Atmospheric thermodynamics

The current Note stems from material presented in a 1-2 hours Training course lecture on “Introduction to moist processes” that originally has been developed by Adrian Tompkins. The aim is to give a short introduction into the principles of atmospheric thermodynamics, and to present a “handy” overview and derivation of the quantities used in numerical weather prediction

The material presented is kept to a minimum, and focuses on the concept of enthalpy of moist air. This should allow the reader to elaborate on more involved thermodynamical problems.

Several textbooks dedicated to atmospheric thermodynamics exist. One might notice that some authors mainly use the notion of “adiabatic” atmospheric processes whereas others use the notion of isentropic processes throughout their derivations. Here we will use both notions.

Contents

1. Ideal gas law
2. First law of thermodynamics
3. Second law of thermodynamics
4. Enthalpy
5. State functions and Maxwell relations
6. Humidity variables
7. Virtual temperature
8. Reversible adiabatic transformation without phase change
9. Reversible adiabatic transformation with phase change
10. Clausius Clapeyron equation
11. Ways of reaching saturation
12. Energy diagrams - Tephigram
13. Saturation adjustment - numerical procedure
14. References