Yang Shih-Sian, Hayakawa Masashi
Independent researcher, Jhongli P.O. Box 9-11, Taoyuan 32099, Taiwan.
Hayakawa Institute of Seismo Electromagnetics, Co. Ltd. (Hi-SEM), University of Electro-Communications (UEC) Alliance Center, 1-1-1 Kojima-cho, Chofu, Tokyo 182-0026, Japan.
Entropy (Basel). 2020 Jan 16;22(1):110. doi: 10.3390/e22010110.
The precursory atmospheric gravity wave (AGW) activity in the stratosphere has been investigated in our previous paper by studying an inland Kumamoto earthquake (EQ). We are interested in whether the same phenomenon occurs or not before another major EQ, especially an oceanic EQ. In this study, we have examined the stratospheric AGW activity before the oceanic 2011 Tohoku EQ (M 9.0), while using the temperature profiles that were retrieved from ERA5. The potential energy (E) of AGW has enhanced from 3 to 7 March, 4-8 days before the EQ. The active region of the precursory AGW first appeared around the EQ epicenter, and then expanded omnidirectionally, but mainly toward the east, covering a wide area of 2500 km (in longitude) by 1500 km (in latitude). We also found the influence of the present AGW activity on some stratospheric parameters. The stratopause was heated and descended; the ozone concentration was also reduced and the zonal wind was reversed at the stratopause altitude before the EQ. These abnormalities of the stratospheric AGW and physical/chemical parameters are most significant on 5-6 March, which are found to be consistent in time and spatial distribution with the lower ionospheric perturbation, as detected by our VLF network observations. We have excluded the other probabilities by the processes of elimination and finally concluded that the abnormal phenomena observed in the present study are EQ precursors, although several potential sources can generate AGW activities and chemical variations in the stratosphere. The present paper shows that the abnormal stratospheric AGW activity has also been detected even before an oceanic EQ, and the AGW activity has obliquely propagated upward and further disturbed the lower ionosphere. This case study has provided further support to the AGW hypothesis of the lithosphere-atmosphere-ionosphere coupling process.
在我们之前的论文中，通过研究熊本地震（内陆地震），对平流层中大气重力波（AGW）的前兆活动进行了调查。我们感兴趣的是，在另一次大地震尤其是海洋地震之前，是否会出现同样的现象。在本研究中，我们利用从ERA5反演得到的温度剖面，研究了2011年东北海洋地震（M 9.0）之前平流层AGW的活动情况。AGW的势能（E）在地震前4 - 8天，即3月3日至7日有所增强。前兆AGW的活跃区域首先出现在震中附近，然后向全方向扩展，但主要向东扩展，覆盖了经度2500公里、纬度1500公里的广阔区域。我们还发现了当前AGW活动对平流层一些参数的影响。平流层顶受热下降；在地震前，平流层顶高度处的臭氧浓度也降低，纬向风发生反转。平流层AGW以及物理/化学参数的这些异常在3月5 - 6日最为显著，发现它们在时间和空间分布上与我们甚低频网络观测检测到的低电离层扰动一致。我们通过排除过程排除了其他可能性，最终得出结论，尽管平流层中几种潜在来源可产生AGW活动和化学变化，但本研究中观测到的异常现象是地震前兆。本文表明，即使在海洋地震之前也检测到了平流层AGW的异常活动，并且AGW活动向上倾斜传播并进一步扰动了低电离层。该案例研究为岩石圈 - 大气 - 电离层耦合过程的AGW假说提供了进一步支持。
