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Lecture 7 Outline - Chapter 7 Transient Atmospheric Flows...

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Sheet1 Page 1 Chapter 7: Transient Atmospheric Flows and Disturbances CHAPTER OUTLINE I. The Impact of Storms on the Landscape A. Storms are phenomena that are more limited than the broad-scale wind and pressure systems. 1. They are transient and temporary. B. Storms involve the flow of air masses as well as a variety of atmospheric disturbances. C. They have short-run and long-run impacts. 1. In some parts of world, have major influence on weather, some on climate. 2. Long-run includes both positive and negative impacts on landscape. a) Positive: promote diversity in vegetative cover, increase size of lakes and ponds, and stimulate plant growth. II. Air Masses and moves as an entity. Such extensive bodies are distinct from one another and compose the troposphere. B. Characteristics 1. Air mass must meet three requirements: a) Must be large (horizontal and vertical). b) Horizontal dimension must have uniform properties (temperature, humidity, and stability). c) Must be distinct from surrounding air, and when moves, must retain that distinction (not be torn apart). C. Origin 1. Formation occurs if air remains over a uniform land or sea surface long enough to acquire A. Air massha large parcel of air that has relatively uniform properties in the horizontal dimension
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Sheet1 Page 2 uniform properties. masses because they are (1) Extensive (2) Physically uniform (3) Associated with air that is stationary or anticyclonic. D. Classification 1. Because source region determines properties of air masses, it is the basis for classifying them. 2. Use a one- or two-letter code. associated with each. E. Movement and Modification 1. Some air masses remain in source region indefinitely. 2. Movement prompts structural change: 3. Moving air mass modifies the weather of region it moves through. F. North American Air Masses 1. Physical geography of U.S. landscape plays a critical role in air-mass interaction. 1 weather/climate. of Pacific air masses. 2. Maritime tropical (mT) air from the Atlantic, Caribbean/Gulf of Mexico strongly influences climate east of the Rockies in the United States, southern Canada, and much of Mexico. a) Primary source of precipitation. Also brings periods of uncomfortable humid heat in summer. 3. Continental tropical (cT) air has insignificant influence on North America, except for a) Source regionshparts of Earthhs surface that are particularly suited to generate air 3. Table 7h1 provides a simplified classification of air masses, along with the properties a) Thermal modificationhheating or cooling from below b) Dynamic modificationhuplift, subsidence, convergence, turbulence c) Moisture modificationhaddition or subtraction of moisture. a) No easthwest mountains to block polar and tropical air flows, so they affect U.S. b) Northhsouth mountain ranges in west modify the movement, therefore the characteristics,
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Sheet1 Page 3 bringing occasional heat waves and drought conditions to the southern Great Plains.
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