The Synchronized Climate System as Seen from the Instrumental Record

Low-dimensional aspects of climate dynamics, as addressed in diverse modeling studies including a spatially coarse-grained GCM that nevertheless shows qualitatively correct intraseasonal monsoon dynamics, provide reasoning in favor of the search for synchronies in representative data of the real system. Namely, in a high-dimensional system, low-dimensional behavior is peremptorily bound to internal dynamic organization as reflected in degenerate, synchronous motions along otherwise largely independent phase space (or signal space) directions. Due to both inherent phase transitions and a major impact on the atmospheric energy balance, water cycle interactions are integral parts of climate variability and change - and may even take the lead in providing the necessary ingredients to the high sensitivity and excitation that makes up a dynamical status of the climate system which bears a sufficient variety of targets for synchronization. Notably in (pre)chaotic regimes, unstable periodic orbits may become manifest in the data due to episodic or persistent, internal or external synchronization. This calls for clarification of the role that nonlinear qualitative dynamics may play in the real climate. That the system's dynamical status is largely unknown (as it is that of its elaborated GCMs) poses challenges when conceptually grasping its past, present and future evolution, or when more operationally considering its potential to form extremes, for example.

Various types of synchronization may be identified in the system's motion as documented by the observational record of the instrumental period, when looking at its representative time series through the glasses of an advanced method of sparse data approximation, the Matching Pursuit (MP) approach. To disentangle the emerging network of oscillatory modes to the degree that climate dynamics turns out to be separable, a large, overcomplete dictionary of frequency modulated (FM) Gabor atoms, as analyzing waveforms, is applied in strictly univariate analyses of customary time series comprising global and regional climate, central European synoptic systems, German precipitation, and runoff across the Elbe river basin. A published first-generation study into the period 1870-1997 at annual resolution is being extended to cover data since the 1850s, and has been updated to 2017 to include the much debated "hiatus" regime - and its presumed termination by the large El Nino of 2015/16. To learn more about decadal climate regimes, the temporal resolution is increased from annually to monthly.

All the evidence from these MP-FM studies, as obtained in subsequent multivariate syntheses, points to dynamically excited regimes of an organized climate system under permanent change - perhaps a (pre)chaotic one at centennial timescales, suggesting a "chaos control" perspective on global climate dynamics and change. Findings and conclusions include, among others, remarkable internal structure of reconstructed insolation, the episodic nature of global warming as reflected in multidecadal temperature modes, their swarm of "interdomain" (phase-frequency) companions across the whole system and period, which unveils an unknown regime character of interannual climate dynamics, deep FM throughout the record, very active monsoon onset dynamics around solar cycle no. 19 (the strongest on record), and structures in the monthly analyses that remind of homoclinic and heteroclinic orbits known from much simpler dynamic systems, which may be blamed for 'spontaneous' extreme excursions. The system seems well-organized, yet complex, down to the river basin scale, and its sparse approximation using the MP-FM tool appears to provide an adequate approach of unveiling its hidden structure.