HR: 1340h
AN: AE23A-0989    [Abstracts]
TI: Spectral characteristics of elves observed by FORMOSAT-2/ISUAL
AU: * Takahashi, Y
EM: yukihiro@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Chikada, S
EM: chikada@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Adachi, T
EM: adachi@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Yamamoto, K
EM: katsura@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Fukunishi, H
EM: fuku@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Su, H
EM: htsu@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, Tainan, Tainan, Tainan 701 Taiwan
AU: Chen, A
EM: alfred@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, Tainan, Tainan, Tainan 701 Taiwan
AU: Hsu, R
EM: rrhsu@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, Tainan, Tainan, Tainan 701 Taiwan
AU: Mende, S
EM: mende@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720-7 United States
AU: Frey, H
EM: hfrey@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720-7 United States
AU: Lee, L
EM: louleer@narl.org.tw
AF: National Space Program Office, Prosperity 1st Road, Science-Based Industrial Park, Hsinchu, 300 Taiwan
AB: Elves is one of the transient luminous events (TLEs) in the upper atmosphere, which would cause significant heating and ionization of the atmosphere. In order to examine their chemical and electromagnetic effects on the lower thermosphere/ionosphere quantitatively, it is required to measure the spectral characteristics of elves with absolute scales as well as its size and forms. However, on the ground observations atmospheric attenuation that is time variable and strongly dependent on wavelength prevents us to obtain the true spectral information. Spacecraft is the only perfect platform to realize the well-calibrated spectral measurement. ISUAL instruments onboard FORMOSAT-2 satellite provided us the first opportunity to measure the absolute optical characteristics of TLEs with sufficient high time resolution. The array photometer (AP), one of three ISUAL instruments, is capable of measurements of absolute luminosity with 16 FOVs aligned in vertical at two wavelength ranges, namely, 360-470 nm for N2 2nd Positive and N2 1st Negative bands and 520-750 nm for N2 1st Positive and N2 Meinel bands. The intensity ratio of those two colors reflects the energy distribution of electrons produced in the elves by impulse electric field from parent lightning discharge in the troposphere. ISUAL already captured over 800 elves. It is recognized that shape of elves is not always doughnut-like but sometimes disk without center hole. Such variety could be caused by intra cloud discharge especially by horizontal component. We selected out 25 elves events from over 700 events captured by ISUAL imager, on the condition that they have enough intensity both in blue and red channels without saturations or contamination by cloud flash. It is also required that the whole emissions of elves are in the coverage of AP_fs FOV and that the parent CG/IC discharges are identified by our ground ELF network. We examined the relationships between the intensity ratio and intensity of each channel, ELF power and geographical location. Indeed the number of 25 is not statistically sufficient, we couldn_ft find out any clear relationship for them at this moment. However, there is a tendency that high blue/red ratio events occur in the summer hemisphere while low blue/red ratio events in the winter hemisphere. This fact suggests that the lower ionospheric structure could affect the characteristics of elves.
DE: 2423 Ionization processes (7823)
DE: 2435 Ionospheric disturbances
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005