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

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.

Climatology of the Vertical Profiles of Polarimetric Radar Variables and Retrieved Microphysical Parameters in Continental/Tropical MCSs and Landfalling Hurricanes

“…The radar microphysical retrieval techniques in ice are still in the process of evaluation and refinement using in situ microphysical airborne and surface observations. However, we believe that Equations 5-10 used in this study is a good first attempt because they produce results consistent with occasional in situ measurements in the proximity of the polarimetric radars (e.g., Murphy et al, 2020;Nguyen et al, 2019;Ryzhkov et al, 1998) and which are in a ballpark of the majority of airborne probes' measurements of IWC, D m , and N t reported in the literature (e.g., Finlon et al, 2019;Heymsfield et al, 2013Heymsfield et al, , 2015Heymsfield et al, , 2017Huang et al, 2021;Leroy et al, 2017;McFarquhar et al, 2007;Stechman et al, 2020). As mentioned before, our retrieved D m is the ratio of the fourth and third moments of the size distribution of equivolume diameters which is different from D mm or median volume (D mv ) size commonly estimated from in situ airborne microphysical probes which measure a maximal particle dimension.…”

“…French Guiana show generally higher values of IWC and N t and lower values of D mm in ice compared to the continental midlatitude MCSs Leroy et al (2017). reported IWC varying from 0.5 to 2.5 g m −3 and D mm in the range between 0.25 and 0.7 mm in the Darwin flights Huang et al (2021). found very similar ranges of IWC and D m during the flights in Cayenne and noted quite high total number concentrations N t between 100 and 200 L −1 .…”

“…in the areas of high-altitude ice in significant concentration with high IWC (HIWC; e.g., Fridlind et al, 2015;Huang et al, 2021;Stanford et al, 2017). One of the possible reasons for such persistent model biases is that the secondary ice production (SIP) may not be appropriately accounted for in the models (Korolev & Leisner, 2020).…”

The impacts of secondary ice production on microphysics and dynamics in tropical convection

“…conducted high-resolution simulations of tropical convection and found significant overestimates of radar reflectivity and underestimates of total ice crystal concentration (N i ). Adding SIP in high-resolution simulations, Huang et al (2022) found a significant improvement in simulated N i compared with the in situ observations.…”

“…Over the last few years, there have been many new efforts based on systematic studies of the effect of SIP on cloud microphysics with the help of cloud simulations (e.g., Phillips et al, 2017Phillips et al, , 2018Sullivan et al, 2018;Hoarau et al, 2018;Fu et al, 2019;Sotiropoulou et al, 2020Sotiropoulou et al, , 2021Dedekind et al, 2021;Hawker et al, 2021;Huang et al, 2021Huang et al, , 2022and others). Most of these modelling efforts have been focused on matching simulated moments of particle size distributions (PSDs) with those observed in situ.…”