Characteristics of TLE-producing lightning in a coastal thunderstorm

Observing from southern Taiwan on 2 August 2010, a thunderstorm near Luzon Island, Philippines, about 500 km away was found to produce 72 transient luminous events (TLEs). Besides optical images, ULF and VLF sferics of lightning from this thunderstorm were also recorded. This work examines the characteristics of TLE-producing lightning through studying their ULF and VLF sferics. The attenuation of ULF and VLF sferics in the Earth cavity is obtained through analyzing the sferics associated with Imager of Sprite and Upper Atmospheric Lightning elves that occurred within ~1500 km of Taiwan. Amplitudes of the ULF and the VLF sferics are found to vary as D^−0.871 and D^−1.207, respectively, where D is the source distance from the sferic stations. After normalizing the sferics from the 2 August 2010 storm to 500 km distance, the ratio of the peak ULF and the VLF magnetic fields is found to be distinct for different TLE-producing lightning. The ratio for the halo-producing lightning is nearly 3 times that of the elve-producing lightning, but it is comparable to that of the halo-sprite-producing lightning, although the ULF strength for the halo-sprite lightning is significantly larger than that for the halo lightning. Therefore, it is possible to distinguish between the TLE-types using the ULF to VLF peak ratio or the strength of ULF/VLF band emissions of the parent lightning. Comparison of numerically simulated and the observed lightning radiation fields indicates that the best fit discharge time of the elve lightning is about 100 µs, while that for the halo-producing lightning is between 200 and 500 µs.