HR: 0800h
AN: AE31B-0167    [Abstracts]
TI: Role of intracloud lightning discharges in occurrences of winter sprites
AU: * Ohkubo, A
EM: ohkubo@pat.geophys.tohoku.ac.jp
AF: Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Fukunihsi, H
EM: fuku@pat.geophys.tohoku.ac.jp
AF: Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Takahashi, Y
EM: yukihiro@pat,geophys.tohoku.ac.jp
AF: Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Adachi, T
EM: adachi@pat.geophys.tohoku.ac.jp
AF: Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AB: Sprite often occur as far as 50 kilometers horizontally away from the location of the parent CG discharges [Lyons, 1996], and long time delays more than 100 milliseconds from the parent CGs to sprite onset are also often reported [Bell et al., 1998; Fllekrug and Reising, 1998]. These results suggest the role of horizontal current channels in lightning discharges producing sprites. However, the role of horizontal components is still an open question. To capture the evolution of lightning discharge inducing sprites, we carried out broadband ELF/VLF sferic measurement during the winter sprite campaign at Tohoku University Iitate observatory (37.7oN, 140.7oE) in Japan. The campaign period is December 15, 2003 to the middle of February. We employed an II-CCD camera and two sets of multi-anode array photometers (MAPs) for optical measurement, and a VLF receiver with a vertical electric field dipole antenna and two horizontal crossed loop magnetic field antennas for VLF sferics measurement. The frequency range of the VLF receiver is 1 to 40 kHz for all antennas and output signals are recorded as an event trigger mode using an A/D board with a sampling rate of 100 kHz. Furthermore we use ELF data recorded at Onagawa Observatory of Tohoku University, Japan [Sato et al., 2003]. Orthogonal search coil magnetometers are installed and the output signals which are amplified and band pass filtered in the range of 1-100 Hz are recorded continuously using an analog-to-digital converter with a sampling rate of 400 Hz. It is found that VLF data associated with sprites show the occurrences of sferic clusters characterized by long durations (10 to 100 milliseconds) and higher frequency components (10 - 40 kHz) without exception. In addition, ELF waveform data show occurrences of positive transient bursts related to continuing currents in lightning discharges just coincidently with the occurrences of sferic clusters. Since sfeirc clusters are likely to be produced by intracloud discharges inducing horizontal current channels, we will discuss about the role of intracloud discharges and continuing horizontal currents in the sprite generation.
DE: 3324 Lightning
DE: 3360 Remote sensing
DE: 0342 Middle atmosphere--energy deposition
DE: 0600 ELECTROMAGNETICS
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting