Selected results from the ISUAL/FORMOSAT2 mission

  • Author(s): Rue-Ron Hsu, Han-Tzong Su, Alfred Bing-Chih Chen, and Cheng-Ling Kuo
  • DOI: 10.3319/TAO.2016.08.23.01
  • Keywords: ISUAL, FORMOSAT2, Transient luminous events (TLEs), Space electricity, Atmospheric electricity
  • 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). It is also the first satellite project with the global survey of transient luminous events (TLEs) as one of the mission objectives. Since the launch of ISUAL/FS2 in 2004, ISUAL has continuously monitored the occurrence of TLEs over the pre-midnight regions in the past ten plus years. As of December 2015, more than forty thousand of 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 and several radio waves detecting ground stations have also been installed to register the lightning- or the TLE-related radio signals called sferics. From analyzing the observed events and the associated sferics, many characteristics of the TLEs have been inferred; among the most notables 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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