The initial stage of cloud lightning imaged in high-resolution

TL;DR

This paper uses high-resolution LOFAR imaging to analyze the early development of cloud lightning, revealing detailed leader propagation and initial breakdown processes within milliseconds of lightning initiation.

Contribution

It introduces a novel high-resolution lightning mapping method and provides new insights into the initial stages of intra-cloud lightning development.

Findings

Negative leaders propagate below the main negative charge layer.

Multiple negative leaders form shortly after lightning initiation.

Normal negative leaders can transition into initial-leader-like states.

Abstract

With LOFAR we have been able to image the development of lightning flashes with meter-scale accuracy and unprecedented detail. We discuss the primary steps behind our most recent lightning mapping method. To demonstrate the capabilities of our technique we show and interpret images of the first few milliseconds of two intra-cloud flashes. In all our flashes the negative leaders propagate in the charge layer below the main negative charge. Among several interesting features we show that in about 2~ms after initiation the Primary Initial Leader triggers the formation of a multitude (more than ten) negative leaders in a rather confined area of the atmosphere. From these only one or two continue to propagate after about 30~ms to extend over kilometers horizontally while another may propagate back to the initiation point. We also show that normal negative leaders can transition into an initial-leader like state, potentially in the presence of strong electric fields. In addition, we show some initial breakdown pulses that occurred during the primary initial leader, and even during two "secondary" initial leaders that developed out of stepped leaders.