HR: 1340h
AN: AE23A-0993    [Abstracts]
TI: Spatiotemporal and Spectral Characteristics of Sprites and Gigantic Jets Derived from ISUAL/Array Photometer Measurements
AU: * Adachi, T
EM: adachi@pat.geophys.tohoku.ac.jp
AF: Tohoku University, Aramaki-Aoba, Sendai, 980-8578 Japan
AU: Fukunishi, H
EM:
AF: Tohoku University, Aramaki-Aoba, Sendai, 980-8578 Japan
AU: Takahashi, Y
EM:
AF: Tohoku University, Aramaki-Aoba, Sendai, 980-8578 Japan
AU: Hiraki, Y
EM:
AF: Tohoku University, Aramaki-Aoba, Sendai, 980-8578 Japan
AU: Yamamoto, K
EM:
AF: Tohoku University, Aramaki-Aoba, Sendai, 980-8578 Japan
AU: Hsu, R
EM:
AF: National Cheng Kung University, Tainan, Tainan, 70148 Taiwan
AU: Su, H
EM:
AF: National Cheng Kung University, Tainan, Tainan, 70148 Taiwan
AU: Chen, A B
EM:
AF: National Cheng Kung University, Tainan, Tainan, 70148 Taiwan
AU: Mende, S B
EM:
AF: University of California, Berkeley, Berkeley, CA 94720 United States
AU: Frey, H U
EM:
AF: University of California, Berkeley, Berkeley, CA 94720 United States
AU: Lee, L C
EM:
AF: National Space Program Office, Hsin-chu, Hsin-chu, 30077 Taiwan
AB: Sprites are electrical discharges above active thunderstorms occurring at mesospheric altitudes [Stanley et al., 1999; Stenbaek-Nielsen et al., 2000] while gigantic jets span from the top of thundercloud to the lower ionosphere [Pasko et al., 2002; Su et al., 2003] In this study, we report the spatiotemporal and spectral characteristics of sprites and gigantic jets observed with the ISUAL/array photometer on the FORMOSAT-2 satellite. The array photometer provides us spectral information by measuring two wave length ranges of 360-470 nm and 520-750 nm selected by blue and red filters, respectively. Each photometer has sixteen channels arrayed in vertical and sampling frequency of 20 kHz for the initial 18 ms and 2kHz for the following 292 ms, with which we can detect fast vertical motion of optical emissions. During the period from July 2004 to July 2005, the ISUAL observed ~130 sprites and a gigantic jet. By analyzing the array photometer data, we clarify that sprites are induced within 1-6 ms after transient emissions of lightning discharges while a gigantic jet is not accompanied with such transient lightning emissions as seen in the sprite events. The initial optical emissions of sprites occur at mesospheric altitudes and propagate upward/downward direction with vertical velocities of 2-11x10⁷ m/s, in close agreement with past observational results [Stanley et al., 1999; McHarg et al., 2002]. On the other hand, optical emissions of a gigantic jet propagate upward from the cloud top with a vertical speed of <1x10⁷ m/s at the initial leading-jet stage [Su et al., 2003]. At the following stage, the upward propagation speed exceeds 4x10⁷ m/s and emissions extend to the lower ionosphere. The obtained results are discussed in association with past observational and theoretical results.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3359 Radiative processes
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005