Above the Clouds: Lightning Sprites
NASA Goddard Space Flight Center
Wed, September 25, 2019 - 4:00 PM
Karl Herzfeld Auditorium of Hannan Hall - Rm 108
ASprite discharges are large scale natural plasma phenomena occurring due to penetration of quasi-electrostatic lightning field to mesospheric/lower ionospheric altitudes.
They consist of filamentary plasma channels known as streamers that are highly non-linear and self-organized ionization waves. It has been generally believed that sprites occur when the lightning field exceeds the conventional breakdown threshold field, Ek, in the lower ionosphere. However, recent analysis of high-speed video observations of sprites and electromagnetic measurements of lightning field found that sprite streamers often appear in the lightning field below the breakdown field with a magnitude as low as 0.2Ek. Current sprite theory can not offer a satisfactory explanation to how sprite streamers can form in such low lightning fields.
Recently, we have found that sprite streamers can be successfully initiated from ionospheric patches in a lightning field below Ek. The origin of those ionization patches may be attributed to ionospheric disturbances created by meteor trails, electrodynamic effects from thunderstorm and/or lightning, and gravity wave breaking. This is the first study showing that the sprite streamer initiation mechanism that we proposed can explain the main properties of sprite streamer initiation, including time scales, spatial scales, and speeds, observed by high-speed cameras.
Refreshments served at 3:45 PM
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