Turbulence effects on Secondary Ice Production: Insights from Point-Particle Direct Numerical Simulations

Ice formation in clouds has long been studied through field measurements and also in laboratories under controlled conditions in cloud chambers. It has been frequently observed that ice particle concentration exceeds those of ice-nucleating particles by several orders of magnitude. This discrepancy suggests the involvement of Secondary Ice Production (SIP) via different mechanisms which remain only partially understood. Consequently, ice multiplication is only very crudely included in cloud models. Another fundamental characteristic of clouds is their turbulent nature. It is already known that turbulence plays a major role in the droplets growth but it could also be important for SIP-mechanisms as it affects the hydrometeors dynamics. In this work, we focus on SIP-mechanisms that involve collisions between particles. Using Direct Numerical Simulations (DNS) of homogeneous-isotropic turbulence at low Reynolds numbers with Lagrangian point-particle tracking allows us to study the influence of turbulence on the collision rate between particles and to compare it with the gravitational collision rate traditionally used in cloud modelling simulations. Furthermore, a model simulating the emission of secondary ice fragments when a collision is detected has been implemented in the code. This enables the analysis of how ice particle population evolves across different scenarios, helping to identify which parameters play a significant role and under which conditions a significant increase in ice concentration occurs. Preliminary results show that it is indeed possible to reproduce an ice explosion phenomenon and its magnitude and triggering moment depend on the initial concentration of ice particles and the turbulent Reynolds number.