Remember… …putting all of this together…the hot, humid, air over the tropics is LESS dense (than all other air masses); this means: (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
Atmos. Circ. Cont… …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?
Atmos. Circ. Cont… …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…
Coriolis Deflection “The apparent deflection of objects moving across Earth’s surface to the right of direction of travel in the Northern Hemisphere and to the left in the Southern Hemisphere.” Different because of difference of speed and width of Earth @ equator vs. poles Increases poleward & as speed increases.
Coriolis Effect The eastward rotation of the earth deflects any moving object away from its initial course the deflection OF THE OBJECT is clockwise in the Northern hemisphere the deflection OF THE OBJECT is counterclockwise in the Southern hemisphere
Wind Patterns At bands between cells air is moving vertically winds are weak and erratic doldrums or intertropical convergence zone (ITCZ) at equator –ascending air Subtropical high pressure belt at 30 o –descending air, very dry
Wind Patterns Within cells air moves horizontally from high to low pressure areas produces strong dependable winds –Trade winds or easterlies –westerlies –polar easterlies
Wind Patterns Within circulation cells air moves horizontally from high to low pressure areas (wind belt) produces strong dependable winds –Trade winds (between 0 and 30 o ) –Westerlies (between 30 and 60 o ) –polar easterlies (between 60 and 90 o )
REMEMBER: Movement of air across a pressure gradient parallel to Earth’s surface is called a wind. Winds are designated according to the direction from which they come. In contrast, ocean currents are designated according to the direction towards which they travel.