Overview

Seeing an isolated thunderstorm from a distance can be awe-inspiring, partly because of its size, partly because of the apparent sense of organization. At this macroscopic level, we may see distinct turrets and sharp, bumpy edges along one side of the storm, evidence of turbulent motions and the rapid penetration of moist, cloudy air into the dry surroundings. The other side of the storm, by contrast, may look diffuse and wispy, evidence of gentler air motions and less abrupt distinctions between cloudy and clear air. These visible macroscale features of mature storms evolved from smaller convective elements in response to the effects of energy conversions on the air motions. We realize that cloudy air is composed of many small, subvisible particles that eventually become precipitation, but it is the macroscale structure of the storm as a whole that compels us to understand the relevant energy conversions and the connections between the microphysics of condensate formation and the macrophysics of cloud development.

The conversion of energy from potential to kinetic is of fundamental importance to cloud formation and evolution. Sometimes this conversion occurs on the atmospheric mesoscale (as when air motions respond to pressure readjustments), sometimes at the microscale (as in the release of latent heat during condensation). We come to understand energy transformations, regardless of scale, through the discipline of thermodynamics. The fundamental principles of thermodynamics are here applied to clouds.