On the Existence of Low-Dimensional Chaos of the Tropical Cyclone Intensity in an Idealized Axisymmetric Simulation

This study examines the potential limit in predicting tropical cyclone (TC) intensity under idealized condi-tions. Using the phase-space reconstruction method for TC intensity time series obtained from the CM1 idealized simula-tions, it is found that CM1 axisymmetric dynamics contain low-dimensional chaos at the maximum intensity equilibrium. Examination of several attractor invariants including the largest Lyapunov exponent, the Sugihara-May correlation, and the correlation dimension captures a consistent range of the chaotic attractor dimension between 4 and 5 for TC intensity at the maximum intensity equilibrium. In addition, the intensity error doubling time estimated from the largest Lyapunov exponent is roughly 1-3 h, which accords with the decay time obtained from the Sugihara-May correlation. Furthermore, the findings in this study reveal a relatively short TC intensity predictability limit for CM1, which is -3-9 h based on the maximum tangential wind but noticeably longer for the minimum central pressure (-12-18 h) after reaching the mature stage. So long as the traditional metrics for TC intensity such as the maximum surface wind or the minimum central pres-sure is used for intensity forecast, our results support that TC intensity forecast errors will not be reduced indefinitely in any model, even in the absence of all model and observational errors. As such, the future improvement of TC intensity forecast should be based on different metrics beyond the absolute intensity errors that are currently used in real-time inten-sity verification.