VLF signatures of ionospheric perturbations associated with winter lightning in the Hokuriku area of Japan

The VLF signature of ionospheric perturbations associated with winter lightning in the Hokuriku area (Japan) were investigated over a 3-month period (December 2000 to February 2001). During this observation period, no optical phenomena were observerd; thus, the presently reported observation period was not so active as the observatian period for the previous winter (Y. Hobara et al. ; Geophys. Res. Lett., 28, 935, 2001). Based on the VLF subionospheric observations of the NWC (Australia) signal obtained at Moshiri (Hokkaido) and Kasugai (near Nagoya), we obtained the following results: (1) Trimpis tend to occur when lightning activity is enhanced, (2) Trimpis are observed when the causative lightning is very close to the great circle path, and (3) the amplitude of the scattered signal is in the range of -12dB to -28dB (with respect to the unperturbed signal), independent of the polarity. These characteristics lead us to conclude that the Trimpis in our observations are due to the electromagnetic pulse of lightning discharges occurring close to the great circle path and with sufficient charge transfer

Characteristics of subionospheric VLF perturbations associated with winter lightning around Japan

VLF signature of ionospheric perturbations associated with winter lightning discharges around Japan has been investigated during 3 months observation (December 2000 through February 2001). During this period it seems that there are no optical phenomena in the Hokuriku area (Sea of Japan side) indicating that our period was not extremely active in lightning as compared with the previous winter (Y. Hobara et al., Geophys. Res. Lett., 28, 935, 2001). Based on the VLF subionospheric observation at Moshiri (Hokkaido) and Maizuru (near Kyoto) for NWC (Australia) and NPM (Hawaii) transmitter signals, we have found the following results; (1) Trimpis tend to occur at least when the lightning activity is enhanced independent of the polarity, (2) Trimpis are observed when the causative lightning is located not only on the Sea of Japan side but also on the Pacific Ocean side, and (3) the occurrence of Trimpis in the Hokuriku area is more enhanced than that on the Pacific side, which is discussed with a special reference to the different meteorological conditions