Secondary Ice Production Invigorates Updrafts but Suppresses Precipitation in Simulated Subtropical Convection

Secondary ice production (SIP) is the process through which the number concentration of ice crystals increases to greatly exceed the number concentration of ice nuclei. Though recent field campaigns investigating SIP within deep convection have revealed important insights, the importance of different pathways (rime splintering, droplet fragmentation, ice-ice collisional breakup, sublimation fragmentation, droplet jet freezing) to total SIP is still uncertain. To investigate these unknowns, we simulated a subtropical deep convective cloud using Lagrangian cloud microphysics. 

Our results indicate that SIP produces stronger updrafts but reduces overall precipitation, reflecting a shift from condensational to vapor depositional growth. We find that droplet fragmentation dominates SIP early in the cloud’s development, while ice-ice collisional breakup becomes increasingly important later as large graupel forms. SIP also greatly increases ice water content and produces a more optically-thick anvil. Colder-temperature ice nuclei delay the onset of SIP and lead to higher overall precipitation despite lower total condensate. Increasing background cloud condensation nuclei (CCN) concentration reduces total precipitation, with a stronger relative reduction when SIP is present. Increasing CCN concentration increases ice water content, though this increase is non-monotonic with CCN concentration when SIP is present.

Our work supports the feasibility of modeling SIP within a Lagrangian microphysical framework, and highlights the complex interactions between SIP, background CCN concentration, and ice nuclei type.