Abstract
Abstract. Regions with high ice water content (HIWC), composed of mainly small ice crystals, frequently occur over convective clouds in the tropics. Such regions can have median mass diameters (MMDs) <300 µm and equivalent radar reflectivities <20 dBZ. To explore formation mechanisms for these HIWCs, high-resolution simulations of tropical convective clouds observed on 26 May 2015 during the High Altitude Ice Crystals – High Ice Water Content (HAIC-HIWC) international field campaign based out of Cayenne, French Guiana, are conducted using the Weather Research and Forecasting (WRF) model with four different bulk microphysics schemes: the WRF single‐moment 6‐class microphysics scheme (WSM6), the Morrison scheme, and the Predicted Particle Properties (P3) scheme with one- and two-ice options. The simulations are evaluated against data from airborne radar and multiple cloud microphysics probes installed on the French Falcon 20 and Canadian National Research Council (NRC) Convair 580 sampling clouds at different heights. WRF simulations with different microphysics schemes generally reproduce the vertical profiles of temperature, dew-point temperature, and winds during this event compared with radiosonde data, and the coverage and evolution of this tropical convective system compared to satellite retrievals. All of the simulations overestimate the intensity and spatial extent of radar reflectivity by over 30 % above the melting layer compared to the airborne X-band radar reflectivity data. They also miss the peak of the observed ice number distribution function for 0.1<Dmax<1 mm. Even though the P3 scheme has a very different approach representing ice, it does not produce greatly different total condensed water content or better comparison to other observations in this tropical convective system. Mixed-phase microphysical processes at −10 ∘C are associated with the overprediction of liquid water content in the simulations with the Morrison and P3 schemes. The ice water content at −10 ∘C increases mainly due to the collection of liquid water by ice particles, which does not increase ice particle number but increases the mass/size of ice particles and contributes to greater simulated radar reflectivity.
Highlights
High concentrations of small ice particles ingested into jet engines can cause power loss and damaging events (Lawson et al, 1998; Mason et al, 2006)
The Stanford et al (2017) Weather Research and Forecasting (WRF) simulations of four tropical deep convection events sampled during the HAIC-high ice water content (HIWC) Darwin campaign showed that three microphysics schemes produced larger median mass diameters (MMDs) for total condensed water content (TWC) > 1 g m−3 at temperatures between −10 and −40 ◦C and a high bias in convective radar reflectivity compared to observations
Radar reflectivity data from the X-band airborne research radar installed on the National Research Council (NRC) Convair 580 (Wolde et al, 2016), TWC measured by the IKP-2, and particle size distribution (PSD) measured by the 2D-S and Precipitation Imaging Probe (PIP) installed on the SAFIRE Falcon 20 and on the NRC Convair 580 are used to statistically evaluate the model simulations
Summary
High concentrations of small ice particles ingested into jet engines can cause power loss and damaging events (Lawson et al, 1998; Mason et al, 2006). The Stanford et al (2017) WRF simulations of four tropical deep convection events sampled during the HAIC-HIWC Darwin campaign showed that three microphysics schemes (one bin and two double-moment bulk schemes; Lynn et al, 2005; Thompson et al, 2008; Morrison et al, 2009) produced larger MMDs for TWC > 1 g m−3 at temperatures between −10 and −40 ◦C and a high bias in convective radar reflectivity compared to observations They hypothesized these differences resulted from errors in parameterized hydrometeor PSDs, single-ice-particle properties (e.g., shape and density), and parameterized microphysical processes.
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