An Analysis of Hurricane Eyewall Ice Using a Novel Lagrangian Trajectory and Growth Model

Abstract Ice crystals in tropical cyclones (TCs) remain infrequently observed and difficult to model using Eulerian microphysics parameterizations. To better understand TC eyewall ice crystal processes, the Ice Crystal Trajectory Growth (ICTG) model, previously applied to an idealized squall line, was used to simulate Lagrangian ice crystal trajectories in a Weather Research and Forecasting (WRF) model simulation of Hurricane Harvey (2017). ICTG includes laboratory‐informed growth equations capable of simulating complex crystal morphologies and is used to assess how initial altitude, radius, and size influence crystal growth and advection. We introduce an initialization technique where the initial crystal locations and sizes best match WRF microphysical fields. Results showed that the initial crystal altitude was most important in determining final mass, shape, location, and likelihood of sublimation; initial size and radial distance played secondary but noticeable roles. The largest final masses began at 8 km altitude and grew predominantly in the dendritic growth zone (−12 to −18C) resulting in plate‐like crystals. Crystals that accumulated the most rime mass began between 7 and 9 km altitude, while crystals above 9 km experienced more radial outward transport often leading to sublimation particularly for smaller crystals. Results using a “super‐particle” method showed that most of the ice mass reached the melting level within or just beyond the eyewall with a large diversity of crystal shapes and sizes. The greatest radial extent of ice was 150 km, supporting recent research suggesting the eyewall is not a dominant source of TC outflow condensate.