Rare measurements of a sprite with halo event driven by a negative lightning discharge over Argentina

Abstract

As part of a collaborative campaign to investigate Transient Lummous Events (TLEs) over South America, coordinated optical, ELF/VLF, and lightning measurements were made of a mesoscale thunderstorm observed on February 22-23, 2006 over northern Argentina that produced 445 TLEs within a ∼6 hour period. Here, we report comprehensive measurements of one of these events, a sprite with halo that was unambiguously associated with a large negative cloud-to-ground (CG) lightning discharge with an impulsive vertical charge moment change (ΔMQv) of -503 C.km. This event was similar in its location, morphology and duration to other positive TLEs observed from this storm. However, the downward extent of the negative streamers was limited to 25 km, and their apparent brightness was lower than that of a comparable positive event. Observations of negative CG events are rare, and these measurements provide fin-ther evidence that sprites can be driven by upward as well as downward electric fields, as predicted by the conventional breakdown mechanism. Copyright 2008 by the American Geophysical Union.