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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.

We present measurements of nearby vertical and horizontal electric fields from leaders and return strokes associated with lightning strikes to the 100-m-tall Gaisberg Tower in Austria obtained in 2007 and 2008. The fields were measured at a distance of about 20m from the tower's vertical axis. Simultaneously with the fields, return-stroke currents were also measured at the top of the tower. The measured data are used to test engineering and electromagnetic models for the return stroke. In general, the agreement between measured waveforms and model-predicted ones is satisfactory.