ATMS 455 – Physical Meteorology

1. ATMS 455 – Physical Meteorology • Today’s lecture objectives: • Thermodynamics Review (W&H 2) • What has ATMS 305 done for me lately? http://www.artcyclopedia.com/feature-2001-08.html

2. ATMS 455 – Physical Meteorology • Today’s lecture topics: • Thermodynamics Review (W&H 2) • First Law of Thermodynamics • Second Law of Thermodynamics • Water in the atmosphere • Clausius Clapeyron Equation • Phase changes

3. First Law of Thermodynamics • Our interest begins primarily with gases because we’re trying to explain processes in the atmosphere http://www.unca.edu/~dmiller/cartoons.html

4. First Law of Thermodynamics • Energy is Conserved E = constant (EKinetic + EPotential + EInternal + EChemical + EMechanical + EElectrical ) = constant our main concern in synoptic meteorology (courtesy F. Remer)

5. First Law of Thermodynamics change in internal energy work done heat added other forms…

6. Heat added or subtracted • Primary heat sources/sinks of concern in ATMS 455 are associated with phase changes of water (latent heat) and with radiation http://www.nba.com/heat/photogallery/photogallery_index.html

7. Work of Expansion dW > 0 • Work Performed by a System on Its Environment Is Positive F (courtesy F. Remer)

8. Work of Expansion • Work Performed on a System by Its Environment Is Negative dW < 0 (courtesy F. Remer)

9. First Law of Thermodynamics • Types of Processes • Isochoric (or Isosteric) • Isobaric • Isothermal • Adiabatic (later lecture) (courtesy F. Remer)

10. Isochoric Process • Changes in • Heat Added or Removed • Temperature • Pressure 273K 373K p V (courtesy F. Remer)

11. Isobaric Process • Changes in • Heat Added or Removed • Temperature • Volume 273K 373K p V (courtesy F. Remer)

12. Isothermal Process • Changes in • Heat Added or Removed • Pressure • Volume 273K 373K p V (courtesy F. Remer)

13. ATMS 305 – Adiabatic Processes • Heat can be added to Polly by many processes (radiation, friction, condensation of water vapor {later}, turbulent transfer of heat), however… (courtesy F. Remer)

14. ATMS 305 – Adiabatic Processes • These processes are often of secondary importance for time periods up to a day… (courtesy F. Remer)

15. ATMS 305 – Adiabatic Processes • Therefore, there is value in applying the First Law of Thermodynamics for adiabatic processes* *Processes in which no heat (dq) is added or withdrawn from a system (Polly Parcel), so that her change in temperature is a result of expansion and compression *Many processes in the atmosphere are dry adiabatic

16. Potential Temperature Example Compare the air at two different levels • 900 mb and 21oC • 700 mb and .5oC (courtesy F. Remer)

17. Potential Temperature 900 mb and 21oC (294K) (courtesy F. Remer)

18. Potential Temperature 700 mb and .5oC (273.5K) (courtesy F. Remer)

19. Potential Temperature 900 mb and 21oC q = 302 K 700 mb and .5oC q = 303 K Air is the same! (courtesy F. Remer)

20. Potential Temperature • Rising Unsaturated Thermal of Air • Parcel Potential Temperature is Constant z Dry Adiabatic Lapse Rate  Gd = 9.8 oC/km T (courtesy F. Remer)

21. Potential Temperature • Measure of Stability • Statically Stable 1000 mb (courtesy F. Remer)

22. First Law of Thermodynamics • Conservation of Energy • Says Nothing About Direction of Energy Transfer (courtesy F. Remer)

23. Second Law of Thermodynamics • Preferred (or Natural) Direction of Energy Transfer • Determines Whether a Process Can Occur (courtesy F. Remer)

24. Second Law of Thermodynamics • Three Types of Thermodynamic Processes • Natural (or Irreversible) • Impossible • Reversible (courtesy F. Remer)

25. Natural (or Irreversible) Process • Physical Processes That Proceed in One Direction But Not The Other • Tends Towards Equilibrium • Equilibrium Only At End of Process (courtesy F. Remer)

26. Hot dQ Cold Natural (or Irreversible) Process • Examples • Thermal Conduction (courtesy F. Remer)

27. Natural (or Irreversible) Process • Examples • Thermal Conduction Increase in Entropy Warm Equilibrium (courtesy F. Remer)

28. Impossible Process • Physical processes that do not occur naturally • Process that takes system from equilibrium (courtesy F. Remer)

29. Impossible Process • Examples • Thermal Conduction Warm (courtesy F. Remer)

30. Impossible Process • Examples • Thermal Conduction Decrease in Entropy Hot Cold (courtesy F. Remer)

31. Reversible Process • Reversal in direction returns substance&environment to original states (courtesy F. Remer)

32. Reversible Process • A conceptual process • Idealized version of how things should be • No processes are truly reversible (courtesy F. Remer)

33. Reversible Process • Useful concept • Helps investigate Second Law and Entropy (courtesy F. Remer)

34. ATMS 305 – The Second Law of Thermodynamics and Entropy • Distinction between a reversible and an irreversible process: • reversible – one can reverse the process and cause the system (e.g. Polly Parcel) and the environment both to return to their original condition • irreversible – one can reverse the process and cause the system to return to its original condition, but the environment will have suffered a change from the original condition http://www.citroen.com/site/htm/en/technologies/today/SensoGearbox

35. Entropy (S) • A thermodynamic state function • Similar to pressure, temperature or volume • Path independent S Extensive – mass dependent (J K-1) s Intensive – mass independent (J kg-1 K-1) (courtesy F. Remer)

36. Entropy (S) • A measure of the energy that is no longer available to do work Hot Cold Cool Lowest Entropy Highest Entropy (courtesy F. Remer)

37. Second Law of Thermodynamics • Intensive (J kg-1 K-1) form of entropy embedded in the Second Law of Thermodynamics

38. Second Law of Thermodynamics • Summary >0 Irreversible Processes =0 Reversible Processes <0 Impossible Processes DStot (courtesy F. Remer)

39. Second Law of Thermodynamics • For any natural (irreversible) process • Final entropy is greater than initial entropy (courtesy F. Remer)

40. Second Law of Thermodynamics • System that has attained maximum entropy cannot undergo further changes Hot Cold Cool Lowest Entropy Highest Entropy (courtesy F. Remer)

41. Entropy & Equilibrium • Entropy Change Hot Cold Cool Lowest Entropy Changes with Time Highest Entropy Does Not Change (courtesy F. Remer)

42. Second Law of Thermodynamics • State of maximum entropy is a state of equilibrium! Hot Cold Cool Lowest Entropy Highest Entropy (courtesy F. Remer)

43. Entropy & Equilibrium • Equilibrium • Properties do not change with time Hot Cold Cool Not in Equilibrium Equilibrium (courtesy F. Remer)

44. H H O Water In the Atmosphere • Unique Substance • Occurs in Three Phases Under Normal Atmospheric Pressures and Temperatures • Gaseous State • Variable 0 – 4% (courtesy F. Remer)

45. Water Vapor Pressure (e) • Ideal Gas Law for Dry Air • Ideal Gas Law for Water Vapor p = pressure of dry air ad = specific volume of dry air Rd = gas constant for dry air e = vapor pressure of water vapor av = specific volume of water vapor Rv = gas constant for water vapor (courtesy F. Remer)

46. Water Vapor Pressure (e) • Partial pressure that water vapor exerts Total Pressure p = pO2+pN2+pH2Ov Water Vapor Pressure e = pH2Ov (courtesy F. Remer)

47. H H O Water Vapor Pressure (e) • Gas Constant of Water Vapor Molecular Weight (Mw ) Hydrogen = 1kg kmol-1 Oxygen = 16 kg kmol-1 Water = 18 kg kmol-1 (courtesy F. Remer)

48. Water in the Atmosphere • Unanswered Questions • How much water vapor can the air “hold”? • When will condensation form? • Is the air saturated? • The Beer Analogy (courtesy F. Remer)

49. The Beer Analogy • You are thirsty! • You would like a beer. • Obey your thirst! (courtesy F. Remer)

50. The Beer Analogy • Pour a glass but watch the foam (courtesy F. Remer)