isotherms = lines of constant temperature dry adiabats = lines of constant potential temperature representing the temperature of a rising parcel of dry air saturated adiabats or pseudoadiabats = lines representing the temperature of a rising parcel saturated with water vapor mixing ratio = lines representing the dewpoint of a rising parcel The lapse rate, dry adiabatic lapse rate (DALR) and moist adiabatic lapse rate (MALR), are obtained. With the help of these lines, parameters such as cloud condensation level, level of free convection, onset of cloud formation. etc. can be derived from the soundings. Example The path or series of states through which a system passes from an initial equilibrium state to a final equilibrium state and can be viewed graphically on a pressure-volume (P-V), pressure-temperature (P-T), and temperature-entropy (T-s) diagrams. There are an infinite number of possible paths from an initial point to an end point in a process. In many cases the path matters, however, changes in the thermodynamic properties depend only on the initial and final states and not upon the path. Consider a gas in cylinder with a free floating piston resting on top of a volume of gas at a temperature . If the gas is heated so that the temperature of the gas goes up to while the piston is allowed to rise to as in Figure 1, then the pressure is kept the same in this process due to the free floating piston being allowed to rise making the process an isobaric process or constant pressure process. This Process Path is a straight horizontal line from state one to state two on a P-V diagram. It is often valuable to calculate the work done in a process. The work done in a process is the area beneath the process path on a P-V diagram. Figure 2 If the process is isobaric, then the work done on the piston is easily calculated. For example, if the gas expands slowly against the piston, the work done by the gas to raise the piston is the force F times the distance d. But the force is just the pressure P of the gas times the area A of the piston, F = PA. Thus W = Fd W = PAd W = P(V2 − V1) Now let’s say that the piston was not able to move smoothly within the cylinder due to static friction with