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

1990年，在明尼苏达大学使用的低照度电视摄像机的首次观测中，发现了从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。研究发现，在平流层、中间层和较低的电离层中，这些现在被称为精灵和精灵的光发射是由强烈的云对地面放电引起的，并且这些现象伴随着强烈的无线电和伽马射线发射。精灵和精灵的光发射被认为是由大气分子/原子和电子之间的碰撞过程激发引起的，这些碰撞过程是由准静态电场或云对地放电产生的电磁脉冲激发的。我们根据高速光度计的光谱观测估计了电子能量。发现在光学发射开始时，胡萝卜状精灵的电子温度峰值为3-25 eV，柱状精灵的电子温度峰值为2-14 eV。在类胡萝卜精灵体中，电子温度随海拔的降低而升高，在海拔~ 80 km处的局部峰值为12 ~ 20 eV，对应于精灵的头发和头部区域之间的间隙。另一方面，可以肯定的是精灵是由负向云对地放电和正向云对地放电造成的。发现精灵的电子能量高达40 eV，这意味着在电离层下部有很强的电离。我们在日本进行了光学观测，在世界上首次展示了精灵和精灵在冬季的出现。我们还分析了以盘状扩散形式出现的“精灵晕”，揭示了其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.