The Impact of Scalar Forcing on Cloud Microphysics Based on Direct Numerical Simulations

Direct numerical simulations of turbulence-cloud-aerosol interactions have gained traction recently. The models are based on homogeneous and isotropic turbulence, the Eulerian transport of scalar quantities and the Lagrangian tracking of cloud droplets and aerosol particles. It is well known that turbulence decays unless a production mechanism exists. Although momentum forcing is common, scalar forcing has not received enough attention. In this work, we investigate two scalar forcing mechanisms, in the spectral and physical space, respectively. The scalars of interest in the present study are temperature, water vapor mixing ratio, and supersaturation. The statistics of forced scalar fields such as the probability density functions, and the spectra are analyzed. The impacts of scalar forcing on cloud and aerosol microphysics are also investigated. Our results show that forcing leads to more fluctuations in the scalar fields and broadens their probability distributions. At the same time, the rate of evaporation decreases. The scalar spectra for forced and unforced cases are different at small scales.