An Investigation of Ice Production Mechanisms in Small Cumuliform Clouds Using a 3D Model with Explicit Microphysics. Part II: Case Study of New Mexico Cumulus Clouds

Abstract

A new 3D model with explicit liquid- and ice-phase microphysics and a detailed treatment of ice nucleation and multiplication processes is applied to study ice formation and evolution in cumulus clouds. Simulation results are compared with in situ observations collected by the National Center for Atmospheric Research King Air aircraft in a cloud over the Magdalena Mountains in New Mexico on 9 August 1987. The model reproduces well the observed cloud in terms of cloud geometry, liquid water content, and concentrations of cloud drops and ice particles (IP). Primary ice nucleation is shown to produce IP in concentrations on the order of 103 m?3 (1 L?1) once the cloud top reaches ?10° to ?12°C. At mature and early dissipating stages of cloud development, ice production is dominated by the rime-splintering (Hallett?Mossop) mechanism, which in some regions generates up to 5 ? 104 m?3 (50 L?1) IP in about 10 min. The predicted maximum of IP concentration is in agreement with observations. The sampling techniques used in the field study, however, do not provide an adequate estimate for the splinter production rate, which exceeds 100 m?3 s?1 in the model.