Overview
This study introduces a novel approach for characterizing the continuous three-dimensional evolution of tropical cyclone (TC) warm cores throughout their life cycle. By applying Empirical Orthogonal Function (EOF) analysis to temperature anomaly data, a thermal phase space was established, enabling the visualization and quantification of key thermal features and their dynamic relationships with TC intensity changes.
Research Context
Previous understandings of the TC warm core have largely relied on statistical averages derived from soundings and satellite products. These methods provide a climatological thermal state but have been noted as insufficient for adequately characterizing the continuous, three-dimensional evolution of the warm core over a TC's entire life cycle.
Approach
The researchers employed Empirical Orthogonal Function (EOF) analysis. This technique was applied to three-dimensional temperature anomalies of Tropical Cyclones (TCs) within the Western North Pacific (WNP) region. The source data for these temperature anomalies was the ERA5 reanalysis dataset, covering the period from 1979 to 2024.
Data and Methodology
- Data Source: ERA5 reanalysis dataset.
- Geographic Scope: Western North Pacific (WNP).
- Time Period: 1979-2024.
- Analysis Technique: Empirical Orthogonal Function (EOF) analysis.
- Variables Analyzed: Three-dimensional temperature anomalies of TCs.
From the EOF analysis, three leading modes were identified. These modes were then used to define a three-dimensional Cartesian coordinate system using their corresponding principal components (PCs). Within this system, two phase parameters were established to define a thermal phase space. One parameter was designed to diagnose the vertical barotropic or baroclinic structure, while the second quantified the horizontal asymmetry of the thermal field.
Findings
The EOF analysis revealed that the three leading modes effectively capture primary characteristics of the TC thermal structure:
- First EOF Mode: Represents the typical warm core structure.
- Second EOF Mode: Characterizes vertical baroclinicity.
- Third EOF Mode: Captures the horizontal asymmetry of temperature anomalies.
The established three-dimensional Cartesian coordinate system, based on the first three principal components (PCs), enabled the definition of a thermal phase space. Within this space, trajectories were observed to capture both the intensity changes and the thermal structural evolution of TCs.
Why This Matters
The EOF-based phase diagrams offer a novel, objective tool for analyzing and diagnosing the structural thermodynamic characteristics of TCs and their intensity evolution. This is achieved by quantifying key thermal features and their dynamic relationships with TC intensity. This capability holds substantial potential for advancing both the theoretical understanding and operational forecasting of tropical cyclones.
Potential Applications
The developed methodology and the resulting phase diagrams offer potential for:
- Analyzing structural thermodynamic characteristics of TCs.
- Diagnosing TC intensity evolution.
- Advancing theoretical understanding of TCs.
- Improving operational forecasting of TCs.