PNNL

Abstract

Cellular cloud patterns associated with mesoscale cellular convection are commonly observed in satellite images of the earth 1-3. The preference for either the closed or open cellular pattern has a profound effect on Earth’s albedo, and therefore strong implications for climate. Using satellite imagery and numerical models we show for the first time how precipitating clouds produce an open cellular cloud pattern that oscillates between different, metastable states. The oscillations are a result of precipitation causing a negative feedback on positively buoyant clouds. Evaporating precipitation drives negatively buoyant downdraughts and the interaction between the outflows of adjacent cells forms surface convergent zones and new cloud formation. In turn, the newly formed clouds produce precipitation and new colliding outflows that are displaced from the previous ones. As successive cycles of this kind unfold, convergence zones alternate with divergence zones and new cloud patterns emerge to replace old ones. The result is an oscillating, self-organised system with a characteristic cell-size and precipitation frequency. The robustness of the system and its connection to network theory 4 is discussed.