Organization of SIP mechanisms among basic cloud types

 Clouds are a fundamental aspect of the Earth’s atmosphere. One of the major challenges in cloud-resolving models (CRM) is the formation and generation of new cloud ice particles from pre-existed ice and liquid. Based on the basic broad cloud types, it is helpful to distinguish between their fundamental microphysical properties. The four basic cloud types are defined as: (1) warm-based convective and stratiform clouds; and (2) cold-based convective and stratiform clouds. Recent studies of ice initiation in clouds have shown that most ice particles in the mixed-phase region of clouds are from secondary ice production (SIP) mechanisms but have generally concentrated on only one specific cloud system.

In this study, Aerosol-Cloud model (AC) is used. AC includes the four mechanisms of secondary ice production as follows: ice-ice collisional breakup, raindrop freezing fragmentation, Hallett-Mossop (HM) process and sublimational breakup. The intent is to generalize the contribution of each SIP mechanism among basic cloud types. The numerical simulations are performed using our AC for each cloud type and validated against in-situ cloud observations. The observational data is collected during four different cloud observational campaigns, each representing a contrasting cloud type than others.

Here, we study the contributions from each process of SIP (HM process, ice-ice collisional breakup, raindrop-freezing fragmentation and sublimational breakup) by performing control simulations of each basic cloud type. For the warm cloud convective clouds, the HM process prevails near freezing level and contributes significantly from 0 to -15^oC. In cold-based convective clouds, the ice-ice collisional breakup is the most dominating SIP mechanism in each cloud type. In warm-based stratiform clouds, the HM process dominates the contribution of ice in the -5 to -15^oC temperature range for updrafts up to 8 m/s. In the slightly warm-based convective clouds, the breakup due to ice-ice collision is the most dominating mechanism for the convective updrafts between -5^oC and cloud top temperatures.