Weather

Basics

2. Circulation Systems - El Niño / La Niña

Worksheet 3:
Weather without the influence of El Niño

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Worksheet 2 shows a map of the condtions experienced during normal weather conditions in the Pacific Ocean. In this worksheet we look at the conditions along a vertical cross section.

Weather without the influence of El Niño. The air flow pattern is known as the Walker Circulation. Animation and design by Julia Heres.

Can you answer the following questions?

1) Trade winds flow from the east towards the west because ...

a) they flow from low pressure regions to high pressure regions.
b) they flow from high pressure regions to low pressure regions.
c) they flow from cold areas to warm areas.
d) they follow the ocean current off the Chilean and Peruvian coast.

2) The Walker circulation shows that the trade winds change ...

a) from dry to moist.
b) from moist to dry.
c) from cold to warm.
d) from warm to cold.

3) Why do the easterly trade winds carry rain to Indonesia?

a) They gather warm and dry air over the western Pacific.
b) They gather cold and moist air over the western Pacific.
c) They gather warm and moist air over the eastern Pacific.
d) They gather warm and moist air over the western Pacific.

4) After convection and rain, the trade winds rise to higher altitudes

a) and then return towards the South.
b) and then return towards the North.
c) and then return towards the East.
d) and then return towards the West.

5) The so called Walker circulation in the Pacific consists of ...

a) easterly winds in the troposphere and westerly winds over the Pacific.
b) easterly winds at high altitudes and westerly winds on the ground.
c) westerly winds on the ground and easterly winds at high altitudes.
d) easterly winds on the ground and westerly winds at high altitudes.

6) When this wind circulation pattern descends off the South American coast ...

a) it reduces the existing low pressure area.
b) it reduces the existing high pressure area.
c) it enhances the existing high pressure area.
d) it enhances the existing low pressure area.

7) The water level in the western Pacific is about 0.5 m higher than that off the South American coast because ...

a) the trade winds push the water from East to West.
b) the trade winds push the water from West to East.
c) the trade winds push the water from North to West.
d) the trade winds push the water from South to West.

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In one sentence:
Normal weather conditions (as a result of the Walker circulation) lead to rain in Indonesia and South East Asia and dry conditions on the west coast of South America.

About this page:

author: Dr. Helmut Schrettenbrunner - University of Nürnberg, Germany
educational reviewing: Dr. Yvonne Schleicher, Julia Heres - University of Nürnberg, Germany
last update: 2003-09-08

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