Impacts of Secondary Ice Production on the Microphysics and Dynamics of Deep Convective Clouds in Different Environments

Abstract. This study numerically investigates the impact of secondary ice production (SIP) on cloud microphysical, and diabatic properties in continental and marine deep convective clouds (DCCs). Four cases are simulated using the Icosahedral Nonhydrostatic (ICON) model with a 2-moment cloud microphysics scheme at 2 km horizontal grid spacing. ICON forms secondary ice via rime splintering, fragmentation during raindrop freezing (RDF), ice-ice collision, and sublimational breakup. A more detailed RDF scheme is implemented and compared to the existing simpler scheme. Both schemes predict similar overall properties in the simulated DCCs, suggesting that a simpler scheme can represent RDF in numerical models.

In the simulated DCCs, SIP processes accurately reproduce observed ice number concentrations. SIP enhances ice numbers by 10–10³, decreasing (increasing) supercooled-liquid (ice) mass by 10–30 %, leading to sustained upper-level glaciation and prolonged convective activity. Including SIP increases surface precipitation by 4 % in marine DCCs, with no significant change in continental DCCs. SIP enhance longwave absorption in the mixed-phase region and increased (20 % in continental and 40 % in marine DCCs) cloud radiative heating. SIP intensifies latent heating by up to 20 %, reaching 20–40 K d⁻¹ in continental and 80 K d⁻¹ in marine DCCs, from increased depositional growth of ice particles. This enhanced diabatic heating increases buoyancy, leading to a 10 % rise in mean vertical velocity, strengthening convection. These findings highlight the pivotal role of SIP in shaping the microphysical structure and dynamical behavior of deep convection, highlighting the need for its representation in numerical models.