Papers Published

1. Frey, H.U. and Mende, S.B. and Cummer, S.A. and Chen, A.B. and Hsu, R.-R. and Su, H.-T. and Chang, Y.-S. and Adachi, T. and Fukunishi, H. and Takahashi, Y., Beta-type stepped leader of elve-producing lightning, Geophysical Research Letters, vol. 32 no. 13 (2005), pp. 13824 - [2005GL023080] .
   (last updated on 2007/04/17)

   Abstract:
   The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) on the Taiwanese FORMOSAT-2 (formerly ROCSAT-2) spacecraft is the first global observatory of transient luminous events (TLEs). During the first 4 months of operation a large number of elves were observed. Elves are obvious with their far ultraviolet (FUV) signature that is less attenuated by atmospheric O₂ at their emission altitude compared to emission from sprites or lightning at lower altitude. About half of all elves were produced by lightning that shows a three-step signature in the photometer signal: (1) An initial brightening in all except the FUV channels, (2) a slow brightness decrease for the next 2-5 milliseconds, and (3) an impulsive increase of signal in all channels. We interpret this specific signature as the initial breakdown with a beta-type stepped leader followed by the bright return stroke of a negative cloud to ground (-CG) lightning. In contrast, sprites follow positive cloud to ground lightning (+CG) without a signature of initial breakdown and stepped leader. Many sprites are associated with the continuing current and can be delayed up to 100 ms after the lightning. Copyright 2005 by the American Geophysical Union.

   Keywords:
   Atmospheric radiation;Ultraviolet radiation;Atmospheric composition;Oxygen;Electric grounding;Electric breakdown;Electric currents;