1.5 The electro-geometric model

Chapter 1.2 has already described that the discharge processes between the cloud and the earth's surface occur in a series of jerks. The leader from the thundercloud thus approaches the earth's surface in a series of jerks, in steps of a few tens of metres at a time.

As the leader approaches the earth with its charge, the electric field strength on objects on the Earth increases rapidly. This happens particularly in exposed areas such as treetops or building roofs. These points produce upward leaders that grow towards the lightning. The point of strike of the lightning is determined by the upward leader that is the first to meet the leader. This creates a connection between the lightning and the ground. This final section of the connection between the cloud charge and the ground, bridged by the upward leader, is referred to as the striking distance, as shown in Figure 1.5.1.