Three types of bidirectional leader development in triggered lightning flashes

Eight cases of bidirectional leader (BL) development in artificially triggered lightning flashes are reported with synchronous high-speed camera images and electric field signals. Based on optical progressing characteristics, the eight cases can be divided into three types: a reflection type, a discontinuity type, and an inducement type. For the reflection type, the tail of a dart leader may begin to extend backward when the leader's head reaches a branch point, or the top of the exploded triggering wire. For the discontinuity type, the initiation of a bidirectional leader below a decayed attempted leader may occur more than once preceding one return stroke. For the inducement type, the approach of another leader with the same polarity will turn a dart leader into a bidirectional leader. The reflection type and inducement type are first observed here. Two cases of the discontinuity type are observed, and both are multiple-bidirectional leaders observed for the first time. For the reflection type and inducement type, there are fluctuations in the electric field related to the BL development. The dissipation of the downward leader slows down the negative increase of the electric field. Once the BL development starts, the downward negative end of the BL moves towards the ground with the E-field negatively increasing. For the discontinuity type, the close electric field result shows no fluctuations. The BL development has a much longer duration than the other two BL types.

Modeling of Bi-Polar Leader Inception and Propagation from Flying Aircraft Prior to a Lightning Strike

Lightning is one of the major environmental threats to aircraft. The lightning strikes during flying are mostly attributed to aircraft-triggered lightning. The first step toward designing suitable protective measures against lightning is identifying the attachment locations. For this purpose, oversimplified approaches are currently employed, which do not represent the associated discharge phenomena. Therefore, in this work, a suitable model is developed for simulating the inception and propagation of bi-polar leader discharge from the aircraft. Modeling of leader discharges requires field computation around the aircraft, which is carried out employing the Surface Charge Simulation Method (SCSM) combined with sub-modeling, which ensures the best accuracy of field computations near nosecone, wingtips, etc. A DC10 aircraft model is considered for the simulation. Simulations are performed for different pairs of leader inception points on aircraft using the developed model. Subsequently, corresponding ambient fields required for stable bi-polar discharge from aircraft are determined. These values are in the range of measured ambient fields reported in the literature. In summary, the present work has come up with a suitable model for simulating the bi-polar leader inception and propagation from the flying aircraft. Using the same, a detailed quantitative description of the discharge phenomena from the aircraft is provided.