WIND: GLOBAL SYSTEMS Chapter 10 General Circulation of the ...

3/22/111234567WIND: GLOBAL SYSTEMSChapter 10General Circulation of the Atmosphere General refers to the average air flow, actual winds will varyconsiderably. Average conditions help identify driving forces. The basic cause of the general circulation is unequal heatingof the Earth’s surface Warm air is transferred from the Tropics to the Poles Cool air is transferred from the Poles to the TropicsGeneral Circulation of the Atmosphere Single Cell Model Assume1. uniform water surface2. Sun always directly overhead the Equator3. Earth does not rotateResult: huge thermally direct convection cell (Hadley)General Circulation of the Atmosphere Three Cell Model Allow earth to spin = three cells (Hadley, Ferrell, Polar) Alternating belts of pressure starting with L at Equator Alternating belts of wind with NE just North of Equator Trade winds Horse Latitudes ITCZ/Subtropical High/Polar Front What causes the high pressure in the hot Subtropical Highzone? What causes the low pressure in the ITCZ?General Circulation of the Atmosphere Average Surface Wind and Pressure: The Real World Semi-permanent high and lows○ Highs: Pacific, Bermuda, Southern oceans○ Lows: Icelandic, Aleutian Northern vs. Southern Hemisphere Major features shift seasonally with the high sun○ North in July, South in Decembe8910111

3/22/11 Major features shift seasonally with the high sun○ North in July, South in Decembe○ Regional highs in Canada and Siberia in winter89101112131415161718192021222324General Circulation of the Atmosphere General Circulation and Precipitation Patterns Rain where air rises (low pressure) Less rain where air sinks (high pressure)General Circulation of the Atmosphere Average Wind Flow and Pressure Patterns Aloft North-South temperature and pressure gradient at highaltitudes creates West-East winds, particularly at mid to highlatitudes.Jet Streams 100-200 kt winds at 10-15km, thousands of km long, several100 km wide and a few km thick (polar and subtropical)Jet Streams Polar and Subtropical Jet Established by steep temperature and pressure gradientsbetween circulation cells. Between tropical-mid-latitude cell (subtropical) and midlatitude-polarcell (polar) Gradients greatest at polar jetJet Streams Topic: Momentum Low-latitudes: atmosphere gains momentum High-latitudes: atmosphere losses momentum252

23243/22/11252627282930313233343536373839 Low-latitudes: atmosphere gains momentum High-latitudes: atmosphere losses momentum Conservation of MomentumAtmosphere Ocean Interactions Global Winds and Surface Ocean Currents Ocean surface dragged by wind, basins react to highpressure circulation forming gyres Cold current, flowing north to south, on west side of continent Warm current, flowing south to north, on east side ofcontinent Oceanic frontAtmosphere Ocean Interactions Upwelling Ekman spiral, Ekman transport Water moving away from the coast causes upwellingAtmosphere Ocean Interactions El Nino and the Southern Oscillation El Nino: irregular warm episode off west coast of SouthAmerica Southern Oscillation: rise in pressure over W Pacific, fall inthe E Pacific, equatorial countercurrent ENSO La Nina Teleconnections: Ocean/atmosphere interactions thatinfluence precipitation patterns in distant parts of the worldAtmosphere Ocean Interactions34041

3435363738394041Atmosphere Ocean Interactions Pacific Decadal Oscillation Reversal in Pacific Ocean temperatures Warm = more Pacific storms Cool = cool, wet NW North America, wetter over the GreatLakes, salmon fisheries declineAtmosphere Ocean Interactions North Atlantic Oscillation Reversal of pressure in North Atlantic Ocean affectingweather in Europe and eastern coast of North America Positive = strong Westerlies, storms in N Europe, wet andmild in eastern US Negative = wet southern Europe and Mediterranean, coldand dry in eastern US3/22/114243444546Atmosphere Ocean Interaction Arctic Oscillation Closely related to NAO Pressure changes between Arctic and adjacent southernareas causes changes upper-level winds Positive = mild winter in US and W Europe Negative = cold US, cold dry Europe, wet MediterraneanHomework for Chapter 10 Chapter 10 Questions for Review, p. 284 #3-5, 7, 15, 18 Chapter 10 Questions for Thought, p. 284 #4, 6 Chapter 10 Problems and Exercises, p. 284 NoneProject for Chapter 9 None4