A methodology of tracking transitioning Cyclones

'Cyclone transition' is a process in which either a tropical cyclone or an extratropical cyclone undergoes a fundamental dynamic and thermodynamic transformation. A 'tropical transition' is a process in which a cold-core extratropical cyclone transforms to a warm-core tropical cyclone, while 'extratropical transition' refers to the opposite mechanism. The transition process is gradual, with no sharp defining threshold representing its commencement or completion. This study develops and explores a methodology of identifying tropical transition and extratropical transition events. Using the 1.50 ERA-Interim reanalysis dataset over the period from 1989 to present, cyclone tracks are derived using The Melbourne University Tracking Scheme. The average temperature difference between the cyclone core and an environmental ring, set at a distance corresponding to the cyclones size, is then calculated throughout the troposphere during the life cycle of the cyclone. This difference represents the index or phase of the cyclone relative to its immediate environment. The lack of a complete cyclone transition climatology and the uncertainty behind the transition process is the motivation for this research, with the overarching aim of placing these systems in climatic perspective. This methodology seeks to create the foundations for further cyclone research.