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Winds
And
Weather

by Jonas Ramoth and Sidney Stephens

Activity Series 5 - Global Winds*

 Summary In this activity, students extend their understanding of convection to consider global winds and the effect of the earth's rotation on the creation of patterns of prevailing wind direction. Concept The rotation of the Earth and global convection currents create prevailing wind patterns at different Earth latitudes. Above the Earth's surface, the gases of the atmosphere flow in great cycles of weather and the longer patterns of climate. These cycles are primarily driven by energy from the sun. More heat energy from the sun falls at the equator than at the poles, and thus air in the tropics is heated and rises. If the earth did not rotate, this warm equatorial air would rise, cool off and sink at the poles creating high-altitude winds from equator to pole, and low altitude winds from pole to equator in the pattern of the familiar convection cell. Such pole to equator winds do not prevail, however, because the rotation of the earth breaks this potential north-south convection cell into 3 cells in each hemisphere. Activity 5a Materials 20 cm diameter cardboard circles Pencils Water
 Procedure Gear-Up: 1. You know from your local studies that cloud movement often indicates the direction of the wind. Look at this photograph of the Earth taken from space. What do you notice about the pattern of the clouds? (They're in swirls.) What do you suppose this tells us about the direction of atmospheric winds? What are your ideas about why the clouds might be curving?
 Explore/ Generalize: 2. Let's see if we can find out what causes the swirl pattern in the clouds. Obtain a circle of cardboard approximately 20 cm in diameter. Push a pencil through the center of the circle. Tilt the cardboard to one side. Place a few drops of water on the cardboard and watch the pat they take as they move downward. Is the path curved or straight? 3. Now, put several drops of water on the cardboard circle and by twisting the pencil spin the cardboard. How does the movement of the cardboard affect the path of the water droplets? 4. Imagine that the water droplets are clouds that are being moved by the wind. What could cause the wind to move in a curved path? (Polar winds from the North come in contact with the Earth's surface. The Earth is rotating at a speed faster than the wind. The speed of the rotating Earth pulls on the Polar winds causing them to curve a bit from their straight path. The swirl pattern in the clouds is caused by this deflection of the southward movement of the polar air currents).
 Activity 5b Explore/ Generalize: 1. Looking down on the North Pole of a globe, spin the globe from the west to the east -counter clockwise). Using a piece of chalk, have a student attempt to draw a straight chalk line on the globe from the 35 degree latitude line to the equator while the globe is spinning. 2. Stop spinning the globe and have students observe the chalk line. Is the chalk line straight? In which direction does the chalk line curve? In the Northern Hemisphere the Earth's rotation causes the wind to curve toward the East. Below the equator the effect of the Earth's rotation is reversed and the North moving winds are pushed to the West. The diagram on the left shows the directions of the Earth's prevailing winds. Prevailing winds are named for the direction from which they blow. Thus, the prevailing westerly winds blow from the west towards the east and the prevailing easterly winds blow from the east towards the west. 3. From looking at the diagram can you tell what direction the prevailing winds blow across United States (the Lower 48)? How about prevailing winds in Barrow? Selawik? Fairbanks? Anchorage? Juneau? Apply/Assess: 4. From your local studies, how important are the prevailing polar easterlies in Selawik?
 5. Looking at a globe and the prevailing winds diagram, identify these areas: « The area where the northeast trade winds and southeast trade winds don't quite meet, called the doldrums, is a calm area where no wind or very little wind blows. Sailing captains tried to avoid this area. Why? « The area in the Atlantic Ocean at 30 N latitude was given the name "Horse latitudes". This area is also very calm. Find the Horse latitudes on the diagram. Spanish ships carrying horses to the New World colonies were often stuck for long periods in these calm seas. When the horses used up their share of thrown overboard to lighten the load and get the ships moving again. « If winds traveling over water bring moisture and moisture is dropped in the form of rain when winds begin to rise over mountains, where would you expect rain forests to be in the United States? In South America?

6. If helium balloons were released from your school and were carried away by winds, eventually popping with the remains drifting to the ground, where would you expect to find the remains of these balloons and why? Be sure to justify your answer using evidence from your studies.

* Adapted from Barr, B. (1994)

Standards

Section I - Observing Locally

Section II - Understanding Wind

Section III - Connecting Globally

Appendix A - Selawik Weather Information from Jonas Ramoth

Appendix B - Assessment

Appendix C - Weather Resource List

Appendix D - Interdisciplinary Integration

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Handbook for Culturally Responsive Science Curriculum by Sidney Stephens
Excerpt: "The information and insights contained in this document will be of interest to anyone involved in bringing local knowledge to bear in school curriculum. Drawing upon the efforts of many people over a period of several years, Sidney Stephens has managed to distill and synthesize the critical ingredients for making the teaching of science relevant and meaningful in culturally adaptable ways."

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