确定十年尺度日长变化的机理，有助于约束液核粘度、内外核边界密度跳跃、穿过核幔边界的磁场强度以及固态内核与地幔如何相互作用等地学中仍未被很好地约束或解决的基本问题。但十年尺度日长变化的物理机制和激发机制仍是悬而未决的国际性难题。前人关于物理机制的相关研究多局限于将地核角动量模型与日长观测在时间域做波形对比，关于激发机制的研究也同样是基于时间域的很弱的相关性。为此，本项目将首先在频率域确定日长变化在十年尺度范围内的不同周期信号，并将它们分别在时间域内剥离且计算相应的激发函数序列。然后采用申请人提出的OSE和AR-z谱方法以及其他经典数据处理方法，首次综合分析十余种全球性的地学观测数据，检测与日长具有相同周期的十年尺度信号并确定这些信号的空间分布信息。综合日长数据和其他地学数据所得到的结果，结合地球滞弹性、流变性等参数信息，最终给出日长十年尺度变化中不同周期信号的物理机制及可能的激发源。

Determining the physical mechanism and excitations of the decadal changes of length of day (LOD), which will help to constrain the viscosity of the liquid core, the density jumps at the inner core boundary, the strength of the magnetic field crossing the core-mantle boundary, and also will help to understand the mechanism of the Earth’s core and mantle interacts, and so on. However, the physical mechanism and excitation mechanism of the decadal changes of LOD are still an unresolved international problems. For the physical mechanism, most of the previous studies used the comparisons of the core geomagnetic angular momentum models with the ΔLOD observation in the time domain. While for the excitation mechanism, few studies have concerned about this, and the relevant researches only based on the weak correlations of the geomagnetic jerks with the LOD in the time domain. Inasmuch as those, this project will first determines the different periodic signals of the ΔLOD in the decadal scale (6-15 years), and further strip them separately in the time domain and calculate the corresponding excitation function sequences of them. Then, upon using the OSE and AR-z spectrum methods proposed in our previous studies (and also using some other classical data-processing methods), we will comprehensive analysis more than ten different types global geoscience dataset for the first time to detect the signals with the same periods as the decadal scale signals in the LOD; the spatial distributions of these signals will also be estimated based on the OSE method. Finally, combining the obtained results above and the published Earth’s parameters, such as the Earth's anelastic and rheology, we will construct the physical mechanisms of the decadal periodic changes of ΔLOD, and give the suggestions about the possible excitations of them.