The Occurrence of Continuing Current in Lightning

Abstract:

Most lightning flashes are comprised of strokes that have a channel to ground in which current flows on the order of one millisecond. While current is flowing in the channel, the channel produces optical emission. Typically, flashes have several of these strokes, resulting in the characteristic “flicker” of lightning when observed with the naked eye.

However, there exists a class of lightning flashes in which one or more strokes sustain continuing current, i.e., a stroke in which a channel exists for tens of milliseconds, during which the channel remains luminous. These flashes are thought to be responsible for destructive events associated with lightning, e.g., forest fires. Despite the high impact, the occurrence of this class of flashes remain largely unexplored on a global scale.

While long range, ground based VLF/LF systems can detect return strokes from hundreds of kilometers away, they are generally incapable of detecting the signature of continuing current flashes. However, optical detectors are well suited to identify this signature.

In this paper, we use data from the Lightning Imaging Sensor (LIS) to identify a continuing current signature and quantify its occurrence on a global scale. Since in general LIS cannot uniquely identify a stroke that comes to ground on a flash by flash basis, we utilize ground based VLF/LF networks to further classify the data. Future applications using the Geostationary Lightning Mapper (GLM) are discussed.