Journal Article

A Model Intercomparison Study to Investigate Mixing Characteristics in Non‐Precipitating Stratocumulus Clouds

Chandrakar, Kamal Kant, Lu, Chunsong, Krueger, Steve, Choi, Kyoung Ock, Ovchinnikov, Mikhail, Zhu, Zeen, Yum, Seong Soo, Hoffmann, Fabian, Shima, Shin‐ichiro, Yin, Chongzhi, Yang, Fan, Hou, Pei, Ren, Yangze, Wu, Peng

2026

Overview

Recent aircraft observations of marine stratocumulus clouds consistently showed that cloud microphysical relationships vary with altitude, indicating inhomogeneous mixing characteristics near cloud top and homogeneous mixing characteristics in mid‐levels of clouds. Here, we conduct model intercomparison of an idealized, non‐precipitating stratocumulus cloud to evaluate model consistency and examine whether simulations can reproduce the observed mixing characteristics. The results show that eleven large‐eddy simulations with various dynamics and microphysics schemes show good agreement on the thermodynamical, microphysical, and dynamical properties of the stratocumulus‐topped boundary layer in a steady state. The inter‐model spread in steady‐state liquid water path is significantly reduced compared to previous model intercomparison studies. This improvement might be due to better models and more consistent initial conditions than those used decades ago. In addition, most simulations, including a low‐dimensional simulation, capture inhomogeneous mixing characteristics near the cloud top and homogeneous mixing characteristics inside the cloud. Moreover, simulations using Lagrangian microphysics schemes agree better with the observed mixing characteristics compared with those using the bin microphysics schemes. Since most simulations do not fully resolve the entrainment process, the apparent mixing characteristics arise from the variations in the resolved cloud properties. Our results support the vertical circulation mixing hypothesis, which suggests that homogeneous mixing characteristics in mid‐levels of clouds are due to the vertical circulation of entrainment‐affected and diluted parcels from the cloud top moved to lower levels. Plain Language Summary Cloud microphysical properties respond differently to entrainment, which can lead to inhomogeneous mixing, where a portion of droplets evaporate completely while the mean droplet size remains constant, or homogeneous mixing, where all droplets evaporate uniformly due to entrained air. Recent aircraft observations of marine stratocumulus clouds showed features of inhomogeneous mixing near the cloud top and homogeneous mixing inside the cloud. One hypothesis is that the cloud top inhomogeneous mixing is physical, but the in‐cloud homogeneous mixing is due to the vertical circulation of entrainment‐affected, diluted parcels from the cloud top. To evaluate this hypothesis, we employ eleven large‐eddy simulation models and one low‐dimensional model to simulate an idealized non‐precipitating stratocumulus cloud. Results show that most simulations capture the observed mixing characteristics, supporting the vertical circulation hypothesis. Moreover, simulations using the microphysics schemes that suffer less from numerical diffusion show better agreement with the observations. Another important finding is that the inter‐model spread is much smaller than in similar model intercomparison studies decades ago, likely reflecting improvements in model formulations and greater consistency in model configurations. Key Points Eleven large‐eddy simulations and one low‐dimensional simulation of an idealized non‐precipitating stratocumulus cloud are conducted The inter‐model spread is reduced compared to previous studies, likely due to improved models and more consistent model setups Most simulations capture the observed mixing characteristics in stratocumulus clouds, supporting the vertical circulation mixing hypothesis

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Aerosols / Aircraft observations / Atmospheric boundary layer / Boundary conditions / Boundary layers / Cloud microphysics / Cloud properties / Clouds / Entrainment / ENVIRONMENTAL SCIENCES / Geoengineering / homogeneous mixing / inhomogeneous mixing / Intercomparison / Microphysics / model intercomparison / non‐precipitating stratocumulus / Radiation / Simulation / Stratocumulus clouds / Vertical circulation