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