On the mimimum length of leader channel and the minimum volume of space charge concentration necessary to initiate lightning flashes in thunderclouds

• Dielectric strength of cloud environment is larger than in situ measured fields.
• Initiation of lightning requires fields to exceed dielectric strength of cloud air.
• Thus, there should be small pockets of high field regions inside the cloud.
• The study shows that these pockets are no larger than a few meters in radius.

Minimum length to which a leader channel has to grow before it can propagate continuously as a stable leader as a function of the background electric field inside a thundercloud is estimated. For electric field magnitudes comparable to the values measured inside thunderclouds, the minimum length of the leader channel that is required for it to propagate continuously is about 3–5 m. In other words, a leader discharge that originated inside a thundercloud has to grow to a length of 3–5 m before it can culminate in a stable and continuously propagating leader discharge that can give rise to a lightning flash. The minimum size of charge concentrations that can make this event possible have radii in the range of 2–4 m and should carry about 300–900 μC of electric charge, respectively. This in turn shows that the high field regions inside the cloud where electrical discharges that can culminate in stable leader discharges, and hence in lightning discharges, may be confined to volumes which are no larger than a few meters in radius.