Lightning leader stepping, K changes, and other observations near an intracloud flash

Abstract

[1] An intracloud lightning flash in central New Mexico began with the initiation of a negative stepped leader at an altitude of 8.2 km above sea level. As this leader propagated eastward and upward, at 9.1 km above sea level it passed about 200 m to the north of a balloon-borne, electric field-change instrument (Esonde). After the first leader stopped, a second negative stepped leader began near the point of origin of the first leader, but it propagated away from the Esonde. From the changes in the electric vectors and the locations of impulsive radio frequency sources detected by a lightning-mapping array (LMA), we conclude the following: (1) The first negative stepped leader was not preceded by any significant charge rearrangement due to positive leaders. (2) Each step of the first negative leader had both a forward-going wave and a step recoil wave that propagated simultaneously backwards away from the leader tip along the existing channel. The presence of a step recoil wave during each step leads to an explanation for the existence of stepping. (3) After the first (nearby) leader stopped, step recoil waves from the second (distant) leader may have found their way onto the channel formed by the first leader. (4) After the second leader stopped, waves carrying negative charge propagated along the channel of the first leader, producing strong K changes in the electric field at the Esonde and providing a good record of the wavefront shapes.