1. As students enter the room, have
the following question written on the board: What do you
think might cause the global wind belts we observed yesterday?
2. Allow students about 5 minutes to record their thoughts
and another 5-10 minutes to share their thoughts and
their rationale. If the class seems stumped by the question,
prompt them to think about other systems on the earth
that move from place to place. Hopefully one student
will bring up the idea of convection as a way to move
air masses around the globe.
3. Show students Overhead One which shows the Earth
and the wind belts and atmospheric cells. Cover the lower
half of the overhead for now. Ask students to make observations
about the cells. What patterns do they notice? [This
should remind them of convection cells, the way the atmospheric
cells meet and converge either pulling air down or pushing
Draw students’ attention to the equatorial
region. In which direction does the air move? [Up] What
would cause the air to rise? Hopefully students will
say heat immediately. If not, ask them how a balloon,
specifically one that carries people, rises. Guide students
via questioning to explain that once the hot air (which
is less dense) has risen into the upper atmosphere, cools
(becomes more dense) and then sinks. Ask students to
look at the map and estimate where they think the majority
of this air sinks into (the air sinks at about the 30tth
parallel. This area is called the Horse Latitudes because
the winds are not very strong in this area .Sailors would
get stuck and throw their horses overboard to lighten
the load of the ship so that lighter winds could carry
5. What do they notice at the 30th parallel? [Air sinks]
60th parallel [Air rises] Polar region? [Air sinks]
students’ attention to the wind belts
at the equator, 30th parallels, 60th parallels, and Polar
Regions. What types of pressure zones exist there? [In
order, there are low, high, low, and high-pressure zones.]
Is there a relationship between the type of pressure
and the direction of the air current? [Low-pressure zones
exist where air rises and high-pressure zones exist where
7. What do students think causes these convection cells?
[Heat from the sun]. Reveal the lower half of the overhead
at this time. Where do the solar rays strike the Earth?
How does this relate to the rising and sinking of air
on the Earth? [Air rises where it is warmed by the sun
and sinks where it is not].
8. Reveal Overhead Two showing the names of the cells
and more specific airflow. Tell students the Hadley Cell
is named for George Hadley who discovered the mechanism
for the easterly motion of the Trade Winds in 1735. Edmond
Halley though, did attempt to explain the process in
1686.The Ferrell Cell is named for William Ferrell who
explained and noted the motion of the Westerlies in the
9. Direct students to estimate how the pressure zones
affect wind flow. Does the wind flow from low pressure
to high pressure or high pressure to low pressure? [High
10. What do students notice about the type of air that
rises and the type that falls? Why does this happen?
[Warm, moist air rises, the rains fall as the air cools
so that only dry air is left to fall].
11. Show students the map of the jet stream at http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml and at
http://www.john-daly.com/guests/jet.htm. Tell students
this air flow actually pushes warm air up into Europe
and keeps the temperatures warm there, especially when
the jet stream winds are slower.
How do students think this movement of cold and warm,
wet and dry air, high and low pressure zones affects
weather in different countries? What do these cells do
to the overall temperature of the Earth? How might these
patterns help us determine where pollutants from one
country are likely to travel?