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Unit 6: Global Wind Systems Unit 6: Global Wind Systems • Relaxation? • Questions on the Reading and Reading Guide • Turn in Reading (GWS) and Writing (Wind) • Pick up Global Wind Systems Packet • Global Wind Systems: • Pressure Centers • Convection Loops • Wind Patterns • Global Wind Systems Writing Assignment Cyclone Anticyclone Cyclone Anticyclone Northern Hemisphere Southern Hemisphere Connection between upper & lower atmosphere flow • Cyclone - low pressure • Near surface, circulation creates convergence • As air converges it rises near center • Rising air cools, H2Og condenses, & may precipitate L • Anticyclone – high pressure • Outward flow near surface creates divergence • Draws air flow from above towards surface at center • Sinking air warms adiabatically, clear skies H Cyclones è Clouds/precipitation L Clouds H Clear skies Worksheet Section 1: Cyclones and Anticyclones, Questions #1-3 Divergence at surface → Convergence above Convergence at surface → Divergence above Convection Loops (Single Cell Model) Videos • https://www.youtube.com/channel/UCylCbuzRsB92Gc1l8ru6VIg/sear ch?query=circulation Worksheet Section 2: Global Wind Belts, Questions # 4-9 Hadley Cell • Circulation cells between equator and sub-tropics • Air rises due to intense heating in vicinity of declination • Low pressure at surface over equator (ITCZ) • Air pushes toward poles, deflected by coriolis • ~ 30°N & S air in upper atmosphere cools & sinks to surface • Sinking air → Subtropical high pressure belt Hadley Cell • Air returns to ITCZ through Trade winds • Trades deflected by Coriolis force • NE trades in northern hemisphere, • SE trades in southern hemisphere Ferrel Cell (Midlatitudes) • Subtropical highs lead to ~westerly winds at surface in midlatitudes • Polar lows around 60 degrees create another band of convergence, clouds, and precipitation • Polar jet stream: more ~westerly winds aloft around 60 degrees latitude • Coriolis force turns diverging air → westerly wind • 30-60° N & S – Mid-latitude Westerlies • Weather systems move generally west-to-east Polar Cell • Another convergence band of low pressures (like ITCZ) around 60 degrees N and S • In upper atmosphere, winds continue poleward • Air subsides (descends to surface) in high-pressure areas near the poles • As surface air returns southward, it is deflected by Coriolis, causing Polar Easterlies Ferrel Cell Polar Cell Key surface features: STH’s, polar front, and polar high’s Mechanism Creating Polar Jet • Jet stream centered over polar front • Steep gradient in temperatures, and therefore, large PGF! Hadley Cell Leads to… • ITCZ/Doldrums/Equatorial Trough: zone of rising air, deep convection, intense precipitation • Subtropical Jet Stream: ~westerly winds aloft at strongest pressure gradient • Subtropical Highs: 2-4 (semi- )persistent cells that intensify and grow in summer • Trade Winds: (N/S)easterly winds at surface Ferrel Cell Leads to… • Midlatitude Westerlies • Convergence at Polar Front • Polar Jet Stream Polar Cell Leads to… • Polar High Pressure Areas beyond 80 degrees latitude • Polar Easterlies Effects of High Pressure Centers over Oceans High Pressure Cells Around the U.S. Hawaiian Bermuda High or High or Pacific Azores High High January Pressure Averages Find on map: • ITCZ • Bermuda High • Hawaiian High • Icelandic Low • Aleutian Low • SH Subtropical Highs • SH Polar Front July Pressure Averages Find on map: • ITCZ • Bermuda High • Hawaiian High • NH Subpolar Lows • SH Subtropical Highs • SH Polar Front Polar Highs Subpolar Lows (Polar Front) Subtropical Highs Equatorial Lows (ITCZ) Subtropical Highs Subpolar Lows (Polar Front) Polar Highs Global Wind Systems Writing Assignment • Choose a place to examine (hopefully the location of your final project) • Locate your chosen place on the maps of average surface winds and pressures in January and July (Figure 9.5 in book or maps in this PPT) • Answer the following questions for your location: • What are the regions from which wind blows into your region? • What might the wind be bringing into your region? • When wind blows out of your region, what region does it blow into? • What might the wind be carrying out of your region? • What large-scale circulation patterns are responsible for these winds (Equatorial Lows? Subtropical Highs? Subpolar Lows? Westerlies? Tradewinds? Polar Easterlies?) .
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