1. NATS 101 Lecture 2 TR Atmospheric Composition Vertical Structure Weather & Climate

2. Lecture 2-Nats 1012 Atmospheric Composition Permanent Gases N 2 and O 2 are most abundant gases Percentages hold constant up to 80 km Ar, Ne, He, and Xe are chemically inert N 2 and O 2 are chemically active, removed & returned Ahrens, Table 1.1, 3 rd Ed.

3. Lecture 2-Nats 1013 N 2 Boiling point: 77 °K or -196°C or –320 °F O 2 Boiling point: 90 °K or -183 °C or -297 °F N 2 and O 2 Balance between input (production) and output (destruction): Input: plant/animal decaying Sink: soil bacteria; oceanic plankton-->nutrients Input: plant photosynthesis Sink: organic matter decay chemical combination (oxidation) breathing

4. Lecture 2-Nats 1014 Atmospheric Composition Important Trace Gases Ahrens, Table 1.1, 3 rd ed. Which of these is now wrong even in the 4th edition of Ahrens?

5. Lecture 2-Nats 1015 Sources vegetative decay volcanic eruptions animal exhalation combustion of fossil fuels (CH 4 + 2 O 2 > 2 H 2 O + CO 2 ) Sinks photosynthesis (oxygen production) dissolves in water phytoplankton absorption (limestone formation) Carbon Dioxide CO 2

6. Lecture 2-Nats 1016 CO 2 Trend “Keeling Curve” Some gases vary by season and over many years. The CO2 trend is the cause for concern about global warming. CO 2 increases in northern spring, decreases in northern fall http://earthguide.ucsd.edu/globalchange/keeling_curve/01.html

7. Lecture 2-Nats 1017 H 2 O Vapor Variability Precipitable Water (mm) Some gases can vary spatially and daily

8. Lecture 2-Nats 1018 Aerosols 1 cm 3 of air can contain as many as 200,000 non-gaseous particles. –dust –dirt (soil) –salt from ocean spray –volcanic ash –water –pollen –pollutants

9. Lecture 2-Nats 1019 Aerosols - Volcanic Ash Fig. 1-4, p.6

10. Lecture 2-Nats 10110 Aerosols - Dust Particles Dust Storm on Interstate 10, between Phoenix and Tucson, AZ.

11. Lecture 2-Nats 10111 Aerosols Provide surfaces upon which water vapor can condense. Provide a surface area or catalyst needed for much atmospheric chemistry. Aerosols can deplete stratospheric ozone. They can also cool the planet by reflecting sunlight back to space.

12. Lecture 2-Nats 10112 Two Important Concepts Let’s introduce two new concepts... Density Pressure

13. Lecture 2-Nats 10113 What is Density? Density (  ) = Mass (M) per unit Volume (V)  = M/V  = Greek letter “rho” Typical Units: kg/m 3, gm/cm 3 Mass = # molecules  molecular weight (gm/mole) Avogadro number (6.023x10 23 molecules/mole)

14. Lecture 2-Nats 10114 Density Change Density (  ) changes by altering either a) # molecules in a constant volume b) volume occupied by the same # molecules a b

15. Lecture 2-Nats 10115 What is Pressure? Pressure (p) = Force (F) per unit Area (A) Typical Units: pounds per square inch (psi), millibars (mb), inches Hg Average pressure at sea-level: 14.7 psi 1013 mb 29.92 in. Hg

16. Lecture 2-Nats 10116 Pressure Can be thought of as weight of air above you. (Note that pressure acts in all directions!) So as elevation increases, pressure decreases. Higher elevation Less air above Lower pressure Lower elevation More air above Higher pressure Bottom Top

17. Lecture 2-Nats 10117 Density and Pressure Variation Key Points 1.Both decrease rapidly with height 2.Air is compressible, i.e. its density varies Ahrens, Fig. 1.5

18. Lecture 2-Nats 10118 Why rapid change with height? Consider a spring with 10 kg bricks on top of it compressible The spring compresses a little more with each addition of a brick. The spring is compressible. 10 kg

19. Lecture 2-Nats 10119 Why rapid change with height? Now consider several 10 kg springs piled on top of each other. Topmost spring compresses the least! Bottom spring compresses the most! The total mass above you decreases rapidly w/height.  mass

20. Lecture 2-Nats 10120 Why rapid change with height? Finally, consider piled-up parcels of air, each with the same # molecules. The bottom parcel is squished the most. Its density is the highest. Density decreases most rapidly at bottom.

21. Lecture 2-Nats 10121 Why rapid change with height? Each parcel has the same mass (i.e. same number of molecules), so the height of a parcel represents the same change in pressure  p. Thus, pressure must decrease most rapidly near the bottom. pppp pppp pppp pppp

22. Lecture 2-Nats 10122 Water versus Air Pressure variation in water acts more like bricks, close to incompressible, instead of like springs. Air: Lower density, Gradual drop Higher density Rapid decrease Bottom Top Bottom Top Water: Constant drop

23. Lecture 2-Nats 10123 A Thinning Atmosphere Bottom Top Lower density, Gradual drop w/elevation Higher density, Rapid decrease w/elevation NASA photo gallery

24. Lecture 2-Nats 10124 Pressure Decreases Exponentially with Height Logarithmic Decrease For each 16 km increase in altitude, pressure drops by factor of 10. 48 km - 1 mb 32 km - 10 mb 16 km - 100 mb 0 km - 1000 mb 100 mb 10 mb 1 mb 16 km 32 km 48 km Ahrens, Fig. 1.5

25. Lecture 2-Nats 10125 Exponential Variation Logarithmic Decrease For each 5.5 km height increase, pressure drops by factor of 2. 16.5 km - 125 mb 11 km - 250 mb 5.5 km - 500 mb 0 km - 1000 mb

26. Lecture 2-Nats 10126 Equation for Pressure Variation We can Quantify Pressure Change with Height

27. Lecture 2-Nats 10127 What is Pressure at 2.8 km? (Summit of Mt. Lemmon) Use Equation for Pressure Change

28. Lecture 2-Nats 10128 What is Pressure at Tucson? Use Equation for Pressure Change Let’s get cocky… How about Denver? Z=1,600 m How about Mt. Everest? Z=8,700 m You try these examples at home for practice

29. Lecture 2-Nats 10129 Temperature (T) Profile More complex than pressure or density Layers based on the Environmental Lapse Rate (ELR), the rate at which temperature decreases with height. inversion isothermal 6.5 o C/km Ahrens, Fig. 1.7

30. Lecture 2-Nats 10130 Higher Atmosphere Molecular Composition Homosphere- gases are well mixed. Below 80 km. Emphasis of Course. Heterosphere- gases separate by molecular weight, with heaviest near bottom. Lighter gases (H, He) escape. Ahrens, Fig. 1.8

31. Lecture 2-Nats 10131 Atmospheric Layers Essentials Thermosphere-above 85 km Temps warm w/height Gases settle by molecular weight (Heterosphere) Mesosphere-50 to 85 km Temps cool w/height Stratosphere-10 to 50 km Temps warm w/height, very dry Troposphere-0 to 10 km (to the nearest 5 km) Temps cool with height Contains “all” H 2 O vapor, weather of public interest

32. Lecture 2-Nats 10132 Summary Many gases make up air N 2 and O 2 account for ~99% Trace gases: CO 2, H 2 O, O 3, etc. Some are very important…more later Pressure and Density Decrease rapidly with height Temperature Complex vertical structure

33. Lecture 2-Nats 10133 Climate and Weather “Climate is what you expect. Weather is what you get.” -Robert A. Heinlein

34. Lecture 2-Nats 10134 Weather Weather – The state of the atmosphere: for a specific place at a particular time Weather Elements 1) Temperature 2) Pressure 3) Humidity 4) Wind 5) Visibility 6) Clouds 7) Significant Weather

35. Lecture 2-Nats 10135 Surface Station Model Temperatures Plotted  F in U.S. Sea Level Pressure Leading 10 or 9 is not plotted Examples: 1013.8 plotted as 138 998.7 plotted as 987 1036.0 plotted as 360 Ahrens, p 431 Responsible for boxed parameters

36. Lecture 2-Nats 10136 Sky Cover and Weather Symbols Ahrens, p 431

37. Lecture 2-Nats 10137 Pressure Tendency Change in pressure over the past 3 hours is also plotted. Also called barometric tendency Ahrens, p 432

38. Lecture 2-Nats 10138 Wind Barbs Direction Wind is going towards Westerly Westerly  from the West Speed (accumulated) Each flag is 50 knots Each full barb is 10 knots Each half barb is 5 knots Ahrens, p 432 65 kts from west

39. Lecture 2-Nats 10139 temperature dew point SLP pressure wind cloud cover Ohio State website

40. Lecture 2-Nats 10140 Practice Surface Station Temperate ( o F) Pressure (mb) Last Three Digits (tens, ones, tenths) Dew Point (later) Moisture Wind Barb Direction and Speed Cloud Cover Tenths total coverage Ahrens, p 431 72 58 111 Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

41. Lecture 2-Nats 10141 Practice Surface Station Sea Level Pressure Leading 10 or 9 is not plotted Examples: 1013.8 plotted as 138 998.7 plotted as 987 1036.0 plotted as 360 Ahrens, p 431 42 18 998 Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

42. Lecture 2-Nats 10142 Surface Map Symbols Fronts Mark the boundary between different air masses…later Significant weather occurs near fronts Current US Map Ahrens, p 432

43. Lecture 2-Nats 10143

44. Lecture 2-Nats 10144 Radiosonde Weather balloons, or radiosondes, sample atmospheric to 10 mb. They measure temperature moisture pressure They are tracked to get winds Ahrens, Fig. 1

45. Lecture 2-Nats 10145 Radiosonde Distribution Radiosondes released at 0000 and at 1200 GMT for a global network of stations. Large gaps in network over oceans and in less affluent nations. Stations ~400 km apart over North America

46. Lecture 2-Nats 10146 Radiosonde for Tucson Example of data taken by weather balloon released over Tucson Temperature (red) Moisture (green) Winds (white) Note variations of all fields with height UA Tucson 1200 RAOB troposphere stratosphere tropopause temperature profile moisture profile wind profile

47. Lecture 2-Nats 10147 Upper-Air Model Conditions at specific pressure level Wind Temperature (  C) Moisture (Later) Height above MSL UA 500mb Analysis Ahrens, p 427 Ahrens, p 431 Responsible for boxed parameters

48. Lecture 2-Nats 10148

49. Lecture 2-Nats 10149 Reading Assignment Ahrens Pages 13-22 Problems 1.17, 1.18, 1.20 (1.17  Chapter 1, Question 17) Pages 25-30 Problems 2.1-2.4 (2.1  Chapter 2, Problem 1) Don’t Forget the 4”x6” Index Cards