Self-organizing criticality in cloud formation?

Abstract

Starting from the phenomenology of cloud formation, we derive a cellular automaton model which turns out to have a strong resemblance to percolation-based growth models. Projections of thereby produced clusters show a realistic fractal dimension of the perimeter, but only at or near the critical percolation threshold p c. A mechanism based on the continuity equation is proposed and numerically tested, which possibly explains why the atmosphere acts in fact near its critical threshold during cloud formation (self-organizing criticality). Numerically, this is achieved by a feedback of the number of ‘active’ sites on the occupation concentration p.