Broad band interferometric measurement of rocket triggered lightning in Japan

Abstract

A broad band interferometer to investigate the location of radio sources due to lightning flashes in two dimension has been manufactured and evaluated during the Rocket Triggered Lightning Experiment in Japan. Having high digitization rate, a broad band interferometer is not able to record the entire radiation process emitted by a lightning discharge. Therefore, we introduced a method of sequential triggering for each electromagnetic pulse that allows to record as long periods of radiation as we need. We obtained several data sets of upward stepped leaders for both negative polarity and positive one during the experiment. The apparent speed of an upward negative leader is estimated at 6 × 105 m/sec. The time intervals between successive electromagnetic pulses are from 11 to 93 microseconds with a mean of 22 microseconds. A triggered lightning to an experimental power transmission tower, normally it is called an altitude triggered lightning, is also conducted. One of the altitude triggered lightning lowered negative charges to the tower. In this case both the negative downward leader and the positive upward one can be generated. Some isolated pulses emitted by the downward negative stepped leader which attaches to the transmission tower are observed and located. Pulses emitted by the positive upward leader penetrated into a negatively charged region of a thundercloud are also observed. The location of radiation sources are distributed within a few degrees of azimuth. The time intervals between successive pulses are from 14 to 188 microseconds with a mean of 78 microseconds.