November 6, 2019
Comparison of Eulerian bin and Lagrangian particle-based schemes in simulations of Pi Chamber dynamics and microphysics
Dr. Wojciech W. Grabowski (Mesoscale and Microscale Meteorology Laboratory, NCAR)
2019년 11월 12일 (화) 16:00
This presentation will discuss a comparison of simulations applying traditional Eulerian bin microphysics scheme with simulations using a novel particle-based Lagrangian approach to simulate CCN activation and droplet growth. The Eulerian bin microphysics solve the evolution equation for the spectral density function, whereas Lagrangian approach follows evolution in time and space of computational particles referred to as super-droplets. Each super-droplet represents a multiplicity of natural droplets that makes the Lagrangian approach computationally feasible. The two schemes apply identical representation of CCN activation and use the same droplet growth equation; these make the direct comparison between the two schemes practical. The study, the first of its kind, applies an idealized simulation setup motivated by laboratory experiments with the Pi Chamber and previous model simulations of the Pi Chamber dynamics and microphysics. Pi Chamber laboratory apparatus considers interaction between turbulence, CCN activation, and cloud droplet growth in moist Rayleigh-Benard convection driven by the temperature and moisture difference between homogeneous horizontal boundaries. Steady-state droplet spectra averaged over the entire chamber are similar, with the mean droplet concentration, mean radius and spectral width close in Eulerian and Lagrangian simulations. Small differences are explained by the inherent differences between the two schemes and their numerical implementation. However, as one might expect, the local droplet spectra differ substantially, again in agreement with the inherent limitations of the theoretical foundation behind each approach. Comparison between simulations, laboratory experiments, and previous theoretical studies of droplet growth in the turbulent environment will be discussed.