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NATS 101 Intro to Weather and Climate Section 05: 2:00PM TTh ILC 150

NATS 101 Intro to Weather and Climate Section 05: 2:00PM TTh ILC 150. Dr. E. Robert Kursinski TAs: Mike Stovern & April Chiriboga. Please turn off cell phones. NATS 101 - 05. Class listserve is working TA hours I need the second notetaker volunteer.

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NATS 101 Intro to Weather and Climate Section 05: 2:00PM TTh ILC 150

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  1. NATS 101 Intro to Weather and Climate Section 05: 2:00PM TTh ILC 150 Dr. E. Robert Kursinski TAs: Mike Stovern & April Chiriboga Please turn off cell phones

  2. NATS 101 - 05 • Class listserve is working • TA hours • I need the second notetaker volunteer. • Come see me after class • Make sure you bring your clicker

  3. LISTSERV So far 45 students signed up on class listserve You can subscribe by sending an email to listserv@listserv.arizona.edu with the following as the only line in the body of the message. subscribe nats101s5fall09 Firstname Lastname Substitute your first name for FirstnameSubstitute your last name for Lastname

  4. NATS 101 - 05Lecture 2Density, Pressure & TemperatureClimate and Weather

  5. Two Important Concepts Let’s introduce two new concepts... Density Pressure

  6. What is Density? Density () = Mass (M) per unit Volume (V)  = M/V  = Greek letter “rho” Typical Units: kg/m3, gm/cm3 Mass = # molecules (mole)  molecular mass (gm/mole) Avogadro number (6.023x1023 molecules/mole)

  7. a b Density Change Density () changes by altering either a) # molecules in a constant volume b) volume occupied by the same # molecules

  8. 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

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

  10. Density and Pressure Variation Key Points • Both decrease rapidly with height • Air is compressible, i.e. its density varies Ahrens, Fig. 1.5

  11. 10 kg 10 kg 10 kg 10 kg 10 kg 10 kg Why rapid change with height? Consider a spring with 10 kg bricks on top of it The spring compresses a little more with each addition of a brick. The spring is compressible.

  12. 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  mass  mass  mass

  13. 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.

  14. 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

  15. Top Bottom A Thinning Atmosphere Lower density, Gradual drop Higher density Rapid decrease NASA photo gallery

  16. Pressure Decreases Exponentially with Height Logarithmic Decrease • For each 16 km increase inaltitude, pressure drops by factor of 10. 48 km - 1 mb 32 km - 10 mb 16 km - 100 mb 0 km - 1000 mb 1 mb 48 km 10 mb 32 km 100 mb 16 km Ahrens, Fig. 1.5

  17. 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

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

  19. Equation for Pressure Variation We can Quantify Pressure Change with Height

  20. What is Pressure at 2.8 km?(Summit of Mt. Lemmon) Use Equation for Pressure Change

  21. 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

  22. inversion isothermal 6.5oC/km 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. Ahrens, Fig. 1.7

  23. 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

  24. 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” H2O vapor, weather of public interest

  25. Summary • Many gases make up air N2 and O2 account for ~99% Trace gases: CO2,H2O, O3, etc. Some are very important…more later • Pressure and Density Decrease rapidly with height • Temperature Complex vertical structure

  26. Climate and Weather “Climate is what you expect. Weather is what you get.” -Robert A. Heinlein

  27. 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 Weather

  28. Surface Station Model Responsible for boxed parameters 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

  29. Sky Cover and Weather Symbols Ahrens, p 431 Ahrens, p 431

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

  31. SLP pressure temperature dew point cloud cover Ohio State website wind

  32. 72 111 58 Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction? Ahrens, p 431 Practice Surface Station Temperate (oF) Pressure (mb) Last Three Digits (tens, ones, tenths) Dew Point (later) Moisture Wind Barb Direction and Speed Cloud Cover Tenths total coverage

  33. 42 998 18 Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction? Ahrens, p 431 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

  34. Surface Map Symbols • Fronts Mark the boundary between different air masses…later Significant weather occurs near fronts Current US Map Ahrens, p 432

  35. Radiosonde Weather balloons, or radiosondes, sample atmospheric to 10 mb. They measuretemperature moisture pressure They are tracked to getwinds Ahrens, Fig. 1

  36. 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

  37. Radiosonde for Tucson stratosphere 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 tropopause troposphere temperature profile moisture profile wind profile

  38. Climate Climate - Average weather and range of weather, computed over many years. Whole year (mean annual precipitation for Tucson, 1970-present) Season (Winter: Dec-Jan-Feb) Month (January rainfall in Tucson) Date (Average, record high and low temperatures for Jan 1 in Tucson)

  39. Climate of TucsonMonthly Averages Individual months can show significant deviations from long-term, monthly means.

  40. Average and Record MAX and MIN Temperatures for Date

  41. Climate of TucsonProbability of Last Freeze Cool Site:Western Region Climate Center

  42. Climate of TucsonProbability of Rain Cool Site:Western Region Climate Center

  43. Climate of TucsonExtreme Rainfall Cool Site:Western Region Climate Center

  44. Climate of TucsonSnow! Cool Site:Western Region Climate Center

  45. Summary • Weather - atmospheric conditions at specific time and place Weather Maps  Instantaneous Values • Climate - average weather and the range of extremes compiled over many years Statistical Quantities  Expected Values

  46. Reading Assignment • Ahrens Pages 25-42 Problems 2.1-2.4, 2.7, 2.9-2.12 (2.1  Chapter 2, Problem 1) • Don’t forget the clickers …

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