Class #6: Wednesday, July 14 Small scale and local winds Chapter 9 1Class #6, Wednesday, July 14, 2010

Wind: small scale and local systems Chapter 9 2Class #6, Wednesday, July 14, 2010

Small-scale winds interacting with the environment Scales of motion – Micro, meso, synoptic Friction and Turbulence in Boundary Layer – Laminar flow – Irregular turbulent motion – Planetary boundary layer (PBL) – Depth of PBL 3Class #6, Wednesday, July 14, 2010

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Small-scale winds interacting with the environment Observations: Eddies & Air Pockets – Eddies on leeward side of solid object – Roll eddies, mountain wave eddy (clear air turbulence) – Increase wind speed/shear deforms layer into wave and air pocket. Force of the Wind – Bridges and hills or rises can modify wind, increasing the force at specific locations. 10Class #6, Wednesday, July 14, 2010

Small-scale winds interacting with the environment Microscale winds blowing over the Earth’s surface – Wind erosion, desert pavements, sand ripples – Snow ripples, snow dunes, snow rollers, snow fences – Windbreak, shelter belt 11Class #6, Wednesday, July 14, 2010

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Determining wind speed and direction Wind characterized by direction, speed, and gustiness Wind direction describes the direction from which it is blowing Topic: Pedaling in the Wind – As wind blows against an object it exerts force (V 2 or P x A) 15Class #6, Wednesday, July 14, 2010

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Determining wind speed and direction Influence of Prevailing Winds – Prevailing most frequently observed direction during a given time period – Impact human and natural landscape – Wind rose Topic: Wind Power – Turbines need moderate, steady winds – Only a few percent of nation’s total energy needs generated by wind power in the first half of the century 18Class #6, Wednesday, July 14, 2010

Determining wind speed and direction Wind Measurements – Wind vane – Pressure plate anemometer – Cup anemometer – Aerovane – Rawinsonde – Wind soundings Observations: Winds from space – QuickScat: scatterometer 19Class #6, Wednesday, July 14, 2010

Local Winds Thermal circulation – Heating and cooling of the atmosphere above the ground create cold, core high and warm, core low pressure cells. – Wind travels from high to low and rises until it cools and begins to sink. 20Class #6, Wednesday, July 14, 2010

Local Winds Sea and Land Breeze – Uneven heating of land and water – Day: land hot, water cold = sea breeze – Night: water hot, land cold = land breeze – Sea breeze front, sea breeze convergence Local Winds and Water – Local winds will change speed and direction as they cross a large body of water due to less friction, greater speed and greater Coriolis effect 21Class #6, Wednesday, July 14, 2010

Fig. 9-22, p Class #6, Wednesday, July 14, 2010

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Stepped Art Fig. 9-25, p Class #6, Wednesday, July 14, 2010

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Local Winds Seasonally Changing Winds: The Monsoon – Arabic for seasonal – Winds change direction seasonably causing extreme dry and wet season – Eastern and southern Asia, North America 30Class #6, Wednesday, July 14, 2010

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Local Winds Mountain and Valley Breeze – On mountain slopes, warm air rises during the day creating a valley breeze; during night nocturnal drainage of cool air creating a mountain breeze – Associated with cumulus clouds in the afternoon Katabatic winds – Cold wind rushes down elevated slopes, usually 10 kts or less but can reach hurricane strength 33Class #6, Wednesday, July 14, 2010

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Local Winds Chinook/Foehn Winds – Dry warm descending on the leeward side of a orographic barrier – Eastern slope of Rockies (chinook), Europe (foehn), Argentina (zonda) Focus: Snow Eaters – Thirsty wind on east side of Rockies that eat or melt snow due to rapid change in temperature 36Class #6, Wednesday, July 14, 2010

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Local Winds Santa Anna Winds – Warm dry that blows from east or northeast don canyons into S. California – Very fast, desiccates vegetation, providing fuel for fires Desert winds – Dust storms, sand storms, dust devil, haboob 38Class #6, Wednesday, July 14, 2010

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Wind: small scale and local systems Chapter 9 42Class #6, Wednesday, July 14, 2010