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Discussion Review 4/4. Midterm questions?. I. Local Winds: Sea Breeze. As the surface warms, convection begins. The rising air “pushes” up the isobars, creating a pressure gradient. As air over land expands, a low pressure system forms at the surface and winds blow from ocean to land.
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I. Local Winds: Sea Breeze As the surface warms, convection begins. The rising air “pushes” up the isobars, creating a pressure gradient. As air over land expands, a low pressure system forms at the surface and winds blow from ocean to land.
Valley Breeze Sun heats the valley walls, which heats the surface air. The heated air (being less dense), rises as a gentle upslope wind. At night, the flow reverses
Mountain Breeze Reverse of valley breeze; happens at night. Cooler, more dense air glides downslope into valley.
Katabatic Winds • Any downslope wind, but usually reserved for downslope winds that are stronger than mountain breezes.
Chinook Winds • Warm, dry, downslope wind that descends on the eastern slope of the Rocky Mountains • Strong westerlies aloft flow over a north-south trending mountain range • As the air descends, it is and • Main source of warmth? compressed warmed Compressional heating.
Santa Ana Winds • A warm, dry wind that blows downhill from east or northeast into southern California • Source of heating? Compressional heating • Cold, dense air from high deserts moves through mountain passes. Warms as it descends into coastal regions.
II. Global Winds • Single Cell Model • Assumptions: • 1. Surface is uniformly covered with water • 2. Sun is always directly over the equator • 3. Earth does not rotate But this does not explain the mid-latitude westerlies! • Three-Cell Model • Allows the earth to spin
ITCZ • Intertropical Convergence Zone • Where the northeast trade winds meet with the southeast trade winds • Usually very wet since rising air develops into huge thunderstorms that drop huge amounts of rain
Sea Level Pressure (Summer) Low pressure systems form over land in N.H summer. Why? ITCZ moved northward. Why? Sun is overhead in NH, so zone of maximum surface heating shits seasonally
Sea Level Pressure (Winter) High pressure forms over land in NH ITCZ moves southward
Ekman Transport • Ocean water is moved by wind • Also affected by Coriolis forces
Ekman Spiral • Wind blows parallel to the coastline. As the wind blows over the ocean, the surface water is moved. • As surface water moves, it bends slightly to the right due to the Coriolis effect. • The water beneath the surface also moves, and it too moves slightly to its right. As the surface water drifts away from the coast, cold, nutrient-rich water from below rises (upwelling) to replace it. Upwelling is the strongest and surface water is the coolest where wind parallels the coast.
El Niño • Easterly trade winds weaken and warm water is transported from the western Pacific to the Eastern Pacific. • Southern Oscillation: seesaw pattern of reversing air pressure at opposite ends of the Pacific Ocean. • ENSO: basically simultaneous pressure reversals and ocean warming. • Global Weather? • W. Pacific: Less rainfall as warm Pacific water moves east • Shift in rain patterns moves subtropical jet stream from normal path • Change in path of sub-tropical jet allows El Niño to affect weather in mid-latitudes
Ferrel cell Hadley cell Trade winds ITCZ Ekman Transport Upwelling ENSO El Niño Key Terms • Sea breeze • Land breeze • Valley breeze • Mountain Breeze • Katabatic wind • Chinook Wind • Santa Ana Winds • Polar cell
Game • First word: without saying key words, walk around the room describing your concept until you find your partner. • Second word: With your partner, play Pictionary with your second words. Be sure to label where high and low pressure systems are, if applicable. • WORDS YOU CANNOT SAY: • Land • Breeze • Sea • Wind • Trade • Cell • Mountain • Etc.
