Processes of optical and radio emissions in the upper atmosphere induced by cloud to ground discharge

1990年，美国明尼苏达大学的一台微光电视摄像机在进行tcst观测时，发现了平流层到电离层的放电现象。自从这一发现以来，人们从地面、飞机和航天飞机上进行了大量的观测。据发现，这类在平流层，中层和低电离层的光发射，现在称为精灵和精灵，是由一个强烈的云对地放电引起的，这种现象伴随着强烈的无线电和伽马射线发射。精灵和精灵的光学发射被认为是由经由大气分子/原子与电子之间的碰撞过程的激发引起的，所述碰撞过程由云对地放电产生的准静态电场或电磁脉冲激励。我们根据高速光度计的光谱观测估计了电子能量。结果表明，在光发射开始时，类胡萝卜子晶和柱状子晶的电子温度分别在3-25 eV和2-14 eV处有一个峰值。在胡萝卜状精灵的身体中，电子温度随着高度的降低而趋于增加，在海拔1080 km处的12-20 eV的局部峰值对应于精灵的头发和头部区域之间的间隙。另一方面，证实了精灵是由负的云对地放电以及一个积极的。电子能量的精灵被发现达到40 eV，这意味着在低电离层的强电离。我们在日本进行了光学观测，并在世界上首次展示了精灵和精灵在冬季的出现。我们还分析了“精灵晕”，它表现为一个弥漫的方式与盘状的形状，揭示了它的发光强度和电子温度的时空结构。

In 1990 a discharge phenomenon from the stratosphere to the ionosphere was found during the tcst observation of a low-light TV camera employed by University of Minnesota. Since this discovery a lot of observations from ground, aircraft and space shuttle have been carried out. It is found that these kinds of optical emissions in the stratosphere, mesosphere and lower ionosphere, now called sprites and elves, are induced by an intense cloud to ground discharge and that the phenomena are accompanied by strong radio and gamma ray emissions. Optical emissions of sprites and elves are considered to be caused by an excitation via collision processes between atmospheric molecules/atoms and electrons that are energized by quasi-static electric field or electromagnetic impulse generated by a cloud to ground discharge. We estimated the electron energies based on the spectral observations with high-speed photometers. It is found that electron temperature has a peak of 3-25 eV for carrot-like sprites and 2-14 eV for column type sprites at the onset of the optical emission. In a body of carrot-like sprites the electron temperature tends to increase as altitude decreases with a local peak of 12-20 eV at an altitude of 〜80 km that corresponds to gap between hair and head region of sprites. On the other hand, it is confirmed that elves are caused by a negative cloud to ground discharge as well as a positive one. Electron energy of elves was found to reach up to 40 eV, which implies a strong ionization in the lower ionosphere. We conducted optical observation in Japan and showed the occurrences of sprites and elves in winter for the first time in the world. We also analyzed the "sprite halo" which appears as a diffuse fashion with a disk-like shape and revealed its time-space structure of luminous intensity and electron temperature.