Efficient ice multiplication from freezing raindrop fragmentation

Abstract Clouds are an important component of our climate system with their life cycle significantly influenced by ice formation. Measured ice concentrations in clouds often exceed the number of ice nucleating particles, a discrepancy attributed to secondary ice processes. However, these processes are not well understood or quantified. One such process, drop fragmentation upon freezing, involves significant uncertainty regarding the number of produced ice particles. Here we identify the occurrence of this process by combining in situ and remote sensing observations during a case of refreezing rain. By categorizing the in situ imagery, we estimate that between 1.2 and 6.1 secondary ice crystals are produced per drop. Drops between 0.5 and 1 mm in diameter were found to be particularly prone to breakup. These results highlight the effectiveness of droplet fragmentation and provide valuable insights for improving the representation of this process in atmospheric models.