HR: 1340h
AN: AE23A-1005    [Abstracts]
TI: A study on TEC monitoring using VHF electromagnetic wave caused by lightning
AU: * Taniguchi, T
EM: taniguti@comf5.comm.eng.osaka-u.ac.jp
AF: Graduate School of Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 5650871 Japan
AU: Morimoto, T
EM: morimoto@comm.eng.osaka-u.ac.jp
AF: Graduate School of Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 5650871 Japan
AU: Kawasaki, Z I
EM: zen@comm.eng.osaka-u.ac.jp
AF: Graduate School of Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 5650871 Japan
AU: Hirata, A
AE23A-1005 AF: Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, 4668555 Japan
AB: This paper analyzes propagation characteristics of wideband electromagnetic (EM) wave in the ionosphere. The influence of total electron contents (TEC) of the ionosphere on the propagation of EM wave is investigated numerically. Our attention is paid to VHF band, which is dominant frequency band of EM waves emitted from lightning discharges. It is reasonable to use these waves because of frequent occurrence in nature, and thus these EM waves experience significant dispersion as compared with microwaves during the propagation in the ionosphere. The refractive index of the propagation in the ionosphere is derived by using the equation of Appleton-Hartree. The ionosphere is divided into slabs with the thickness of 1 km, in which the parameters of ionosphere are assumed as constant. Particularly, the altitude distribution of electron density is taken into consideration. From Maxwell_fs equations in an anisotropic medium, the propagation constant of a plane wave can be obtained, and transfer function in each layer can be derived. The transfer function from the lower boundary of the ionosphere to an arbitrary altitude can be obtained by multiplying them. From this transfer function and a known incident EM wave, an electric field of the EM wave at arbitrary altitude can be obtained by the inverse Fourier transform. Variations of pulse width and difference in the arrival time between each frequency component due to the dispersion in the ionosphere were revealed. It was found that the difference in the arrival time between the frequency components of 26 MHz and 48 MHz is about 30μs in daytime. This result was in good agreement with the data obtained from the FORTE satellite. Additionally, the mode splitting at the low frequency was confirmed. When the EM wave propagates through the ionosphere, the left circular component travels as ordinary mode (O-mode), while the right circular component travels as extraordinary mode (X-mode). The O-mode arrives first, with the separation determined by the background magnetic field. The point to be stressed is that group delay of the EM wave was dependent on the altitude distribution of electron density, especially when the peak electron density was the order of 10¹²[m^-3] or more.
DE: 0644 Numerical methods
DE: 2400 IONOSPHERE (6929)
DE: 2487 Wave propagation (0689, 3285, 4275, 4455, 6934)
DE: 3324 Lightning
DE: 6934 Ionospheric propagation (0689, 2487, 3285, 4275, 4455)
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005