Clouds have immense beauty and variety. They show weather patterns on a global scale, as viewed by satellites. Yet they are made of tiny droplets that fall gently through the air. Clouds can have richly complex fractal shapes, and a wide range of sizes (The World Meteorological Organization (WMO) updated their International Cloud Atlas in 2017 (WMO-No. 407). It is an excellent resource that you can access online at www.wmocloudatlas.org). Clouds form when air becomes saturated. Saturation can occur by adding water, by cooling, or by mixing; hence, Lagrangian water and heat budgets are useful. The buoyancy of the cloudy air and the static stability of the environment determine the vertical extent of the cloud. Fogs are clouds that touch the ground. Their location in the atmospheric boundary layer means that turbulent transport of heat and moisture from the underlying surface affects their formation, growth, and dissipation.
- 6.1: Processes Causing Saturation
- Clouds are saturated portions of the atmosphere where small water droplets or ice crystals have fall velocities so slow that they appear visibly suspended in the air. Thus, to understand clouds we need to understand how air can become saturated.
- 6.2: Cloud Indentification
- You can easily find beautiful photos of all the clouds mentioned below by pointing your webbrowser search engine at “cloud classification”, “cloud identification”, “cloud types”, or “International Cloud Atlas”. You can also use web search engines to find images of any named cloud. To help keep the cost of this book reasonable, I do not include any cloud photos.
- 6.3: Cloud Organization
- Clouds frequently become organized into patterns during stormy weather. This organization is discussed in the chapters on Fronts, Midlatitude Cyclones, Thunderstorms, and Tropical Cyclones. Also, sometimes large-scale processes can organize clouds even during periods of fair weather, as discussed here.
- 6.7: Fractal Cloud Shapes
- Fractals are patterns made of the superposition of similar shapes having a range of sizes. An example is a dendrite snow flake. It has arms protruding from the center. Each of those arms has smaller arms attached, and each of those has even smaller arms. Other aspects of meteorology exhibit fractal geometry, including lightning, turbulence, and clouds. Fractals are defined next, and then are applied to cloud shadows.