摘要More than 99% sprites are initiated by positive cloud-to-ground (+CG) lightning with high charge moment change (CMC), and there exists a paradox between sprite and lightning with their observed polarity and CMC [Williams et al., 2007]. Two scientific data, including the Imager of Sprite Upper Atmosphere Lightning (ISUAL) TLE database and the magnetic field measurements at extremely low frequency (ELF) band-pass are used to re-investigate this paradox from the global view with a long timeline.
In this study, the ISUAL-captured sprites from 2009 to 2015 and with the distance within 5,000km from either Lulin or Duke ELF stations are selected to analyze their electric characteristics including polarity and CMC. 127 –CG sprites are surprisingly identified, up to 20% of all polarity-identified sprites. These negative sprites mainly congregate in the low latitude region, within 20 degrees in latitude. Further statistics show that more than 80% negative sprites appear with halo signatures, but the ~70% of the positive sprites prefer to be produced without other types of TLEs. The CMC distribution of the sprites analyzed in this study is similar to lightning one, and indicates both positive and negative sprites are triggered by high CMC lightning. In this work, negative sprites are found in low latitude which are missing due to the geographic constraint of the ground observation in the past studies, and their distribution and electric characteristics show the sprite paradox doesn’t exist anymore, but a new theoretical model for negative sprite is necessary.
|監督員||Bing-Chih Chen (Supervisor)|