A Comparison of Cloud Coverage over Africa

Illustration of Hadley Cell
To use a NASA satellite data to contrast amounts of cloud coverage over different climate regions in Africa
Grade Level: 8 – 12
Estimated Time for Completing Activity: One 50-minute class period
Learning Outcomes:
  • Explain how Earth’s major air circulations affect global weather patterns
  • Relate local weather patterns to climate
  • Identify different climate regions
  • Describe conditions for cloud formation along the Equator
  • Access data and import into Excel
  • Familiarity with producing graphs in Excel
  • Familiarity with locating places using atlases, globes, maps
  • Spreadsheet program
  • Atlas or Globe
Lesson Links:

Clouds are collections of water vapor in the atmosphere. Moisture collects in the atmosphere due to the evaporation of water, thus evaporation plays an essential role in the water cycle. Earth’s oceans are huge sources of water for evaporation.

On and near the Equator, where average solar radiation is greatest and moisture plentiful, air is warmed at the surface and rises (convection). This creates a band of low air pressure which draws in surface air from the subtropics (23.5 – 30 degrees N and S). When this subtropical air reaches the Equator, it converges and rises into the upper atmosphere (convergence). The rising air leads to the formation of large towering cumulus clouds. The air attains a maximum vertical altitude of about 14 kilometers (top of the troposphere), and then begins flowing horizontally to the North and South Poles. This rising air comprises one segment of a circulation pattern called the Hadley Cell (see diagram above). The Hadley Cell eventually returns air to the surface of the earth, near 30 deg N and S.

The descending portion of the Hadley Cell produces a band of high air pressure at these latitudes called the subtropical high. Winds are generated between the subtropical high and the equatorial band of low pressure because air moves from high pressure toward low pressure. These winds are deflected from east to west as they travel toward the equator by the Coriolis force and are called the Trade Winds.

Frequent cloud cover and precipitation occur along this band of convergence and convection and is called the Intertropical Convergence Zone (ITCZ). The descending air at the subtropical high inhibits cloud formation. Because of the Earth’s tilt, and thus the latitude of maximum solar radiation, there are seasonal shifts northward and southward of the location of the ITCZ and subtropical high


Open the microset for cloud cover over Aswan, Egypt (24N, 32E) and Kampala, Uganda (0N, 32E). The microset is a text file that can be read by Microsoft Excel. Follow these steps to create a graph of the data in Microsoft Excel.

1. Import the microset text file. (See instructions in link section)
2. Highlight the columns beginning with Date, Aswan, Egypt, and Kampala, Uganda.
3. Under the Insert menu, click Chart.5. Choose your line preference, click Next.
4. For Chart Type highlight line, click Next.
5. Choose your line preference, click Next.
6. Type in Cloud Cover, ‘Date’, and ‘Percent’ for Chart Title, Category (X) axis, and Value (Y) axis, click Next.
7. Select As new sheet, click finish. This places the graph on another spreadsheet. If you want the graph on the same spreadsheet as the data, you change nothing and click finish.

For easier comparison, put both datasets on the same graph (See example Excel graph in links section). Another way for comparison is to make individual graphs of each location’s data, and print the graph on a transparency.


1. How does the Hadley Cell affect weather for these two cities? What is the explanation for one city being cloudier than the other?
2. Using the graphs for your basis, can you identify which city is more likely to have more rainfall? Which city is more likely to have less rainfall?
3. Can you make any conclusions about the different climate regions (i.e. desert, tropical, semi-tropical, temperate)?
4. Does there appear to be a seasonal pattern? If so, describe the pattern.
5. Knowing that the Hadley Cell affects weather north and south of the Equator, what do you believe will happen south of the Equator? Will it be cloudier or less cloudy?


1. You are the secretary of agriculture in Egypt. It is your responsibility to help the farmers have successful crops using the resources available. Knowing how the cloud cover affects climate, what type of crops would you advise a farmer to grow so that the crop will thrive in its environment? How would you advise the farmer to manage his or her water resources? Answer these same questions, but now you are the secretary of agriculture in Uganda. Make a list with your suggestions for each country. Do you think farmers in the US make similar decisions as their counterparts in Africa?

2. Climate affects the people living within its regions. Climate is a trend of the kind of weather a particular place has. How would living in Aswan, Egypt, be different from living where you are now? List a few of those differences. How would living in Kampala, Uganda, be different from living where you are now? How will your life be affected by the different climate and weather? List a few of those differences.

3. Climate can sometimes have devastating effects on civilizations. For example, some scientists now believe that climate change may have had an effect on the ancient Maya civilization that flourished on the Yucatan Peninsula. See the link titled ‘Climate and the Collapse of Maya Civilization’. If this topic strikes your curiosity, use the LAS (using the same parameters as given in the procedure) to explore other places around the globe and hypothesize how changes in cloud coverage and climate (especially those related to the ITCZ) could potentially impact the people living there.

Lesson plan contributed by Erica Alston, NASA

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