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Geophysical Research Letters


This paper reports observation and modeling of five negative sprites occurring above two Florida thunderstorms. The sprites were triggered by unusual types of negative cloud-to-ground (CG) lightning discharges with impulse charge moment change ranging from 600 to 1300 C km and charge transfer characterized by a timescale of 0.1-0.2 ms. The negative sprite typically consists of a few generally vertical elements that each contain a bright core and dimmer streamers extending from the core in both downward and upward directions. Modeling results using the measured charge moment change waveforms indicate that the lower ionosphere was significantly modified by the CGs and the lower ionospheric density might have been increased by nearly 4 orders of magnitude due to the most intense CG. Finally, streamer modeling results show that the ionospheric inhomogeneities produced by atmospheric gravity waves can initiate negative sprite streamers, assuming that they can modulate the ionization coefficient.



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