Title The electric field changes and UHF radiations caused by the lightning in Japan
Author(s) Z.-I. Kawasaki, T. Kanao, K. Matsuura, M. Nakano, K. Horii and K. Nakamura
Journal Geophysical Research Letters, 18, 9, 1711-1714 (1991)
Abstract The electric field changes, the magnetic field changes, and UHF radiation were observed during the rocket-triggered lightning experiment in winter storms. A remarkable discrepancy is noticed between electromagnetic field changes of flashes triggered with a rocket and an isolated wire that struck a power tower and flashes with a rocket and a grounded wire. Flashes to tower have a distinguishable first pulse of a large amplitude, which, we speculate, occurs at the moment of attachment of a measurements indicate that the triggered lightning process starts with a pulse series resembling a negative stepped leader. The electric field change records of rocket-triggered lightning in winter storms do not show the presence of rapid field variations typical for return strokes in natural cloud-to-ground flashes.

Title Long Laser-Induced Discharge in Atmospheric Air
Author(s) Z.-I. Kawasaki, K. Matuura, E. Fujiwara, Y. Izawa, K. Nakamura, C. Yamanaka
Journal Res. Lett. Atmos. Electr., 12, 139-142, (1992)
Abstract Long-gap discharge induction experiments are carried out by using a TEA CO2 Laser with the maximum energy of 100 Joules, to investigate the feasibility of Laser-Induced Lightning. A Laser-Induced flash over length of 6 m has been realized by using a new type focusing mirror. The relation between fifty percent flashover voltages, so called V50, and discharge length is presented.

Title Common physical processes in natural and triggered lightning in winter storms in Japan
Author(s) Z.-I. Kawasaki and V. Mazur
Journal J. of Geophys. Res., 97, D12, 12935-12945 (1992)
Abstract An analysis of measurements of electric, magnetic, and radiation field variations produced by rocket-triggered discharges in winter storms in Japan shows that a discharge initiated by a rocket with trailing and grounded wire is a negative leader that consists of continuous current and a pulse series associated with streamer development at the tip. The negative leader is not followed by a process analogous to a return stroke in cloud-to-ground flashes. Application of the electrostatic model of lightning as a bidirectional and uncharged leader in an ambient electric field to analysis of rocket-initiated discharges and positive cloud-to-ground flashes uncovers the commonality of processes occurring in both types of discharges.

Title Experiment of triggered lightning with rocket in Indonesia ; stroke to a lightning conductor
Author(s) K. Horii, S.Sumi, K. Nakamura, M.Yoda, Z.-I. Kawasaki, K.T. Sirait and A.M. Sunoto
Journal Trans. IEE of Japan, 113-B, 10, 1172-1173 (1993)

Title The study of the possibility of lightning triggering by means of a laser
Author(s) D. Wang, T. Ushio, Z.-I. Kawasaki, K. Matsuura, Y. Shimada, S. Uchida, C. Yamanaka, Y. Izawa, Y. Sonoi and N. Simokura
Journal J. Atmos. Electr., 14, 49-55 (1994)
Abstract To study the possibility of triggering techniques of lightning discharges with a laser plasma, several experiments were carried out with a CO2 pulse laser and a switching voltage generator. The following results were obtained. Both long straight discharges and zigzag discharges were induced with a laser plasma channel and the strong guiding effect of the laser channel has been confirmed. Laboratory investigation of the necessary condition for initiating and guiding a streamer with a laser plasma channel reveals that, (1) the necessary electric field for initiating a streamer with a laser plasma depends closely on the absorbed energy used to produce laser plasma channels and the minimum electric field is about 200kV/m, and (2) the necessary electric field for guiding a streamer by a laser plasma is lower than that of initiating a streamer and the minimum electric field is about 170kV/m. The simple calculation of the electric field distribution at the top of a grounded tower shows that a laser plasma channel may trigger a lightning discharge from the top of the tower.

Title A perliminary study on laser-triggered lightning
Author(s) D. Wang, Z.-I. Kawasaki, K. Matsuura, Y. Shimada, S. Uchida, C. Yamanaka, E. Fujiwara, Y. Izawa, N. Simokura and Y. Sonoi
Journal J. of Geophysical Research, 99, D8, 16907-16912 (1994)
Abstract As a preliminary study on triggering lightning with a CO2 high-power laser, we carried out laser-triggered discharge experiments to investigate the necessary conditions for initiating and guiding an electrical streamer with a CO2 laser-produced plasma channel. We found the following. (1) The necessary electric field for initiating a streamer with the plasma channel depends closely on the absorbed energy for producing the plasma channel and not on the length of the plasma channel. The higher the absorbed energy, the smaller the necessary electric field. The minimum electric field is about 200kV/m. (2) The necessary electric field for guiding a streamer by the plasma channel is lower than that for initiating a streamer. The minimum electric field is about 170kV/m. Furthermore, we observed the electric field at the top of a 50-m tower and the field on the ground simultaneously during 10 Japanese winter thunderstorms. The observed results agree with theoretical calculations showing that the field at the top of a 50-m tower is on average 2 orders larger than the field on the ground. We conclude that it is highly possible to trigger a lightning discharge if we shoot a CO2 laser-produced plasma channel upward through the top of a high grounded tower under conditions of high thunderstorm electric fields.

Title A Possible Way to Trigger Lightning Using a Laser
Author(s) D. Wang, T. Ushio, Z.-I. Kawasaki, K. Matsuura, Y. Shimada, S. Uchida, C. Yamanaka, Y. Izawa, Y. Sonoi and N. Simokura
Journal J. of Atmospheric and Terrestrial Physics, 57, 5, 456-466 (1995)
Abstract To study the possibility of triggering lightning with a laser plasma, laboratory laser-induced discharge experiments have been carried out and the following results were obtained. Both long straight and zigzag laser induced discharges between rod-rod electrodes were realized and the effective guiding effect of laser channels for electrical discharges was confirmed. With plane-plane electrode configuration, the investigation concerning the necessary condition for initiating and guiding a streamer reveals that the necessary electric field for initiating a streamer with a laser plasma depends closely on the absorbed energy used to produce laser plasma channels, the minimum electric field is about 200 kV/m, and that the necessary electric field for guiding a streamer by a laser plasma is lower than that for initiating a streamer and the minimum electric field is about 170 kV/m. We propose to use the local electric field near the top of a grounded tower as the necessary field for a laser-produced channel to trigger an upward leader and have proved that this is feasible.

Title Progression of Leader System in Long Gap Laser Triggered Discharges
Author(s) D. Wang, N. Takagi, T. Watanabe, T. Ushio, Z.-I. Kawasaki, K. Matsuura, Y. Shimada, S. Uchida and C. Yamanaka
Journal J. of Atmospheric Electricity, 15, 2, 67-74 (1995)
Abstract The progression of laser induced discharges was observed through their streak photo taken by an ICC (Image Converter Camera). It was noted that in laser induced discharges, leaders initiate at a time lag of about 2-3 Ás after the firing of laser. This may be the time necessary for a plasma bead to grow into a critical size enough to initiate a streamer. Laser-guided leaders appear to have the same behavior in progression of natural leaders, but they have higher propagation velocities and no branches. A laser induced discharge generally consists of the following stages: Stage I with rapid propagation speed and bright illumination, stage II with slow speed and no illumination, stage III with bidirectional propagation velocities for the stages I, II, III are about 2x106m/s, 5x105m/s, 2x106m/s, respectively. No correlation can be found between the velocities of the different stages. The velocities for backward leader, reillumination process and connecting leader were estimated to be 2x106m/s, 1.5x107m/s and 2.4x106m/s, respectively.