BIOL 373 Lecture Notes - Cool Air, Intertropical Convergence Zone, Rain Shadow
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Ecology and the Distribution of Life
: What is Ecology?
Ecology: scientific study of the rich and varied interactions between organisms and their
Communities: embracing all the organisms living together in the same area
Ecosystems: embracing all organisms in an area plus their physical environment
Biosphere: system that embraces all regions of the planet where organisms live
Environment: encompasses both abiotic and biotic factors
: How are Climates Distributed on Earth?
Climate of a region is the average of the atmospheric conditions found over a long term.
Weather is the short-term state of those conditions.
Climates vary greatly because different places receive different amounts of solar energy.
Solar energy drives global climates
Every place on Earth receives the same total number of hours of sunlight but not the same
amount of solar energy; this depends primarily on the angle of sunlight.
Higher latitudes experience greater variation in both day length and the angle or arriving solar
energy over the course of a year = greater seasonal variation in temperature.
Air temperature decreases with elevation: when air rises, it expands, its pressure and
temperature drop, and it releases moisture; when a parcel of air descends, it is compressed, its
pressure rises, its temperature increases, and it takes up moisture.
Global air circulation patterns result from the global variation in solar energy input and from the
spinning of Earth on its axis.
Air rises when it is heated by the sun and is replaced by air that flows in toward the equator
from the north and south produces the intertropical convergence zone.
Cool air cannot hold as much moisture as warm air, so heavy rains fall in the intertropical
Air that moves into the intertropical convergence zone to replace the rising air is replaced by air
At the poles, air descends.
Spinning of Earth on its axis influences surface winds. As air mass moves toward equator, it
encounters an increasingly faster spin, and its rotational movement is slower than that of the
Earth beneath it. As an air mass moves poleward, it confronts an increasingly slower spin, and
speeds up relative to the Earth beneath it.
Air masses moving latitudinally are deflected to the right in the N. Hemisphere and to the left in
the S. Hemisphere.
Air masses moving toward the equator from the north and south veer to become northeast and
southeast trade winds.
Air masses moving away from the equator veer and become westerly winds that prevail at mid-
When prevailing winds bring air masses into contact with a mountain range, the air rises to pass
over the mountains, cooling as it does. Clouds form on the windward side and release moisture
as rain or snow. On the leeward side, dry air descends, warms and picks up moisture resulting in
a rain shadow on the leeward side.