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Chapter 8
Atmospheric Circulation and Pressure Distributions
• General Atmospheric Circulation
– Well defined global pressure zones
– Creates predominant wind motions
– The largest wind systems define the general circulation of the planet
• Three-Cell Model
– _____________ – tropical cell driven by heat
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– Farrell Cell
• Located in the middle-latitudes between 300 and 600 latitude
– Polar Cell – polar cell driven by temperature differences
• Located between 600 latitude and poles
– _______________ – an established low pressure zone near the equator
• intertropical convergence zone (ITCZ)
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• Sometimes called “doldrums”
• Migrates with changing seasons
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– Subtropical Highs – established high pressure zones around 30 latitude
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• Establishes the Northeast and southeast trade winds
- Subpolar Lows – established low pressure zones at high latitudes
• Abundant clouds and precipitation
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• Migrates with changing seasons
• Establishes the north and south westerlies
- ____________ – established high pressure zones at the poles
• Sinking air and lack of precipitation
• Establishes the north and south easterlies
– The three-celled model vs. reality: the bottom line
• Hadley cells are close approximations of real world
• Ferrel and polar cells do not approximate the real world
• Model is unrepresentative of flow aloft
• Continents and topographic features cause flaws in the model
• Semi-Permanent Pressure Cells
– Northern hemisphere cells
• Winter
– Aleutian Low, Icelandic Low, and Siberian High dominate
• Summer
– Hawaiian High, Bermuda High, and Tibetan Low dominate
• The Upper Troposphere
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– Westerly winds in the upper atmosphere
• Air motions directed towards poles
• Redirected by Coriolis deflection
– Westerly winds aloft result
– Jet streams -
• Polar jet is located along the polar front
• Subtropical jet is located near the equator within the Hadley cell
• Stronger winds exist during winter
– Troughs
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– Ridges
• A bump in the upper air heights
– Rossby waves (_______________)
• Wavelengths and amplitudes vary
• Transfers energy from equator and the poles
• Ocean Currents
– Deflected by coriolis effect creating clockwise and counter clockwise motions
– Gulf Stream
• Major Wind Systems
– _________________ – seasonal variations created by wind and pressure reversals
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– Land has cold high pressure, while water is warmer and lower pressure
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– Land is warmer low pressure, while water is cooler high pressure
– Air flows from water to land (onshore)
• Orographic enhancement
– Foehn, Chinook and Santa Ana (Fall) winds
• Orographic induced
• Responsible for greatest 1-minute temp. change
• Foehn and Chinook occur in winter, while Santa Ana’s typically in fall
• Compression warming on lee side
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– Katabatic winds
• Cold, dense air flowing down mountain slopes
• Common in Antarctica and Greenland
– Sea breeze –
• During day land becomes hot and lower pressure than water
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• Breeze migrates inland as day progresses
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– Land breeze
• During night land becomes cooler and higher pressure than water
• Wind blows from land to water
– Valley and mountain breeze
• Differential heating of valley and higher elevations
• Diurnal wind shift
• Valley breeze blows up from the valley
• Mountain breeze blows down the mountain
• Air-Sea Interactions
– Walker circulation
• A westward flow of surface air over the equatorial Pacific
– ___________ - Unusually warm water in the eastern equatorial Pacific Ocean
• Linked to global weather anomalies
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• Southern Oscillation – pressure differences between western and eastern Pacific
– SOI Index determines magnitude difference
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• Distinct global teleconnection patterns result
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• Strengthened “normal” conditions
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End of Chapter 8
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