Thermodynamic diagrams are diagrams used to represent the thermodynamic states of a (typically fluid) material and the consequences of manipulating this material. For example, a temperature-entropy diagram (T-S diagram) can be used to demonstrate the behavior of a fluid as it is changed by a compressor.
Especially in meteorology they are used to analyze the current state of the atmosphere derived from the measurements of radiosondes, usually obtained with meteorological balloons. In such diagrams, the temperature and humidity values (represented by the dew point) are shown with respect to the pressure. Thus, the diagram gives at first glance the actual atmospheric stratification and vertical distribution of water vapor. A later analysis gives the actual base and the upper height of the convective clouds or possible instabilities in the stratification.
By assuming the amount of energy due to solar radiation it is possible to predict the temperature, humidity and wind of 2 m during the day, the development of the boundary layer of the atmosphere, the appearance and development of clouds and the conditions to fly during the day.
The main characteristic of thermodynamic diagrams is the equivalence between the area in the diagram and the energy. When air changes pressure and temperature during a process and prescribes a closed curve within the diagram, the area enclosed by this curve is proportional to the energy that has been gained or released by air.