Magnetic measurements of thunderstorm currents: 1. Continuing currents in lightning

Long-continuing currents in lightning were measured with a fluxgate magnetometer. The results confirm earlier New Mexico work in which electrostatic field and photographic measurements were used in calculating these currents. On the basis of an analysis of 14 long-continuing strokes, the currents are found to average 184 amp. The average negative charge lowered to earth is 31 coul, and the average duration is 174 msec. A comparison of these results with the direct strike measurements of Hagenguth and Anderson, and Berger, shows reasonable agreement. Magnetic effects produced by the stepped leader, in two instances, were used in estimating the leader current. Values of 50 and 63 amp are indicated. It appears feasible to use a magnetometer of shorter time response (1 msec or better) to measure leader currents and such intracloud current events as K changes. It is concluded that the magnetometer method is well suited to the measurement of thunderstorm current phenomena ‘at a distance’