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

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

7. 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.

8. Composition

9. Composition Top two make up ~ 99 percent

10. Composition Argon is most of the last 1 percent

11. Composition Trace constituents of dry air

12. Composition Last constituent is highly variable

13. 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.

14. 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.

15. Water vapor is a variable gas

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

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

18. Carbon Dioxide

19. 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

21. Vertical Structure of the Atmosphere

22. Environmental variables • Temperature

23. There are large horizontal temperature variations

24. There are also large vertical variations in temperature

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

26. 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

27. Layer Classification (by temperature)

28. Layer Classification (by temperature) TRANSITIONS TO SPACE

29. Layer Classifications BY TEMPERATURE

30. Layer Classifications BY CHEMICAL COMPOSITION

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

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

33. Layer Classifications BY ELECTRIFICATION

34. 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

35. Environmental variables • Temperature • Pressure

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

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

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

39. 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

40. 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

41. 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

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

43. 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

44. 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

45. 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

46. 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

47. Normal Range

48. Environmental variables • Temperature • Pressure • Density

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