conserved variable diagram

A thermodynamic diagram for the atmosphere used for studying cloud processes.

One conserved variable representing heat or temperature is usually plotted along the abscissa, while the another conserved variable representing the conservation of water is plotted along the ordinate. The variables are chosen to be those that are conserved for both saturated and unsaturated motion. Examples of conserved variables are equivalent potential temperature θ_e, liquid water potential temperature θ_L, moist static energy s_e, liquid water static energy s_L, total water mixing ratio r_T, saturation point pressure P_SP, and saturation point temperature T_SP. These variables are not conserved for processes such as precipitation, radiative cooling, and mixing. When a third variable representing height z or pressure P is also indicated in the diagram, then there is enough information to define completely the thermodynamic state and water content of the air. Examples of popular sets of variables are (P, θ_e,r_T), (P, θ_L, r_T), (P, s_e, r_T), (P, s_L, r_T), and (P, P_SP, T_SP).
Bohren, C. F., and B. A. Albrecht 1998. Atmospheric Thermodynamics. 402 pp.

A collection of ideas and axioms, leading to differential equations specifying rates of change, that describes our experience with processes that involve fluxes of heat and changes in energy content.