Comment on egusphere-2025-3158

Résumé fourni par la source

Abstract. Secondary ice production (SIP) plays an important role in tropical deep convection, yet its representation in models remains uncertain. This study incorporates multiple SIP mechanisms, including droplet fragmentation (Mode 1 and Mode 2) and ice–ice collisional breakup, into the CASIM microphysics scheme of the UK Met Office Unified Model, and evaluates their impacts through a real-case simulation of a Hector thunderstorm. SIP enhances ice number concentration in upper cloud layers, with values up to 3 orders of magnitude higher than the no-SIP case, particularly above −10 °C. Ice water content (IWC) increases by a factor of 3–5 in the anvil region, contributing to more extensive upper-level cloud coverage. These microphysical changes reduce outgoing longwave radiation (OLR) by ~3.2 W m−2 (1.3 %) and increase outgoing shortwave radiation (OSR) by ~4.5 W m−2 (1.8 %) over a 6-hour analysis period and a 110 km × 110 km domain. SIP modifies precipitation structure, enhancing local rainfall near the convective core while reducing domain-averaged precipitation by ~8 %. Peak rainfall rates remain only slightly affected, consistent with the minor changes (<1 m s−1) in maximum updraft velocity. Among the tested mechanisms, ice–ice collisional breakup shows negligible impact under warm, graupel-sparse tropical conditions. Ensemble experiments confirm that these effects are robust and exceed the influence of meteorological variability. These results highlight the importance of representing SIP processes in cloud-resolving models of tropical convection and accounting for their environmental dependence.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.