Observation of Compact Intracloud Discharges using VHF broadband interferometer

Compact Intracloud Discharges (CIDs) is a distinct intracloud lightning discharge characterized by strong VHF emissions, and one of the most mysterious lightning events. In this paper, the CIDs channel evolution images obtained by using VHF broadband interferometers are presented for the first time. Analysis of 11 CIDs shows that the channels of CIDs develop mainly in a vertical direction. The vertical scale of CIDs is in the range of 0.40 - 1.9 km. The average duration of VHF broadband emissions is 15 μs. The average apparent speed of CIDs is in a range of 0.44 - 1.0 × 10⁸ m/s with a mean value of 0.61×10⁸ m/s. The temporal-spatial evolution of the radiation sources of the CIDs shows an oscillation pattern, confirming the previous prediction that there is an oscillating current being reflected at the two ends of the CIDs channel. The estimated speed of the current wave in the CIDs channel is in a range of 0.56 - 2.6 × 10⁸ m/s with a mean value of 1.4 × 10⁸ m/s.