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Atmospheric Circulation
Integrated Science
Unequal heating of the Earth’s surface and atmosphere by the sun and terrestrial radiation drives
convection within the atmosphere and oceans, producing clouds, high and low pressure zones, global
winds, and ocean currents. Air circulating via convection cells and acted upon by the Coriolis effect
redistribute that heat energy. These patterns create bands of warmer, wetter regions and bands of
cooler, drier regions at specific latitudes. This pattern creates a diversity of conditions for life and results
in the existence of different biomes (global ecosystems) on the planet.
Convection Cell Circulation • Areas of earth’s surface receiving more radiation generate warmer air.
This warm air becomes less dense and rises. As the air cools at altitude, it sinks, creating a convection
current. The spinning of the Earth on its axis creates not one big cell, but a set of three cells in each
hemisphere
1. Alongside one edge of your world map, draw 3 convection cells in each hemisphere showing
the rise of warmer, less dense air and sinking of cool, dry air. Air rises and sinks at roughly 30
degree latitude intervals.
2. Use red to indicate warmer air and blue to indicate cooler air.
3. Label the cells
0
- 30 degrees N & S latitude are Hadley cells
30 – 60 degrees are Ferrel Cells
60 – 90 degrees are Polar Cells
Pressure Zones • At sea level, dense sinking air creates higher atmospheric pressure and less dense
rising air creates zones of low pressure.
4. Label regions of air pressure lows (L) and highs (H) on the map.
Clouds and Precipitation • Warm air can hold more water vapor than cool air. As higher altitude air
cools, the vapor condenses, forming clouds. This is most pronounced in the tropics, over the InterTropical
Convergence Zone (ITCZ), but also has an impact in the temperate zones.
5. Highlight the ITCZ clouds on the map, and to a lesser extent the temperate zone clouds.
Surface Wind Patterns • Wind is created as air moves from high pressure to low pressure regions. The
winds are deflected from a straight path by the Coriolis Effect. In the northerm hemisphere, they curve to
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the right; in the southern hemisphere, to the left.
6. Look at your convection cells to determine the direction of each band of winds. Curve
your arrows to show the effect of the Earths rotation. Use different colored arrows to
diagram the direction of each set of surface winds. Create a key to show which color
relates to which wind current.
• Trade winds (from 30 degrees to equator to the west)
• Westerlies (from 30 degrees to 60 degrees to the east)
• Polar Easterlies (from 90 degrees to 60 degrees to the west)
Distribution of Biomes • The varying conditions of air as it circulates directly determines ecosystems
across the globe.
7. Rising warm air and associated clouds create bands of forests. Shade these forested regions in
light green in the tropics and dark green at higher latitudes.
8. Sinking cool air carries little moisture, and so deserts form here. Shade the temperate deserts
brown and the polar deserts blue.
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Evidence • Choose 2 or more cities from the list below. Based on the latitude of each, make hypotheses
about the parameters you drew onto your map: temperature, precipitation, air pressure, wind direction,
and cloud cover. Research the cities to find quantitative data to test your hypotheses with. Convert to
metric where needed. Record in a data table.
City
Latitude
City
Latitude
Yuma, Arizona, USA
32N
Iquitos, Peru
0
Whitehorse, Yukon, Canada
60N
Bagdad, Iraq
33N
San Jose, Costa Rica
10N
McMurdo Station, Antarctica
77S
Barrow, Alaska USA
71N
Oslo, Norway
59N
Caribou, Maine, USA
46N
Kinshasa, Congo
4S
Upernavik, Greenland
70N
Ciudad Juárez, Chihuahua, Mexico
32N
Munich, Germany
48N
Oslo, Norway
60N
Analysis • As directed in your lab notebook, with particular emphasis on patterns on the map citing your
city research as evidence/data and the inferences you may reasonably draw from them.
Patterns: relate as many of the variables to each other as possible:
radiant energy
directness (angle) of radiation
latitude,
air temp
air kinetic energy
air density
air rising
air sinking
air pressure
convection cell direction
wind direction
cloud cover
dry climate
wet climate
forests
deserts
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Follow-up questions
1. What are the factors that combine to move air around in the troposphere? What are all of these
factors dependent on?
2. Hurricanes form over warm ocean waters in the Atlantic. Explain why.
3. Imagine a hurricane forms at 30 degrees N and 80 degrees west. Predict two locations (one in the
US and one in another country) where that hurricane may reach land. Include a description of the
surface wind current that would bring it to those places.
4. Use the map to explain why Arizona is predominantly desert and western Washington State
primarily temperate forest.
5. Your friend is very excited about an upcoming trip to Cancun, Mexico. (on the Yucatan peninsula
at 25 degrees N latitude and 90 degrees W longitude) He says to you: “I love the desert - I hope I
get to see some cactus!” Is his excitement warranted? Let him down easy.
6. Many people picture the arctic as a cold, often snowy place. Does your map support this? Explain.
Teacher Notes:
Relate radiation to air temp
Air temp to density
http://en.wikipedia.org/wiki/List_of_cities_by_latitude#Equator
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