Atmosphere
• 78% nitrogen, 21% oxygen
Water Vapor
• up to 4% by volume
• leaves atmosphere as dew, rain or snow
Density of Air
• Warm air is less dense than cold air
• Humid air is less dense than dry air
Air Movement
• Air near sealevel is packed by pressure
• As air rises - expands and cools
• As air descends- compresses and warms
Fig. 7-2a, p. 149
Figure 6.6
Precipitation
• Warm air can hold more water vapor than cool air
• As air rises, it cools and water vapor may condense into clouds and eventually precipitation
Atmospheric Circulation
• Wind = mass movement of air
• wind patterns caused by variations in solar heating and earth’s rotation
Figure 6.2albedo = % reflected back
Ice has a high albedo
Figure 6.1
Uneven Solar Heating & Atmospheric Circulation
• Air is warmed in the tropics and rises
• Air is cooled near the poles and falls
Figure 6.7
Figure 6.8
Fictional, non-spinning earth with sun rotating around the earth
Influence of the rotation of the earth…
Fig. 7-9, p. 152
Figure 6.9
Figure 6.10a
Figure 6.10b
Coriolis Effect
• The eastward rotation of the earth deflects any moving object away from its initial course
• the deflection is clockwise in the Northern hemisphere
• the deflection is counterclockwise in the Southern hemisphere
p. 153
Figure 6.11
Wind Patterns
• At bands between cells air is moving vertically
• winds are weak and erratic• doldrums or intertropical convergence zone
(ITCZ) at equator 0o
– ascending air (rising)
• Subtropical high pressure belt at 30o
– descending air (falling), very dry
Wind Patterns
• Within cells air moves horizontally from high to low pressure areas
• produces strong dependable winds– Trade winds (between 0 and 30o)– Westerlies (between 30 and 60o)– polar easterlies (between 60 and 90o)
Table 6.2
Actual Atmospheric Circulation
• 6 cell model is a representation of average flow
• local details of circulation vary due to different surface conditions
Fig. 7-13, p. 156
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