Main objective of this study is to examine simplication of electromagnetic measurement in ELFVLF band to monitor thunderstorm activity. To detect lightning discharge, receivers in ELF-VLF band are installed with unprecedented density (about 30 km apart) to make detection sensitivity to be high. To reduce data size, sampling rate of our electromagnetic measurement is set as 100 kHz, which is relatively lower than that of recent lightning observation to monitor thunderstorm activity, and precision of geolocation becomes about 10 km. Additionally, electrostatic field is also measured to monitor temporal variation of charge separation and discharge in cloud. In this paper, observation result of thundercloud above Ebina City, Kanagawa, Japan on September 6th, 2014 is summarized. Initial result indicates that charge and discharge in cloud at the early stages of isolated thunderstorm could be detected by using radio observation in ELF-VLF band and electrostatic measurement. This result indicates that electromagnetic measurement in ELF-VLF band, which has been traditionally designed to monitor lightning activity on a synoptic scale, can be utilized to monitor thunderstorm whose horizontal scale is about 10 km and to decrease cost of lightning observation substantially.
