Development and Applications of a Novel Ice Crystal Trajectory Growth (ICTG) Model
Restricted (Penn State Only)
- Author:
- Laurencin, Chelsey
- Graduate Program:
- Meteorology and Atmospheric Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 10, 2022
- Committee Members:
- David Stensrud, Program Head/Chair
Jerry Harrington, Major Field Member
Manzhu Yu, Outside Unit & Field Member
Matthew Kumjian, Major Field Member
Anthony Didlake, Chair & Dissertation Advisor
Anders Jensen, Special Member - Keywords:
- ice crystal
microphysics
numerical modeling
ice physics
precipitation
Lagrangian modeling - Abstract:
- A major challenge in numerical weather prediction models is the ability to accurately simulate the microphysical structures and growth of ice hydrometeors in clouds. Eulerian bulk microphysics schemes in these models tend to obscure the properties and evolution of individual ice crystals, which often result in inaccurate simulations of storm precipitation features. To address this issue, this PhD dissertation project seeks to develop a novel Lagrangian ice crystal trajectory growth (ICTG) model that tracks the evolving properties of ice crystals along their trajectories and limits the assumptions on the distributions that crystals must follow. The model is evaluated on a quasi-idealized squall line simulation, where we test the sensitivity of the trajectory simulations to initial crystal size, location relative to the convective updraft, growth parameterization, and crystal mass distribution hypothesis. Simulations are conducted using both the Thompson and ISHMAEL microphysics schemes. The sensitivity tests show that the facet-based mass distribution hypothesis is needed to produce realistic trajectories, and ledge nucleation growth is needed to produce thin, faceted crystals. Crystals initialized in the ISHMAEL simulation are larger and therefore fall out closer to the leading convective line, whereas the initially smaller crystals in the Thompson simulation are mostly transported to the stratiform region. These differences in initial size contribute to differences in the degree of rearward transport of the crystals, the amount of growth occurring in the stratiform region, and the distributions that the crystal properties follow. For both simulations, the crystals growing in the stratiform region grow to sizes comparable to the initially larger crystals falling out in the convective region, supporting past observations of enhanced dendritic growth in the stratiform region of squall lines. Proof-of-concept simulations using Hurricane Harvey (2017) show that ice crystals initialized in the eyewall reach the melting level in above the reflectivity maximum below the melting level, consistent with past observational studies. The consistency of the spatial distributions of ice crystal properties and trajectories with past studies suggests that the ICTG model can be used as a tool for future studies examining the microphysical growth processes contributing to the precipitation structure in various glaciated clouds.