@article{PrasadWittKieneletal.2009,
  author    = {Prasad, Sushama and Witt, Annette and Kienel, Ulrike and Dulski, Peter and Bauer, Eva and Yancheva, Gergana},
  title     = {The 8.2 ka event : evidence for seasonal differences and the rate of climate change in western Europe},
  issn      = {0921-8181},
  doi       = {10.1016/j.gloplacha.2009.03.011},
  year      = {2009},
  abstract  = {Recent studies have drawn attention to differences in the seasonal impact of the 8.2 ka event, with longer cooler summers and shorter cooler/drier winters. However, there are no data available on the simultaneity or the rate of onset of the seasonal changes in Europe. Based on the microfacies and geochemical analyses of seasonally laminated varved sediments from Holzmaar, we present evidence of differences in duration and onset time of changes in summer temperature and winter rainfall during the 8.2 ka event. Since both summer and winter climate signals are co-registered within a single varve, there can be no ambiguity about the phasing and duration of the signals. Our data show that the onset and withdrawal of the 8.2 ka summer cooling occurred within a year, and that summer rains were reduced or absent during the investigated period. The onset of cooler summers preceded the onset of winter dryness by ca. 28 years. In view of the differences in nature and duration of the impact of the 8.2 ka event we suggest that a clearer definition of the 8.2 ka event (summer cooling or winter cooling/dryness) needs to be developed. Based on regional comparison and available modelling studies we also discuss the roles of solar variability, changes in North Atlantic Thermohaline circulation, and North Atlantic Circulation (NAO) during the period under consideration. Wavelet analyses of seasonal laminae indicates that the longer NAO cycles, linked to changes in the N. Atlantic temperatures, were more frequent during the drier periods.},
  language  = {en}
}
@article{WittSchumann2005,
  author    = {Witt, Annette and Schumann, A. Y.},
  title     = {Holocene climate variability on millennial scales recorded in Greenland ice cores},
  issn      = {1023-5809},
  year      = {2005},
  language  = {en}
}
@article{FeudelWittGellertetal.2005,
  author    = {Feudel, Fred and Witt, Annette and Gellert, Marcus and Kurths, J{\"u}rgen and Grebogi, Celso and Sanjuan, Miguel Angel Fernandez},
  title     = {Intersections of stable and unstable manifolds : the skeleton of Lagrangian chaos},
  year      = {2005},
  abstract  = {We study Hamiltonian chaos generated by the dynamics of passive tracers moving in a two-dimensional fluid flow and describe the complex structure formed in a chaotic layer that separates a vortex region from the shear flow. The stable and unstable manifolds of unstable periodic orbits are computed. It is shown that their intersections in the Poincare map as an invariant set of homoclinic points constitute the backbone of the chaotic layer. Special attention is paid to the finite time properties of the chaotic layer. In particular, finite time Lyapunov exponents are computed and a scaling law of the variance of their distribution is derived. Additionally, the box counting dimension as an effective dimension to characterize the fractal properties of the layer is estimated for different duration times of simulation. Its behavior in the asymptotic time limit is discussed. By computing the Lyapunov exponents and by applying methods of symbolic dynamics, the formation of the layer as a function of the external forcing strength, which in turn represents the perturbation of the originally integrable system, is characterized. In particular, it is shown that the capture of KAM tori by the layer has a remarkable influence on the averaged Lyapunov exponents. (C) 2004 Elsevier Ltd. All rights reserved},
  language  = {en}
}
@article{WittSchumann2005,
  author    = {Witt, Annette and Schumann, A. Y.},
  title     = {Holocene climate variability on millennial scales recorded in Greenland ice cores},
  issn      = {1023-5809},
  year      = {2005},
  abstract  = {Climate variability is triggered by several solar and orbital cycles as well as by the intern ocean dynamics. Consequently, paleoclimate proxy records are expected to vary on very different time scales ranging from subdecadal to millennial duration. We demonstrate, that Foster's (Foster, 1996) wavelet analysis technique is an appropriate tool for investigating temporarily changing spectral properties of records characterized by awkward sampling quality, which is a typical feature of climate proxy records. By applying it to the Holocene part of different glaciochemical records of Greenland ice cores we proof evidence for a significant contribution of the 1.47 kiloyears cycle over alomst the entire Holocene},
  language  = {en}
}
@article{FeudelGellertRuedigeretal.2003,
  author    = {Feudel, Fred and Gellert, Marcus and R{\"u}diger, Sten and Witt, Annette and Seehafer, Norbert},
  title     = {Dynamo effect in a driven helical flow},
  year      = {2003},
  language  = {en}
}
@article{PolitiWitt1999,
  author    = {Politi, Antonio and Witt, Annette},
  title     = {Fractal dimension of space-time chaos},
  year      = {1999},
  language  = {en}
}
@article{BraunFeudelGebogietal.1999,
  author    = {Braun, Robert and Feudel, Fred and Gebogi, C. and Kurths, J{\"u}rgen and Witt, Annette},
  title     = {Tracer dynamics in a flow of driven vortices},
  year      = {1999},
  language  = {en}
}
@article{WittSpanoNeimanetal.1999,
  author    = {Witt, Annette and Spano, M. and Neiman, Alexander and Moss, F. and Dolan, K.},
  title     = {Surrogates for finding unstable periodic orbits in noisy data sets},
  year      = {1999},
  language  = {en}
}
@article{LaiGrebogiFeudeletal.1998,
  author    = {Lai, Ying Cheng and Grebogi, Celso and Feudel, Ulrike and Witt, Annette},
  title     = {Basin bifurcation in quasiperiodically forced systems},
  year      = {1998},
  language  = {en}
}
@article{WittKurthsPikovskij1998,
  author    = {Witt, Annette and Kurths, J{\"u}rgen and Pikovskij, Arkadij},
  title     = {Testing stationarity in time series},
  year      = {1998},
  language  = {en}
}