Download Major Air Circulation

Major Air Circulation
Atmospheric circulation is the movement of air at all levels of the atmosphere
over the entire planet. The driving force behind atmospheric circulation is solar energy, which
heats the atmosphere with different intensities at the equator, the middle latitudes, and the poles.
The rotation of Earth on its axis which creates the Coriolis Effect and the unequal arrangement
of land and water masses on the planet also contribute to various features of atmospheric
circulation.
There are three wind cells or circulation belts between the equator and each pole: the
trade winds (Hadley cells), prevailing westerlies (Ferrell cells), and polar easterlies (polar
Hadley cells). As air is heated at the equator, it rises in the troposphere leaving behind low
pressure developing at the equator. The ITCZ is located in this region. The ITCZ (Intertropical
Convergence Zone) is the region on earth, located at the Equator, which experiences increased
precipitation due to the warm air rising at the poles.
When the air reaches the top of the troposphere it begins to move toward the poles,
cooling in the process. At about 30 degrees latitude north and south, the cooled air descends
back to the surface, pushing the air below it toward the equator, because air always moves
toward areas of low pressure. While most of the trade-wind air that sinks at 30 degrees latitude
returns to the equator, some of it flows poleward.
At about 60 degrees latitude north and south, this air mass meets much colder polar air
(the areas where this occurs are known as polar fronts). The warmer air is forced upward into
the troposphere by the colder air where most of it moves back toward the equator, sinking at
about 30 degrees latitude to continue the cycle again. These second circulation belts over the
middle latitudes between 30 degrees and 60 degrees are the prevailing westerlies or Ferrell
cells.
The air at the top of polar fronts that does not return toward the equator moves, instead,
poleward. At the poles, this air cools, sinks, and flows back to 60 degrees latitude north and
south. These third circulation belts over the poles are known as polar easterlies or polar Hadley
cells because they flow in the same direction as the Hadley cells near the equator. However,
they are not as powerful since they lack the solar energy present at the equator.
Major Air Circulation
Student Sheet
Directions:
Use your textbook, the provided diagrams, and the given background information to answer the following questions.
1. Color the following diagram using pg. 541 as a guide.
2. What is atmospheric circulation?
3. What is the driving force behind atmospheric circulation?
4. List two factors that cause the wind systems on Earth.
5. How many wind belts are between the Equator and the North Pole?
6. What is the ITCZ?
7. Describe the following wind belts (include direction of flow, latitude, etc…)
Trade Winds = ______________________________________________________________
Westerlies = ________________________________________________________________
Polar Easterlies = ____________________________________________________________
8. Explain what happens to the air at each of the following latitudes:
0° Equator - _________________________________________________________________
30°N/S - ____________________________________________________________________
60°N/S - ____________________________________________________________________
90°N/S - ____________________________________________________________________