[1] We report intensified high speed video observations of two mesospheric transient luminous events acquired at 5000 and 7200 frames per second. Downward streamers appear to initiate either spontaneously or from brightening inhomogeneities at the bottom of a halo, and branch as they propagate downward. Simultaneously, a brighter column expands upward and downward from the initiation point. This expansion is usually followed by the development of bright upward propagating streamers that originate from the bottom of the expanding bright column and that terminate in diffuse emissions. The lower portions of these upward streamers are typically brighter and more persistent and form the bright core of the sprite. A new phenomenon is observed in which the tips of downwardmoving sprite streamers are attracted to and, in some cases, collide with adjacent streamer channels. The points of streamer collision appear to become long-persisting sprite beads, which have been suggested previously to affect mesospheric chemistry. Other persistent beads appear to form spontaneously on the downward streamer channels near the lower edge of the bright upper portion of the sprite.

Gigantic jets are the clearest manifestation of direct electrical coupling between tropospheric thunderstorms and the ionosphere. They are leaders 1-3 that emerge from electrical breakdown near the top of thunderstorms 4 and extend all the way to the lower edge of the ionosphere near 90 km altitude 5 . By contrast, blue jets 6 and other related events 7,8 terminate at much lower altitudes. Gigantic jets have been observed from the ground 5,9,10 and from orbit 11 . Some seem to be consistent with an upward-propagating negative discharge of 1,000 to 2,000 C km total charge moment change 9 , but others have not been connected to distinguishable electromagnetic signatures 10 . Here we report simultaneous low-light video images and low-frequency magnetic field measurements of a gigantic jet that demonstrate the presence and dynamics of a substantial electric charge transfer between the troposphere and the ionosphere. The signatures presented here confirm the negative polarity of gigantic jets 4 and constrain the lightning processes associated with them. The observed total charge transfer from the thunderstorm to the ionosphere is 144 C for the assumed channel length of 75 km, which is comparable to the charge transfer in strong cloud-to-ground lightning strokes.At a field site near Duke University, we routinely monitor optical emissions above thunderstorms and measure <0

[1] As part of a collaborative campaign to investigate Transient Luminous 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 (DM Qv ) of À503 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 further evidence that sprites can be driven by upward as well as downward electric fields, as predicted by the conventional breakdown mechanism.Citation: Taylor, M. J., et al. (2008), Rare measurements of a sprite with halo event driven by a negative lightning discharge over Argentina, Geophys. Res. Lett., 35, L14812,

During the night of 22–23 February 2006, more than 400 middle‐atmospheric optical discharges were observed above one large thunderstorm system over northeastern Argentina. These transient luminous events (TLEs) were imaged during the Southern Brazil Sprite Campaign, the first campaign to focus on TLEs over southern Brazil, northeastern Argentina, and Uruguay. All of the TLEs were imaged from the Brazilian Southern Space Observatory (SSO) near Santa Maria, which is nearly in the center of the southernmost Brazilian state of Rio Grande do Sul. Although the fields of view of the imaging cameras were too narrow to view the entire storm, the more than 400 confirmed TLEs imaged indicate that this storm ranks as the third most active TLE producer ever reported. Hence, storms in this region of South America might be some of the leading TLE generators on Earth.