You can read more about the Hadley Cells by visiting the NASA website link below.

Transcription

1 Environmental Literacy Framework Activity 5B-Full of Hot Air Preview Focus Question: How is climate affected by air and ocean currents? The distribution of heat around the globe is not even. Due to the tilt of the Earth, the Sun s angle is higher near the Equator than at the poles. This means more energy is received by the lower latitudes (near the Equator) than at the higher latitudes (near the poles). Systems in nature tend to even out the distribution of heat, and the Earth as a system is no different. Both the atmosphere and the oceans work to achieve this equalization. The diagram below illustrates Hadley Cells. In 1735, amateur meteorologist George Hadley proposed a system of convection currents that reach from the poles to the Equator. These large convection cells drive the global winds while creating our weather patterns and climate regions. Even though Hadley's theory was incorrect in some of its assumptions, the convection currents still carry his name today. You can read more about the Hadley Cells by visiting the NASA website link below. Time 50 min. Materials Clear plastic shoebox (12" x 6" x 4") Sturdy box, strong enough to hold the shoebox filled with water Insulated cup, the height of the sturdy box Source of hot water Blue and red food coloring Blue ice cube (made ahead) Hobby knife Pipette Vocabulary (Terms) Convection currents Density Equatorial Equinox Latitude Polar Solstice Image source: 243

2 Environmental Literacy Framework Activity 5B-Full of Hot Air Above is a picture of the amount of energy (watts/square meter; W/m2) received by the Earth on June 1, 2007 (near Summer Solstice). Notice the difference between the Northern Hemisphere and the Southern Hemisphere. What do you think this graph would look like in December, close to Winter Solstice? What would it look like in March, close to the Spring Equinox? The Earth as a system will continually work to equalize heat to all regions, moving heat from the warm, equatorial latitudes to the cool, polar latitudes. This movement of heat in the form of atmospheric winds and ocean currents keeps the polar areas from being too cold and the equatorial regions from being too warm. The Earth depends on this movement to maintain the climate regions we know today. 244

3 Prepare Activity Steps: NOTE: The physics of air movement in the atmosphere and water in the oceans is very similar. Keep in mind that because gases are invisible and difficult to observe, in this model, we use water to represent the gases in the atmosphere. 1. Acquire a clear plastic shoebox and a sturdy cardboard box that is slightly larger than the clear plastic shoebox. The second box will serve as a stand for the plastic shoebox and water so be sure it is a strong box (Picture A). 2. You will also need a cup to hold the hot water inside the cardboard box. For best results, make sure the height of the cup fits snugly inside the box (Picture C). 3. On top of the box, trace around the top of the cup with a pencil or pen (Picture B). Then use a sharp implement, such as a hobby knife, to cut a hole in the box just large enough for the heat to move from the cup to the plastic shoebox (Picture C). 4. Set up the clear plastic shoebox container and cardboard box as in Picture C. Fill the plastic container with water to about 1 inch below the top. 5. Wait until the water has settled and there is no longer any movement (2-3 min.). A B C D 245

4 (Continue Activity Steps) 6. Carefully, slide the cup full of hot water into the box, under the hole you cut in the box (Picture C). 7. Using the pipette, carefully place several drops of red food coloring on the bottom of the water near the end of the container where you cut the hole in the box (Picture D). 8. Watch what happens. As water or air is heated, it expands, becomes less dense than its surroundings, and rises. Colder air or water will move in to replace it. This creates the winds in the atmosphere and the currents in the oceans. Since these movements are caused by heat, they are called convection currents. 9. Place a blue ice cube in the water at the other end of the container. You will be able to see these movements even more clearly in your container as cold blue water sinks and replaces the warm red water as it rises. 10. Look at the diagram of Global Wind Patterns, below, and compare what you just observed to the circulation patterns for the atmosphere. Global Wind Patterns 246

5 Ponder What do you think would happen to the distribution of heat energy around the Earth system if the global wind patterns were to change? How would the climate regions around the world be changed if the winds or surface ocean currents changed? 247

6 Practice Got the Big Idea? Winds and ocean currents help distribute heat around the world. This works to warm the polar regions and cool the equatorial regions. Our climate systems and regions depend on this movement and distribution of heat. The polar regions would be much colder and the equatorial regions would be much hotter if this distribution of heat were to stop. Plan Your Presentation Come up with a question or statement to engage your visitors about the movement of heat around the world. Prepare a visual to go along with your demonstration showing how different latitudes on Earth receive different amounts of energy from the Sun. Practice explaining how warm air rises and is replaced by colder, dense air in the Earth s atmosphere. Explain how the laws of physics involved in the movement of air currents are the same for movement of water currents in the oceanic system. Warm water rises and is replaced by colder, denser water. Your station requires ice cubes to be made ahead of time and a supply of hot water. Decide how you will keep the ice cubes frozen and the hot water hot during your presentation. Coolers and thermoses may work well for you. Present Ask your visitors to predict what will happen before you begin the demonstration. Have them draw what the container will look like after 1 minute and after 3 minutes. Share with them how this demonstration is a model for both the Earth s atmosphere and oceans as the Earth system continually works to move heat away from the equator toward the polar regions. Ask them what they think would happen to climate regions around the Earth if these currents were to suddenly stop. Help them understand how important the Earth s system of convection currents is in maintaining the global climate regions. 248

7 Background Information for the Teacher Activity NSES CLEP ELF In this hands-on activity, learners create a model to demonstrate the pattern of movement in the Earth s atmosphere of warm and cold air masses. The model further helps to illustrate how heat is distributed around the globe. NSES Physical Science Std B: Energy is transferred in many ways. Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature. The sun is a major source of energy for changes on the earth's surface. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation. Earth Science Std D Clouds, formed by the condensation of water vapor, affect weather and climate. The atmosphere has different properties at different elevations. The sun is the major source of energy for phenomena on the earth's surface, such as growth of plants, winds, ocean currents, and the water cycle. Seasons result from variations in the amount of the sun's energy hitting the surface, due to the tilt of the earth's rotation on its axis and the length of the day. CLEP 1A: Sunlight reaching Earth can heat the land, ocean, and atmosphere. Some of that sunlight is reflected back to space by the surface, clouds, or ice. Much of the sunlight that reaches Earth is absorbed and warms the planet. 1D: Gradual changes in Earth s rotation and orbit around the Sun change the intensity of sunlight received in our planet s polar and equatorial regions. 2A: Earth s climate is influenced by interactions involving the Sun, ocean, atmosphere, clouds, ice, land, and life. 2F: The interconnectedness of Earth s systems means that a significant change in any one component of the climate system can influence the equilibrium of the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system. 5A: The components and processes of Earth s climate system are subject to the same physical laws as the rest of the Universe. Therefore, the behavior of the climate system can be understood and predicted through careful, systematic study. 5E: Scientists have conducted extensive research on the fundamental characteristics of the climate system and their understanding will continue to improve. Atmosphere 4: Atmospheric circulations transport matter and energy. Atmosphere 4a: Energy is exchanged between the atmosphere and other Earth systems via evaporation and precipitation of water, radiative transfer, and thermal convection. Atmosphere 4b: Unequal heating of Earth s surface produces movement in the atmosphere. 249

8 NSES: National Science Education Standards ( CLEP: Climate Literacy Essential Principles ( ELF: Environmental Literacy Framework ( The distribution of heat around the globe is not even. As shown in the net radiation diagram below, the equatorial regions of the Earth receive more energy than the polar regions. This inequality is due to the fact that the Earth is a sphere and not a flat plane. A second reason also contributes to the unequal heating of the Earth s surface and oceans: Earth s axial tilt. For example, have you ever wondered why the average January temperature is warmer in Texas than in Michigan? The explanation is that Earth is tilted relative to the plane of the orbit around the Sun. This angle means that in the winter in the Northern Hemisphere, more hours of sunlight reach Texas than Michigan and the sunlight is at a higher angle, so the heating is more intense. (See graphic on next page) Source: NASA EOS article 250

9 Source: Systems in nature tend to even out the distribution of heat, and the Earth as a system is no different. The constant, unending movement of air and water among Earth s surfaces, oceans, and atmosphere redistributes heat (thermal energy) around the globe. Was this not the case, the Earth would undergo extreme temperature fluctuations like that of the Moon. The ocean and atmosphere are a coupled, or interlocked, system. They share common characteristics in that they both are fluids and they can redistribute heat energy and matter via convection. The global wind system has been observed, diagrammed, and discussed for many centuries. George Hadley, in 1735, was the first to propose a global system of convection cells that stretch from the poles to the Equator. These cells form due to temperature and density differences in the atmosphere. As the Sun warms the air in the tropics, it becomes less dense and flows upward. While the warm air is rising, it loses heat and moisture in the process of creating large tropical storms. This cooling air flows northward and gradually begins sinking. At the same time, cold, dense air is sinking at the poles and flowing southward towards the Equator. That volume of air is replaced by air from the tropics. If Earth did not rotate on its axis, there would only be one of these cells in each hemisphere. However, the rotational forces of the Earth cause a deflection in the moving air, creating not one, but three Hadley cells, shown in the diagram at the beginning of this unit. These large convection cells drive the global winds, while creating our weather patterns and subsequent climate regions. 251

10 As a result of the Hadley Cells, there are three major global wind systems: polar easterlies, prevailing westerlies, and the trade winds. These large, planetary-scale winds travel thousands of kilometers over time periods of weeks to months. These winds are what carried the great sailing vessels of the world discoverers in the past, as well as the ocean sailors of today. Where the ocean and atmosphere are in contact, kinetic energy (energy of motion) is passed from the moving air to the ocean surface via friction. This frictional force drives the ocean surface currents. The shallow surface ocean currents move in tandem with the wind. The surface currents move approximately 25% of the heat around the globe while the air currents move the other 75%. References: Lutgens, Edward J. Tarbuck, Frederick K. The Atmosphere: An Introduction to Meteorology. New Jersey: Prentice Hall, NWS Jetstream Glossary Unit Activity Vocabulary Word Definition Atmosphere Full of Hot Air Convection currents One of the major modes of heat transfers by the movement of mass, liquid, or gas. Atmosphere Full of Hot Air Density The calculated mass per unit volume of a substance. Less dense fluids and gases float on more dense fluids and gases unless they mix. Hot air is less dense than cold air, which is why a hot air balloon rises. Atmosphere Full of Hot Air Equatorial Refers to the Equator of the Earth. Atmosphere Full of Hot Air Equinox Occurs twice a year on a day in March and September, when the tilt of the Earth is neither towards, nor away from the Sun. On these two days, the day length and night length equal 12 hours. Atmosphere Full of Hot Air Latitude Circular lines around the Earth that measure the angular distance from the Equator in degrees. The Equator is 0 o latitude, and divides the Earth into the Northern and Southern hemispheres. Atmosphere Full of Hot Air Polar Refers to the regions of the Earth near the poles. Atmosphere Full of Hot Air Solstice An event that occurs twice a year when the Sun reaches the most northern and most southern extremes. 252