Understanding threshold-crossing events: New approaches to use computer models for time series analysis of complex systems

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Many complex dynamical systems exhibit threshold-crossing behaviour, i.e. sudden flips between fundamentally different states of operation. The cause of these flips is often poorly understood, despite their fundamental importance for the dynamics of these systems. A prominent example are so far unexplained, large-amplitude (10-15 K) switchings in glacial climate, the Dansgaard-Oeschger (DO) events, which show an apparent tendency to recur preferably in near multiples of about 1470 years.The aim of this project is to develop and apply new techniques, based on computer models, for improved time series analyses of threshold-crossing events. The main objective is to understand what caused DO events in glacial climate. Several hypotheses were proposed to explain these climate shifts and their characteristic recurrence time. But testing these hypotheses is highly non-trivial and requires new conceptual approaches, based e.g. on null-hypothesis testing with surrogate data, on recurrence plot methods and, possibly, on complex networks. I expect that this project could give new insight into main causes of natural climate variability and concerning the potential occurrence of large-amplitude climate instabilities in the future. Moreover, since threshold-crossing behaviour exists in many dynamical systems, this project could also give new stimulus to innovative time series analyses of complex systems far beyond geoscience.