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 6.2 albedo = % 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 0 o –ascending air (rising) Subtropical high pressure belt at 30 o –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 30 o ) –Westerlies (between 30 and 60 o ) –polar easterlies (between 60 and 90 o )

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