ATMS 455 Physical Meteorology

1. Today�s lecture objectives: Thermodynamics Review (W&H 2) What has ATMS 305 done for me lately? ATMS 455 � Physical Meteorology

2. 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 ATMS 455 � Physical Meteorology

3. First Law of Thermodynamics Our interest begins primarily with gases because we�re trying to explain processes in the atmosphere

4. First Law of Thermodynamics Energy is Conserved

5. First Law of Thermodynamics

6. Heat added or subtracted

7. Work of Expansion

8. Work of Expansion Work Performed on a System by Its Environment Is Negative

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

10. Isochoric Process Changes in Heat Added or Removed Temperature Pressure

11. Isobaric Process Changes in Heat Added or Removed Temperature Volume

12. Isothermal Process Changes in Heat Added or Removed Pressure Volume

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�

14. ATMS 305 � Adiabatic Processes These processes are often of secondary importance for time periods up to a day�

15. ATMS 305 � Adiabatic Processes Therefore, there is value in applying the First Law of Thermodynamics for adiabatic processes*

16. Potential Temperature Example Compare the air at two different levels 900 mb and 21oC 700 mb and .5oC

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

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

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

20. Potential Temperature Rising Unsaturated Thermal of Air Parcel Potential Temperature is Constant

21. Potential Temperature Measure of Stability Statically Stable

22. First Law of Thermodynamics Conservation of Energy Says Nothing About Direction of Energy Transfer

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

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

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

26. Natural (or Irreversible) Process Examples Thermal Conduction

27. Natural (or Irreversible) Process Examples Thermal Conduction

28. Impossible Process Physical processes that do not occur naturally Process that takes system from equilibrium

29. Impossible Process Examples Thermal Conduction

30. Impossible Process Examples Thermal Conduction

31. Reversible Process Reversal in direction returns substance & environment to original states

32. Reversible Process A conceptual process Idealized version of how things should be No processes are truly reversible

33. Reversible Process Useful concept Helps investigate Second Law and Entropy

34. 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 ATMS 305 � The Second Law of Thermodynamics and Entropy

35. Entropy (S) A thermodynamic state function Similar to pressure, temperature or volume Path independent

36. Entropy (S) A measure of the energy that is no longer available to do work

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

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

40. Second Law of Thermodynamics System that has attained maximum entropy cannot undergo further changes

41. Entropy & Equilibrium Entropy Change

42. Second Law of Thermodynamics State of maximum entropy is a state of equilibrium!

43. Entropy & Equilibrium Equilibrium Properties do not change with time

44. Water In the Atmosphere Unique Substance Occurs in Three Phases Under Normal Atmospheric Pressures and Temperatures Gaseous State Variable 0 � 4%

45. Water Vapor Pressure (e) Ideal Gas Law for Dry Air Ideal Gas Law for Water Vapor

46. Water Vapor Pressure (e) Partial pressure that water vapor exerts

47. Water Vapor Pressure (e) Gas Constant of Water Vapor

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

49. The Beer Analogy You are thirsty! You would like a beer. Obey your thirst!

50. The Beer Analogy Pour a glass but watch the foam

51. The Beer Analogy Wait! Some joker put a hole in the bottom of your Styrofoam cup! It is leaking!

52. The Beer Analogy Having had many beers already, you are intrigued by the phenomena!

53. The Beer Analogy

54. The Beer Analogy

55. The Beer Analogy

56. The Beer Analogy The cup fills up Height becomes constant Equilibrium Reached

57. The Beer Analogy What do you do?

58. The Beer Analogy Get a new cup!

59. Evaporation Similar to what happens to water in the atmosphere

60. Evaporation Molecules in liquid water attract each other In motion

61. Evaporation Collisions Molecules near surface gain velocity by collisions

62. Evaporation Fast moving molecules leave the surface Evaporation

63. Evaporation Rate of evaporation Constant Function of water temperature

64. Evaporation Soon, there are many water molecules in the air

65. Evaporation Slower molecules return to water surface Condensation

66. Evaporation Rate of Condensation Variable Function of water vapor mass in air

67. Evaporation Net Evaporation Number leaving water surface is greater than the number returning Evaporation greater than condensation

68. Evaporation Rate at which molecule return increases with time Evaporation continues to pump moisture into air Water vapor increases with time

69. Equilibrium Eventually, equal rates of condensation and evaporation �Air is saturated� Equilibrium

70. Equilibrium At Equilibrium

71. Equilibrium At Equilibrium Rate of evaporation is a function of temperature

72. Equilibrium At Equilibrium Rate of condensation depends on water vapor mass Also a function of temperature

73. Equilibrium At Equilibrium

74. Equilibrium Water Vapor Partial Pressure Function of mass of water vapor How do we know the mass (or pressure)?

75. Equilibrium Curve Equilibrium Rate of condensation = Rate of evaporation es water vapor pressure at equilibrium (saturation)

76. Condensation Water Vapor Pressure > Equilibrium

77. Condensation Water Vapor Pressure > Equilibrium

78. Condensation Water Vapor Pressure > Equilibrium

79. Evaporation Water Vapor Pressure < Equilibrium

80. Evaporation Water Vapor Pressure < Equilibrium

81. Evaporation Water Vapor Pressure < Equilibrium

82. ATMS 305 � Water Vapor in the Air Effects of a saturated air parcel ascent coupled with its adiabatic descent (irreversible* ): Net increase in the temperature and potential temperature of the parcel Decrease in moisture content No change in the equivalent potential or wet-bulb potential temperature

83. Equilibrium Curve Where do these numbers come from?

84. Clausius-Clapeyron Equation

85. Clausius-Clapeyron Equation

86. Applications of Clausius-Clapeyron Equation Variation in Boiling Point

87. Applications of Clausius-Clapeyron Equation Variation in boiling point Under normal atmospheric conditions

88. Homogeneous System Every variable has the same value for every point of the system Dry air Water vapor by itself

89. Heterogeneous System Several portions within the system having the same values but different from each other

90. Heterogeneous System Water Vapor Can Exist in Three Phases

91. Water in Equilibrium Acts as ideal gas by itself

92. Water in Equilibrium Does not act as ideal gas in presence of liquid water or ice

93. Water in Equilibrium Vapor Phase Defined by two state variables Liquid Phase Defined by two state variables

94. Water in Equilibrium At equilibrium

95. Water in Equilibrium Equilibrium Curve Water Vapor Pressure is a Function of Temperature

96. Water in Equilibrium P-V Diagram Water as an Ideal Gas

97. Water in Equilibrium Amagat-Andrews Diagram (a.k.a. Phase Diagram)

98. Water in Equilibrium Vapor Phase (A to B) Ideal Gas Law Decrease Volume Increase Pressure Heat Removed

99. Water in Equilibrium Liquid & Vapor Phase (B) Slight Change in Volume Causes Condensation

100. Water in Equilibrium Liquid & Vapor Phase (B to C) Condensation Volume Decreasing Constant Pressure Constant Temperature

101. Water in Equilibrium Liquid & Vapor Phase (B to C) Condensation Water Vapor Pressure is at Equilibrium (es)

102. Water in Equilibrium Liquid Phase (C) All Water Vapor Has Condensed

103. Water in Equilibrium Liquid Phase (C to D) Volume Decreases Little Virtually Incompressible

104. Water in Equilibrium Critical Point Upper limit No condensation above Critical Point Water vapor obeys Ideal Gas Law above Critical Point

105. Latent Heat Homogeneous System Isobaric Process Heat Added or Removed Temperature Change Volume Change

106. Latent Heat Heterogeneous System The heat absorbed (or given away) by the system during an isobaric, also an isothermal, phase transition

107. Latent Heat Energy required to change the molecular configuration of a substance

108. Latent Heat Amount of heat added or removed depends on Mass of water Type of phase change

109. Latent Heat Heat Absorbed (dQ > 0)

110. Latent Heat Heat Released (dQ < 0)

111. Latent Heat Varies with temperature

112. Equilibrium with Ice What about water vapor vs. ice?

113. Equilibrium with Ice Phase Diagram Lower temperature Lower saturation vapor pressure

114. Equilibrium with Ice Clausius-Clapeyron Equation Use the Latent Heat of Sublimation

115. Equilibrium with Ice Equilibrium Curve for Ice Ice Saturation Vapor Pressure (esi) Lower Than Liquid Water Saturation Vapor Pressure (esw)

116. Equilibrium with Ice Supercooled Liquid Water (SLW) Liquid Water at Temperatures Colder Than 0oC Metastable Condition Exists in the Absence of ice

117. Equilibrium with Ice Vapor to Liquid Vapor to Ice

118. Equilibrium with Ice Triple Point

119. Equilibrium with Ice Isothermal Compression Constant Temperature Increasing Pressure Decreasing Volume Heat Removed

120. Three Dimensional Phase Diagram

121. Equilibrium with Ice Isobaric Cooling Constant Pressure Temperature Decreasing Volume Decreasing Heat Removed

122. Three Dimensional Phase Diagram

123. Summary Latent Heats at 273 K