Cloud patterns in which clouds are organised in bands are not an unusual sight. The photo on the left shows a cloud pattern produced by an internal wave. The air rises with the crest of the wave, cooling in the process, which produces condensation (cloud formation). It sinks in the troughs, causing warming and evaporation of the cloud moisture. The wave crests then become visible as cloud bands. The photo was taken near Mount Lawson (30 km west of Brisbane, Australia) and the wave was travelling towards Brisbane city, while it was a fine still day on the ground. © Judith Hall, reproduced by permission.

The photo on the right shows a rare observation of breaking clouds. It was taken in the winter of 2009/2010 on the North Sea island Nordstrand. The photographer says that it was seen for only a few minutes, which indicates rapid active breaking. © Gerhard Schwagmeier, reproduced by permission.