Bidirectional leader development in sprite‐producing positive cloud‐to‐ground flashes: Origins and characteristics of positive and negative leaders

Abstract

Thirty-five sprite-producing lightning flashes were recorded in nine nights in different seasons at the east coast of Spain with a 3D Lightning Mapping Array (LMA) since July 2011. A low-frequency time-of-arrival network provided data on emissions from return strokes and intracloud processes and a very-high-frequency interferometer network produced complementary lightning data. This study analyzes the bidirectional development of flashes in order to understand the positioning and timing of the positive cloud-to-ground stroke (+CG) and its consequences for charge neutralization by negative leaders, affecting sprite morphology. A summary of negative leader extents, altitudes, and speeds before and after the + CG stroke is provided, as well as positive leader origins and inferred speeds. Negative leader speeds exhibited modes at 10 5 and 5 × 10 5 m s À1. Five examples with different evolutions are discussed: (1) Slow bidirectional development with negative leader termination before the + CG stroke; (2) Fast bidirectional development with the negative leader continuing after the + CG stroke. (3) Slow-fast bidirectional development with a negative leader exhibiting a sudden lowering and speed increase; (4) Fast secondary bidirectional development from an in-cloud horizontal positive leader. Negative leaders propagated rapidly into the upper positive charge layer, continuing after the + CG stroke; (5) Slow bidirectional development with a long negative leader (50 km) subject to cutoff while the original positive leader remained trapped inside negative charge. A + CG stroke subsequently occurred under the old negative leader channel. Carrot sprites tended to be associated with fast extending leaders after the stroke, columniform/mixed sprites with slower side branches.

A Thermodynamic, kinematic and microphysical analysis of a jet and gigantic jet‐producing Florida thunderstorm

“…Yet this does not always appear to be the case with some reports in the literature of negative GJs occurring during the later stages of a thunderstorm's life cycle [e.g., Soula et al, 2011;Meyer et al, 2013]. Under these circumstances, it is possible that upper level shear may also play a role by enhancing the mixing at storm top or by differentially advecting the upper charge region downstream of the main central charge [van der Velde et al, 2010]. However, it is thought that the latter would tend to promote IC flashes within the anvil region rather than produce a jet or GJ [Riousset et al, 2010].…”

“…Both of these tropical systems had low-level jet-like (LLJ) features associated with them [McCaul, 1987]. Three separate oceanic cases (not included Tables 3-5) were also recorded near the island of San Andrés, Columbia [van der Velde et al, 2014b]. These include a single GJ at 0205 UTC on 23 December 2011, another isolated GJ at 0920 UTC on 12 September 2013, and three GJs between 0846 and 0943 UTC on 18 September 2013.…”

“…Early studies indicated that these events might be exclusively maritime [Su et al, 2003]. While this is no longer the case, jet events do appear to have a predilection for tropical disturbances [e.g., Cummer et al, 2009;Soula et al, 2011;Lu et al, 2011;Huang et al, 2012] and oceanic convection in general [van der Velde et al, 2010]. In contrast to jets, there is no direct evidence of a conductive current path to the cloud top below sprites, elves, or halos.…”

Characteristics of lightning flashes generating sprites above storms

“…These flashes supposedly follow trajectories of charged ice particles toward the stratiform region of the storm system [19,20]. Some of these flashes can be considered as spider lightning [21,22].…”

“…Some of these flashes can be considered as spider lightning [21,22]. In a recent work [20] the authors identified different modes of evolution of the negative leaders throughout the thundercloud system that can explain the positioning and timing of the positive +CG strokes. Thus, the negative leaders may propagate at various altitudes with different velocities and over various distances, while generating several multiple +CG strokes.…”