2002 Fiscal Year Final Research Report Summary
Nonlinear full-wave analysis of atmospheric luminous emissions above lightning discharges
| Project/Area Number |
13640447
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | Kanazawa University |
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Principal Investigator |
NAGANO Isamu Kanazawa University, Graduate School of Natural Science and Technology, Professor, 自然科学研究科, 教授 (50019775)
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| Co-Investigator(Kenkyū-buntansha) |
YAGITANI Satoshi Kanazawa University, Graduate School of Natural Science and Technology, Associate Professor, 自然科学研究科, 助教授 (30251937)
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| Project Period (FY) |
2001 – 2002
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| Keywords | Lightning discharge / Electromagnetic pulse / Ionosphere / Optical emission / Elves / Electron heating / Full wave analysis / Parallel computation |
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| Research Abstract |
We have investigated the generation mechanism of "elves," the expanding optical rings created 85-95 km above lightning flashes. Elves are believed to be generated through the excitation of the first positive band of nitrogen molecule, which is stimulated by the electron heating due to the lightning-generated intense electromagnetic pulses (EMPs) illuminating the lower ionosphere. By using a full-wave analysis, we have computed rigorously the propagation in a magnetized ionosphere of the EMPs radiated by lightning current strokes. When incident into the lower ionosphere, an intense EMP heats the electrons and then enhances the collision frequency there, causing the absorption of the EMP energy. Though the full wave analysis cannot treat such a nonlinear temporal change of ionospheric parameters, we have approximately incorporated this effect into the calculation by modifying the up-going EMP in the ionosphere. Making use of a newly developed parallel-computation system with 10 PCs, we have computed the temporal and spatial evolution of elves. Computed results have shown that an optical ring is created at the altitudes of 85-100 km above the lightning, quickly expanding horizontally over 200 km within < 1 ms, which is consistent with the actual observations of elves. It has also been found that because of the EMP propagation in the whistler mode along the Earth's magnetic field line above 90 km, there appears appreciable north-south and east-west asymmetry in the elves ring structures.
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