Upward Lightning Observed by LF Broadband Interferometer

Abstract

We have been designing and developing a 3-D lightning location system based on the broadband digital interferometry technique in LF bands. The LF broadband digital interferometer (LF DITF) consists of four or more LF receivers which detect electromagnetic (EM) waves in a wide frequency range from 400 Hz to 1 MHz associated with lightning discharges. Since each receiver detects EM waves in LF, the LF DITF is able to locate lightning discharges in several hundred kilometers. During the winter season in 2010-2011, a simultaneous observation of a LF DITF, a VHF DITF, and Rogowski coils was conducted in Hokuriku, Japan, which borders the Sea of Japan, for evaluation of the LF DITF for locating upward leaders and further understanding of winter lightning in Japan. We show the time series variation of the cases of a bipolar lightning flash and of an upward negative flash.