Abstract. The propagation effect on electromagnetic pulses associated with negative return strokes is evaluated from data observed by direction finders for lightning location equipped with GPS clocks. Nine direction finders constitute a network in the northern part of the Honshu Island of Japan, which locates lightning by a method combining the direction finding and the time-of-arrival (TOA) technique. The delay of the peak of an electromagnetic pulse was evaluated to be negligible in propagation over seawater for distances less than 300 km, and its average was about 1.8/ The estimated arrival time of an electromagnetic pulse, based on the arrival time of the peak and the trigger time, gives smaller delay than the simple arrival time of the peak, but the difference is not significant. It would be better to compensate the peak time by evaluating the propagation effect in obtaining an estimate of the arrival time, to improve the accuracy of lightning location by using the TOA technique.

Abstract. Cloud-to-ground lightning flashes on and around the island of Java, Indonesia, in the tropical maritime continent region, were observed continuously by a magnetic direction-finder network for lightning location from December 1994 to January 1996. The annual ground flash density, estimated by correcting the raw data by using the detection efficiency of the network,

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SummaryA new technique of lightning location utilizing data of arrival time difference and direction of electromagnetic waves from 2 stations or 3 stations is evaluated. Combination of available modes in this time-difference and direction (TDD) technique can achieve accurate lightning location in a wider coverage area than that of the time-of-arrival technique. Simulation shows that TDD technique is capable of retrieving the site error curve in the magnetic direction finding considerably accurately. Systematic timing error associated with propagation effect deteriorates the accuracy of the TOA lightning location, especially in the exterior base line area. The existence of this phenomenon is confirmed by analyzing real lightning data.