General remarks

Thermodynamic charts or diagrams are used to provide graphical solutions to some of the processes which were described in the previous chapters. The diagrams contain isobars, isotherms, dry adiabats, pseudoadiabats, lines of constant saturation mixing ratio and auxiliary lines. We will be very brief in our discussion and omit the description of various auxiliary lines that are needed, for example, in the construction of the pressure–height curve of a particular sounding. A full discussion of thermodynamic diagrams can be found in various reference books. Our reference goes to an excellent manual entitled Use of the Skew T-Log p Diagram in Analysis and Forecasting which was published in 1961 by the United States Air Force.

Energy changes due to thermodynamic processes are of great importance in many meteorological considerations. Therefore, it is of primary importance that the area enclosed by lines on a particular diagram representing a cyclic process are equal to or at least proportional to the work done during such a process. The ordinary work diagram with coordinates (p, v) is not very suitable for meteorological applications since v is not an observed quantity. Therefore, it is desirable to construct diagrams with coordinates pressure and temperature, two quantities which are regularly observed.