The Atmosphere UNIT 9 STANDARDS: NCES 2.5.1, 2.5.2, LESSON 1

Lesson Objectives In this lesson, you will learn about: The composition, structure, and properties that make up the Earth’s atmosphere How solar energy fuels weather and climate How water moves in the atmosphere

Atmospheric Composition Composition Ancient Greeks thought air was one of the four elements. When meteorologists describe air, they’re referring to air in the lowest layer, the troposphere. From here we can go on to say that the atmosphere (or air in the atmosphere) is mostly a mixture of gases. What is called pure air is a mixture of four major gases, plus small traces of other gases.

Four Major Gases Nitrogen (N 2 ): Nitrogen is the most abundant gas in the air. Oxygen (O 2 ): Oxygen is used by animal life in the respiration process. Two gas compounds are water (H 2 O) and carbon dioxide (CO 2 ). Argon (Ar): Argon is chemically inactive, but is of lesser value to us. Its most common use is in electric light bulbs.

Major gases Carbon dioxide (CO 2 ): There is not much carbon dioxide in the air. However, it is one of the most important gases in the atmosphere. It’s used by green plants during photosynthesis to produce simple sugars. The plants give off oxygen into the atmosphere as a waste product of photosynthesis. Carbon dioxide is the “greenhouse gas” along with water that helps hold in the atmospheric heat. Water Vapor (H 2 O): This is the gaseous form of water and can be found in the atmosphere. It helps to trap heat and keep the earth warm. It is found in clouds, fog, snow, hail, and rain.

Oxygen-Carbon Dioxide Cycle CO 2 is given off as a waste product from animals during respiration. Plants then use the CO 2 for photosynthesis. This use of CO 2 by the plants removes CO 2 from the atmosphere. Plants give off O 2 in the photosynthesis process as a waste product. Animals use the O 2.

Composition of Air Summary

Ozone Another component of the atmosphere is ozone. This gas is formed when a third oxygen atom binds with oxygen gas. It is important because it absorbs ultraviolet rays from the Sun. There is evidence the ozone layer is thinning over the poles.

Structure of the Atmosphere Scientists who study the atmosphere are called meteorologists. They have found that the atmosphere is striated, that is, it has several different layers. Each layer differs from the others in: 1. temperature, 2. chemical composition, 3. physical properties.

Lower Atmosphere Level 1 Level 1 The lower atmosphere is called the troposphere. This is the layer nearest the earth. Its depth varies from 8 kilometers (4.8 miles) over the poles to about 17.6 kilometers (11 miles) over the equator. Most of our weather is located in this layer. This includes such things as clouds and warm and cold air masses. Almost all of the water in the entire atmosphere is found here. We live in the troposphere, at the bottom of the earth’s atmosphere. We are under the pressure of all the air above us. An instrument called a barometer measures atmospheric pressure. If you listen to the weather report on television, you may hear the weather mention the barometric pressure. When air pressure drops, a storm is coming.

Lower Atmosphere Level 2 Level 2 The Stratosphere The next layer is colder, the average temperature is -40 o C. The stratosphere extends above the troposphere to an average of 50 kilometers (30 miles). Two important features associated with the stratosphere are: 1. The jet stream is an enormous current of air. It’s between the troposphere and the stratosphere. These winds blow from west to east at 200 miles per hour. 2. The ozone layer is found within the upper region of the stratosphere.

Upper Atmosphere Level 3 Level 3 The Mesosphere The mesosphere is above the stratosphere and extends up to fifty miles (80 kilometers) above the earth’s surface. The temperature here falls to around -100 o C as you reach the top of the mesosphere. Near the top, the temperature stops falling.

Upper Atmosphere Level 4 Level 4 The Thermosphere The thermosphere extends from 80 to 960 kilometers (50 miles to 600 miles) above the earth. It contains most of the ionosphere, which is not a layer of the atmosphere but is very important to us. The Aurora Borealis is found here.

Upper Atmosphere Level 5 The Exosphere Here the atmosphere is so thin that it barely exists. There are very few air molecules in this region. The composition is mostly hydrogen and helium gases. Beyond the exosphere is outer space---vast emptiness.

Upper Atmosphere Summary

Solar Fundamentals Radiation Conduction Convection Energy transfer from a higher temp to a lower temp. 50% of all energy is reflected back to space. The transfer of energy between two objects that are touching. Hot pot on a stove. The movement of energy due to different densities of the air. Warm air rises and cool air settles. The Sun is the source of all energy in the atmosphere.

Solar Energy Transfer Summary

Section Review Describe the importance of water vapor in the atmosphere. Rank the main atmospheric gases from most abundant to least abundant. Bases on your understanding, what can you say about the summer temperature in a large city compared to those in the surrounding countryside. In what layer does the weather occur?