Atmosphere’s Structural Components & Characteristics AICE EM: Atmosphere Key Content 1

Atmosphere: Thin, spherical envelope of gases surrounding the earth’s surface. Decay of organic molecules from bodies and waste. (______cycle) Source of atmospheric nitrogen: ____________ Which cycles maintain levels of H2O, CO2, O2? ________________________ Water cycle & carbon cycle Other: .9% Ar, .1% other (including water vapor)

Atmospheric pressure (millibars) 200 400 600 800 1,000 120 75 200 400 600 800 1,000 120 75 110 Temperature Thermosphere 65 100 90 Mesopause 55 80 Mesosphere 45 70 Altitude (kilometers) Altitude (miles) 60 Stratopause 35 50 Stratosphere 40 25 Figure 18.3 Natural capital: The earth’s atmosphere is a dynamic system that includes four layers. The average temperature of the atmosphere varies with altitude (red line). Most UV radiation from the sun is absorbed by ozone (O3), found primarily in the stratosphere in the ozone layer 17–26 kilometers (10–16 miles) above sea level. Question: Why do you think the temperature falls and rises twice, going from lower to higher altitudes? 30 Tropopause 15 20 Ozone layer 10 Pressure Troposphere 5 (Sea level) Pressure = 1,000 millibars at ground level –80 –40 40 80 120 Temperature (˚C) Fig. 18-3, p. 470

Layers of the Atmosphere Troposphere Stratosphere Mesosphere Thermosphere (including ionosphere) Exosphere

Describe Each Atmospheric Layer Composition- what is it made up of? Temperature differences in chemical compositions of the layers cause temp. to vary Pressure Solar activity Density variation Air density can be defined as the number of air molecules per unit volume (number density). Air molecules are held near the earth by gravity. In other words, air has weight. In addition gases, like air, are easily compressed, i.e., squeeze a gas together and its number density increases. The weight of all of the air above a given point in the atmosphere squeezes air molecules closer together, which causes their numbers in a given volume to increase (increase in number density). The more air above a level (and hence the more weight of air above a level), the greater the squeezing effect (or compression). Since air density is the number of air molecules in a given space (volume), air density is typically greatest at the surface or sea level (where it is squeezed by the weight of the entire atmosphere above) and decreases as we move up in the atmosphere because the weight of air above becomes less and hence there is less of a squeezing effect

Troposphere—inner layer --extends 11 miles above sea level at the tropics and about 4 miles above north and south poles. COMPOSITION: Air that we breathe Nitrogen (78%) Oxygen (21%) Green house gases (1%)= Water vapor, carbon dioxide, methane Absorb and release energy that warms the lower atmosphere Almost all weather comes from this layer TEMPERATURE: In the troposphere, temperature DECREASES with INCREASING altitude. This is because sunlight heats the surface. DENSITY: Density is the greatest at sea level or in this layer because of the weight of everything above it **the temperature decreases with altitude. Reason: troposphere's gases absorb very little of the incoming solar radiation. Instead, the ground absorbs this radiation and then heats the tropospheric air by conduction and convection.

Stratosphere—atmospheric sunscreen --extends 11-31 miles above the earth’s surface COMPOSITION: Similar to troposphere with two notable exceptions Water vapor concentration is 1/1000 of that of troposphere Ozone (O3) concentration is much higher TEMPERATURE: Temperature INCREASES with altitude Ozone, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun. The absorption of UV radiation by ozone causes heating in the stratosphere. DENSITY: Density is less than the troposphere, decreases as altitude increases

Mesosphere—upper layer --extends 60-35 miles above the earth’s surface COMPOSITION: millions of meteors melt and vaporize while entering the atmosphere and collide with gas particles, so even here there can be found suspended particles of heavy metals such as iron, potassium, silicon and other refractory materials. Due to the high rate of chemical reactions the mesosphere is an unstable and active region where  carbon dioxide, oxides of nitrates, and water crystals are formed emitting radiation TEMPERATURE: Temperature DECREASES with altitude Chemical reactions and less pressure/ density temperature is around -80 ° C (-112°F) DENSITY: Density is less than the troposphere, decreases as altitude increases

Thermosphere (ionosphere)—upper layer --extends 56-621 miles above the earth’s surface COMPOSITION:  In the thermosphere and above, gas particles collide so infrequently that the gases become somewhat separated based on the types of chemical elements they contain. Energetic ultraviolet and X-ray photons from the Sun also break apart molecules in the thermosphere. In the upper thermosphere, atomic oxygen (O), atomic nitrogen (N), and helium (He) are the main components of air. TEMPERATURE: Temperatures climb sharply in the lower thermosphere (below 200 to 300 km altitude), then level off and hold fairly steady with increasing altitude above that height. Solar activity strongly influences temperature in the thermosphere. DENSITY: Although the thermosphere is considered part of Earth's atmosphere, the air density is so low in this layer that most of the thermosphere is what we normally think of as outer space. The space shuttle and the International Space Station both orbit Earth within the thermosphere!

change as altitude increases? Why does Temperature change as altitude increases? In the earth’s atmosphere, pressure, which is related to the number of molecules per unit volume, decreases exponentially with altitude. Thus, if a parcel of air from the surface rises (because of wind flowing up the side of a mountain, for example), it undergoes an expansion, from higher to lower pressure. When you allow air to expand, it cools. This phenomenon is familiar to everyone--stick your finger on the valve of a car tire, and let some air escape. It is not cool inside the tire, but as the air comes out it expands and thus cools.

Click here Solar radiation Reflected by atmosphere Radiated by as heat UV radiation Lower Stratosphere (ozone layer) Most absorbed by ozone Troposphere Visible light Heat radiated by the earth Figure 3.8 Solar capital: flow of energy to and from the earth. See an animation based on this figure at CengageNOW. Heat Absorbed by the earth Greenhouse effect Fig. 3-8, p. 56

Heat Transfer at the Surface

Earth’s Energy Budget

Earth’s Energy Budget Latitudinal Heat Balance averaged over the entire year In the Zone extending 38 degrees on both sides of the equator, the amount of incoming solar radiation exceeds the loss from outgoing earth radiation. The reverse is true for the middle and high (polar) latitudes, where losses from outgoing Earth exceeds gains from incoming solar radiation.

Troposphere & Weather Troposphere is the weather maker Almost all clouds All precipitation All violent storms Discussed in Atmosphere Key Question 2