Three‐Dimensional Reconstruction of Cloud‐to‐Ground Lightning Using High‐Speed Video and VHF Broadband Interferometer

Abstract

The time resolved three‐dimensional (3‐D) spatial reconstruction of lightning channels using high‐speed video (HSV) images and VHF broadband interferometer (BITF) data is first presented in this paper. Because VHF and optical radiations in step formation process occur with time separation no more than 1 μs, the observation data of BITF and HSV at two different sites provide the possibility of reconstructing the time resolved 3‐D channel of lightning. With the proposed procedures for 3‐D reconstruction of leader channels, dart leaders as well as stepped leaders with complex multiple branches can be well reconstructed. The differences between 2‐D speeds and 3‐D speeds of leader channels are analyzed by comparing the development of leader channels in 2‐D and 3‐D space. Since return stroke (RS) usually follows the path of previous leader channels, the 3‐D speeds of the return strokes are first estimated by combination with the 3‐D structure of the preceding leaders and HSV image sequences. For the fourth RS, the ratios of the 3‐D to 2‐D RS speeds increase with height, and the largest ratio of the 3‐D to 2‐D return stroke speeds can reach 2.03, which is larger than the result of triggered lightning reported by Idone. Since BITF can detect lightning radiation in a 360° view, correlated BITF and HSV observations increase the 3‐D detection probability than dual‐station HSV observations, which is helpful to obtain more events and deeper understanding of the lightning process.

Observation Results and Discussion on an Upward Leader Followed by a Long Continuing Current After a Return Stroke

“…Both the third and fourth RSs were typical subsequent RSs, which followed the same channel as the second RS. The average 3‐D speed of the third RS was larger than 4.67 × 10 7 m/s, while the average speed of the fourth RS was about 3.49 × 10 7 m/s (Li et al, ). The third RS developed faster than the fourth RS, and several HSV images of the third RS were severely saturated, which indicated that charge neutralization of the fourth RS was less than that of the third RS.…”

“…With the 3-D reconstruction results of the dart leader before the third RS using HSV images and VHF data (Li et al, 2017), the upward P1 discharge process analyzed here occurred at 5.30 km from HSV in site B. With the tips of the upward P1 discharge process identified in each frame, the 2-D speeds of the upward P1 discharge process calculated are shown in Figure 3.…”

Observed Variation of Three‐Dimensional Return Stroke Speeds Along the Channel in Rocket‐Triggered Lightning

“…Reconstruct the 3-D channels of dart leaders by correlating MARCOS data and HSV frames from two different sites (Li et al, 2017). Reconstruct the 3-D channels of dart leaders by correlating MARCOS data and HSV frames from two different sites (Li et al, 2017).…”

“…(1). Reconstruct the 3-D channels of dart leaders by correlating MARCOS data and HSV frames from two different sites (Li et al, 2017). (2).…”

“…With the 3-D reconstruction method based on VHF and HSV data (Li et al, 2017), the 3-D temporal-spatial evolution of the leader discharge channel is obtained as shown in Figure 3c. The development of the 3-D discharge channel for the leader can be seen clearly, and the straight channel in the bottom part of the 3-D channel corresponds to the trace of the metal wire after evaporation.…”