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Unformatted text preview: rbaceous plants. ! Low plant species diversity, low
productivity, and low aboveground
biomass. ! Animal diversity also tends to be low. migration Why Are the Tropics Wet?
! Areas along the equator receive the most moisture; locations
at about 30º N and 30º S latitude are among the driest on
as warm air rises and cools=, is dropped over the=ropid,/xl9 ! A major cycle in global air circulation, called a Hadley cell,
is responsible for this pattern. Why Are the Tropics Warm and
the Poles Cold?
! Areas of the world are warm if
they receive a large amount of
sunlight per unit area; they are
cold if they receive a small
amount of sunlight per unit area. ! Earth s spherical shape dictates
that regions at or near the
equator receive more sunlight
per unit area than regions that
are closer to the poles, due to
the angle at which the solar
radiation hits the Earth. What Causes Seasonality in Weather?
! Seasons—regular, annual fluctuations in temperature, precipitation, or both
—result from Earth s 23.5º tilt on its axis. ! In June, the Northern Hemisphere is tilted toward the Sun, so it faces the Sun most directly and receives the largest amount of solar radiation per unit
area. ! In December, the Southern Hemispher...
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- Winter '11