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High-speed video images of 24 downward negative lightning flashes terminating on tall structures in Guangzhou are selected to analyse the connecting behaviour of the downward and upward leaders during the attachment process preceding the first return stroke. Three types of leader connecting behaviour have been observed: Type I, the tip of downward leader (DL) to the tip of upward connecting leader (UCL), which accounts for 42% of all the events (10/24); Type II, the DL's tip to the lateral surface of UCL, which accounts for 50% (12/24); and Type III, the combination of Types I and II, which accounts for 8% (2/24). For the two cases of Type III behaviour, each case had two junction points (one with Type I and the other with Type II behaviour) between the downward and upward leaders. Therefore, Types I and II can be viewed as the two basic types of the leader connecting behaviour during the attachment process in negative lightning. No attachment process exhibited the connection of the UCL's tip to the lateral surface of DL. The presence of multiple DL branches and their integrated effect on the development of positive UCL/UCLs are likely to be the main reasons for the Type II behaviour.

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This study investigates the initial stage (IS) and return stroke (RS) currents of 50 triggered lightning flashes (TLFs) that were conducted in southern China. The IS of the negative TLFs has a longer duration and larger average current, charge transfer, and action integral than those reported elsewhere, with geometric means (GMs) of 347.9 ms, 132.5 A, 45.1 C, and 10.0 × 103 A2 s, respectively. Two positive TLFs containing no RS have much greater average currents, charge transfers, and action integrals in the IS when compared with the negative TLFs. The RS has a greater peak current (17.2 kA; GM, same to below), charge transfer within 1 ms (1.3 C), and action integral within 1 ms (5.8 × 103 A2 s), and shorter 10% to 90% rise time (0.4 μs) than elsewhere. The peak current is prominently correlated with the rate of rise, charge transfer within 1 ms, and action integral within 1 ms. Furthermore, when the total duration of the RS and any following continuing currents is longer than 40 ms, the peak current, charge transfer within 1 ms, and action integral within 1 ms of the RS are seldom greater than 25 kA, 2.6 C, and 15 × 103 A2 s, respectively. It is indicated that TLFs containing RSs tend to have a longer duration but a smaller charge transfer during the IS than those without RS. The peak current of the RS is weakly correlated with its preceding silence period when there was no channel base current.