On Multi-Timescale Variability of Temperature in China in Modulated Annual Cycle Reference Frame |
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Authors: | QIAN Cheng Zhaohua WU FU Congbin and ZHOU Tianjun |
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Affiliation: | Key Laboratory of Regional Climate-Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,Department of Meteorology & Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, Florida, USA,Key Laboratory of Regional Climate-Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, Institute for Climate and Global Change Research, Nanjing University, Nanjing 210093,State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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Abstract: | The traditional anomaly (TA) reference frame and its corresponding anomaly
for a given data span changes with the extension of data length. In this study, the
modulated annual cycle (MAC), instead of the widely used climatological mean annual
cycle, is used as an alternative reference frame for computing climate anomalies to
study the multi-timescale variability of surface air temperature (SAT) in China based
on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition
(EEMD) method is used to separate daily SAT into a high frequency component, a MAC
component, an interannual component, and a decadal-to-trend component. The results
show that the EEMD method can reflect historical events reasonably well, indicating
its adaptive and temporally local characteristics. It is shown that MAC is a temporally
local reference frame and will not be altered over a particular time span by an extension
of data length, thereby making it easier for physical interpretation. In the MAC reference
frame, the low frequency component is found more suitable for studying the interannual to
longer timescale variability (ILV) than a 13-month window running mean, which does not
exclude the annual cycle. It is also better than other traditional versions (annual or
summer or winter mean) of ILV, which contains a portion of the annual cycle. The analysis
reveals that the variability of the annual cycle could be as large as the magnitude of
interannual variability. The possible physical causes of different timescale variability
of SAT in China are further discussed. |
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Keywords: | modulated annual cycle the Ensemble Empirical Mode Decomposition climate anomaly climate normal variability of surface air temperature in China |
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