BIO120 Lecture 1: Distributional aspects of biodiversity
Distribution of solar energy:
Since the equator is tilted 23.5˚ with respect to the path the follows in its orbit
around the sun, therefore:
o At higher latitude, light strikes at a lower angle, and is spread over a
greater area. At the equator, the sun shines almost perpendicular on
earth’s surface.(Figure 4.1)
o In Northern Hemisphere, seasonal variation in temperature increases
significantly (less ocean to moderate temperature change.
Ex: at 60˚N, the average coldest month is -12˚C and the average
warmest month is 16˚C, differ by 28˚C. (Figure 4.3)
o The tropic of Cancer and the Tropic of Capricorn are two lines where the
sun is directly overhead at noon on the two solstices.
o Tropic of Cancer: lie at 23.5˚ North of the equator (sun is directly
overhead at June 21)
o Tropic of Capricorn: located 23.5˚ South of the equator( sun is directly
overhead at December 21) Precipitation:
Warming air cools down as it rises, as it cools down its ability to hold water vapor
decreases heavy rain.
As the cool air continues to expand and replaced from below by surface-level air
moving in. this type of circulation pattern is
called Hadley circulation.
The Coriolis Effect and jet streams:
Coriolis effect: the effect of the earth’s rotation on the circulation patterns of the
atmosphere and oceans, which causes winds and currents to veer to the right of
their direction of travel in the Northern Hemisphere and to the left in the Southern
Jet Stream: A rapidly moving west-to-east air current that forms at the high altitude
junction of 2 atmospheric circulation cells (Hadley and Ferrel cells).
Coupled cells + Coriolis effect =
prevailing wind patterns The intertropical convergence:
Intertropical convergence: The region where surface currents of air from the
northern and southern subtropics meet near the equator and begin to rise under
the warming influence of the sun
As air cools down and moves away from the intertropical convergence, it
becomes denser and begins to sinkcreated a high atmospheric pressure, dry
descending air masses. This area is called the subtropical high-pressure belts.
Because the earth is tilted, Intertropical Convergence Zone shifts seasonally,