Thermodynamics of moist air

Abstract

Up to now, we have described the dynamics of a dry atmosphere, which is a gas with well-mixed components but without water vapor. In this and the next chapters, we will explain the basic properties and the governing equations of moist air. Moist air is a mixture of dry air and water in which water experiences phase changes between vapor, liquid water, and ice. Interactions between the various phases of water play fundamental roles in mesoscale moist circulation (i.e., 1–10 km horizontal scale convection). In this book, however, we are mainly concerned with the large-scale dynamics of the atmosphere, which can be described using a simplified formulation of moist thermodynamics. We mainly consider a mixture of vapor and liquid water and assume that the two phases are in phase equilibrium. The ice phase and interactions between different phases will not be explicitly considered.