On the upper and lower limits of peak current of first return strokes in negative lightning flashes

It is shown that the peak current of a return stroke is determined by the background electric field that exists between the cloud and the ground. Assuming 150 kV/m as the largest background electric field that can exist below thunderclouds, it is estimated that the largest negative first return stroke peak current that can exist in nature is about 300 kA in temperate regions and about 450 kA–500 kA in the tropics. Since corona discharges from trees, bushes and other protrusions and upward initiated discharges from tall structures limit the maximum electric field that can exist below thunderclouds over land, there is a high probability for these strong discharges to take place over the oceans. In the study it is also estimated that the smallest value of the return stroke current that can exist in nature lies in the range of 3.0 kA to 1.5 kA with the most probable value located in the vicinity of 2 kA.