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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. 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. 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. 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. 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. 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. 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. 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. 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. 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? Atmospheric Pressure 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. 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.