Global Importance of Secondary Ice Production

Measured ice crystal number concentrations are often orders of magnitude higher than the number concentrations of ice nucleating particles, indicating the existence of secondary ice production (SIP) in clouds. Here, we present the first study to examine the global importance of SIP through the droplet shattering during freezing of rain, ice-ice collision fragmentation, and rime splintering, using a global climate model. Our results show that SIP happens quite uniformly in the two hemispheres and dominates the ice formation in the moderately cold clouds with temperatures warmer than -15 degrees C. SIP decreases the global annual average liquid water path by -14.6 g m(-2) (-22%), increases the ice water path by 8.7 g m(-2) (23%), improving the model agreement with observations. SIP changes the global annual average shortwave, longwave, and net cloud forcing by 2.1, -1.0, and 1.1 W m(-2), respectively, highlighting the importance of SIP on cloud properties on the global scale.

Automated summary

SIP occurs uniformly in both hemispheres and dominates ice formation in moderately cold clouds. It affects global water paths and cloud forcing, improving model agreement with observations.