Imaging and spectrophotometric measurement of lightning by JEM-GLIMS

The purpose of the present study is to clarify the optical characteristics of lightning and to assess the effectiveness of multi-color imaging and photometric measurements in advancing our understanding of the discharge physics, meteorological aspects, and climatological properties of lightning. The instrument used here is JEM-GLIMS on board the international space station. GLIMS observes lightning and TLEs in the nadir direction with optical and radio sensors: dual-color imagers, six-color photometers, a VLF monopole antenna and a set of VHF interferometer. Since the initial operation in November 2012, GLIMS detected 1035 lightning events by imagers and photometers. The estimated peak irradiance of lightning at a wavelength range of 600-900 nm was in the range of 3.3x10-5-6.1x10-3 W/m2 with a median value of 2.4x10-3 W/m2, which is roughly equivalent to the top 10 % bright lightning events observed by FORTE in the past. The obtained photometric data showed various lightning waveforms. In some cases, one or several distinctive impulsive emissions occur and sometimes continuous emissions follow, which are suggestive of return strokes and continuing current. While in other cases, the waveform data consist of numerous intermittent optical pulses suggesting the occurrence of intra-cloud discharges. Interestingly, spectral data show the red-shift of the color of lightning at the time of possible return stroke, which could also be used as an indicator of ground discharge. Concurrent image data show complicated spatial structures which are variable from event to event in terms of pattern complexity, horizontal size, and optical intensity. These results suggest that GLIMS efficiently obtains spatiotemporal and spectral properties of lightning. In the paper, we will thoroughly examine the data obtained by the GLIMS dual-color imager and spectrophotometer.