Transformations, changes in the structure or composition of something, are common in our everyday world. Lakes freeze in the winter; ponds dry up on hot summer days. Salt melts ice and dissolves in water. Such examples may be classified as either physical or chemical, if you wish, but many natural phenomena represent blends of both disciplines. Of primary interest is the notion that the entity in question (here, water or salt) has undergone a change of one sort or another. Learning how transformations proceed in nature is a fundamental goal of science, so we are often concerned with “processes” and “mechanisms”, the sequence of discrete events that leads to a particular outcome. Clouds owe their existence to particular transformations: Water vapor changes into liquid droplets, and those droplets later freeze when the temperature becomes low enough. Clouds would never form (or dissipate) were water not to change, be transformed from one state to another. We simply cannot understand much about clouds without dealing with transformations in detail. In fact, it is often useful to view clouds as processes, rather than as objects or entities. This part of the book lays out the guiding principles upon which to build our deeper understanding of atmospheric processes leading to clouds.

Natural transformations take place when a system deviates in some way from its most balanced or equilibrium state.