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

A new 3D model with explicit liquid- and ice-phase microphysics and a detai led 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 At mospheric Research King Air aircraft in a cloud over the Magdalena Mountain s in New Mexico on 9 August 1987. The model reproduces well the observed cl oud in terms of cloud geometry, liquid water content, and concentrations of cloud drops and ics particles (IP). Primary ice nucleation is shown to pro duce IP In concentrations on the order of 10(3) m(-3) (I L-1) once the clou d top reaches - 10 degrees to - 12 degrees C. At mature and early dissipati ng stages of cloud development, ice production is dominated by the rime-spl intering (Hallett-Mossop) mechanism, which in some regions generater, up to 5 x 10(4) m(-3) (50 L-1) IP in about 10 min. The predicted maximum of IP c oncentration is in agreement with observations. The sampling techniques use d in the held study. however, do not provide an adequate estimate tor the s plinter production rate, which exceeds 100 m(-3) s(-1) in the model.