TY  - JOUR
A1  - Herzschuh, Ulrike
A1  - Cao, Xianyong
A1  - Laepple, Thomas
A1  - Dallmeyer, Anne
A1  - Telford, Richard J.
A1  - Ni, Jian
A1  - Chen, Fahu
A1  - Kong, Zhaochen
A1  - Liu, Guangxiu
A1  - Liu, Kam-Biu
A1  - Liu, Xingqi
A1  - Stebich, Martina
A1  - Tang, Lingyu
A1  - Tian, Fang
A1  - Wang, Yongbo
A1  - Wischnewski, Juliane
A1  - Xu, Qinghai
A1  - Yan, Shun
A1  - Yang, Zhenjing
A1  - Yu, Ge
A1  - Zhang, Yun
A1  - Zhao, Yan
A1  - Zheng, Zhuo
T1  - Position and orientation of the westerly jet determined Holocene rainfall patterns in China
JF  - Nature Communications
N2  - Proxy-based reconstructions and modeling of Holocene spatiotemporal precipitation patterns for China and Mongolia have hitherto yielded contradictory results indicating that the basic mechanisms behind the East Asian Summer Monsoon and its interaction with the westerly jet stream remain poorly understood. We present quantitative reconstructions of Holocene precipitation derived from 101 fossil pollen records and analyse them with the help of a minimal empirical model. We show that the westerly jet-stream axis shifted gradually southward and became less tilted since the middle Holocene. This was tracked by the summer monsoon rain band resulting in an early-Holocene precipitation maximum over most of western China, a mid-Holocene maximum in north-central and northeastern China, and a late-Holocene maximum in southeastern China. Our results suggest that a correct simulation of the orientation and position of the westerly jet stream is crucial to the reliable prediction of precipitation patterns in China and Mongolia.
Y1  - 2019
U6  - https://doi.org/10.1038/s41467-019-09866-8
SN  - 2041-1723
VL  - 10
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Reschke, Maria
A1  - Kunz, Torben
A1  - Laepple, Thomas
T1  - Comparing methods for analysing time scale dependent correlations in irregularly sampled time series data
JF  - Computers & geosciences : an international journal devoted to the publication of papers on all aspects of geocomputation and to the distribution of computer programs and test data sets ; an official journal of the International Association for Mathematical Geology
N2  - Time series derived from paleoclimate archives are often irregularly sampled in time and thus not analysable using standard statistical methods such as correlation analyses. Although measures for the similarity between time series have been proposed for irregular time series, they do not account for the time scale dependency of the relationship. Stochastically distributed temporal sampling irregularities act qualitatively as a low-pass filter reducing the influence of fast variations from frequencies higher than about 0.5 (Delta t(max))(-1) , where Delta t(max), is the maximum time interval between observations. This may lead to overestimated correlations if the true correlation increases with time scale. Typically, correlations are underestimated due to a non-simultaneous sampling of time series. Here, we investigated different techniques to estimate time scale dependent correlations of weakly irregularly sampled time series, with a particular focus on different resampling methods and filters of varying complexity. The methods were tested on ensembles of synthetic time series that mimic the characteristics of Holocene marine sediment temperature proxy records. We found that a linear interpolation of the irregular time series onto a regular grid, followed by a simple Gaussian filter was the best approach to deal with the irregularity and account for the time scale dependence. This approach had both, minimal filter artefacts, particularly on short time scales, and a minimal loss of information due to filter length.
KW  - Irregular sampling
KW  - Time scale dependence
KW  - Correlation
KW  - Resampling methods
Y1  - 2018
U6  - https://doi.org/10.1016/j.cageo.2018.11.009
SN  - 0098-3004
SN  - 1873-7803
VL  - 123
SP  - 65
EP  - 72
PB  - Elsevier
CY  - Oxford
ER  -