Inhomogeneous Mixing Processes in Clouds: Toward Mixed-Phase Clouds

Clouds are one of the biggest unknowns in the climate system. This is especially true for mixed-phase clouds (MPCs), which consists of liquid and ice hydrometeors. This coexistence enables the Wegener-Bergeron-Findeisen (WBF) process, which describes the growth of the ice phase at the expense of the liquid phase and results in an accelerated dissipation of the cloud by precipitation. We will present modeling results employing a highly detailed Lagrangian cloud microphysical model, coupled to an idealized dynamical driver that represents fluid dynamics from the Kolmogorov scale to the scale of the largest entraining eddies. By explicitly simulating entrainment of cloud-free air and its subsequent mixing, we identify two MPC inhomogeneous processes. The first process addresses the nucleation of entrained aerosols to ice crystals, which is decelerated if the mixing process is sufficiently slow. The commensurate lower ice crystal concentration is disadvantageous to WBF. The second process is caused by the finite rate transport of water vapor from the liquid droplets to the ice crystals. An entrainment event may increase the distance between these particles, also decelerating WBF. Since both effects counteract WBF, they may contribute to the longevity of MPCs observed in the Arctic.