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Geo D Unit 6 Lecture Chapter 11 pages 271-282, all of Chapter 12, and Chapter 14 pages 559-363 and pages 370-377 CHAPTER 11 PAGES 271-282 Key Atmospheric Gases • The atmosphere is made up of many gases • 99% nitrogen and oxygen • Water vapor and carbon dioxide determine temperature • Particulates are solids floating around in the air that water vapor can condense on Ozone 3 oxygen molecules bonded together • Located in the stratosphere • Absorbs UV rays and protect us from the sun Layers of the Atmosphere • Troposphere- closest to Earth, where most of the weather occurs, gets colder as your go higher • Stratosphere- contains ozone, gets warmer as you go higher • Mesosphere- very few molecules, coldest layer, gets colder as you go higher • Thermosphere- hottest layer, gets hotter as you go higher • Beyond the thermosphere is the exosphere which leads us into space Solar Fundamentals • • • • • • • Radiation: The sun radiates onto Earth 50% absorbed by the surface 15% absorbed by atmosphere 25% reflected from clouds back into space 4% reflected by surface back into space 6% reflected by atmosphere back into space • Conduction: • Transfer of heat to solids • Done by contact • Convection: • Transfer of heat to liquids and gases • Creates convection cells in the atmosphere Temperature verses Heat • Temperature • Measure of the average kinetic energy of molecules • Heat • Transfer of energy because of a difference in temperature • Moves from high to low Measuring Temperature • In the United States we use Fahrenheit • For science class we will use Celsius or Kelvin • To convert from Celsius to Kelvin, simply add 273 • 0 C = 273 K (freezing point of water) • 100 C = 373 K (boiling point of water) Dew Point • Dew point is the temperature when air reaches saturation • Once dew point is reached, condensation happens (water vapor forms into water drops) Vertical Temperature Changes • In the troposphere, temperature decreases as elevation increases • Cooling of 10 C for every 1000m increase • This is the dry adiabatic lapse rate • The height at which condensation occurs is called the lifted condensation level (LCL) • Above the LCL, air cools more slowly Air Pressure and Density • The density of air is proportional to the number of particles present • The density of air decreases as you move from the crust out into the atmosphere Pressure Temperature Density Relationship • Temperature is directly proportional to pressure • Temperature decreases=pressure decreases • Ex: Moving higher up Mt. Everest • Pressure and density also directly proportional • Pressure decreases=density decreases Temperature Inversions • An exception to the rule that pressure and temperature decrease with height in the troposphere is an inversion • Commonly happens when cities are in a basin and pollution becomes trapped there Wind • Caused by unequal heating of the earth’s surface • Cool air sinks, warm air rises and allow for areas with differences in air pressure • Wind speeds increase with altitude because there is less friction with objects and the earth CHAPTER 12 Meteorology • Meteorology is the study of atmospheric phenomena • Hydrometeors are the items that contain water like clouds, rain, fog, etc • Lithometeors are condensation nuclei like smoke and dust • Electrometeors are the items that are a visible or audible manifestation of electricity like thunder and lightning Weather verses Climate • Weather • Current state of the atmosphere • Short term • Climate • Long term variations in weather for a particular area • The continual motion of air and water reallocates heat energy among Earth’s surface, oceans, and atmosphere and helps keep balance Air Masses • Air masses are large bodies of air over a certain area • Those that form over land are drier than those over water • • • • • • • Warm and dry = cT continental tropical Warm and humid= mT maritime tropical Cold and dry =cP continental polar Cold and humid=mP maritime polar Arctic A All 5 air masses can be found in N America Modification happens when they move away from their source regions Weather Systems • The Coriolis Effect is the deflection of air to the right in the N Hemisphere and to the left in Southern • Caused by the rotation of the earth Global Wind Systems • At the equator are the doldrums where ships would become stranded due to weak winds • Trade winds occur above and below the equator • Moves to the west • Also known as the Hadley cell • Between the trades and the westerlies is a calm belt with weak winds called the horse latitudes • Boats become stranded here • The prevailing westerlies blow to the east • The polar easterlies blow to the west Jet Streams • Jet streams are narrow bands of fast, high altitude winds • Move up to 185 km/h • Two main jet streams: • 1. polar jet stream • 2. subtropical jet stream Fronts • A front is a narrow region separating two air masses of different densities • Their interaction brings dramatic changes in the weather • 4 types of fronts: • 1. cold front • 2. warm front • 3. stationary front • 4. occluded front Cold Front • • • • Cold, dense air displaces warm air Forces the air up along a steep front Clouds, showers, sometimes thunderstorms Drawn as a solid blue line with solid blue triangles Warm Front • • • • Advancing warm air displaces cold air Develops a gradual frontal slope Extensive cloudiness and precipitation Drawn as a solid red line with solid red semicircles Stationary Front • Small temperature and pressure difference between two air masses • The boundary between them stalls • Mild weather patterns • Drawn as a combo of warm and cold front symbols Occluded Front • Cold air moves so fast that it wedges warm air upward • That cold air collides with an advancing cold front • Precipitation is common • Drawn as alternating purple triangles and semi circles Pressure Systems • High Pressure • Air moves outward in a clockwise direction in N Hemisphere • Fair weather • Low Pressure • Moves inward in a counter-clockwise direction in N Hemisphere • Clouds and precipitation Gathering Weather Data • • • • • Thermometers measure temperature Barometers measure air pressure Anemometers measure wind speed Hygrometer measures humidity Ceilometer measures the height of the clouds • Radiosonde measures temperature, air pressure, and humidity • Sends radio signals back to the ground station from heights of 30,000m Doppler Radar • The Doppler effect is the change in frequency based on movement towards or away from the observer • Doppler radar plots the speed that raindrops moved toward or away due to wind Weather Satellites • Weather satellites use both visible light and other forms of radiation to observe the atmosphere • Infrared satellites detect changes in thermal energy • Allow scientists to determine the temperature of a cloud to determine its type and height Weather Analysis • A station model is a record of weather data for a particular site at a particular time • Isopleths are lines that connect points of equal values • Temperature= isotherms • Pressure= isobars, closer together are stronger winds Forecasts • Short term • Digital forecasts • Done by high speed computers • Uses numerical data • Analog forecasts • Use past events • • • • • Long term Less accurate Less detailed Vague Used more for seasonal forecasts CHAPTER 14 PAGES 359-363 AND 370-377 Climate • Climate describes the long term weather patterns of an area • Variations in temperature, precipitation, wind, etc • Data is such as daily high and low temps, rainfall, wind speed and direction, humidity, and air pressure is collected • Averaged on a monthly or annual basis for 30 years • This determines the normals (standard value) Causes of Climate • 1. latitude • The closer to the equator, the more direct the sun’s rays hit and therefore receives more solar radiation • 2. topography • Closeness to lakes and oceans • Warmer in winter and cooler in summer than inland areas • Mountain climates cooler than sea level • Windward side of mountains are wet and cool, leeward side is dry and warm • • • • • • 3. air masses Warm and dry = cT continental tropical Warm and humid= mT maritime tropical Cold and dry =cP continental polar Cold and humid=mP maritime polar Arctic A Short term climate changes • Seasons are short term periods of climate change caused by variations in daylight, temperature, and weather patterns El Nino • El Niño is a warm ocean current that develops off the western coast of S America • When the high pressure system and its trade winds weaken, changes in weather occur • Causes stormy weather to normally dry places and drought conditions to normally wet Natural Changes to Climate • 1. solar activity • The sun’s sunspot cycles last about 11 years • A period of low sunspot activity is called a Maunder Minimum, causes colder temperatures • 2. Earth’s orbit • Earth’s orbit becomes more elliptical then more circular and so on back and forth • When the orbit elongates, the earth is closer to the sun, and temperatures become warmer • 3. Earth’s tilt • Angle varies from 22.2 degrees to 24.5 every 41,000 years • Differences in angle could cause seasons to become more severe • 4. Earth’s wobble • By the year 14,000 Earth’s axis will point toward the star Vega instead of Polaris • This will cause more extreme seasons • 5. volcanic activity • When volcanoes erupt, they send out immense quantities of dust into the atmosphere which blocks incoming solar radiation The Human Factor • The greenhouse effect allows for life to survive on earth, because a small portion of radiation is not allowed to reflect back into space • This effect is impacted by the amount of greenhouse gases in the atmosphere • These include carbon dioxide, methane, and water vapor Global Warming • Temperatures have increased over the past 200 years • This warming is causes a melting of the polar ice caps • This would then causes a rise in sea level • Scientists are not all in agreement about what is causing global warming • Most blame our carbon dioxide output due to burning fossil fuels