The close lightning electromagnetic environment: Dart-leader electric field change versus distance

Net electric field changes due to dart leaders in triggered lightning from experiments conducted in 1997, 1998, and 1999 at the International Center f or Lightning Research and Testing at Camp Blanding, Florida, are analyzed a nd compared with similar data obtained in 1993 at Camp Blanding and at Fort McClellan, Alabama. In 1997-1999 the fields were measured at 2-10 stations with distances from the lightning channel ranging from 10 to 621 m, while in 1993 the fields were measured at three distances, 30, 50, and 110 in, in Florida and at two distances, about 10 and 20 m, in Alabama. With a few ex ceptions, the 1997-1999 data indicate that the distance dependence of the l eader electric field change is close to an inverse proportionality (r(-1)), in contrast to the 1993 data in which a somewhat weaker distance dependenc e was observed. The typically observed r(-1) dependence is consistent with a uniform distribution of leader charge along the bottom kilometer or so of the channel.