Owing to its low-frequency phase oscillation, the MJO is often thought to be less chaotic and more predictable than the mid-latitude synoptic disturbances. The prevailing MJO theories are basically linear, neglecting the nonlinear effects. However, using robust chaos detection technique, we demonstrate that the MJO amplitude evolution is deterministic chaotic, signifying the importance of the nonlinear dynamics.
Combining delay embedding and Koopman operator theory, we show that the evolution of MJO amplitude can be split into periodic part that has discrete spectra and aperiodic part that has continuous spectra. We find that the discrete spectra and the related periodic obits construct the key components of the MJO amplitude evolution, while the continuous spectra, representing the chaotic behavior, is produced by mixing of the discrete spectra through nonlinear interaction. By comparing the discrete spectra, we further reveal the coupling between the MJO amplitude evolution and background moisture.
The results shed light on how to resolve nonlinear dynamics in climate system and provide a practical way for detecting potential nonlinear coupling between different subsystems.
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