15:45 〜 16:00
[PEM13-08] 熊本地震前の地表面垂直運動と電離圏
キーワード：地表面垂直運動、電離圏、ダイナモ電場
We studied the role of vertical ground motion as a driving force to excite acoustic gravity wave, which disturbs the ionosphere before Kumamoto earthquake. Data acquired with the slant gages distributed around the epicenter of Kumamoto earthquake which occurred on 14 April 2016 are used. Power spectrum density (PSD) is calculated from the vertical components measured with the slant gages. When the PSD increases, Daytime NmF2 reduces, and night time NmF2 increases, which can be explained by the intensified dynamo electric field. Two conditions to disturb ionosphere by the small ground motion are; the period of ground motion should be shorter than 2 hour, and the ground motion should continuously exist at least for one day, so that wave energy is continuously injected to the atmosphere. The PSD shows the minimum 5 days before, increases 2 days before, and then reduces one day before, following the drastic increase. Large part of the frequency spectrum of the ground motion appears around several 10 minutes to 2 hours.