An Investigation of Ice Microphysics in Tropical Cyclones Using the Ice Crystal Trajectory Growth (ICTG) Model

open_access
Open Access
Author:
Rojas, Bruno
Graduate Program:
Meteorology and Atmospheric Science
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 17, 2026
Committee Members:
Paul Markowski, Program Head/Chair
Jerry Harrington, Major Field Member
John Peters, Major Field Member
Anthony Didlake, Chair & Dissertation Advisor
David Williams, Outside Unit & Field Member
Keywords:
Tropical Cyclones
Microphysics
Abstract:
Tropical cyclone (TC) intensity forecasts, particularly rapid intensification (RI), remain a significant challenge for numerical weather prediction (NWP) models. One of the primary drivers of TC intensification is latent heat release associated with the formation and growth of cloud and precipitation particles, which contributes to pressure falls within the storm. Ice particles are of particular interest because they influence TCs through their radiative properties, cloud structures, and complex microphysical processes, yet remain difficult to observe and model. Ice crystal properties such as mass, aspect ratio, and density depend on the thermodynamic and kinematic environments experienced throughout their lifetimes. Conventional Eulerian models cannot track these evolving properties and instead rely on simplified representations. This dissertation seeks to improve understanding of TC ice processes through the use of the Ice Crystal Trajectory Growth (ICTG) model, a Lagrangian framework developed by \cite{Laurencin2023_thesis} that simulates crystal growth and evolution along particle trajectories. The ICTG model was applied to a Weather Research and Forecasting (WRF) simulation of Hurricane Harvey (2017), a major hurricane that underwent rapid intensification prior to landfall. Improvements to ICTG included constraining particle initialization to regions of active ice production and sampling a broader range of initial particle sizes consistent with the WRF microphysics scheme. The model was applied to the eyewall, where microphysical processes are closely linked to storm intensification. Results showed that initial altitude was the primary factor controlling crystal trajectories and properties, followed by radial location and initial size. Crystals originating near 8 km altitude achieved the largest masses and frequently developed plate-like habits within the dendritic growth zone. Analysis of shear-induced storm asymmetries revealed that vortex tilt promoted sublimation of crystals in the eye left-of-shear, while outward transport produced enhanced heating at large radii in the upshear-right quadrant. During RI, a deepening tangential wind vortex and stronger outflow increased crystal residence times and radial transport distances. The simulations also identified a seeder–feeder process in which eyewall-generated ice enhanced latent heating in nearby rainbands. These findings provide new insight into TC ice processes and can help improve the representation of microphysics in NWP models.