By Sid Perkins
From San Francisco, at the 2001 fall meeting of the American Geophysical Union
Current U.S. Air Force operating procedures recommend that ground crews for aircraft and other personnel stop working outdoors when lightning is spotted within 5 nautical miles (nmi). However, a new analysis by the service suggests that that distance may not be adequate to fully protect the people or their planes.
Todd M. McNamara, a meteorologist at the Air Force Institute of Technology at Wright-Patterson Air Force Base near Dayton, Ohio, analyzed the path of more than 1.5 million cloud-to-ground lightning strikes around Florida’s Kennedy Space Center. A detection system there can map a lightning bolt’s trajectory in three dimensions. Records from the network of instruments show that more than 30 percent of the cloud-to-ground strikes between March 1997 and December 2000 traveled horizontal distances of more than 5 nmi, or 9.25 kilometers, from their point of origin.
The current safety limit was extended from 3 nmi in April 1996 after a bolt of lightning from a storm 5 nmi away killed one airman and injured several others refueling an aircraft at a base in the Florida panhandle.
