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WIND Global And Local

Wind. What is wind?What causes wind?. . Wind results from the horizontal motion of air fromareas of high surface pressure to areas of low surfacepressure.. . . High (cool). Low (warm). . Surface. High. . . . . . Building a Model of Global Wind Circulation (1st Order Winds). N. Warm surface conditions or strongly rising air often produce low surface pressureCold surface conditions or strongly descending air often produce high surface pressure.

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WIND Global And Local

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    2. Wind What is wind? What causes wind?

    3. Building a Model of Global Wind Circulation (1st Order Winds) Warm surface conditions or strongly rising air often produce low surface pressure Cold surface conditions or strongly descending air often produce high surface pressure

    4. The Polar regions should consist of sinking cold air and high pressure. The equatorial region should exhibit rising warm air and low pressure.

    5. Air masses diverge when they collide with an obstruction, including the earth’s surface and high level temperature inversions.

    6. At roughly 300 north and south of the equator air that was warmed at the equator sinks back towards the surface as it cools and is forced into the decreasing circumference of the earth. Sinking air warms so these areas are dry and sunny.

    7. Again, when these air masses collide with the surface, they diverge. Notice the emerging pattern of alternate bands of high and low pressure. When surface air masses collide the effect is termed convergence.

    8. Also notice the cyclical pattern of air motion between the equator and 300 N and S. These are the so-called Hadley Cells. These convection cells are almost always present in the tropical regions. They greatly affect weather around the globe.

    9. Convergence between the tropics creates a large region of generally low pressure called the intertropical convergence zone (ITCZ). This area is often wet and cloudy.

    10. Note that we now see warm midlatitude air colliding (converging) with cold polar air at roughly 600 N and S of the equator. These Polar Fronts are other areas of relatively low pressure, atmospheric instability, and, as we’ll see, the source of most mid-latitude storms. T

    11. Warm air, of course, rises above the colder air from the polar regions, but convection cells here are not as common as at the ITCZ.

    12. Now that we have finished this profile view of earth circulation let’s transfer the surface winds onto the diagram.

    13. We have a problem. This diagram does not accurately depict Earth’s prevailing winds. Why? We have neglected to consider that the earth is in constant rotation. This has a dramatic effect on wind direction.

    14. The Coriolis Force Apparent deflection of all free-moving objects from a straight path. Caused by the Earth rotation eastward, out from under the path of the object. Result? Deflection to RIGHT in Northern Hemisphere Deflection to LEFT in Southern Hemisphere Zero Coriolis at Equator; max. at poles.

    15. Thus, in actuality, the Coriolis force deflects all winds to the right of their intended direction in the northern hemisphere and to the left in the southern hemisphere.

    16. Each band of resulting prevailing winds is named. Winds are labeled by their source direction (“where they came from”).

    17. The intertropical convergence zone (ITCZ) is characterized by frequent clouds and rain because of rising air. Their can be no wind at all here since most air is rising. These calms areas are the Doldrums. Intertropical Convergence Zone (ITCZ) Warm Humid Rains

    18. Sinking air warms so these areas are dry and sunny. The lack of horizontal air movement means there can be little to no wind here. These areas are called the Horse Latitudes. Subtropical High-Pressure Cells: Warm Desert Air

    19. Subtropical High-Pressure Cells: Hot Desert Air

    20. Arctic and Antarctic High Pressure Very dry, despite general snow cover. Precipitation is rare and gentle, but may not melt. Polar High Pressure Cells: Frigid Deserts

    22. Map View of Wind Circulation

    23. Ocean Currents driven by prevailing winds

    24. Ocean Currents

    25. Exceptions to the Model-Seasonal Variation and Localized Winds Seasonal Latitude Shift Monsoons Mountain-Valley Winds Land-Sea Breezes Santa Ana Winds

    26. Seasonal Shift of Winds and Pressure Cells (January)

    27. Seasonal Shift of Winds and Pressure Cells (July)

    28. Monsoon Seasonal reversal of winds, not a storm Arabic origin: ‘mausim’ meaning season

    30. Mountain-Valley Breezes

    31. Land and Sea Breezes

    32. Compressional Heating Winds (Santa Ana Winds, Chinooks, Foehn Winds)

    33. Santa Ana Winds San Diego, October 2003

    34. Summary There are six components to the global circulation model. From Pole to Equator they are: polar highs, subpolar lows (polar front), westerlies, subtropical highs (Hawaiian High), trade winds, and the intertropical convergence zone (ITCZ). All of these patterns are displaced seasonally by earth-sun relationships. Local and regional winds are sometimes more prevalent than the broader scale global winds of the model. Ocean currents are driven by prevailing winds.

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