Cloud droplet diffusional growth in homogeneous isotropic turbulence: bin microphysics versus Lagrangian super-droplet simulations

Abstract. The increase in the spectral width of an initially monodisperse population cloud droplets homogeneous isotropic turbulence is investigated by applying a finite-difference fluid flow model combined with either Eulerian bin microphysics or Lagrangian particle-based scheme. forced variant so-called linear forcing method that maintains mean turbulent kinetic energy (TKE) and TKE partitioning between velocity components. latter important for maintaining quasi-steady supersaturation fluctuations drive width. We apply large computational domain (643 m3), one domains considered Thomas et al. (2020). simulations 1 m grid length are spirit implicit eddy simulation (ILES), is, small-scale dissipation provided numerics. This contrast to scaled-up direct numerical (DNS) applied Two intensities three different droplet concentrations considered. Analytic solutions derived Sardina (2015), valid case when integral timescale much larger than phase relaxation timescale, used guide comparison two techniques. approach reproduces scalings relatively well. Representing time more challenging because appropriately high resolution space needed. 0.5 µm only sufficient lowest concentration (26 cm−3). For highest (650 cm−3), order magnitude smaller size barely sufficient. not expected be high-TKE case, schemes represent similar departures. Finally, same all featuring low TKE, can compare point-by-point results. Such shows very close temperature water vapor values across differences simulated radii explained fundamental methodologies, diffusion small number particles microphysics.