A special case of Bénard cells with an aspect ratio of 3:1. It was first observed in the laboratory as convection in a shallow liquid, heated from below (as in a skillet) or cooled from above by evaporation (as in metallic paint). Such observations have similarities to convection in shallow cells in atmospheric layers as in cirrocumulus, with upward motion at the center, where cloud forms, and descending motion at the edges, which are clear.