Stephenson F R, Morrison L V, Hohenkerk C Y
University of Durham , Durham, UK.
Pevensey , East Sussex, UK.
Proc Math Phys Eng Sci. 2016 Dec;472(2196):20160404. doi: 10.1098/rspa.2016.0404.
New compilations of records of ancient and medieval eclipses in the period 720 BC to AD 1600, and of lunar occultations of stars in AD 1600-2015, are analysed to investigate variations in the Earth's rate of rotation. It is found that the rate of rotation departs from uniformity, such that the change in the length of the mean solar day (lod) increases at an average rate of +1.8 ms per century. This is significantly less than the rate predicted on the basis of tidal friction, which is +2.3 ms per century. Besides this linear change in the lod, there are fluctuations about this trend on time scales of decades to centuries. A power spectral density analysis of fluctuations in the range 2-30 years follows a power law with exponent -1.3, and there is evidence of increased power at a period of 6 years. There is some indication of an oscillation in the lod with a period of roughly 1500 years. Our measurements of the Earth's rotation for the period 720 BC to AD 2015 set firm boundaries for future work on post-glacial rebound and core-mantle coupling which are invoked to explain the departures from tidal friction.
分析了公元前720年至公元1600年古代和中世纪日食记录以及公元1600 - 2015年恒星月掩星记录的新汇编，以研究地球自转速率的变化。研究发现，自转速率偏离均匀性，平均太阳日长度（lod）的变化以每世纪+1.8毫秒的平均速率增加。这明显小于基于潮汐摩擦预测的速率，即每世纪+2.3毫秒。除了lod的这种线性变化外，在数十年到数百年的时间尺度上，围绕这一趋势还存在波动。对2 - 30年范围内波动的功率谱密度分析遵循指数为-1.3的幂律，并且有证据表明在6年周期处功率增加。有迹象表明lod存在大约1500年周期的振荡。我们对公元前720年至公元2015年期间地球自转的测量为未来关于后冰期回弹和地核 - 地幔耦合的研究设定了明确界限，这些研究被用来解释与潮汐摩擦的偏差。
