwise in N. Hemi. Middle-Latitude Cyclones • Middle-Latitude Cyclones are large centers of low pressure that travel form west to east. • Last about 1-1/2 weeks and occur between Florida and Alaska Life cycle of middle-latitude cyclone Mid-Latitude Cyclones often resemble a “comma” Pg 472 With Mid-Latitude Cyclones come storm systems….thunderstorms, tornados and hurricanes http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/ sat.rxml