Abstract:
The ISUAL gigantic jets (GJs) are categorized into three types from their generating sequence and spectral properties. Generating sequence of the type I GJs resembles that reported previously; after the fully developed jet (FDJ) established the discharge channel, the ISUAL photometers registered a peak that was from a return-stroke-like process. The associated ULF (ultra-low-frequency) sferics of these type I GJs indicates that they are negative cloud-to-ionosphere discharges (-CIs). Type II GJs begin as blue jets and then developed into GJs in similar to 100 ms. Blue jets also frequently occurred at the same region before and after the type II GJs. No identifiable ULF sferics of the type II GJs were found, though an extra event that has + CI ULF signature is probably a type II GJ. The FDJ streamer brightness of the type I GJs is similar to 3.4 times of that of the type II GJs. These evidences suggest that the type II GJs are composed of positive streamers. Type III GJs were preceded by lightning, and a GJ subsequently occurred near this preceding lightning. The spectral data of the type III GJs are dominated by lightning signals and the ULF data have high background noise; thus both cannot be properly analyzed. However, the average brightness of the type III GJs falls between those of the other two types of GJs. We propose that the discharge polarity of the type III GJs can be either negative or positive, depending on the type of the charge imbalance left by the trigger lightning.
