Gravity Wave Activity in the Stratosphere before the 2011 Tohoku Earthquake as the Mechanism of Lithosphere-atmosphere-ionosphere Coupling

Shih-Sian Yang; Masashi Hayakawa

doi:10.3390/e22010110

Gravity Wave Activity in the Stratosphere before the 2011 Tohoku Earthquake as the Mechanism of Lithosphere-atmosphere-ionosphere Coupling

Entropy (Basel). 2020 Jan 16;22(1):110. doi: 10.3390/e22010110.

Authors

Shih-Sian Yang^{1

2}, Masashi Hayakawa^{2

3

4}

Affiliations

¹ Independent researcher, Jhongli P.O. Box 9-11, Taoyuan 32099, Taiwan.
² 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.
³ Advanced Wireless & Communications Research Center, UEC, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan.
⁴ Geoscent Technologies Inc., 2-8-11 Akasaka, Minato-ku, Tokyo 107-0052, Japan.

Abstract

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_w 9.0), while using the temperature profiles that were retrieved from ERA5. The potential energy (E_P) 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.

Keywords: atmospheric gravity wave; lithosphere-atmosphere-ionosphere coupling; reanalysis data; stratopause temperature and height; subionospheric VLF observations; the 2011 Tohoku earthquake.