Supersaturation–Droplet Interactions in Idealized Turbulent Cloud Convection and Evaluation of a New Subgrid Model

Document Type

Article

Publication Date

9-1-2026

Abstract

Turbulent fluctuations of supersaturation, driven by water vapor and temperature variability, significantly influence cloud droplet activation and drop size distributions (DSDs). Accurate modeling of this variability is challenging because of the complex interactions among turbulent mixing and the phase change itself, affecting the variabilities and covariabilities of scalar fields. In Chandrakar et al., we introduced a new subgrid-scale model to capture supersaturation variability in such complex conditions. In this study, the performance of this model, coupled with droplet growth via a set of Lagrangian stochastic differential equations in large-eddy simulations (LESs), is evaluated against the reference direct numerical simulations (DNSs) of the Pi convection cloud chamber. Lagrangian statistics of water vapor, temperature, supersaturation, and droplet growth from LES with the new subgrid model capture both the magnitudes and structures in DNS at two different sidewall forcings. Most importantly, the LES coupled with the subgrid-scale model reproduces DSDs from the reference DNS for both forcings. DNS results also show notable differences in the Lagrangian statistics of water vapor, temperature, supersaturation, droplet size, and their cross correlations under clean versus polluted cloud conditions. A relatively broader DSD in the clean condition and damped supersaturation fluctuations in the polluted condition occur. A theoretical scaling of the second-order structure function of droplet size is presented, which is consistent with simulation results. Overall, this study provides a tested framework for improved modeling of subgrid-scale interactions between the supersaturation field and cloud particles in future atmospheric cloud simulations.

Publication Title

Journal of the Atmospheric Sciences

Link to Full Text

Share

COinS