Aerosol memory in stratocumulus clouds leads to noise-induced patterns and non-ergodic sampling

Abstract

Stratocumulus cloud decks exhibit bistability between patterns of high (closed cells) and low (open cells) cloud fraction. Localized transitions between these two states (pockets of open cells) have been observed but their underlying mechanism remains unclear. We model stratocumulus and their interaction with atmospheric aerosol as a data-driven and physics-informed stochastic dynamical system with time-dependent parameters. This allows us to show that pockets of open cells result from noise-induced transitions between the stratocumulus patterns. We find comparable timescales for these transitions, mesoscale self-organization into patterns and the evolution of large-scale parameters. This lack of timescale separation corresponds to an aerosol memory in cloud evolution and means that the sampling of stratocumulus states by polar-orbiting satellites lacks the encoding of process information that would be present for an asymptotic and ergodic sampling.