The Atmosphere

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• Weather: the condition of Earth's atmosphere at a particular time and place Atmosphere: the envelope of gases that surrounds the planet

1. Composition of the atmosphere

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   • Earth's atmosphere is made up of nitrogen, oxygen, carbon dioxide, water vapor, and many other gases, as well as particles of liquids and solids.
   1. Nitrogen

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      • Nitrogen is the most common gas in the atmosphere, and it makes up three fourths of the air we breathe.
   2. Oxygen

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      • Like nitrogen, oxygen in the air moves through a natural cycle involving living things. Oxygen is used slowly in any processes .
   3. Carbon Dioxide

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      • Carbon dioxide is essential to life because plants take in carbon dioxide from the air to make food. When plant and animal cells break down food to produce energy, they give of carbon dioxide as a waste product.
   4. Water Vapor

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      • Water Vapor: water in the form of a gas. Water vapor plays an important role in the weather. Clouds form when water vapor condenses out of the air to form tiny droplets of liquid water or crystals of ice.
   5. Other Gases

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      • Oxygen and nitrogen together make up 99 percent of dry air. Argon and carbon dioxide make upmost of the other one percent. The remaining gases are called trace gases because only small amounts of them are present.
   6. Particles

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      • Pure air consists of only gases, but it only exists in laboratories. The air we breathe also contains tiny solid and liquid particles of dust, smoke, salt, and other chemicals.
2. Importance of the Atmosphere

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   • Earth's atmosphere makes conditions on Earth suitable for living things.
3. Air Quality

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   • Pollutants: harmful substances in the air, water, or soil.
   1. Sources of Pollution

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      • Most air pollution is the result of burning fossil fuels, such as coal, oil, gasoline, and diesel fuel.
   2. Smog and Acid Rain

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      • Photochemical smog: the brown haze that develops in sunny cities. Acid rain: rain that contains more acid than normal. 
4. Improving Air quality

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   • Even though the air quality int he country has decreased over the past 30 year, there are still American cities that are polluted.

1. Properties of Air

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   • Because air has mass, it also has other properties, including density and pressure.
   1. Density

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      • Density: The amount of mass in a given volume of air.
   2. Pressure

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      • Pressure: The force pushing on an area or surface. Air pressure: the result of the weight of a column of air pushing down on an area. Air pressure can change from day to day.
2. Measuring Air Pressure

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   • Barometer: an instrument that is used to measure air pressure. Two kinds of barometers are mercury barometers and aneroid barometers.
   1. Mercury Barometers

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      • Mercury Barometer: consists of a glass tube open at the bottom end and partially filled with mercury.
   2. Aneroid Barometers

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      • Aneroid Barometer: has an airtight metal chamber.
   3. Units of Air Pressure

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      • Weather reports  use several different units for air pressure. It is ,measured by inches of mercury, or millibars. 
3. Altitude and the Properties of Air

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   • Altitude: elevation, is the distance above sea level of the surface of the oceans.
   1. Altitude Affects Air Pressure

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      • Air pressure is greater at sea level. Air near the top of the atmosphere has lower air pressure.
   2. Altitude Also Affects Density

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      • As you go up through the atmosphere, the density of the air decreases. The gas molecules that make up the atmosphere are farther apart at high altitudes than they are at sea level.

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• The movement of heat in the atmosphere  causes temperatures to change, winds to blow, and rain to fall.

1. Energy From the Sun

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   • Electromagnetic Waves: a form of energy that can move through the vacuum of space. Radiation: the direct transfer of energy by electromagnetic waves. Most of the energy from the sun travels to earth in the form of visible light.
   1. Visible Light

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      • Visible light includes all the colors you see in a rainbow, and the different colors are the result of different wavelengths.
   2. Non-Visible Radiation

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      • Infrared Radiation: a form of electromagnetic energy that has wavelengths that are longer than red light. Ultra-violet Radiation: an invisible form of energy with wavelengths that are shorter than violet light.
2. Energy in the Atmosphere

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   • Scattering: a process in which dust particles and gases in the atmosphere reflect light in all directions. Some sunlight is absorbed or reflected by the atmosphere before it can reach the surface. The rest passes through the atmosphere to the surface.
3. Energy at Earth's Surface

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   • When Earth's surface is heated, it radiates most of the energy back into the atmosphere as infrared radiation. Greenhouse Effect: the process by which gases hold heat in the air.

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• Scientists divide Earth's atmosphere into four main layers classified according to changes in temperature. These layers are the troposphere, stratosphere, mesosphere, and the  thermosphere.

1. The Troposphere

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   • Troposphere: the inner, or lowest layer of Earth's atmosphere. The troposphere is the layer of the atmosphere in which Earth's weather occurs.
2. The Stratosphere

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   • Stratosphere: the layer of the atmosphere that extends from the top of the troposphere to about 50 kilometers above Earth's surface. The stratosphere is the second layer of the atmosphere and contains the ozone layer.
3. The Mesosphere

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   • Mesosphere: the layer above the stratosphere, where there is a drop in temperature. The mesosphere is the layer of the atmosphere that protects the Earth's surface from being hit by most meteoroids.
4. The Thermosphere

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   • Thermosphere: the layer that extends from 80 kilometers above the Earth's surface outward into space. The thermosphere is the outermost layer of Earth's atmosphere . Temperature: the average amount of energy of motion of each molecule o fa substance. Ionosphere: The lower layer of the thermosphere which begins about 80 kilometers above the surface, and extends to about 400 kilometers. Exosphere: the out portion of the thermosphere which extends from 400 kilometers outward for thousands and thousands of kilometers.

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• Heat transfer in the troposphere plays an important role in influencing Earth's weather.

1. Thermal Energy and Temperature

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   • Thermal Energy: the total energy of motion in the particles of a substance The faster the particles are moving, the more energy they have. Energy is the average amount of energy of motion of each particle of a substance.
   1. Measuring Temperature

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      • Thermometer: a thin glass tube with a bulb on one end that contains a liquid, usually colored alcohol.  Air temperature is usually measured with a thermometer. 
   2. Temperature Scales

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      • Temperature is measured in degrees, either Fahrenheit or Celsius. The boiling point of pure water is 100 degrees Celsius, and the freezing point is  0 degrees Celsius.
2. How Heat is Transferred

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   • Heat: the transfer of thermal energy from a hotter object to a cooler one. Heat is transferred in three different ways within the atmosphere: radiation, conduction, and convection.
   1. Radiation

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      • Radiation is the direct transfer of energy by electromagnetic waves.
   2. Conduction

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      • Conduction: the direct transfer of heat from one substance to another substance that is touching. The closer together the particles  in a substance are, the more effectively they can conduct heat. Air and water do not conduct heat very well.
   3. Convection

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      • Convection: the transfer of heat by the movement of a fluid.
   4. Heating the Troposphere

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      • Convection Currents: The upward movement of warm air and the downward movement of cold air. Within the troposphere, heat is transferred by mostly by convection.

1. Global Wind Belts

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   • The major global wind belts are the trade winds, the polar easterlies, and the prevailing westerlies.
   1. Doldrums

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      • Regions near the equator with little or no wind are called the doldrums. Cool air moves into the equator, but is warmed rapidly and rises before it moves very far, which is why there is very little horizontal movement, so the the winds near the equator are very weak.
   2. Horse Latitudes

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      • Latitude: the distance from the equator, measured in degrees. At about 30 degrees north and south latitudes, the air stops moving toward the poles and sinks. In each of these regions, another belt of calm air forms. The latitudes 30 degrees north and south of the equator came to be called the horse latitudes.
   3. Trade Winds

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      • When cold air over the horse latitudes sinks, it produces a region of high pressure which caused surface winds to blow both toward the equator and away from it. The winds that blow toward the equator are turned west by the Coriolis effect. As a result, these steady easterly winds are called the trade winds.
   4. Prevailing Westerlies

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      • In the mid-latitudes, between 30 degrees and 60 degrees north and south, winds that blow toward the poles are turned toward the east by the Coriolis effect, and are called the prevailing westerlies because they blow from west to east. They play an important role in Earth's weather.
   5. Polar Easteries

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      • Cold air near the poles sinks and flows back toward lower latitudes  and gets shifted west by the Coriolis effect, producing polar easterlies.The polar easterlies meet the prevailing westerlies along a region called the polar front. The mixing of warm and cold air along the polar front has a major effect on weather in the United States.
   6. Jet Streams

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      • Jet Streams: bands of high-speed winds above Earth's surface. they generally blow from west to east at speeds of 200 to 400 kilometers per hour. As jet streams travel around Earth, they wander north and south along a wavy path.
2. Global Winds

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   • Global Winds: winds that blow steadily from specific directions over long distances. Global winds are created by the unequal heating of Earth's surface. But unlike the local winds, global winds occur over a large area.
   1. The Coriolis Effect

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      • Coriolis effect: the way Earth's rotation makes wind curve. If earth did not rotate, global winds would blow in a straight line from the poles to the equator.
   2. Global Convection Currents

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      • Temperature differences between the equator and the poles produce giant convection currents in the atmosphere. Higher in the atmosphere, the air flows away from the equator toward the poles. Those air movements produce global winds.
3. Local Winds

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   • Local Winds: winds that blow over short distances. Local winds are caused by the unequal heating of the Earth' s surface within a small area.
   1. Sea Breeze

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      • Sea Breeze: a local wind that blows from an ocean or lake(during the day). As the sun heats the Earth's surface during the day, the land warms up faster than the water.
   2. Land Breeze

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      • Land Breeze: the flow of air from land to a body of water is called a land breeze( at night). At night, the land cools faster than the water, so the air over the land becomes cooler than the air over than the air over the water.
4. What is Wind

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   • Wind: the horizontal movement of air from an area of high pressure to an area of lower pressure. Winds are caused by differences in air pressure. most different air pressures are caused by the unequal heating of the atmosphere. 
   1. Measuring Winds

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      • Anemometer: an instrument that measures wind speed. Wind direction is measured by a wind vane. The name of a wind tells you where it's coming from.
   2. Wind-Chill Factor

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      • Wind-Chill Factor: the increasing cooling a wind can cause.The wind blowing over your skin removes body heat. The stronger the wind, the colder you feel.