A delta- Eddington calculation of the cloud albedo agreed well with the albedo measured during an overflight of the cloud. This is thought to be related to radiatively generated convective cells in the cloud. The cloud layer is above an initially neutral subcloud layer and below a strong capping inversion. As convection sets in, negatively buoyant cloud top air is mixed down into the top of the neutral subcloud layer and destabilizes it, causing the model to jump to a new steady state with a characteristic profile of convective kinetic energy. Figure 12.1 shows the growth of convective cells in the mid-cloud horizontal plane.
Lighter shades indicate upward motion.
Clearly the cellular pattern is closed, as is expected for a dominantly top-cooled system. Figure 12.2 shows a vertical slice through the model in three variables. The upper panel shows the potential temperature perturbations generated by convection. The convective cells are clearly visible. The second panel shows that the downdrafts generated at cloud top extend all the way to the surface, thereby forcing the whole boundary layer.