Identification of the Madden–Julian Oscillation With Data‐Driven Koopman Spectral Analysis
Abstract
The Madden‐Julian Oscillation (MJO), the dominant mode of tropical intraseasonal variability, is commonly identified using the realtime multivariate MJO (RMM) index based on joint empirical orthogonal function (EOF) analysis of near‐equatorial upper and lower level zonal winds and outgoing longwave radiation. Here, in place of conventional EOFs, we apply an operator‐theoretic formalism based on dynamic systems theory (the Koopman operator) to extract an analog to RMM that exhibits certain features that refine the characterization and predictability of the MJO. In particular, the spectrum of Koopman operator eigenfunctions, with eigenvalues corresponding to mode periods, contains a leading intraseasonal mode with period of ∼50 days. Moreover, the amplitude of this leading intraseasonal eigenfunction exhibits a seasonal modulation clearly peaked in boreal winter. Finally, the phase space formed by the complex Koopman MJO eigenfunction exhibits a smoother temporal evolution and higher degree of autocorrelation than RMM, which may contribute to enhanced predictive skill.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- May 17, 2023
- Source ID
- 10.1029/2023gl102743
Entities
People
- Benjamin R Lintner
- Dimitrios Giannakis
- Joanna Sławińska
- Max Pike
Organizations
- Dartmouth College
- Division of Atmospheric and Geospace Sciences
- National Science Foundation
- National Science Foundation Division of Mathematical Sciences
- Office of Naval Research
- Rutgers University