2000 Fiscal Year Final Research Report Summary
Processes of optical and radio emissions in the upper atmosphere induced by cloud to ground discharge
| Project/Area Number |
10304036
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (A).
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Space and upper atmospheric physics
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
FUKUNISHI Hiroshi Tohoku University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (90099937)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
MURATA Isao Graduate School of Science, Tohoku University, Research Associate, 大学院・理学研究科, 助手 (00291245)
TAKAHASHI Yukihiro Graduate School of Science, Tohoku University, Lecturer, 大学院・理学研究科, 講師 (50236329)
WATANABE Shigeto Hokkaido University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (90271577)
NAGANO Isamu Kanazawa University, Graduate School of Technology, Professor, 工学部, 教授 (50019775)
SAKANOI Takeshi Graduate School of Science, Tohoku University, Research Associate, 大学院・理学研究科, 助手 (80271857)
|
|---|
| Project Period (FY) |
1998 – 2000
|
| Keywords | sprites / elves / lightning / mesosphere / thermosphere / Hokuriku / winter / spectrum |
|---|
| Research Abstract |
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.
|
