Using a low-frequency lightning location system comprising nine stations, we have observed and analyzed 374 large and bipolar electric field change waveforms that occurred during the winter of 2012-2013. Since the waveforms are different from those produced by any well-studied lightning discharge processes, we refer to these source discharge events using a new name: large bipolar events (LBEs). LBEs can be characterized by the following features: (1) All have the same polarity as negative return stroke. (2) All exhibit a single bipolar pulse with a pulse width around 15 μs and similar positive and negative cycles. (3) All are located on the land along the Japan Sea coast, indicating they are probably associated with high grounded objects. (4) Most LBEs produce very large electric field changes that are even larger than that of positive and negative return strokes. (5) Most LBEs are temporally isolated within several milliseconds but are frequently followed by intracloud discharges after tens of milliseconds. (6) Most LBEs produce a single well-distinguished ionospheric reflection pulse, and the time difference between LBE pulse and the corresponding reflection pulse can be used to calculate ionospheric reflection height. It is speculated that LBE is a type of powerful and transient lightning discharge event produced within a compact region of strong electric field formed when the negative charge layer in thunderclouds is very close to the top of a tall grounded object.
Phased array radar with unprecedented high temporal and spatial resolution is used for the first time to analyze structures of thunderstorms producing lightning narrow bipolar events (NBEs). Locations of NBEs generally correspond well with the deepest convection, but in some thunderstorms extending higher than 15 km, positive NBEs cluster around, rather than right at the center of the core of deep convection. Negative NBEs are generally higher than positive NBEs and are usually produced at the cloud top of the thunderstorm. Positive NBEs, on the other hand, are always located well inside the thundercloud. It seems that negative NBEs can only be produced in very vigorous thunderstorms with cloud tops higher than about 14 km. Numerous thunderstorms with lower height produce few negative NBEs, indicating a height threshold for NBE production. On the basis of these findings, it becomes very convenient and accurate to monitor severe thunderstorms with negative NBEs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.