Microphysical processes producing high ice water contents (HIWCs) in tropical convective clouds during the HAIC-HIWC field campaign: Evaluation of simulations using bulk microphysical schemes

Abstract

Regions with high ice water content (HIWC),composed of mainly small ice crystals, frequently occurover convective clouds in the tropics. Such regions can havemedian mass diameters (MMDs) <300 μm and equivalentradar refiectivities <20 dBZ. To explore formation mecha-nisms for these HIWCs, high-resolution simulations of trop-ical convective clouds observed on 26 May 2015 during theHigh Altitude Ice Crystals - High Ice Water Content (HAIC-HIWC) international field campaign based out of Cayenne,French Guiana, are conducted using the Weather Researchand Forecasting (WRF) model with four different bulk mi-crophysics schemes: the WRF single-moment 6-class micro-physics scheme (WSM6), the Morrison scheme, and the Pre-dicted Particle Properties (P3) scheme with one- and two-ice options. The simulations are evaluated against data fromairborne radar and multiple cloud microphysics probes in-stalled on the French Falcon 20 and Canadian National Re-search Council (NRC) Convair 580 sampling clouds at dif-ferent heights. WRF simulations with different microphysicsschemes generally reproduce the vertical profiles of temper-ature, dew-point temperature, and winds during this eventcompared with radiosonde data, and the coverage and evolu-tion of this tropical convective system compared to satelliteretrievals. All of the simulations overestimate the intensityand spatial extent of radar reflectivity by over 30% abovethe melting layer compared to the airborne X-band radar re-flectivity data. They also miss the peak of the observed icenumber distribution function for 0.1< Dmax <1 mm. Eventhough the P3 scheme has a very different approach repre-senting ice, it does not produce greatly different total con-densed water content or better comparison to other observa-tions in this tropical convective system. Mixed-phase micro-physical processes at -10 °C are associated with the over-prediction of liquid water content in the simulations with theMorrison and P3 schemes. The ice water content at -10 °C increases mainly due to the collection of liquid water by iceparticles, which does not increase ice particle number butincreases the mass/size of ice particles and contributes togreater simulated radar reflectivity.