Isual Publications 2014

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201411 61 Shu-Chun Chang, Rue-Ron Hsu, Sung-Ming Huang, Han-Tzong Su1, Cheng-Ling Kuo, Jung-Kung Chou, Li-Jou Lee, Yeng-Jung Wu andAlfred B. Chen( 201411 ), Characteristics of TLE-producing lightning in a coastal thunderstorm, Journal of Geophysical Research: Space Physics, accepted, , (SCI, IF=3.174, RANK=23/172,GEOSCIENCES, MULTIDISCIPLINARY, Cited=0)

Observing from southern Taiwan on 2 August 2010, a thunderstorm near Luzon Island-Philippines about 500 km away was found to produce 72 transient luminous events (TLEs). Besides optical images, ULF and VLF sferics of lightning from this thunderstorm were also recorded. This work examines the characteristics of TLE-producing lightning through studying their ULF and VLF sferics. The attenuation of ULF and VLF sferics in the Earth cavity is obtained through analyzing the sferics associated with ISUAL elves that occurred within ~1500 km of Taiwan. Amplitudes of the ULF and the VLF sferics are found to vary as D-0.871 and D-1.207, respectively; where D is the source distance from the sferic stations. After normalizing the sferics from the 2 August 2010 storm to 500 km distance, the ratio of the peak ULF and the VLF magnetic fields is found to be distinct for different TLE-producing lightning. The ratio for the halo-producing lightning is nearly three times that of the elve-producing lightning, but it is comparable to that of the halo-sprite-producing lightning; although the ULF strength for the halo-sprite lightning is significantly larger than that for the halo lightning. Therefore, it is possible to distinguish between the TLE-types using the ULF to VLF peak ratio or the strength of ULF/VLF band emissions of the parent lightning. Comparison of numerically-simulated and the observed lightning radiation fields indicates that the best fit discharge time of the elve-lightning is about 100 µs, while that for the halo-producing lightning is between 200 and 500 µs.

201507 62 Offroy M, T. Farges, P. Gailard, C. L. Kuo, A. B. Chen, R. R. Hsu, H. T. Su, Y. Takahashi, S. B. Mende, and H. U. Frey( 201507 ), Multivariate analysis of dim elves from ISUAL observations, Journal of Geophysical Research: Atmosperes, (SCI, IF=3.174, RANK=23/172,GEOSCIENCES, MULTIDISCIPLINARY, Cited=0)

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite launched in 2004 recorded transient energetic event mechanisms that generate Transient Luminous Events (TLEs). ISUAL have an imager and a spectrophotometer that analyze TLEs all over the world. Among those phenomena, one is particularity complex to detect and is called elves. They are induced by lightning flashes with the electromagnetic pulse (EMP) which heat the base of ionosphere. TheirAbstract brightness depends of the lightning peak current and their time resolution after a lightning flash is around 0.1 ms. As a consequence, their lifetime makes them complex to be detecting if no elves appear in the imager. ISUAL often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible TLEs in the imager. These FUV events are called "dim" elves. They are too weak to be observed by the imager but have enough photo emission response on the FUV band to be detected by the spectrophotometer. Therefore, it is important to develop some mathematical tools to analyze the data for next spatial mission. For this purpose, a dataset is set up with no TLEs identified events in ISUAL database. A multivariate approach was applied to characterize the events from the dataset. The first one is the Principal Component Analysis (PCA) and the second one is the PARallel FACtor analysis (PARAFAC). This new insight strategy demonstrates the potential for
the characterization between lightning and TLEs without prior knowledge with the FUV spectral band selectivity.

201508 63 Marc Offroy, Thomas Farges, Cheng Ling Kuo, Alfred Bing-Chih Chen, Rue-Ron Hsu, Han-Tzong Su, Yukihiro Takahashi, Stephen B. Mende, Harald U. Frey ( 201508 ), Temporal and radiometric statistics on lightning flashes observed from space with the ISUAL spectrophotometer, Journal of Geophysical Research: Atmosperes, Volume 120, 7586-7598, (SCI, IF=3.174, RANK=23/172, GEOSCIENCES, MULTIDISCIPLINARY, Cited=0)

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite was launched in 2004 and records transient luminous events (TLEs). ISUAL is an instrument composed of an imager and a multichannel spectrophotometer which is able to measure the brightness from far ultraviolet to near infrared for TLEs and lightning flashes. Several types of TLEs have been identified, classified, and documented between 2004 and 2014. However, no statistical analyses on lightning have already been realized. In this paper, we focus on lightning flashes which did not induce TLEs. Statistics about brightness or temporal dynamic are presented from fitted waveforms from far ultraviolet to near infrared, after having corrected for atmospheric effects for each spectrophotometer channels. We demonstrate that the lightning/satellite distance and the altitude of the lightning need to be taken into account. The lightning waveforms from each spectrophotometer channel could be modeled as an exponential pulsed function which the shape could be explained by the photon propagation in the cloud. The median values at 777.4 nm are 1.63 × 10−6 W m−2 for the maximum brightness, 5.85 × 104 J for the total energy at the source, 414 µs for the full width half maximum, 620 µs for the full width at quarter of maximum, and 170 µs for the risetime. Results are compared with previous experiments performed from visible to near-infrared domains. The median temporal variables for near-infrared waveforms are shorter than the values of the UV waveforms.

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