Characteristics of downward leader in a positive cloud‐to‐ground lightning flash observed by high‐speed video camera and electric field changes

Abstract

Leader process in a positive single‐stroke cloud‐to‐ground lightning flash was captured by a high‐speed video camera with a time resolution of 1000 frames/s. The positive leader process and the intracloud discharge process before the return stroke, which lasted about 600 ms, are studied in detail by combining the data from fast and slow antenna. The channel branches seemed to develop horizontally with a speed of the order of 104 m/s during the initial stage just outside the thundercloud. The luminous duration of the leader was about 12 ms, and the luminous intensity at the tip was much stronger than the channel behind it, presented obviously a stepped‐like characteristic. The 2‐D propagation speed of the stepped‐like leader ranged from 0.1 × 105 m/s to 3.8 × 105 m/s. The time interval between 26 leader pulses during the last 0.5 ms just before the stroke was about 17 μs according to E‐field changes.

Characteristics of positive cloud‐to‐ground lightning in Da Hinggan Ling forest region at relatively high latitude, northeastern China

“…However, electric field measurements showed that positive flashes are sometimes preceded by pronounced intracloud discharge lasting 100-200 ms, rather than the preliminary breakdown process [Rust et al, 1981;Fuquay, 1982]. Optical records confirmed that positive CG flashes can be initiated from a channel branch of intracloud discharge [Kong et al, 2008;Saba et al, 2009], and the weak preliminarily breakdown process is replaced by IC discharge in this case.…”

“…[28] Rakov [2003] suggested that +CG flashes might be generated by intracloud lightning that extends horizontally. The optical observation and lightning mapping results with very high frequency (VHF) imaging also proved that some channels of intracloud lightning can produce +CG strokes [Kong et al, 2008;Saba et al, 2009;Lu et al, 2013]. Saba et al [2009] found that leaders with both polarities might trigger positive CG strokes.…”

“…The first type corresponds to the ordinary +CG [27] Of all the positive CGs in our data set, 118 (63.78%) of the positive CG flashes were ordinary positive CG flash, 39 (21.08%) exhibited IC discharge only after the strokes, 10 (5.41%) exhibited IC discharge only before the strokes, and 18 (9.73%) had IC discharge both before and after the strokes (see Table 5). If the IC discharge was recorded during the 200 ms pre-trigger time and no obvious preliminary breakdown and leader processes can be identified, we attribute this kind of positive CG flashes to be initiated by intracloud discharges, as found by Kong et al [2008] and Saba et al [2008] using high-speed video observations. The preliminary breakdown and leader processes are not considered as intracloud discharge in our analysis.…”

Seasonal, Regional, and Storm-Scale Variability of Cloud-to-Ground Lightning Characteristics in Florida

“…Interestingly, S10 also reported that some 1CG strokes produced a new ground contact while the CC from a previous stroke was still in progress. Positive downward leaders also can be initiated by the CC phase of IC discharges (e.g., Kong et al 2008). S10 concluded that the spatial and temporal criteria presently used to group 2CG strokes into flashes may not be valid for 1CG, and that the very concept of a lightning flash being a group of strokes that are collocated in space and time should be reconsidered for 1CG.…”

A gigantic jet event observed over a thunderstorm in mainland China

“…These lightnings occur in the troposphere and have been extensively studied [1][2][3][4][5][6][7][8][9][10][11]. However, there are another type of lightning discharges which occur above the thunderstorms, with the top altitude even reaching the ionosphere.…”