Monday, January 30th Key Question: How do the layers of the atmosphere affect us? HW: Read Chapter 15, Section 2, take notes and answer Self Check questions 1-5. 1

Layers of the Atmosphere Earth’s atmosphere has 5 layers, each with unique properties. Lower layers include the troposphere and stratosphere. Upper layers are the mesosphere, thermosphere, and exosphere. The troposphere and stratosphere contain most of the air. 2

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Layers of the Atmosphere The Troposphere Lowest layer beginning at Earth’s surface and extending to an elevation of 7-20km (4-12 miles or 23-65,000 feet). It contains 99 percent of the water vapor and 75-80% of the atmosphere’s mass; densest layer. Rising and falling airflow; heated from below; this keeps air flow stirred up and variable (wind). Almost all of our weather occurs in this layer. Life layer – life as we know it exists here. Jet stream is just below the tropopause; winds move at approximately 250mph or 400kmph. Separated from the stratosphere by the tropopause; the boundary where trend in temperature changes. 4

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Layers of the Atmosphere The Stratosphere Directly above troposphere, extends 10-50km (6-30+ miles) above Earth's surface (31miles). Stratopause separates from next layer above. Most ozone in this layer (O3). Heated from top down due to ozone. Very stable air due to temperature stratification; very little convection or mixing of air; airflow mostly horizontal. Dry air; almost no clouds. PSC’s (polar stratospheric clouds or nacreous clouds) are in lower area. These clouds promote “holes” in ozone layer due to chemical reactions. CFC’s (Chloroflourocarbons) and other materials (volcanic gasses, meteorite materials, rocket exhaust, etc.) can collect in the stratosphere due to lack of vertical convection. Atmosphere at top is 1000 times thinner than at sea level. Aircraft and weather balloons cannot pass this level. Lighting called “blue jets” can occur above thunderstorms and extend to upper limits of stratosphere. Waves of air from troposphere can move air, otherwise very stable. 6

Layers of the Atmosphere A chlorine atom from chlorofluorocarbon molecule breaks the ozone molecule apart. One oxygen atom combines with chlorine atom and the rest form a regular, two-atom oxygen molecule. Result: more UV radiation reaches Earth's surface. 7

Layers of the Atmosphere Destruction of ozone molecules seems to cause seasonal reduction in ozone over Antarctica called the ozone hole. Every year in late Aug. or early Sept. ozone in atmosphere over Antarctica begins to decrease. By October, it reaches lowest values and begins to increase. By December, the ozone hole disappears. 8

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Layers of the Atmosphere The Mesosphere The mesosphere extends from the top of the stratosphere to about 85 km above Earth. Separated above by the mesopause where trend in temperatures changes. Coldest layer. Meteors burn up in this layer. Least studied layer because it is hard to access. Noctilucent clouds are present over the poles. Lighting called “sprites” and “ELVES” also appear above thunderclouds. Waves of air from stratosphere move the air, otherwise very stable. 10

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Layers of the Atmosphere The Thermosphere Named for its high temperatures. Solar activity causes temperature variation. Widest layer, but low density air. Density so low that most of it is considered “outer space” because “space” begins at approximately 100km (62 miles). Found between 85 km and 500 km(50-300miles!) above Earth. Space Shuttles, the International Space Station, and many satellites orbit here. Most X-ray and some UV radiation is absorbed here. Aurora Borealis (northern and southern lights) occur here. Electrically neutral, but ions are created by solar radiation, creating ionosphere. 12

Layers of the Atmosphere The Ionosphere Located within mesosphere and thermosphere. Allows radio waves to travel great distances. During day, energy from Sun interacts with particles in ionosphere, causing them to absorb AM radio frequencies (no transmission). At night, without solar energy, AM radio transmissions reflect off the ionosphere, allowing radio transmissions to travel far. 13

Atmospheric Pressure Matter has mass. Weight is a measure of the pull of gravity on an object’s mass. Gas has mass, so gas has weight. Force exerted on an area is known as pressure. As Earth's gravity pulls the gases toward its surface, the weight of these gases presses down on the air below, creating air pressure. Reflection Question: Why is it harder to breath at higher elevations? 14

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Temperature in Atmospheric Layers Solar radiation passes through atmosphere from top down. Question: How is the atmosphere heated? Answer: Each layer is different. Different gasses have varying ability to absorb radiant energy. 16

Temperature in Atmospheric Layers Troposphere: heated from bottom up because N2 and 02 do not absorb radiant energy well and CO2 and other greenhouse gases are densest at bottom. Stratosphere: heated from top down because O3 (ozone) is high concentration at top. Mesosphere: heated from bottom up due to decreasing ozone %. Thermosphere & Exosphere heat from top down due to ability of gas molecules to absorb energy individually. 17