Michael Zakrzewski March 31, 1999
Mr. Oshogobor G001
blow from a specific direction and almost always cover longer distances than local
winds. Both local winds and global winds are caused by differences in air pressure
due to unequal heating of the atmosphere.
During the day, the air over a land area is often warmer than the air over a
water. As the warm air over the land rises, the cooler air over the sea moves inland
to tale its place. This flow of air from the sea to the land is called a sea breeze.
is now warmer than the air over the land. This warm air over the sea rises. The
cooler air over the land moves to replace the rising warm air over the sea. A flow of
air from the land to the sea is called a land breeze. A land breeze is also called an
land breeze blows from the land to the sea. A sea breeze blows from the sea to the
land. Most local winds that we are familiar with are named according to the
direction from which they are blowing. A major land and sea breeze is called a
blows from the land to the ocean. During the rest of the year, it blows from ocean
to the land. When a monsoon blows from the ocean to the land, it brings in warm,
moist air. This results in a rainy season with warm temperatures and huge amounts
of rain. The rainy season is important to many because it provides the water needed
for farming. Monsoon winds are very common in Asia.
In areas near the equator the sun is almost directly overhead for most of the year.
slanting rays from the sun. The slanting rays do not heat the Earth?s surface as
rapidly as the direct rays do. So temperatures near the poles are lower than those
near the equator. At the equator, the warm air rises and moves toward the poles.
At the poles, the cooler air sinks and moves toward the equator. This movement
produces a global pattern of air circulation.
Global winds do not move directly from north to south or from south to north.
Because the Earth rotates, or spins on its axis, from west to east, the paths of the
winds shift in relation to the Earth?s surface. All winds in the Northern Hemisphere
curve to the right as thy move. In the Southern Hemisphere, winds curve to the left.
This shift in wind direction is called Coriolis effect. The Coriolis effect is the
apparent shift in the path of any fluid or object moving above the surface of the
At the Equator surface winds are quite calm. These winds are called the
doldrums. A belt of air around the equator receives much of the sun?s radiant
energy. The warm rising air produces a low pressure area that extends many
kilometers north and south of the Equator. Cooler high pressure air would normaly
flow into such an area creating winds. But the cooler air is warmed so rapidly near
the Equator that the winds which form cannot move into the low pressure area. As
a result any winds that do not form are weak.
About 30 degrees north and south of the equator the warm air rising from the
equator cools and begins to sink. Here, the sky is usually clear. There are few
toward the equator. The rest of the sinking air continues to move toward the poles.
The air moving back toward the equator forms a belt of warm steady winds. These
winds are called trade winds. In the Northern Hemisphere, the Coriolis effect
deflects the trade winds to the right. These winds called the northeast trades, blow
from northeast to southwest. In the Southern Hemisphere the trade winds are
deflected to the left.
The cool sinking air that continues to move toward the north and south poles
is also influenced by the Coriolis effect. In the Northern Hemisphere the air is
deflected to the right. In the Southern Hemisphere it is deflected to the left. So in
both hemispheres the winds appear to travel west to east. These winds are called
the prevailing westerlies. Unlike the trade winds the prevailing westerlies are often
In both hemispheres the westerlies start rising and cooling between fifty
degrees and sixty degrees latitude as they approach the poles. Here they meet
extremely cold air flowing towards the equator from the poles. This band of cold air
is deflected west by the Coriolis effect. As a result the winds appear to travel from
east to west and they are called the polar easterlies. The polar easterlies are cold
but weak winds.
Meteorologists and weather observers use a wind vane to determine the
direction of the wind on the earth?s surface. A wind vane points in to the wind. An
anemometer is used to measure wind speed. Wind speed is usually expressed in
meters per second, miles per second or knots. One knot is equal to 1,850 meters