Alternative Interpretation of MJO teleconnection via dynamical mode decomposition

Abstract The Madden-Julian Oscillation (MJO) is the key tropical variability having widespread impact on worldwide extreme events via its global teleconnections. Yet, the dynamics of the MJO teleconnection are not fully understood, especially on how MJO teleconnection interacts with extratropical climate variability and how it responds to various MJO propagation speeds. In this study, we present an alternative dynamical view of MJO teleconnection using the method of dynamical mode decomposition (DMD). The DMD can identify spatiotemporal coherent structures from high-dimensional nonlinear flow. When applying this method to tropospheric upper-level atmosphere, the dynamics of unforced motion can be spectrally decomposed into DMD modes and the MJO teleconnection can be interpreted as spatiotemporal resonance between these modes and the forcing by MJO. As some DMD modes have regional spatial features resembling some climate variabilities, such as the Pacific North American (PNA) and North Atlantic Oscillation (NAO), the interaction between these modes and the MJO forcing explains how MJO-forced circulation modulates those climate variabilities on intraseasonal time scales. The analysis also explains how MJO teleconnection responds to fast and slow MJOs, in terms of temporal resonance between the DMD modes and the MJO’s propagation speed. The study further compares this alternative view of MJO teleconnection in terms of DMD with the classical view in terms of dynamics associated with the vorticity equation. The results here have implications for model simulation and prediction of MJO teleconnections.