Intercomparison between observed and simulated variability in global ocean heat content using empirical mode decompositi
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Intercomparison between observed and simulated variability in global ocean heat content using empirical mode decomposition, part I: modulated annual cycle Xianyao Chen • Yuanling Zhang • Min Zhang Ying Feng • Zhaohua Wu • Fangli Qiao • Norden Eh Huang
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Received: 16 July 2012 / Accepted: 1 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract This study proposes a new more precise and detailed method to examine the performance of IPCC AR4 models in simulation of nonlinear variability of global ocean heat content (OHC) on the annual time scale during 1950–1999. The method is based on the intercomparison of modulated annual cycle (MAC) of OHC and its instantaneous frequency (IF), derived by Empirical Mode Decomposition and Hilbert-Huang Transformation. In addition to indicate the general agreement in gross features globally between models and observation, our results point out the problems both in observation and in modeling. In the well observed Northern Hemisphere, models exhibit extremely good skills to capture nonlinear annual variability of OHC. The simulated MACs are highly correlated with observations ([0.95) and the IF of MACs varies coherently with each other. However, in sparsely observed Southern Hemisphere (SH), even though the simulated MACs highly correlate with observations, the IF shows significant difference. This comparisons show that the models exhibit coherent variability of IF of MACs in SH
Electronic supplementary material The online version of this article (doi:10.1007/s00382-012-1554-2) contains supplementary material, which is available to authorized users. X. Chen (&) Y. Zhang M. Zhang Y. Feng F. Qiao N. E. Huang Key Laboratory of Data Analysis and Applications, The First Institute of Oceanography, State Oceanic Administration, 6 Xianxia Ling Road, Qingdao 266061, China e-mail: [email protected] Z. Wu Florida State University, Tallahassee, FL, USA N. E. Huang National Central University, Chung-Li, Taiwan, ROC
with each other, but not with observations, revealing the problems in the objective analyzed dataset using sparse observations. In the well observed tropic region, the models lack the coherence with the observations, indicating inadequate physics of the models in the tropical area. These results illustrate that the proposed method can be used routinely to identify problems in both models and in observation of the global ocean as a critical component of global climate change. Keywords Ocean heat content Modulated annual cycle Empirical mode decomposition Instantaneous frequency Instantaneous amplitude CMIP3
1 Introduction Confidence on any climate models to provide plausible quantitative estimates of future events is based on the capability of models to reproduce observed past climate variability in multi-time and spatial scales (Knutti et al. 2010). This requires the objective and quantitative assessments and evaluations of climate models on the simulation of different components of climate system, such as temperature or precipitation (Meehl et al. 200
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