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 sea level is packed by pressure As air rises - expands and cools
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Fig. 7-5, p. 136
(a) Less dense air rises (like a hot air balloon);
(b) As it rises (vertical) the pressure decreases;
(c) As pressure decreases, air EXPANDS;
(d) As it expands, it COOLS
…then the reverse again…+ horizontal (wind) movement
…When you add the horizontal (wind) movement it pushes this (originating hot, dry, tropical air) BOTH up and out (North/South) for distribution throughout the entire atmosphere. How?
Tropical air rises, meets density around it (more dense than that above it but less dense than that below it) so it can’t “move” vertically …but it must go somewhere!
SIDEWAYS! (joins Atmospheric Circ. pattern, moving horizontally, toward POLES) & as it rises poleward it COOLS, gets more dense, and falls back (toward equator) again…and again…