Preprints
https://doi.org/10.5194/acp-2021-781
https://doi.org/10.5194/acp-2021-781

  27 Oct 2021

27 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Microphysical processes producing high ice water contents (HIWCs) in tropical convective clouds during the HAIC-HIWC field campaign: dominant role of secondary ice production

Yongjie Huang1, Wei Wu2, Greg M. McFarquhar2,3, Ming Xue1,3, Hugh Morrison4, Jason Milbrandt5, Alexei V. Korolev6, Yachao Hu2,7, Zhipeng Qu6, Mengistu Wolde8, Cuong Nguyen8, Alfons Schwarzenboeck9, and Ivan Heckman6 Yongjie Huang et al.
  • 1Center for Analysis and Prediction of Storms, University of Oklahoma, Norman, OK, USA
  • 2Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, OK, USA
  • 3School of Meteorology, University of Oklahoma, Norman, OK, USA
  • 4Mesoscale and Microscale Meteorology Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 5Environment and Climate Change Canada, Dorval, Quebec, Canada
  • 6Environment and Climate Change Canada, Toronto, ON, Canada
  • 7Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
  • 8National Research Council Canada, Ottawa, Canada
  • 9Université Clermont Auvergne, CNRS, UMR 6016, Laboratoire de Météor Physique, Clermont-Ferrand, France

Abstract. High ice water content (HIWC) regions in tropical deep convective clouds, composed of high concentrations of small ice crystals, were not reproduced by Weather Research and Forecasting (WRF) model simulations at 1-km horizontal grid spacing using four different bulk microphysics schemes (i.e., 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) for conditions encountered during the High Altitude Ice Crystals (HAIC)-HIWC experiment. Instead, overestimates of radar reflectivity and underestimates of ice number concentrations were realized. To explore formation mechanisms for large numbers of small ice crystals in tropical convection, a series of quasi-idealized WRF simulations varying the model resolution, aerosol profile, and representation of secondary ice production (SIP) processes are conducted based on an observed radiosonde released at Cayenne during the HAIC-HIWC field campaign. The P3 two-ice scheme, which has two “free” ice categories to represent all ice-phase hydrometeors, is used. Regardless of the horizontal grid spacing or aerosol profile used, without including SIP processes the model produces total ice number concentrations about two orders of magnitude less than observed at −10 °C and about an order of magnitude less than observed at −30 °C, but slightly overestimates the total ice number concentrations at −45 °C. Three simulations including one of three SIP mechanisms separately (i.e., the Hallett-Mossop mechanism, fragmentation during ice–ice collisions, and shattering of freezing droplets) also do not replicate observed HIWCs, with the results of the simulation including shattering of freezing droplets most closely resembling the observations. The simulation including all three SIP processes successfully produces HIWC regions at all temperature levels remarkably consistent with the observations in terms of ice number concentrations and radar reflectivity, which is not replicated using the original P3 two-ice scheme. This simulation shows that primary ice production plays a key role in generating HIWC regions at t < 30 min at temperatures < −40 °C, shattering of freezing droplets dominates ice particle production in HIWC regions at temperatures > − 15 °C during the early stage of convection, and fragmentation during ice–ice collisions dominates at temperatures > −15 °C during the later stage of convection and at temperatures < −20 °C over the whole convection period. This study confirms the dominant role of SIP processes in the formation of numerous small crystals in HIWC regions.

Yongjie Huang et al.

Status: open (until 10 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-781', Minghui Diao, 22 Nov 2021 reply
  • RC2: 'Comment on acp-2021-781', Emma Järvinen, 29 Nov 2021 reply

Yongjie Huang et al.

Yongjie Huang et al.

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Short summary
Numerous small ice crystals in tropical convective storms are difficult to detect and could be potentially hazardous for commercial aircraft. Previous numerical simulations failed to reproduce this phenomenon and hypothesized that key microphysical processes are still lacking in current models to realistically simulate the phenomenon. This study uses numerical experiments to confirm the dominant role of secondary ice production in the formation of these large numbers of small ice crystals.
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