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Ch. 22 The Atmosphere • The layer of gases that surround the Earth or a mixture of gases that surrounds a planet. • Protects us from most of the sun’s harmful radiation • Regulates the temperature of Earth’s surface Composition of the Atmosphere • Air = a mixture of gases (elements and compounds), liquids, and solid particles • • • • Nitrogen = 78% Oxygen = 21% Argon = 0.9% Carbon dioxide = 0.04% (400 PPM) Nitrogen Oxygen • 78% N₂ • 21% O2 • The biological processes of Photosynthesis and Cellular Respiration move oxygen from the atmosphere to living organisms and back to the atmosphere. • Forest fires, the burning of fossil fuels, and the weathering of some rocks also remove oxygen from air. • Oxygen is necessary for making ATP, the energy source of cells. • Nitrogen cycle - moves nitrogen from the air to the soil (bacteria), then to plants and animals, and then back to the air. • Nitrogen is necessary for creating DNA (nitrogen bases) and proteins (amino acids). Water vapor • Gaseous water H2O(l) • Varies depending on time of day, location, and season. • Both biological (transpiration, which is evaporation from plants) and geological (evaporation) processes can add water vapor to the atmosphere. • Both condensation and precipitation can remove it. Ozone • O3 - a gas made of 3 Oxygen molecules. • Forms the ozone layer • Absorbs or reflects harmful UV (ultraviolet) radiation from the sun. • Chlorofluorocarbons (CFC’s) destroy ozone particles by breaking them apart. • CFC’s were originally found in the coolants of refrigerators and air conditioners. • Two “holes” in the ozone, one over each pole. • CFC ‘s were banned, it will take years and years to recover. Ozone hole • UV radiation damages DNA • This protective layer is not evenly distributed and varies with latitude and time of year. • In 1985, it was noticed that the ozone layer was unusually thin over Antarctica; a similar hole exists over the Arctic. • The thinness allows greater amounts of UV rays to reach the surface. Think, Pair, Share What kinds of solid particles do you think are found in the atmosphere? Particulates • Solid particles • Volcanic ash and dust from eruptions • Ash from forest fires • Microscopic organisms • Soil or mineral particles lifted by winds, esp. tornadoes and wind storms • Pollen from plants carried by the wind • Salt from the ocean as sea spray evaporates • Particles from meteors that are vaporized as they enter and burn up in Earth’s atmosphere Air Pressure – decreases with altitude Link Atmospheric Pressure • Gravity holds the gases of the atmosphere near Earth’s surface. • As a result, the gases are compressed and exert a force on the surface they are pushing down on. • The force per unit area that is exerted on a surface by the weight of the atmosphere. • Atmospheric pressure is exerted equally in all directions. • The atmosphere gets thinner at higher altitudes. The pull of gravity decreases with height and the air molecules spread further apart and exert less pressure on each other. • Atmospheric pressure decreases as altitude increases. • As temperature increases (hotter), Atm. pressure (at sea level) decreases. Heat causes the molecules to move farther apart. • Air that contains a lot of water vapor is less dense than drier air because water vapor has less mass than nitrogen or oxygen; the lighter water vapor molecules replace an equal amount of nitrogen and oxygen, which makes the volume of air less dense. Measuring Atmospheric Pressure • Three units for measuring atmospheric pressure. • Atmospheres (atm) • Millimeters or inches of mercury (mmHg or inHg) • Millibars (mb) • Standard atmospheric pressure: 1 atm = 760 mm Hg = 1000 mb • Average atm. Pressure at sea level = 1 atm. • Instrument – Barometer Mercurial Barometer • Atm. Pressure pushes on the liquid mercury in a well at the base of the barometer. • The pressure pushes the mercury up to a certain height inside a tube. • The greater the atm. pressure, the higher the mercury rises. Aneroid Barometer • More commonly used • Contains a sealed metal container that has had most of the air removed to form a partial vacuum. • Changes in the atm. Pressure cause the metal container to bend inward or bulge out. • These changes move a pointer on a scale. • Can also be used to measure altitude above sea level altimeter. • Since higher altitudes have lower pressures, a lower pressure reading can be interpreted as an increased altitude reading. 4 Main Layers of the Atmosphere • Show distinctive temperature changes with increasing altitude. • Temperature differences mainly result from how solar energy is absorbed as it moves through the atmosphere. Troposphere • Closest to the Earth’s surface • Extends from the surface to approx. 12 km above the surface • Nearly all weather occurs here • Almost all water vapor and carbon dioxide is found in this layer • Temperature decreases as altitude increases. (air is heated from radiation off the surface) • Tropopause • 12 km above surface • Boundary between troposphere and stratosphere • Temperatures stop decreasing Stratosphere • Extends from the tropopause to 50 km above the surface • Contains almost all of the ozone (ozone layer) • Jet airplanes usually fly here • Temperature increases as altitude increases – due to heat being absorbed by the ozone layer - Lower stratosphere = -60oC - Upper stratosphere = 0oC • Stratopause • boundary between the stratosphere and the mesosphere. Mesosphere • approx. 50 km to 80 km above the surface of the Earth. • Temperature decreases as altitude increases • the upper boundary of the mesosphere: temperature = -90oC (the coldest temp. in the atmosphere) • Mesopause – the upper boundary of the mesosphere – temperature = -90oC. Thermosphere • • • • • Extends 80 km outwards Temperature increases as altitude increases. – Warmer, due to the absorption of solar radiation by nitrogen and oxygen atoms – Temperatures = 1,000oC + Air particles are very far apart. Ionosphere • Lower region of thermosphere, • 80 – 400 km • Gases absorb solar radiation causing the atoms to lose electrons and to produce ions and free electrons – create the auroras. Exosphere • Outer region of the thermosphere, extends for 1000’s of km. • Spacecrafts orbit here • Blends with the complete vacuum of space. Aurora Borealis • A glow in the night sky produced in the upper atmosphere by ionized particles from the solar wind interacting with Earth’s magnetic field • Earth’s atmosphere is heated – Mostly by the transfer of energy from the sun – Some absorption of the sun’s rays by gases in the atmosphere – Some heat enters the atmosphere indirectly as ocean and land surfaces absorb solar energy and then give off that energy as heat Radiation - travels at 300,000 km/s • Refers to all energy that travels through space as waves (Electromagnetic Spectrum). The Atmosphere and Solar Radiation Solar Radiation • When solar energy reaches the surface, it is either absorbed or reflected • depends on color, texture, composition, volume, mass, transparency, state of matter, and specific heat of the material on which the radiation falls • The sun’s intensity and amount of time it is shining also influence how much energy is absorbed or reflected. Albedo • The fraction of the solar radiation that is reflected by a particular surface is called the albedo. • 30% of the solar radiation that reaches Earth is reflected (Earth has average albedo of 0.3 or 30%) Absorption • All radiation with wavelengths shorter than visible light are absorbed by molecules of N and O in the thermosphere and mesophere (x-rays, gamma rays and UV rays). • In the stratosphere, UV rays are absorbed and act upon Oxygen to form Ozone. • Most of the waves that reach the lower atmosphere (visible, infrared) have longer wavelengths. • Infrared is absorbed by carbon dioxide, water vapor and other complex molecules in the troposphere. • Very little visible light is absorbed as it passes through the atmosphere. Scattering Scattering is what makes the sky appear blue and the sun appear red at sunrise and sunset. • Clouds, dust, water droplets, and gas molecules disrupt the path of radiation and cause scattering. • Scattering occurs when the rays are reflected and bent so that the waves travel in all directions; some rays go back out into space and some continue towards Earth’s surface. • As a result, sunlight hits the Earth from all directions. Absorption and Infrared Energy • When rocks, soil, water and other surface materials absorb solar radiation (short wave infrared and visible). These materials get warmed. • The heated materials convert the energy into infrared waves of longer wavelengths and reemit them back into the air. • Water vapor and carbon dioxide in the atmosphere absorb these rays. • This absorption heats the lower atmosphere and keeps Earth’s surface warmer than it would be if there were no atmosphere (Greenhouse Effect). • . Global Warming • Generally, the amount of solar radiation entering Earth’s atmosphere equals the amount escaping. • However, human activities (burning of fossil fuels) as well as natural causes are changing the balance and are causing the average temperature of the atmosphere to increase. Latitude and Season • Latitude is the primary factor that affects the amount of solar energy that reaches any point on Earth’s surface. • The earth is a sphere, the sun’s rays do not strike all areas at the same angle. • At the equator, it hits at nearly a 90o angle, but at other areas it is spread out (shallow angle) and is not as intense. • Temperature varies seasonally because of the tilt of Earth’s axis. • As Earth revolves around the sun once each year, the portion of Earth’s surface that receives the most intense sunlight changes. • Tilted toward the sun, more intense and hotter temperatures; tilted away, less intense, lower temperatures SEASONS Temperature Inversions • An atmospheric condition when warm air (less dense) traps cool air underneath it • Temperature inversions can make pollution worse by trapping polluted air near the surface of the earth. • Air pollutants – any substance in the atmosphere that is harmful to living organisms. • Main source of air pollution – burning of fossil fuels (sulfur dioxide gas, hydrocarbons, nitrogen oxides, carbon monoxide, lead, etc.) • Smog results (smoke and fog) RADIATION CONDUCTION CONVECTION Conduction • Involves the transfer of heat energy through matter by direct contact. – Heat causes molecules to move faster. • A conductor is a material that can transfer heat. – Air is a poor conductor. • Only the lowest levels of the atmosphere are heated by conduction (from contact with the earth that has been heated by sun via radiation). Convection • Involves the transfer of heat energy within a liquid or gas through the motion of the liquid or gas caused by density differences. • As air is heated by radiation or conduction, it becomes less dense and rises (pushed up by adjacent cooler air) the cooler air becomes warmer and rises. As the warm air rises it cools – being more dense it sinks (convection cell). – Warm air exerts less pressure so the atmospheric pressure is lower beneath a warm air mass. • As dense, cool air moves into a low pressure region (warmer air), the less dense warmer air is pushed upward. These pressure differences create winds. Winds • Winds are produced from differences in air pressures • Air moves from high pressures to low pressures. • Winds are named for the direction from which they blow (where they originate) – Prevailing Westerlies blow from the WEST. – Polar Easterlies blow from the EAST. Instruments • A wind vane measures wind direction • An anemometer, with spinning cups, measures the speed of wind. Beaufort Scale Measures relative Wind speed and force. The Coriolis Effect • The tendency of a moving object to follow a curved path rather than a straight path because of the rotation of Earth (winds and ocean currents). • The farther a wind travels, the more it is influenced by the Coriolis effect. • The faster an object travels, the greater the Coriolus effect. – Each point on Earth makes one complete rotation every day; points near the equator travel farther and faster in a day than points closer to the poles. – When air moves toward the poles, it travels faster than the land beneath it; due to rotation the air appears to follow a curved path. • Objects are deflected to the right in the Northern hemisphere and to the left in the Southern hemisphere. Global Winds • Move across the Earth’s surface. • Curve due to the Coriolis effect. • Winds always move from high to low pressures. – High pressure regions tend to form where colder air sinks – Low pressure regions tend to form where warmer air rises Wind Belts Trade winds : 0o – 30o North and South Latitude • Flow toward the equator. • Northern hemisphere – Northeast trade winds • Southern hemisphere – Southeast trade winds Prevailing Westerlies: 30o – 60o N and S Latitude • Flow toward the poles • Blow throughout the contiguous United States Polar Easterlies: 60o – 90o N and S Latitude • flow toward the equator Wind Cells • Air masses that do NOT move across the surface but move upward (away from Earth’s surface) due to convection caused by warming (convection cells). Doldrums: at 0o (equator) • In this warmer, low pressure air zone most movement is upward (rising). • Surface winds are weak and variable. • Tropical storms are formed here. Horse Latitudes: at 30o N and S Latitude • In this cooler, high pressure air zone most movement is down toward the surface (sinking). • Surface winds are weak and variable. Jet Streams • Circle the globe • In upper troposphere • A narrow band of strong winds • POLAR JET STREAM • Affects the U.S. • For the East Coast, brings in weather systems from the west • Can bring in colder air from the North. • SUBTROPICAL JET STREAM Local Winds * blow over a limited (smaller) area * Local temperature variations cause local winds * Land surfaces heat up faster than water surfaces SEA BREEZES LAND BREEZES • A cool wind moving from the cooler water to warmer land. • During the day, the land heats up faster than the water. • The warm air above the land rises and the cooler air over the water moves to replace it. • Sea breezes blow during the day. • A cool wind moving from the cooler land to the warmer water. • At night, the land cools more rapidly than the water • Land breezes blow at night. SEA BREEZE LAND BREEZE Valley Breezes • During daylight hours, a gentle breeze blows upslope. • Forms when warm air from the valleys moves upslope. • Days tend to be warmer. Mountain Breezes • At night, the mountains cool more quickly than the valleys do. • The cool air descends from the mountain peaks toward the valleys. • Nights tend to cool off. Wind Chill • The effect of the wind on temperature • How the temperature really feels