Numerical simulation of stable or unstable stratified cloud-mixing region

In this work, we investigate the evolution of a two-phase system composed of clear air and unsaturated water vapor, including advected Lagrangian particles as water droplets. This, as a whole, represents an idealized cloud–clear air configuration. The flow evolves within a decaying, shearless, and stratified turbulent field, where both stably and unstably stratified conditions are considered. This configuration allows us to isolate and analyze the fundamental mechanisms governing the system and the interaction between microscale turbulence and buoyancy-driven motions. Significant focus is placed on the role of buoyancy in generating wavelike responses in the velocity and thermodynamic fields. These responses are examined and compared to the theoretical behavior of internal gravity waves (IGWs), with attention to the amplification or damping of vertical velocity fluctuations as a function of the intensity of stratification and initial conditions. To achieve this, high-resolution direct numerical simulations (DNS) are performed using a pseudo-spectral solver with two-phase coupling, including droplet population dynamics in the cloudy region. The initial conditions consist of two turbulent regions with different turbulent kinetic energies (TKE), smoothly connected through a transition layer, thereby mimicking a realistic cloud–clear air interface. Following the numerical method, a spectral analysis is conducted in both spatial and temporal domains to identify the dominant wave structures and their interactions with the turbulent background. The balance between turbulence and gravity is studied to unravel the processes that control cloud–clear air mixing and the emergence of coherent wave patterns where possible. The results highlight the dynamics of stratified turbulence and its role in atmospheric circulation, implying a better understanding of cloud physics.