Chen (2025) Mechanisms of Topographic Steering and Track Morphology of Typhoon-like Vortices over Complex Terrain: A Dynamic Model Approach

Identification

• Journal: Atmosphere
• Year: 2025
• Date: 2025-12-31
• Authors: Hung-Cheng Chen
• DOI: 10.3390/atmos17010060

Research Groups

School of Mechatronics and Intelligent Manufacturing, Huanggang Normal University, China.

Short Summary

This study investigates how complex terrain steers typhoon-like vortices, revealing that vortex intensity, terrain geometry, and interaction time govern track morphology and predictability. It introduces a diagnostic framework to map zones of high track divergence and convergence, providing a physically interpretable basis for understanding forecast uncertainty over mountainous regions like Taiwan.

Objective

• To develop a quantitative framework for diagnosing and interpreting typhoon track sensitivity over complex terrain using a PV-based dynamic model.
• To identify and quantify the spatial structure of track predictability, delineating Track Diverging Zones (TDZ), Track Converging Zones (TCZ), and a Boundary Track (BT).
• To clarify the controlling roles of vortex intensity, impinging angle, and terrain geometry in shaping track morphology and transitions between different behaviors.
• To compare predictability characteristics over idealized and realistic topography, separating generic features from those specific to Taiwan's orography.
• To provide a theoretical basis for improving typhoon track forecasting by informing forecasters about intrinsically more or less reliable scenarios.

Study Configuration

• Spatial Scale: Idealized bell-shaped mountain (zonal half-width: 40 km, meridional half-width: 120 km, maximum height: 3000 m, major axis orientation: 15°). Realistic topography of Taiwan Island (Central Mountain Range rising above 3 km, width approximately 150 km, steep eastern escarpment, rugged multi-peaked spine).
• Temporal Scale: Simulation durations ranging from 16.67 hours to 50.00 hours, depending on the impinging angle and terrain interaction time. Vortex intensity decay timescale (T_d) of 15 hours.

Methodology and Data

• Models used: Potential Vorticity (PV)-based dynamic model, which incorporates topographic steering through a Meridional Adjusting Velocity (MAV) and a Topographic Adjusting Parameter (α). The model uses a point-vortex trajectory integration scheme with finite-core corrections and a Forward Euler time-stepping method. An exponential decay model for vortex intensity is incorporated for realistic simulations.
• Data sources: Idealized bell-shaped mountain defined by an equation. Realistic Taiwan topography derived from a digital elevation model. Model validation in previous work used high-resolution best-track data from the Central Weather Administration (CWA) for Typhoon Soudelor (2015).

Main Results

• Typhoon track evolution over complex terrain is governed by a triad of controls: vortex intensity (quantified by the topographic adjusting parameter α), terrain geometry (quantified by the rate of change in topographic height d h B * / d t * ), and interaction time (modulated by the impinging angle γ).
• A Track Divergence Percentage (td) diagnostic framework identifies distinct predictability regimes: Track Diverging Zones (TDZ) where tracks rapidly spread (td > 0, up to >700% in idealized, >4000% in realistic simulations), Track Converging Zones (TCZ) where tracks cluster (t_d < 0, approaching -100%), and a Boundary Track (BT) separating these regimes.
• Shallower impinging angles significantly amplify track deflection and divergence, leading to extreme track morphologies including terrain capture and cyclonic looping for stronger vortices in idealized settings.
• Realistic Taiwan topography introduces fine-scale oscillations onto tracks due to its rugged, multi-peaked nature, and vortex intensity decay systematically damps the lee-side northward recovery, altering track morphology compared to constant-intensity idealized simulations.
• Kinematic analysis shows that vortex drifting speed variations correlate with track sensitivity; near-stagnation points (where speed drops to 2–4 m/s) lead to explosive track divergence due to prolonged interaction time.

Contributions

• Development of a novel, physically interpretable diagnostic framework (Track Divergence Percentage, TDZ, TCZ, BT) to quantify and map typhoon track sensitivity and predictability over complex terrain.
• Systematic identification and quantification of the three primary control mechanisms (vortex intensity, terrain geometry, interaction time) governing typhoon track morphology and predictability.
• Demonstration of how realistic topographic complexity and vortex intensity decay modulate the fundamental predictability structure, revealing emergent phenomena like hyper-sensitivity and terrain capture.
• Providing a theoretical basis for interpreting ensemble spread and assessing forecast confidence in operational typhoon forecasting over mountainous regions, particularly for landfalling typhoons in Taiwan.

Funding

• National Natural Science Foundation of China, Grant No. 42275064.

Citation

@article{Chen2025Mechanisms,
  author = {Chen, Hung-Cheng},
  title = {Mechanisms of Topographic Steering and Track Morphology of Typhoon-like Vortices over Complex Terrain: A Dynamic Model Approach},
  journal = {Atmosphere},
  year = {2025},
  doi = {10.3390/atmos17010060},
  url = {https://doi.org/10.3390/atmos17010060}
}