Abstract
Experimental data show that the peak currents of first and subsequent lightning return strokes in negative ground flashes increase with decreasing latitude. In this paper, the reason for this dependence of peak return stroke current on latitude is explained using the fact that the height of the charge centers increases with decreasing latitude. Results show that in tropical regions where the height to the negative charge center is about 8 km, the median values of the first and the subsequent return stroke peak currents are about 42 kA and 15 kA, respectively. If the height to the charge center is larger than 8 km, the peak currents will also become larger. For example, if the location of the charge center is increased to about 9 km, the median values of the first and subsequent return stroke peak currents will increase to about 45 kA and 16 kA respectively. The same reasoning shows that, even in the same geographical region, the peak return stroke current may decrease as the elevation of the ground where the lightning strikes take place increases. The results also indicate that the peak subsequent return stroke current in tower-initiated negative lightning flashes decreases as the height of the tower increases. These theoretical predictions are in general agreement with the available experimental data.
Highlights
The first study that clearly demonstrated the dependence of negative lightning return stroke peak current on latitude was conducted by Orville in the United States [1]
Even though the derived peak current of the return stroke depends on the model used by the lightning location system to interpret the electromagnetic data, the results showed a clear indication that the return stroke peak current increased with decreasing latitude
The peak return stroke currents that one would obtain in different geographical regions with different heights to the charge center are plotted against the peak
Summary
The first study that clearly demonstrated the dependence of negative lightning return stroke peak current on latitude was conducted by Orville in the United States [1]. After reviewing the literature on the current measurements in different countries, Rakov and Dulzon [2,3] and Pinto et al [4] argued that the peak first return stroke current tends to increase as the latitude decreases. This result was further strengthened when a comparison was made of the peak currents measured in negative lightning strikes to towers by Berger [5] in temperate Switzerland and Visacro et al [6] in tropical Brazil.
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