Geomagnetic conjugate observation of therinospheric waves at midlatitudes

(1)研究了用气辉成像仪在日本茂名观测到的夜间中尺度行进电离层扰动(MSTID)。在OI(630.0 nm和777.4 nm)的气辉图像中，该结构被确认为以50m/S的速度向西南移动的NW-SE带结构。我们发现，-1.2mV/m的电场振荡足以重现观测到的气辉幅度。这个模拟的电场与DMSP F15卫星在我们观测期间经过茂崎上空时观测到的电场相当。DMSP离子漂移数据表明，偏振电场的振荡与气辉图像中的MSTID结构有关。(2)我们发现在两个半球都有大范围的赤道F区气辉亏损延伸到中低纬度。观测点位于中低纬地磁共轭点。在日本SATA(磁纬24°N)及其地磁共轭点澳大利亚达尔文(磁纬22°S)，用两台全天成像仪同时观测到了赤道等离子体气泡造成的630.0 nm气辉强度的明显耗尽。这些观测表明，赤道电离层中的等离子体损耗沿着地磁线延伸。(3)我们首次报道了在中纬度地区使用两台全天气辉成像仪同时观测到两个半球地磁共轭点处的MSTID。日本SATA的一台630纳米全天成像仪探测到了波前从西北向东南拉长的MSTID。在澳大利亚达尔文地磁共轭点观测到波前从西南向东北方向拉长的MSTID。沿地磁力线从达尔文绘制到其磁共轭点的MSTID结构与SATA图像中的MSTID结构非常吻合。这一结果表明，极化电场在MSTID的产生中起着重要作用。

(1)We have investigated a nighttime medium-scale traveling ionospheric disturbance(MSTID) observed by an airglow imager at Shigaraki, Japan. The structure was identified in the airglow images of OI (630.0 nm and 777.4 nm) as NW-SE band structures moving southwestward with a velocity of 50 m/s. We found that an electric field oscillation of -1.2 mV/m was sufficient to reproduce the observed airglow amplitudes. This modeled electric field was comparable to that observed by the DMSP F15 satellite as it passed over Shigaraki during our observing period. The DMSP ion drift data show that the oscillation of the polarization electric field correlated with the MSTID structure in the airglow image.(2)We found a large-scale equatorial F-region airglow depletions extending to low-midlatitudes in both hemispheres. The observational sites were located at low-midlatitude geomagnetic conjugate points. Clear depletions of 630.0-nm airglow intensity due to equaterial plasma bubbles were simultaneously observed with two all-sky imagers at Sata, Japan (magnetic latitude 24° N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22° S). These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.(3)We report for the first time simultaneous observations of MSTIDs at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky imager at Sata, Japan, detected MSTIDs with a wave front elongated from NW to SE. MSTIDs with a wave front elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines coincide closely with those in the Sata images. This result suggests that polarization electric field plays an important role in the generation of MSTIDs.