Characteristics of dart leader and attempted leader in a triggered lightning

Abstract

• Intuitive high-speed camera images exhibit clear attempted leaders and dart leaders, along with an analysis of development features and electric field characteristics, which makes up for the deficiency that other observation methods are easy to confuse the leader types. • A dart leader in a dart leader-return stroke sequence is considered similar to attempted leaders based on two-dimensional speed, light variation along the channel, and time intervals. • Dart leaders and attempted leaders are thought to be able to convert to each other which is related to the carried amount of charge. Attempted leaders (ALs) are a kind of downward leaders which unsuccessfully initiate a following return stroke in natural cloud-to-ground lightning and artificially triggered lightning. The relationship between ALs and dart leaders (DLs) is a topic of great concern. Some reported cases of ALs were difficult to identify. A negative artificially triggered lightning case was reported, including five dart leader-return stroke (DL-RS) sequences and two ALs in intuitively visual images. In this case, the two-dimensional (2D) speed of two ALs had an average of 0.46 × 10 7 m/s. The sum and maximum brightness of two ALs both increased initially and then slid down. The maximum brightness either descended from the beginning or remained for a while and then went down. Compared with DLs, the upper part of AL channels became obviously faint. Interestingly, the DL in the 4th DL-RS sequence performed like ALs. On the contrary, AL1 was similar to DLs in the early stage of development. DLs and ALs are considered to convert to each other. DLs convert to ALs when there is not enough negative charge for carrying from the cloud to the leader channel. Once the carrying charge is abundant, ALs convert to DLs as a result of initiating return strokes.