Characteristics of Lightning Associated with Long Recovery Early VLF Events

Wednesday, 17 December 2014
Daniel Abrahm Kotovsky1, Robert C Moore1, Yanan Zhu1, John Turk Pilkey2, Jaime A Caicedo1, Brian Hare1, Vladimir A Rakov1, Douglas M Jordan3 and Martin A Uman4, (1)University of Florida, Ft Walton Beach, FL, United States, (2)University of Florida, Winter Haven, FL, United States, (3)Univ of Florida, Starke, FL, United States, (4)Univ Florida, Gainesville, FL, United States
A recently discovered category of long recovery, early VLF scattering events (LOREs) indicate that the quasi-electostatic and electromagnetic radiation fields from lightning discharges are capable of producing long lasting disturbances (up to tens of minutes) in the D-region of the ionosphere. Analysis of causative VLF radio atmospherics of 52 LOREs reveals that >76% exhibit detectable precursor radiation just prior to (typically within 4 msec of) the causative lightning return stroke. In contrast, such radiation is detected for <22% of 52 regular recovery early events, and <21% of 142 National Lightning Detection Network recorded discharges (peak current magnitude >50 kA, within 1500 km of the nearest receiver). By comparison with electric field measurements and lightning mapping array data, preliminary breakdown in natural, negative cloud-to-ground flashes is shown to produce VLF precursor radiation similar in most observable respects to those associated with VLF scattering events. It is thereby inferred that strong preliminary breakdown (and fast stepped leaders) are predominant features of discharges capable of producing long lasting D-region disturbances.