Application of the AR-z Spectrum to Polar Motion: A Possible First Detection of the Inner Core Wobble and Its Implications for the Density of Earth's Core
Application of the AR-z Spectrum to Polar Motion: A Possible First Detection of the Inner Core Wobble and Its Implications for the Density of Earth's Core
复制标题
AR-z 光谱在极地运动中的应用：可能首次检测到内核摆动及其对地核密度的影响
DOI：
10.1029/2019gl085268
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发表时间：
2019-12-06
影响因子：
5.2
通讯作者：
Li, Mengkui
中科院分区：
文献类型：
--
作者：
Ding, Hao;Pan, YuanJin;Li, Mengkui
地球内核边界处的密度跳跃很少受到地震数据的约束。跳跃的一项敏感测量是内核摆动（ICW）的本征周期。尽管对 ICW 的理论研究已经进行了数十年，但尚未有观测到的 ICW 信号的报道。为了提高检测水平，这里我们使用最近提出的AR-z方法来分析1960-2017年的极移时间序列。我们最终确定了 +8.7 +/- 0.2 年的顺行运动，振幅为 2.67 +/- 0.04 毫弧秒。在确认该信号几乎是稳态振荡并且大气/海洋/水文效应似乎无法激发该信号后，我们谨慎地建议该8.7年信号可能是ICW。根据这一建议，我们重建了一个新的一维密度模型，其内核边界密度跳跃为 507 +/- 15 kg/m(3)。这个新模型还可以比初步参考地球模型更好地拟合地震泛音 2 S1。 简单语言摘要 ICW 的本征周期与内核边界 (ICB) 处的密度跃变直接相关（对此仍知之甚少）。尽管对ICW的理论研究已经进行了几十年，但只有Guo等人。 (2005) 尝试在 PM 时间序列中检测 ICW，但没有成功。在本研究中，我们使用 AR-z 频谱，它比傅里叶（和最大熵）频谱具有明显更高的灵敏度和频率分辨率，特别是在信噪比较低时。我们将 PM 提出的 +8.7 +/- 0.2 年顺行动议确定为可能的 ICW。我们的结果为ICB的密度跳跃提供了有用的限制，并且可以进一步加强对地球深层结构和动力学的理解。
The density jump at the inner core boundary of the Earth is poorly constrained by seismic data. One sensitive measure of the jump is the eigenperiod of the inner core wobble (ICW). Although theoretical studies on the ICW have been ongoing for decades, no observed ICW signal has been reported. To increase the detection level, here we use a recently proposed AR-z method to analyze the 1960-2017 polar motion time series. We finally identify a +8.7 +/- 0.2 year prograde motion with an 2.67 +/- 0.04 milliarcsecond amplitude. After confirming that this signal is almost a stationary oscillation and that atmospheric/oceanic/hydrological effects cannot seem to excite this signal, we carefully suggest that this 8.7 year signal is possibly the ICW. According to this suggestion, we reconstruct a new 1-D density model with a 507 +/- 15 kg/m(3) inner core boundary density jump. This new model can also provide a better fit than Preliminary Reference Earth model to the seismic overtone 2 S1.Plain Language Summary The eigenperiod of the ICW is directly related to the density jump at the inner core boundary (ICB) (which is still poorly known). Although theoretical studies on the ICW have been ongoing for decades, only Guo et al. (2005) have tried unsuccessfully to detect the ICW in the PM time series. In this study, we use the AR-z spectrum, which has significantly higher sensitivity and frequency resolution than the Fourier (and maximum-entropy) spectrum, especially when the signal-to-noise ratio is low. We identify a +8.7 +/- 0.2 year prograde motion from the PM as the possible ICW. Our results provide useful constraints on the density jump at the ICB and can further strengthen the understanding of Earth's deep structure and dynamics.