Attenuation and excitation of the similar to 6 year oscillation in the length-of-day variation
Attenuation and excitation of the similar to 6 year oscillation in the length-of-day variation
复制标题
日长变化类似6年振荡的衰减和激发
DOI：
10.1016/j.epsl.2018.12.003
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发表时间：
2019
影响因子：
5.3
通讯作者：
Ding Hao
中科院分区：
文献类型：
--
作者：
Ding Hao
我们仔细地重新分析了∼6年振荡(SYO)，它以前在地球的日长变化(ΔLOD)中被发现，被认为对于理解核-地幔相互作用和核动力学是重要的。基于长周期Δ年记录(1760年-2018年)的Morlet小波和AR-z谱，我们识别出8个长周期信号，∼149年，∼68年，∼33年，∼22.3年，∼18.6年，∼13.5年，∼11年和∼8.5年，除18.6年信号外，其他信号首次被清楚地识别出来，尽管其物理机制还有待进一步了解(其中一些可能与扭波或磁阿基米德-科里奥利斯波有关)。剔除大气/海洋角动量效应、季节/潮汐信号和1962-2016年ΔLOD时间序列的8个低频信号后，得到了一个干净得多的同步辐射序列，证实了剩余序列中同步辐射没有明显的衰减趋势。在对这一SYO时间序列进行去卷积处理后，我们首先验证了SYO的品质因数Q不能小于200。假设同步辐射的衰减主要是由地幔的电磁耦合引起的，取地幔电导Gm=108 S，则地幔的径向磁场强度Bm应大于0.31mT。此外，我们还首次从ΔLOD的反卷积计算了同步光的激发函数，结果表明同步光似乎是连续激发的。通过地磁突变与同步振荡激发函数的比较，发现两者之间没有明显的相关性，但也不能排除地磁突变作为同步振荡的一种激发源的可能性。我们的发现对于建立SYO的系统物理机制是必要的，对于约束地核的磁场B也是有用的。
We carefully reanalyze the∼ 6-yr oscillation (SYO), which has been previously found in the Earth's length of day variation (ΔLOD) and has been considered important for understanding the core–mantle interactions and core dynamics. Based on the Morlet wavelet and AR-z spectra of a long-period yearly ΔLOD record (1760–2018), we identify eight long period signals,∼ 149 yr,∼ 68 yr,∼ 33 yr,∼ 22.3 yr,∼ 18.6 yr,∼ 13.5 yr,∼ 11 yr and∼ 8.5 yr signals; except the 18.6 yr signal, the other signals are clearly identified for the first time, although the physical mechanisms need to be understood (some of them may relative to the torsional waves or Magnetic-Archimede-Coriolis waves). After removing the atmospheric/oceanic angular momentum effects, the seasonal/tidal signals and the eight low-frequency signals from the 1962–2016 ΔLOD time series (from EOPC04), a much cleaner sequence for the SYO is obtained, and we confirm that there is no clear decay trend for the SYO in the residual sequence. After using a deconvolution method to this SYO time series, we first validate that the quality factor Q of the SYO cannot be less than 200. Assuming the attenuation of SYO is mainly caused by the electromagnetic coupling at CMB, and taking the mantle conductance G m= 10 8 S, the radial magnetic field strength B m at the CMB should be larger than 0.31 mT. In addition, for the first time, we calculate the excitation function of the SYO from the deconvolution of ΔLOD, and the results demonstrate that the SYO seems to be continuously excited. By comparing the geomagnetic jerks with the excitation function of the SYO, no clear correlation has been found between them, while we also cannot rule out the possibility of the geomagnetic jerks as one kind of the excitation sources of the SYO. Our findings are necessary for building a systematic physical mechanism of the SYO, and useful for constraining the magnetic field B of the Earth's core.