Jon Ahlquist 9/14/2006MET1010 Intro to the Atmosphere 1Chapter 1:The Earth and Its AtmosphereOverview of the Earth’s atmosphereThe solar systemComposition of the atmosphere & greenhouse gasesThe early atmosphereVertical structure of the atmosphereA brief look at air pressure and air densityLayers of the atmosphereThe radiosonde (weather balloon)Weather and climateMeteorology- A brief historySatellite’s view of the weatherWeather & climate in our livesSolar System (p. 2, figure not to scale) 1st 4 planets are “small” and rocky:Mercury (looks like Earth’s moon), Venus (covered with clouds; surface is hundreds of degrees hot),Earth (93 million miles from Sun, 8 min for light to travel to Earth), Mars Asteroid belt (not shown in figure) 4 “gas giants”: Jupiter and Saturn, Uranus , Neptune(1stletters of last 3 spell SUN) Pluto: dwarf planet; rock, water ice, frozen methaneAsteroid belt between Mars & JupiterRemembering Order of Planets You can use the following sentence to help you remember the order of the “nine” planets:My very educated mother just showed us nine planets. Each word of the preceding sentence begins with the letter of the next planet as you go out from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto As of August, 2006, Pluto was reclassified as one of several “dwarf planets” because a number of other small similar bodies have been identified beyond Neptune.Atmospheric Composition (pp. 2-8) Hydrogen: primary component of Sun & “gas giant” planets. Hydrogen almost certainly primary component of Earth’s early atmosphere, but gravity on Earth & other inner planets not strong enough to prevent escape of hydrogen to space. Earth’s current atmosphere probably developed from volcanic gases (outgassing from volcanoes) Earth’s air: roughly 80% nitrogen (N2) and 20% oxygen (O2). Next most abundant gases are water vapor and argon (type of inert gas), each about 1% of atmosphere. Other gases present in minute amounts (much less than 1%: trace gases). Some are “greenhouse” gases which influence the Earth’s temperature.Greenhouse gases (pp. 5-6; more in chap 2) The two most important greenhouse gases: water vapor (H20, about 1% of atmosphere) and carbon dioxide (CO2, about 0.04%). We’ll say more in chapter 2. Amount of CO2has been steadily increasing due to burning. Graph below shows last 50 years. Also note annual cycle in CO2: lower in summer when plants absorb more CO2, higher in winter when plants die and release CO2.Year: 1958 1965 1975 1985 1995 2005Fig. 1.5, p. 6, CO2amountGreenhouse gases (cont) Other important greenhouse gases that are trace gases: Methane (produced by plants & animals) Nitrous oxide (laughing gas) Ozone (O3, i.e., 3 oxygen atoms) Chlorofluorocarbons (CFCs) Chlorofluorocarbons (CFCs) also destroy ozone in stratosphere, which protects life from ultraviolet (UV) light. Without UV absorption, most plants and animals would die. If stratospheric ozone were compressed to sea level pressure, it would be a layer about 1/8 inch thick. Ozone in stratosphere helpful to life by absorbing UV butharmful near surface when breathed (main part of smog). Ozone amount recovering (Research published in 2006) http://www.sciencedaily.com/releases/2006/08/060830215811.htmJon Ahlquist 9/14/2006MET1010 Intro to the Atmosphere 2Special Topic: Breath of Fresh Air (p. 4) You are constantly breathing history. Pick any historical person and key event in his or her life. Examples: Archimedes shouting, “Eureka!” Julius Caesar saying, “Veni, vidi, vici.” Cleopatra talking with Marc Anthony Martin Luther King, Jr., saying, “I have a dream.” Each breath you take may contain a molecule exhaled by that person at the chosen event.Pressure (pp. 9-10) Pressure = force / area Mean sea level pressure of air = 15 lb/sq in= 30 inches of mercury= 1013 millibars (mb) (units used on TV for hurricanes)= 1013 hectopascals (hPa) (metric system) If the surface pressure changes by a few percent, that is a BIG change. Record high surface pressure:1084 mb in Siberia (1968), only 7% above average. Record low surface pressure:870 mb in Typhoon Tip (1979), 14% below average. Because of small changes in surface pressure, pressure is measured to 5 digits of accuracy (to tenth of millibar)to follow weather changes.Example of pressure calculation How much pressure does someone exertwhen lying on a bed? Solution: Pressure = force /area, soconsider someone who weighs about 150 lbsArea lying down ≈ 6 ft x 1ft = 72x12 ≈ 750 sq inches Therefore, pressure in lying on a bed =150 / 750 = 1/5 lb per square inch,which is very little. Let’s test this!Bed of nails: This bed has 1 nail per sq inch. By the calculation in the last graphic, this is only 1/5 lb per nail, which is no problem.Air Pressure Decreases with Increasing Height Air is held to the Earth by gravity, i.e., it has weight. Pressure at any given height is due to the weight of the air that lies above that height. This is just like a human tower. Pressure on one’s shoulders depends on the weight above. Person at the bottom experiences the greatest pressure. Air at the surface experiences the greatest pressure, and pressure decreases as you go up.Density (p. 9) Density = mass/volume High density means lots of material (mass) in small volume Exponential decrease with height Density & pressure atop Mount Everest are about 30% of sea level values Air density near surface:about 1 kg/m3 (2 lb / cubic yard) Density liquid water density is 1000 kg/m3 (over 1700 lb / cubic yard), so liquid water is 1000 times denser than air.p. 10, fig. 1.8Jon Ahlquist 9/14/2006MET1010 Intro to the Atmosphere 3Why does density decrease with height? Air, like any gas, is compressible. That is, you can squeeze it into a smaller volume, making it denser At the surface where the pressure is greatest, the compression is greatest, so the density is greatest As pressure decreases going up, compression decreases, so density decreasesp. 10, fig. 1.8Atmospheric layers (p. 11, fig 1.10) Hot top: oxygen absorbs sunlight Warm middle: ozone absorbs ultraviolet Warm surface: Ground absorbs sunlightTEMPERATURELayers &
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