Stratocumulus to cumulus transition in the presence of elevated smoke layers

Abstract

The transition from stratocumulus to cumulus clouds in the presence of elevated light-absorbing smoke layers is investigated with idealized large-eddy simulations. A smoke layer is placed 1 km above stratocumulus top and evolves with the cloud fields over the course of a 3 day simulation. The simulations presented vary the smoke-generated heating and the moisture content of the smoke layer. A control case without smoke is simulated for comparison. On day 2 of the transition, when still above cloud, smoke generates a more broken cloud field than the control case, depending weakly on the strength of the aerosol heating but strongly on the water vapor content in the smoke layer. Following nighttime recovery and contact with the stratocumulus, smoke hinders the transition by strengthening the inversion, limiting boundary layer deepening and reducing precipitation-related breakup. This modulation delays the transition, which may extend the stratocumulus deck westward, with concomitant implications for climate forcing.