Wind, Air Pressure and El Niño #2- A Reading Activity


Rationale/Objectives/Purpose:
To give practice with feedback in reading comprehension.
Time Required:
Safety Issues:
None.
Materials:
Print-out of the reading.
Reading:
Wind, Air Pressure, and El Niño
Winds are the movement of air. Air usually moves from areas of higher pressure to areas of lower pressure. This makes sense - just like when the elastic walls of the balloon are squeezing air inside a balloon. If you let go of the opening of a balloon, 'wind' blows out from the higher pressure area inside the balloon to the lower pressure area outside the balloon.

 
Winds that blow over oceans move the water - that's why you get currents of moving water. The water at the surface of the oceans is warmer than deeper water. The warmer, lighter water 'floats' on top of the colder, denser water. If winds blow in one particular direction for a long period of time, much of the warm surface water will be moved.

 
Air pressure is usually higher on the eastern side of the Pacific Ocean near South America. Air pressure is usually lower over the western side of the Pacific Ocean near Australia. This causes the winds over the Pacific Ocean to blow from east to west. These winds are known as "trade winds."

 
The trade winds cause warm water to be blown away from South America's coast toward Australia. The result is a large 'pool' of warm water in the western Pacific Ocean. Because warm water evaporates easily, thus causing more clouds and rainfall, there is usually a lot of rain over the western Pacific Ocean.

 
During an El Niño event, the air pressure over the western Pacific rises and the air pressure over the eastern Pacific falls. The trade winds decrease in strength, or even reverse. Therefore, the warmer surface water is not moved away from South America's coast, so there is more rainfall around South America and less in the western Pacific.

 
What causes the change in air pressure over the eastern and western Pacific? Scientists continue to work on the details to decipher this complex climate phenomenon.  It has been observed that when the pressure goes up one on side of the Pacific, it goes down on the other side. This is called the Southern Oscillation and was first noticed in the 1920's by Sir Gilbert Walker.
Procedure:
Students- Read first. Then answer the questions.
Assessment:
Match the following terms.
1. Causes wind A.Western Pacific
2. Movement of air B.Observed Southern Oscillation
3. A cause of currents of water C.Wind
4. Floats on top, less dense D.Wind blowing over water
5. East-to-west winds over the Pacific E. Air Pressure differences
6. Usual location of a large pool of warm water F. Southern Oscillation
7. Results from evaporation of warm water G. Trade Winds
8. Happens during an El Niño event H. Warm water
9. See-saw pattern of air pressure over Pacific I. Rain
10. Sir Gilbert Walker J. Rise in air pressure in western Pacific, trade winds lessen or reverse, more rainfall around eastern pacific
Teacher Background:
Answer Key 1. E 2. C 3. D 4. H 5. G 6. A 7. I 8. J 9. F 10. B
Extensions:
Use the reading section and make up other questions or essay questions.