Spike formation on supercooled water droplets collected by micrometer ice crystals

Abstract This study presents evidence of spike formation in droplets freezing on small ice crystals, measuring only a few micrometers in size. Spike formation was exclusively observed on columnar ice crystals formed at approximately −6°C, while no such phenomena were detected on hexagonal plate crystals formed at around −22°C. These findings are in agreement with previous research, which indicates that spike formation requires droplet freezing near the melting point. The formation of spikes during the early riming stages holds significant implications, as these structures can eject new ice particles. This study suggests that the Hallett–Mossop mechanism may activate at the onset of riming, challenging the conventional view that millimeter‐sized graupel particles are necessary for splinter ejection. This mechanism has profound implications for amplifying ice particle concentrations in mixed‐phase clouds, potentially influencing precipitation processes, atmospheric dynamics, and global climate systems.