Determination of a diurnal cycle in subtropical cyclones using persistent homology.

This study investigates the presence of a diurnal cycle in subtropical cyclones using persistent homology. While diurnal cycles in tropical cyclones are well-characterized as cyclic temperature pulses propagating outward from the center, their existence in subtropical cyclones remains uncertain.

To address this, the research employs topological data analysis (TDA) methods, including zero-order homology and merge trees, to analyze the radial temperature profile. The radial temperature profile is computed as an integral over circular regions around the cyclone center, allowing for comparison across time. Differences between profiles are thresholded, distance transformations are applied, and sub-level sets with merge trees are used to track dominant temperature structures. The maximum persistence of these structures is analyzed using Fourier transform to identify cyclic behavior.