Recovery of the 6-year signal in length of day and its long-term decreasing trend

There is a significant 6-year oscillation signal (called 6-year signal in this paper) existing in the interannual variations of length of day (LOD). It is unclear to understand its nature variation features. This paper extracts quantitatively the 6-year signal, from 1962~2012, using normal Morlet wa...

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Bibliographic Details
Published in:Earth, planets, and space planets, and space, 2015-10, Vol.67 (1), p.1-11, Article 161
Main Authors: Duan, Pengshuo, Liu, Genyou, Liu, Lintao, Hu, Xiaogang, Hao, Xiaoguang, Huang, Yong, Zhang, Zhimin, Wang, Binbin
Format: Article
Language:English
Subjects:
Amplitudes
Earth
Earth and Environmental Science
Earth Sciences
Fourier analysis
Frequency domains
Geodesy
Geology
Geophysics/Geodesy
Morlet wavelet
Reduction
Trends
Wavelet analysis
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Summary:There is a significant 6-year oscillation signal (called 6-year signal in this paper) existing in the interannual variations of length of day (LOD). It is unclear to understand its nature variation features. This paper extracts quantitatively the 6-year signal, from 1962~2012, using normal Morlet wavelet (NMWT) method combining wavelet packet and Fourier analysis technique, for the first time, and we investigate it in both time and frequency domains. The results indicate that the amplitude of a 6-year signal shows a long-term decreasing trend and the total amplitude reduction is about 0.05 ms during the past 50 years. The ratio of above reduction to the mean amplitude of 0.124 ms reaches 40 %. For interpreting the phenomenon on the above long-term decreasing trend, this paper proposes two alternatives; however, there is still no firm conclusion and it is required to be further explored.
ISSN:1880-5981
1880-5981
DOI:10.1186/s40623-015-0328-6