Creeping Leader Surface Spark Discharge on Low-Conductive Natural and Artificial Objects

How can the lightning strike into a dry tree be explained or is the starting of an upward leader discharge at a towering object of insulating material possible? These electrical discharge processes can be explained by creeping spark and flashover at the air-insulator interface on these objects. For this, a network modelling approach for the creeping discharge is presented and based on the theoretical investigations as well as scaled experiments, it could be shown that a rapidly propagating creeping discharge leads to a flashover of the object made of insulating material in times significantly shorter than a microsecond and subsequently an upward leader can start immediately from its tip.