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Overview of Earth's Atmosphere: Composition, Layers, and Environmental Variables

Explore the composition, layers, and environmental variables of the Earth's atmosphere. Learn about the importance of greenhouse gases, vertical structure, classification by temperature and chemical composition, atmospheric pressure, and more.

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Overview of Earth's Atmosphere: Composition, Layers, and Environmental Variables

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  1. THE ATMOSPHERE Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University

  2. Ahrens, Ch. 1

  3. Overview of the Earth’s Atmosphere

  4. Definition • Atmosphere • The envelope of gases that surrounds a planet and is held to it by the planet’s gravity

  5. Height of Earth’s Atmosphere • A few hundred kilometers • Gradually transitions into outer space • 50% of its mass is within 5 ½ km of the surface. • 99% of its mass is within 30 km of the surface. • Most of the “weather” happens within 10 to 15 km of the surface.

  6. Composition

  7. Composition Top two make up ~ 99 percent

  8. Composition Argon is most of the last 1 percent

  9. Composition Trace constituents of dry air

  10. Composition Last constituent is highly variable

  11. Most gases are invisible • Nitrogen, oxygen, argon, water vapor, carbon dioxide, etc.. • Clouds are not made of water vapor • condensed vapor in the form of liquid droplets. • Smog is visible • contains reactants of nitrogen and ozone.

  12. Amount of nitrogen and oxygen is approximately constant over long term. • Amount of some trace gases varies from place to place and from time to time.

  13. Water vapor is a variable gas

  14. Importance of some variable gases • These are all greenhousegases

  15. The amount of many of these greenhouse gases has been steadily increasing • carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons

  16. Carbon Dioxide

  17. Other variable components • Aerosols • tiny soil, salt, and ash particles suspended in the air • Pollutants • sulfur and nitrogen oxides, hydrocarbons, etc. • Some pollutants are aerosols (ex. soot) • Both from human and natural sources

  18. Vertical Structure of the Atmosphere

  19. Environmental variables • Temperature

  20. There are large horizontal temperature variations

  21. There are also large vertical variations in temperature

  22. Temperature often used to define “layers” of atmosphere, aka “spheres”

  23. Atmospheric layers • Most weather occurs in the troposphere • Since temperature normally decreases with height in the troposphere, when the temperature increases with height, it is called a temperature inversion. • The famous ozone layer that is being destroyed by human pollutants is in the stratosphere • The thermosphere extends to the exosphere

  24. Layer Classification (by temperature)

  25. Layer Classification (by temperature) TRANSITIONS TO SPACE

  26. Layer Classifications BY TEMPERATURE

  27. Layer Classifications BY CHEMICAL COMPOSITION

  28. Layer Classifications HOMOSPHERE IS WELL MIXED – GASES ARE NOT VERTICALLY SORTED BY WEIGHT

  29. Layer Classifications HETEROSPHERE IS NOT WELL MIXED – GASES ARE VERTICALLY SORTED BY WEIGHT

  30. Layer Classifications BY ELECTRIFICATION

  31. The Ionosphere • Electrified region of the upper atmosphere • Extends from the upper stratosphere up to the exosphere • Gases are ionized • They have lost or gained electrons

  32. Environmental variables • Temperature • Pressure

  33. Atmospheric Pressure • The pressure exerted by the weight of the air above

  34. Atmospheric Pressure • The pressure exerted by the weight of the air above • Force (weight) is mass x acceleration F = ma

  35. Atmospheric Pressure • The pressure exerted by the weight of the air above • Force (weight) is mass x acceleration • Gravity is an acceleration F = mg

  36. Atmospheric Pressure • The pressure exerted by the weight of the air above • Force (weight) is mass x acceleration • Gravity is an acceleration • Pressure is force per unit area p = mg/A

  37. Atmospheric Pressure • The pressure exerted by the weight of the air above • Force (weight) is mass x acceleration • Gravity is an acceleration • Pressure is force per unit area • Millibars (mb) are preferred unit in meteorology • 1 millibar = 1 hectoPascal (hPa) • Older units: inches of mercury and psi

  38. Varies much more in the vertical than the horizontal • Horizontal variations • Tens of millibars over thousands of kilometers • Vertical variations • Hundreds of millibars in ten kilometers • ALWAYS decreases with height

  39. Less mass over your head here… …than here.

  40. Vertical Pressure Profile • Pressure decreases with altitude at a curved (exponential) rate • Near the surface a linear estimate of 10 mb per 100 m works well

  41. Vertical Pressure Profile • Pressure decreases with altitude at a curved (exponential) rate • Near the surface a linear estimate of 10 mb per 100 m works well MEAN SEA LEVEL VALUE IS ABOUT 1013.25 hPa

  42. Vertical Pressure Profile • Pressure decreases with altitude at a curved (exponential) rate • Near the surface a linear estimate of 10 mb per 100 m works well MEAN HEIGHT OF 500 hPa IS 5.5 KM ASL

  43. Average sea level pressure (SLP) • 1013.25 hPa • 29.92 inHg (inches of mercury) • 14.7 lb/in2 • Normal range of sea level pressure • 960 to 1045 mb • 960 – strong low pressure system • 1045 – strong high in the winter

  44. Normal Range

  45. Environmental variables • Temperature • Pressure • Density

  46. Air density • Density = mass/volume • ALWAYS decreases with height • The atmosphere is denser closer to the surface • Gravity pulls air toward the planet

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