Initiation of lightning flashes simultaneously observed from space and the ground: Narrow bipolar events

We investigate the initiation of four lightning flashes detected from ground by means of the Colombia Lightning Mapping Array (Colombia-LMA) and simultaneously observed from space by the optical sensors of the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station (ISS), the Geostationary Lightning Mapper (GLM), and the Lightning Imaging Sensor on the ISS. The initiations of the flashes are characterized by isolated and predominant optical blue pulses (337.0 nm). In three of the flashes, red emissions (777.4 nm), a dominant line of hot lightning, were not detected during their initiation. In these cases, the initiations were also accompanied by bipolar VLF/LF waveform with a narrow short duration (<40 µs) and VHF emissions with high radio frequency power (