Towards the assimilation of tree-ring-width records using ensemble Kalman filtering techniques
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- 作者：Walter Acevedo ; Sebastian Reich ; Ulrich Cubasch
- 关键词：Proxy forward modeling ; Data assimilation ; Fuzzy logic ; Ensemble Kalman filter ; Paleoclimate reconstruction
- 刊名：Climate Dynamics
- 出版年：2016
- 出版时间：March 2016
- 年：2016
- 卷：46
- 期：5-6
- 页码：1909-1920
- 全文大小：1,849 KB
- 刊物类别：Earth and Environmental Science
- 刊物主题：Earth sciences
Geophysics and Geodesy
Meteorology and Climatology
Oceanography - 出版者：Springer Berlin / Heidelberg
- ISSN：1432-0894
文摘
This paper investigates the applicability of the Vaganov–Shashkin–Lite (VSL) forward model for tree-ring-width chronologies as observation operator within a proxy data assimilation (DA) setting. Based on the principle of limiting factors, VSL combines temperature and moisture time series in a nonlinear fashion to obtain simulated TRW chronologies. When used as observation operator, this modelling approach implies three compounding, challenging features: (1) time averaging, (2) “switching recording” of 2 variables and (3) bounded response windows leading to “thresholded response”. We generate pseudo-TRW observations from a chaotic 2-scale dynamical system, used as a cartoon of the atmosphere-land system, and attempt to assimilate them via ensemble Kalman filtering techniques. Results within our simplified setting reveal that VSL’s nonlinearities may lead to considerable loss of assimilation skill, as compared to the utilization of a time-averaged (TA) linear observation operator. In order to understand this undesired effect, we embed VSL’s formulation into the framework of fuzzy logic (FL) theory, which thereby exposes multiple representations of the principle of limiting factors. DA experiments employing three alternative growth rate functions disclose a strong link between the lack of smoothness of the growth rate function and the loss of optimality in the estimate of the TA state. Accordingly, VSL’s performance as observation operator can be enhanced by resorting to smoother FL representations of the principle of limiting factors. This finding fosters new interpretations of tree-ring-growth limitation processes.