Selected results from the ISUAL/FORMOSAT2 mission

  • A report on the salient results of the ISUAL transient luminous event mission
  • The global distribution and occurrence rate of TLEs are presented
  • The characteristics of the TLEs inferred from the ISUAL data are discussed

The ISUAL (Imager of Sprites and Upper Atmospheric Lightning) is a scientific payload onboard the FORMOSAT2 satellite (FS2). This the first satellite project survey of global transient luminous events (TLEs) as one of the mission objectives. Since the ISUAL/FS2 launch in 2004, ISUAL has continuously monitored TLE occurrences over pre-midnight regions in the past ten plus years. As of December 2015, more than forty thousand TLEs, including the sub-species like elves, sprites, sprite-halos, blue jets and gigantic jets, have been recorded from this space platform. In the meantime, as the supporting facilities to the space-borne ISUAL experiment, ground optical imagery systems have been deployed to observe TLEs occurring near Taiwan with several radio wave detection ground stations also installed to register lightning- or TLE-related radio signals called sferics. From analyzing the observed events and the associated sferics, many TLE characteristics have been inferred. Among the most notable factors are the global distributions, the occurrence rates, and the charge injection and the energy impact to the upper atmosphere. In this article, the ISUAL payload, the auxiliary ground facilities and a few selected TLE survey results from the ISUAL mission are concisely presented.

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