Numerical simulations of aerosol scavenging in deep convective clouds using a three-moment microphysical scheme

We present a novel parameterization for aerosol particle (AP) hydrometeor interactions in three-moment microphysics scheme in a three-dimensional numerical model. Physical processes such as AP scavenging, nucleation and their wash-out by precipitation are being investigated using this approach. APs investigated had properties of silver-iodide (AgI) and were of submicron sizes.
Firstly, we developed and calculated spectral scavenging coefficients for all known scavenging mechanisms, including: Brownian and turbulent diffusion, inertial impaction, directional interception, thermophoresis, diffusiophoresis and electroscavenging. The calculation and analysis of individual scavenging processes was done using parcel models in which cloud droplets, raindrops, ice crystals, snow and graupel were participating in AP collection. For electroscavenging we assumed a Boltzmann charge distribution on APs and hydrometeors were either positively or negatively charged. Results were similar for both the positively charged and negatively charged hydrometeors. For cloud droplets, which contribute to AP scavenging the most, the trajectory method was also implemented. This allowed the calculations of kernels due to image charge alongside the Coulomb force. For other scavenging processes and other hydrometeors, the flux method was used.
Secondly, all the mentioned processes were implemented into a three-moment microphysics scheme within a three-dimensional, non-hydrostatic Advanced Regional Prediction System (ARPS) model (Vučković et al., 2022, 2023). Ice nucleation parameterization for silver-iodide APs was also implemented (Vučković et al., 2022, 2025). Prognostic equations for the number and the mass of APs in the air and in all hydrometeor categories were developed.
The proposed methodology allows for the explicit tracing of aerosols through different hydrometeor species due to microphysical processes which enables the numerical investigation of a chain of events regarding cloud seeding applications. Our analysis indicates that electroscavenging has a dominant effect on AP collection for medium and large particles from the size range we considered, especially for highly electrified clouds. Brownian diffusion is primarily responsible for the removal of small APs. Graupel and raindrops have the least effect on AP collection, while cloud ice and snow can have effects comparable to cloud droplets in highly electrified clouds.
The proposed software could have the potential to be used in both cloud seeding efficiency studies and operationally.

References:
Vučković, V., D. Vujović, and A. Jovanović, 2022: Aerosol parameterisation in a three-moment microphysical scheme: Numerical simulation of submicron-sized aerosol scavenging. Atmos Res, 273, 106148, https://doi.org/10.1016/j.atmosres.2022.106148.
Vučković, V., D. Vujović, and D. Savić, 2023: Influence of electrostatic collection on scavenging of submicron-sized aerosols by cloud droplets and raindrops. Aerosol Science and Technology, 57, https://doi.org/10.1080/02786826.2023.2251551.
Vučković, V., Vujović, D., Savić, D., & Filipović, L. 2025: Impact of electro- collection and ice nucleation on aerosol scavenging. Aerosol Science and Technology, 1–21. https://doi.org/10.1080/02786826.2024.2441289.

Acknowledgment:

This research was supported by the Science Fund of the Republic of Serbia, No. 7389, Project Extreme weather events in Serbia - analysis, modelling and impacts” - EXTREMES

Poster: link