[S11-1] Geo & space technologies to study pre–earthquake processes: Observation, modeling, forecasting I

[S11-1-02] Modification of ionosphere before March 11 2011 Tohoku earthquake

^○Koichiro Oyama^{1, 2, 3}, C.H Chen¹, L Bankov⁴, M Devi⁵, K Ryu⁶, J.Y Liu⁷, H Liu², T Uozumi² (1.National Cheng Kung University, Tainan, Taiwan, 2.Kyushu University, Fukuoka, Japan, 3.Coltd Asia Space Enviornment Research Consortium, Sagamihara, Japan, 4.Space Research Institute, Sophia, Bulgaria, 5.Gauhati University, Assam, India, 6.Korean Advanced Institute of Science and Technology, Daejeon, Korea, 7.National Central University, Jhong-Li, Taiwan)

invited

Ionosphere disturbance which was seen prior to an earthquake which occurred on 11 March2011 off the coast of Tohoku was studied. Ionosphere data which were used are: O+ density acquired with US satellite DMSP, and NmF2, and h'F obtained by ionosondes. Global Ionosphere Model (GIM) is used as side evidence to compliment findings from DMSP data and ground based data..
Although during the earthquake preparation period, magnetic disturbance is strong, global survey of ground based foF2 shows that special disturbance is limited to earthquake area. Satellite data(DMSP and GIM) analysis shows three important findings before the occurrence of the earthquake; (1) Over geomagnetic equator enhancement of O+ is found, (2) midlatitude trough is formed before the earthquake and it moves toward lower latitude as EQ day approaches, and (3) no clear difference of O+ behavior between east and west of the epicenter is identified. Night time NmF2 at high latitude ionosonde stations such as Khavalovsk, and Beijin shows 2 days oscillation from 5 March and disappears on the 12th March. As the latitude of the station is lower, 2 days oscillation becomes unclear, and the duration of the appearance is shorter.
In order to explain both ground based and satellite data consistently, one idea of enhanced east/west ward dynamo electric field during daytime/ nighttime is discussed. We presume gravity wave of very small amplitude as a source of dynamo E field modification. Internal gravity wave of extremely small amplitude cause d by ground motion interact with planetary scales waves below 10 km , and is amplified. The amplified IGW propagate to the dynamo region. Several observational facts which are favour to the generation of IGW are described. Finally we stress the need of satellite constellation in order to obtain the global morphology of ionosphere disturbance and to identify the mechanism, which at least provides us the material to judge applicability to future earthquake prediction.