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Jennifer Pogue March 6, 2012 Origin The earliest atmosphere was believed to be Hydrogen and Helium Why? They were the most abundant gases of the universe. Methane and ammonia were also found in high concentrations. Where did it go? It escaped into space. Why? Earth’s gravity was too weak to hold the light gases in place. The Second Atmosphere Steam vents and volcanoes vented gases which collected in the atmosphere **We are assuming the gases vented by volcanoes then is the same as the gases now. Water vapor (80%), carbon dioxide (10%), nitrogen (~5%) How did the composition change? CO2 –Locked into sedimentary rocks, i.e. limestone H2O—condensed to form the ground water or clouds The concentration of CO2 and H2O decreased leaving N2 to increase in concentration . Nitrogen is relatively inactive chemically. Oxygen increased as plants converted carbon dioxide through photosynthesis. Proof is in the rocks Precipitation of limestone in great quantities. The oxidation of iron to form banded deposits in early rocks. The distribution of various minerals in most early sedimentary rocks. Evidence of an Early Atmosphere Limestone (Stone Museum) Banded-iron (Stone Museum) Today’s Composition We have lots more oxygen (~21%) and lots less carbon dioxide. Both of these are good things Composition Comparison 78% Nitrogen 4-6% 21% Oxygen <1% 0.9% Argon 0-1% 0.033% Carbon Dioxide 10% 0-4% Water Vapor 80% 0-0.000007% Ozone 0% <1% Other Gases 3-4% Heat & our atmosphere Three methods heat moves through our atmosphere Conduction Convection Radiation Layers Troposphere Stratosphere Mesosphere Thermosphere Ionosphere Exosphere Troposphere 0-12 miles Thickness varies depending on where you are on earth. Thicker around the equator. Thinner at the poles. Temperature decreases as you go up in the troposphere. Most weather occurs here. The layer we are in. Most airplanes fly here Tropopause (about 12 miles up) The boundary between the troposphere and stratosphere The altitude where the temperature stops dropping It’s about -60°F 90% of the atmosphere is below the tropopause. Stratosphere (12-31 miles up) Lower limit mixes with the troposphere to form the jet stream Air gets warmer as you increase in altitude Prevents convection causes the top of the anvil shaped storm clouds (cumulonimbus) This is called a temperature inversion Why the temperature inversion? The ozone layer Considered part of the middle atmosphere The Ozone Layer High concentration at about 15 miles up Absorbs most of the sun’s ultraviolet rays The absorption causes the temperature increase Stratopause (31 miles up) The boundary between the stratosphere and mesosphere The temperature stops increasing About 5°F 99.9% of the atmosphere is below stratopause Mesosphere (31 to 56 miles up) Gases get thinner and thinner Temperature decreases as altitude increases Molecules are very far apart Slow down meteors Part of the middle atmosphere Mesopause The boundary between mesosphere and thermosphere Temperature stops decreasing Low temp is -184°F Thermosphere (up to 375 miles) Known as the upper atmosphere The “Hot” Layer Ultraviolet and x-ray radiation absorbed by the molecules in this layer Auroras occur in this layer Ionosphere Not really a layer of its own A part of the thermosphere Responsible for bouncing sound waves around the earth Exosphere (up to 6200 miles up) This is the layer in which atoms and molecules escape into space and satellites orbit the earth. Jennifer Pogue March 6, 2012 Water The water can be in solid, liquid or gas form. In a gaseous form in our atmosphere, we call it water vapor. It gets there through evaporation of surface water. The water removes heat from the surface as it evaporates. Evaporation is a cooling process. Phases changes Humidity Water vapor present in the atmosphere Specific humidity The number of grams of water vapor per kilogram of air Capacity is different for every temperature. Capacity basically doubles for every increase of 11°C Relative Humidity Compares the actual amount of water vapor in the air to the maximum amount of water vapor the air can hold Given as a percentage Relative Humidity The Equation actual R.H. x100 saturation How is it measured? A sling psychrometer Measure the difference in temperatures Drier air the more cooling from evaporation the greater the difference the lower the relative humidity If there is no difference, the air is saturated and won’t accept any more water vapor. The Dew Point The temperature at which saturation occurs and condensation begins. As warm, moist air cools off over night, the cooler air can hold less water vapor. The vapor condenses to form suspended droplets (i.e. fog) or if on a surface, dew. You get frost if the air temperature is below 0°C. The more water vapor in the air, the less the air has to cool in order for condensation to occur higher dew point. Condensation Happens under two conditions: Have to have a material for water to condense onto Air must cool to or below its dew point The particles onto which condensation occurs are called condensation nuclei. Usually “dirt” in the atmosphere Must have these to have fog! Cloud Formation 1. 2. 3. 4. 5. 6. Humid air rises Air begins to cool Cool air can’t hold as much water Air temp reaches dew point temp Air is saturated 100% relative humidity Water vapor condenses to water drops around a nuclei like dust particles or smoke (forms clouds) Cloud Types Stratus—layered, low clouds Cumulus—puffy clouds, group upward, flat bases Cirrus—high, feathery clouds; like curls of hair Nimbus—rain clouds Prefixes used: Strato-layered Cumulo-puffy Alto—mid-height Cirro—high in height Nimbo—dark, rain Low Level Clouds Below about 2000 meters Stratus Nimbostratus Stratocumulus Stratus Uniform gray, cover the sky Stratocumulus Low, lumpy, gray Nimbostratus Dark gray, ragged, may or may not be able to see the edges Altocumulus About as wide as your thumb when you hold it at arm’s length Altostratus Usually form ahead of continuous rain/snow clouds Cirrus High, long, thin, wispy Made of ice Cirrocumulus Long rows of small rounded puffs Width of little finger when held at arm’s length Cirrostratus Sheet-like thin clouds that cover the sky Usually a precursor to rain/snow Vertical Cloud Development Clouds grow up into the atmosphere instead of outward across the sky Develop by warm air rising from the surface Cumulus Cotton balls with definite outline and flat base About the size of your fist or larger when held at arm’s length Nimbocumulus Thunderstorm clouds Works Cited Department of Maritime Civilizations - University of Haifa. “Earth Origins and Formation.” 10 Apr 2006. <http://maritime.haifa.ac.il/departm/lessons/ocean/lect03.htm>. Pflueger, Nathan. “The Origins of the Atmosphere.” 14 Oct 2003. 11 Apr 2006. <http://eugevir.tripod.com/origins/atmosphere.html>. Stimac, John. “The Atmosphere – origin and structure.” 11 Apr 2006. <http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html>. Stone Museum. “Types of Rock.” 10 Apr 2006. <http://www.geol.sci.hiroshimau.ac.jp/~geotect/stonemuseum/Classification-j.html>. http://www.srh.noaa.gov/jetstream/atmos/layers.htm http://www.windows2universe.org/earth/Atmosphere/clouds/clou d_types.html
