Download Global Winds Review and Practice - Liberty Union High School District

Answer all questions in your notebook in complete sentences (or copy down the question) so you know what
you were asked.
Global Winds Review and Practice
Explore: The winds in Indiana can blow from any direction on any given day, but weather systems almost always
travel from the west to the east. If you look at the weather in Illinois today, you might expect that weather
tomorrow in Indiana. That is because we live in an area called the Prevailing Westerlies where weather is pushed
from west to east. The Earth has definite wind patterns. These patterns are a result of how the Sun heats the Earth
combined with the rotation of the Earth. These wind patterns influence the types of climate around the world.
1. How might the Sun have an effect on global wind patterns?
2. How might the rotation of the Earth affect global wind patterns?
Explore: Air that is moving across the surface of the earth is called wind. The Sun heats the surface of the Earth
and the surface heats the air. The equator receives the most direct sunlight and the poles receive the least amount
of sunlight.
The surface at the equator is very humid. Rain forests and ocean surfaces are plentiful at the equator adding more
humidity to the air. Humid air is less dense then dry air. Warmer air is less dense then cooler air. The air at the
poles is cooler and water vapor does not exist well in cooler air. Therefore the cool, dry air at the poles is much
denser than the warm, humid air at the equator.
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Why is the air less dense at the equator than at the poles?
In the above diagram labeled with the “EQUATOR”, why is the air rising?
How is the surface air moving; toward the equator or away from the equator?
How is upper air moving; toward the equator or away from the equator?
Explore:
If global winds were only affected by the heating of the Sun, global winds
would look like this diagram.   
The Equator would become very hot and humid causing that air to rise and
flow toward the poles. At the poles the air would cool and sink returning to
the Equator along the surface.
Global Winds Review and Practice
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However, the Earth is rotating and this prevents the air from
traveling in a straight line. The Earth’s rotation forces the air to
the right in the northern hemisphere and to the left in the
southern hemisphere (a result of the coriolis effect) resulting in
a global pattern described in the this diagram   
This creates six bands of circulation, three in the northern
hemisphere and three in the southern hemisphere.
The diagram is labeled with three numbered areas with each
named cell. The surface winds in each cell are also named.
1) The Hadley Cell is named after George Hadley (1685-1768)
an amateur meteorologist who suggested that they existed.
The air rises at the equator (0°) and sinks at about 30° N
and S latitude moving back toward the equator at the surface. These surface winds are called Trade Winds and
are winds blowing generally from east to west. Hurricanes develop in the Trade Winds.
2) The Ferrel Cell, suggested by William Ferrel (1817-1891), describes the sinking air at 30° N and S latitude as
moving also northward. This northward surface air is deflected to the right by the Earth’s rotation becoming
surface winds blowing generally from west to east. This area, between 30° latitude and 60° latitude forms an
area known as the Prevailing Westerlies (sometimes known as the Stormy Westerlies).
3) The Polar Cell. Here air rises at 60° latitude and moves toward the poles (90°) where the air cools and sinks.
This results in surface winds moving generally from east to west known as the Polar Easterlies. The sinking air
creates polar deserts, but not like the deserts that you usually think of. The poles do not get a lot of snow, but
the snow they do get builds up year after year into deep snow packs.
This creates a global system that seems very uniform, but several factors complicate the image. Landmasses, ocean
currents, and seasonal changes cause this orderly global wind pattern to fluctuate.
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What prevents simple global surface winds from blowing from the poles to the equator?
Describe how air moves in the Hadley Cell region:
Describe how air moves in the Ferrel Cell region:
Describe how air moves in the Polar Cell region:
Copy the following table in to your notebook and fill it in:
Convection Cell
Within
Latitudes:
Name of
Surface winds:
Direction
of winds
Hadley
Ferrel
Polar
Global Winds Review and Practice
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Between each of the three cells are areas of high and low pressure at the surface.
At 0° latitude are the Doldrums: Along the equator between the north and south Trade Winds there is a band of
low pressure. Within this band of lifting air, there is very little surface wind. For this reason, sailing ships would get
caught in this area and spend days waiting for enough wind to carry them out. This area became known as the
doldrums as ships would slow and float aimlessly.
At 30° latitude are the Horse Latitudes: Along 30° north and south latitude between the Trade Winds and the
Prevailing Westerlies is an area of high pressure. Within this band of sinking air, there is very little surface wind.
For this reason, sailing ships would get caught in this area and spend days waiting for enough wind to carry them
out. In the centuries following Columbus’ voyage, sailing ships would cross this band of high pressure en route to
the new world. They carried people and supplies along with horses. There were no horses in the new world and
horses were essential to the Europeans as a mode of transportation. Sailing ships would get caught in these
windless areas and as supplies began to disappear, the horses became dispensable and were the first to be
abandoned. For this reason this band became known as the horse latitudes. Because air is sinking along this band
and because clouds do not form in sinking air, the major deserts of the world can be found at 60° latitude. Deserts
form in areas where air is normally sinking, either along 60° latitude or on the lee side of mountains.
At 60° latitude are the Subpolar Lows: Along 60° latitudes between the Prevailing Westerlies and the Polar
Easterlies there is a band of low pressure. This is also an area vacant of surface winds but with no historic
significance.
11. Why is the area along the equator known as the doldrums?
12. Why do deserts form along 30° latitude?
Label the diagram using the following words: Horse Latitudes, Polar easterlies, Trade Winds, Doldrums, Prevailing
Westerlies, and Subpolar Low. On the globe, using arrows, show the general direction of the wind in each of the
three areas.
Global Winds Review and Practice
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