AbstractCloud droplet activation is usually modeled using Twomey-type parameterizations, wherein cloud droplets are created when a critical supersaturation for the available cloud condensation nuclei (CCN) is exceeded. However, these parameterizations do not account for the existence of haze particles. Recent observations show that haze particles exist in a convection cloud chamber especially in polluted conditions. The microphysics schemes previously used for large-eddy simulations of the cloud chamber could not fully resolve haze particles and the associated processes, including their activation and deactivation. Here, we develop and adapt haze-capable bin and Lagrangian microphysics schemes to properly resolve the activation and deactivation processes. Results are compared with the Twomey-type CCN-based bin microphysics scheme in which haze particles are not resolved. We find that results from the haze-capable bin microphysics scheme agree well with those from the Lagrangian microphysics scheme. However, both schemes significantly differ from those from a CCN-based bin microphysics scheme unless CCN regeneration is considered. Haze particles from the recycling of deactivated cloud droplets can strongly enhance cloud droplet number concentration due to a positive feedback in haze-cloud interactions. Haze particle size distributions are more realistic when considering solute and curvature effects that enable representing the complete physics of the activation process. Our study suggests that haze particles and their interactions with cloud droplets may have a strong impact on cloud properties when supersaturation fluctuations are comparable to mean supersaturation, as is the case in the cloud chamber and likely is the case in the atmosphere especially in polluted conditions.
Published: June 22, 2023