A two‐parameter stochastic process for Dansgaard‐Oeschger events

Abstract

Various climatic processes are thought to evolve as rapid, shift‐like events, which points at the presence of nonlinear dynamics. Time series analysis of nonlinear processes, however, is not trivial, for example, because of the difficulty in coming up with a realistic random process as a viable null hypothesis. In this methodology paper we construct a basic two‐parameter process of shift‐like excursions in an excitable system with a threshold. We demonstrate that this stochastic process, in comparison with a specific one‐parameter process, can better reproduce main features of the waiting time histogram of abrupt glacial climate events, the Dansgaard‐Oeschger events, as seen in two paleoclimatic proxy records, the North Greenland Ice core Project (NGRIP) ice core and the Sofular stalagmite δ18O records. We use the two‐parameter process to test some arguments that were proposed in the ongoing discussion of a possible solar role in triggering Dansgaard‐Oeschger events. Using our approach, we suggest for future studies to generate time series of random events which can serve as a more plausible null hypothesis for Monte Carlo based statistical tests on the regularity of shift‐like processes such as Dansgaard‐Oeschger events.