Spectral Early-Warning Signals for Sudden Changes in Time-Dependent Flow Patterns

• Main Authors: Moussa Ndour, Kathrin Padberg-Gehle, Martin Rasmussen
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Fluids
• Subjects: Lagrangian transport; probabilistic approach; transfer operator; singular value decomposition; coherent set; bifurcation
• Online Access: https://www.mdpi.com/2311-5521/6/2/49

Lagrangian coherent sets are known to crucially determine transport and mixing processes in non-autonomous flows. Prominent examples include vortices and jets in geophysical fluid flows. Coherent sets can be identified computationally by a probabilistic transfer-operator-based approach within a set-oriented numerical framework. Here, we study sudden changes in flow patterns that correspond to bifurcations of coherent sets. Significant changes in the spectral properties of a numerical transfer operator are heuristically related to critical events in the phase space of a time-dependent system. The transfer operator approach is applied to different example systems of increasing complexity. In particular, we study the 2002 splitting event of the Antarctic polar vortex.