Interaction and orientation dynamics of charged columnar ice crystals

Understanding the interaction and settling behaviour of ice crystals in clouds is essential for improving remote sensing retrievals and accurately modelling the Earth's radiation budget. The orientation distribution of these crystals also gives rise to distinctive optical phenomena such as sundogs and light pillars. In this study, we examine the interaction dynamics of two charged columnar ice crystals settling under gravity, a morphology commonly observed in atmospheric ice. We first use slender body theory, appropriate for high aspect ratio particles, to characterise the hydrodynamic interactions between two settling rods in a quiescent fluid. This approach captures the mutual disturbance flows that lead to changes in their orientation and settling paths. Building on this, we analyse how electrostatic forces further modify their trajectories and relative alignment. Our results show that electrostatic interactions can significantly influence particle orientation: the resulting electrostatic torque may reinforce or counteract the hydrodynamic tendency for alignment, depending on the particles' relative positions and orientations. These findings provide fundamental insight into the microphysical behaviour of ice crystals in low turbulence intensity environments, with implications for cloud optics and particle-resolved modelling.