Research on Lightning Activity in the Tropics

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1. In the first year, the lightning location system, consisting of three electromagnetic pulse receivers, was installed. These receivers are precisely time-synchronized by GSP,and observe lightning electromagnetic pulses including their incoming directions. In the second year, a fourth station was added to improve the performance of the system.2. A new technique of lightning location, which combines the direction finding and the time-of-arrival techniques, is employed in the Java lightning location system. The theoretical analysis shows that the new technique is quite effective in increasing the detection efficiency without much deteriorating the location accuracy. The time-of-arrival technique requires at least three stations simultaneously receiving the same electromagnetic pulse to locate its source, whereas two stations only are required in the new technique. The influence of the apparent propagation delay of the electromagnetic pulse over land due to its finite conductivity is theoretically investigated, and the similarity of the theoretical and observed results proves that the finite ground conductivity really affects the location accuracy. These newly obtained results are published on the Transactions of IEE of Japan.3. The analysis of data for one and a half years reveals the following lightning characteristics in the tropics. The yearly variation is characterized by the rainy season and the dry season. Lightning activity is observed almost every day during the rainy season roughly from October until April. The characteristics of lightning do not much differ from those of summer in Japan, though the lightning flash density is about one order higher on the Java Island. The diurnal variation exists and differs on the land and on the sea. These characteristics of lightning in the maritime-continent area are revealed for the first time, and will be presented at the International Conference on Atmospheric Electricity in June 1996.