TY  - JOUR
A1  - Witt, Annette
A1  - Schumann, A. Y.
T1  - Holocene climate variability on millennial scales recorded in Greenland ice cores
Y1  - 2005
SN  - 1023-5809
ER  - 
TY  - JOUR
A1  - Feudel, Fred
A1  - Witt, Annette
A1  - Gellert, Marcus
A1  - Kurths, Jürgen
A1  - Grebogi, Celso
A1  - Sanjuan, Miguel Angel Fernandez
T1  - Intersections of stable and unstable manifolds : the skeleton of Lagrangian chaos
N2  - 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
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Witt, Annette
A1  - Schumann, A. Y.
T1  - Holocene climate variability on millennial scales recorded in Greenland ice cores
N2  - 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
Y1  - 2005
SN  - 1023-5809
ER  -