HR: 0800h
AN: AE31B-0165    [Abstracts]
TI: Spatial and Temporal Structures of Sprites Observed with the Array Photometer on board the ROCSAT-2 Satellite
AU: * Adachi, T
EM: adachi@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai, 980-8578 Japan
AU: Fukunishi, H
EM: fuku@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai, 980-8578 Japan
AU: Takahashi, Y
EM: yukihiro@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai, 980-8578 Japan
AU: Hsu, R
EM: rrhsu@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, No.1, Ta-Hsueh Road, Tainan, 70148 Taiwan
AU: Su, H
EM: htsu@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, No.1, Ta-Hsueh Road, Tainan, 70148 Taiwan
AU: Chen, A
EM: alfred@phys.ncku.edu.tw
AF: Physics Department, National Cheng Kung University, No.1, Ta-Hsueh Road, Tainan, 70148 Taiwan
AU: Mende, S B
EM: mende@ssl.berkeley.edu.nospam
AF: Space Sciences Laboratory, University of California at Berkeley, Centennial Drive at Grizzly Peak, Berkeley, CA 94720-7450 United States
AU: Frey, H U
EM: hfrey@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California at Berkeley, Centennial Drive at Grizzly Peak, Berkeley, CA 94720-7450 United States
AU: Lee, L
EM: loulee@nspo.gov.tw
AF: National Space Program Office, 8F, 9, Prosperity 1st Road, Science-Based Industrial Park, Hsin-Chu, 30077 Taiwan
AB: Sprites are transient luminous events at the altitude of the mesosphere mostly induced by positive cloud-to-ground lightning discharges (+CGs). Past theoretical and experimental studies put forward the quasi-electrostatic (QE) model in which energetic electrons accelerated by the QE fields excite and ionize ambient neutral particles such as nitrogen molecules through collision processes. By measuring the spatio-temporal evolution and spectral characteristics of optical emissions, it is possible to investigate the physical and chemical processes occurring in sprites quantitatively. Miyasato et al. [2004] estimated electron energies by analyzing sprite data obtained from ground-based observations with a dual-color photometer, and suggested that strong ionizations occur at the initial stage of sprite halo. Ground spectral information of sprites, however, has large uncertainty due to the attenuation effects by atmospheric molecules and aerosol particles along the light path from the sprite emission region to the ground observation site. For that reason, optical observations from space are essential for the precise estimation of absolute luminosity. The ROCSAT-2 satellite with a scientific payload named ISUAL (Imager of Sprites/Upper Atmospheric Lightning) is the first satellite which observes transient luminous events such as sprites from space. The ISUAL is composed of an imager, a spectrophotometer, and an array photometer (AP). The AP 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. The AP has 16 channels arrayed in vertical and spatial resolution corresponds to ~11 km in the case of sprites occurring at the limb point 3315 km away from the satellite. The time resolution of 50 or 500 ŸEs enables us to detect vertical motions of sprites which have an average duration of several to tens of ms. From the middle of July to the end of August in 2004, we observed ~2210 lightning flashes, ~20 sprites, and ~100 elves. The average observation frequency of lightning and sprite flashes are 55 and 0.5 per day, respectively. The AP succeeded in detecting clear upward/downward vertical motions of sprites in both the blue and red channels with quite high signal-to-noise ratios. In this study, we discuss the spatio-temporal evolution and spectral characteristics of sprites in detail.
DE: 6061 Remote sensing
DE: 6062 Satellites
DE: 3324 Lightning
DE: 3329 Mesoscale meteorology
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting