摘要：A new parameterization of the Wegener–Bergeron–Findeisen (WBF) process has been
developed, and implemented in the general circulation model CAM-Oslo. The new
parameterization scheme has important implications for the process of phase
transition in mixed-phase clouds. The new treatment of the WBF process replaces a
previous formulation, in which the onset of the WBF effect depended on a threshold
value of the mixing ratio of cloud ice. As no observational guidance for such a
threshold value exists, the previous treatment added uncertainty to estimates of
aerosol effects on mixed-phase clouds. The new scheme takes subgrid variability
into account when simulating the WBF process, allowing for smoother phase
transitions in mixed-phase clouds compared to the previous approach. The new
parameterization yields a model state which gives reasonable agreement with
observed quantities, allowing for calculations of aerosol effects on mixed-phase
clouds involving a reduced number of tunable parameters. Furthermore, we find a
significant sensitivity to perturbations in ice nuclei concentrations with the new
parameterization, which leads to a reversal of the traditional cloud lifetime effect.
