Isual Publications 2014

COM_FABRIK_ORDERpublish time # Citation abstract
200712 81 A. Yoshida, Y. Takahashi, M. Sato, T. Adachi, H. Fukunishi, S. Kondo, R. R. Hsu, H. T. Su, A. B. Chen, H. U. Frey, S. B. Mende, and L.C. Lee( 200712 ).The relationship between sprite luminous intensity and electrical property of parent lightning discharges using FORMOSAT-2/ISUAL data, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

Sprite, transient luminous phenomena induced by tropospheric lightning discharge in the mesosphere, has been extensively investigated for almost two decades. However, due to the atmospheric absorption and scattering, it is difficult to estimate its exact luminous intensity with ground base observation. Recently, FORMOSAT-2/ISUAL observed many sprite optical emissions without such atmospheric effects. The data enable us to discuss their luminosity and the parent lightning characteristics quantitatively. In this paper, we firstly report the relationships between them based on FORMOSAT-2/ISUAL and ELF network data. In order to estimate sprite luminosity, we use ISUAL/array photometer data. The array photometer consists of two photometers measuring two wavelength ranges, that is, 360-470 nm (blue) and 520-750 nm (red), with sixteen channels arrayed in vertical each. We can estimate the electron energy of sprite from the ratio between blue and red color intensities. Some channels with sprite are contaminated by scattering emission from cloud-to-ground and/or cloud-to-cloud lightning discharges. From contaminated data we subtract lightning emission using lightning channel data. Then, we can estimate corrected sprite luminosity integrated temporally and spatially. In addition, we estimate its parent lightning charge moment from ELF data. The result of comparison between luminosity of carrot type sprite and the charge moment shows that they have positive correlation, indicating that charge moment is one of the essential parameters that determine sprite luminosity. We also analyzed the ratio between blue and red emissions and found that there exists also positive correlation between the ratio and charge moment of parent lightning. This result seems consistent with quasi- electrostatic model assuming the electric field over thunderstorm is proportional to the lightning charge moment and that it determines sprite occurrence and its luminosity. Furthermore, we classified sprites into three types, that is, halo, carrot, and column, and discuss their relative luminous intensity and their relationship to the characteristics of parent lightning.

200712 82 L. Y. Tsai, J. K. Chou, C. L. Kuo, Y. J. Lee, A. B. Chen, H. T. Su, R. R. Hsu, H. U. Frey, S. B. Mende, H. Fukunishi, Y. Takahashi, and L.C. Lee( 200712 ).Origin Of The Pancake-Shaped And The Donut-Shaped Elves, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

Among the known species of upper atmospheric transient luminous events, elve is the most abundant in the ISUAL recorded events. The correlation between elves and their causative lightning is an interesting problem needed to be addressed. We selected 760 elves with distinct morphology from the 4000-plus elves recorded by ISUAL since June 2004. From these elves, the occurrence ratio between the pancake-shape and the donut- shape elves is deduced and the value is around unity. This ratio was unexpected since the known occurrence ratio between the cloud discharges (IC) and the cloud-to ground flashes (CG) is known to be around three to one. To explore the root cause(s) behind this discrepancy, a 2-dimensional EMP model with horizontal lightning components are studied numerically. The results show that the initiating current for the pancake elves from ICs is substantially higher than that for the donut elves from CGs. The morphological origin of these two distinct types of elves will also be discussed.

200712 83 M. Parrot, H. U. Frey, Y. Takahashi, A. B. Chen, R. R. Hsu, and H. T. Su( 200712 ).VLF EM signatures recorded by DEMETER at the time of ISUAL TLEs, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

DEMETER is an ionospheric micro-satellite launched on a polar orbit at an altitude of 710 km in June 2004. Its main scientific objectives are to study the ionospheric perturbations in relation with seismic and anthropogenic activities. Therefore, its scientific payload allows to measure electromagnetic waves and plasma parameters all around the Earth except in the auroral zones. There are two modes: a survey mode where only spectra with low frequency (~ 20 Hz) and time (2 s.) resolution are available and a burst where waveforms up to 20 kHz are recorded. The ISUAL (Imager of Sprites and Upper Atmospheric Lightning) experiment on FORMOSAT 2 (the former ROCSAT 2) determines spatial, temporal and spectral properties of lightning induced upper atmospheric TLEs (Transient Luminous Events): sprites, elves, blue jets, etc. FORMOSAT 2 has been launched in May 2004 onto a Sun-synchronous orbit located at 890 kilometers. The two satellites cover the same time period but they are not synchronized and simultaneous observations are only possible when DEMETER is at two specific locations beyond the coast of Chili and beyond the east coast of Australia. At these two locations the two satellites are magnetically conjugated (FORMOSAT 2 being in the Northern hemisphere). This paper will show the characteristics of some events simultaneously observed by the two satellites (Electromagnetic emissions and TLEs).

200712 84 T. Y. Huang, C. Y. Chiang, C. L. Kuo, J. B. Nee, A. B. Chen, H. T. Su, and R. R. Hsu( 200712 ).On the Lightning Induced Transient Emissions (LITEs) in the OH Airglow Region with ISUAL Observations, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

Elves and sprites are the two recently observed lightning induced transient emissions (LITEs) in the mesosphere. Observations of elves by ISUAL broadband filter onboard the FORMOSAT-II satellite have sometimes shown a transient brightness at or below the OH airglow altitude in the event of a lightning flash. It is generally accepted that electrons heated by lightning EMPs impact N2 species to produce the optical emissions. Given that the sudden brightness oftentimes occurred at the OH airglow altitude and that OH species require only 3 to 4 eV to produce optical emissions, it is very possible that OH species can be another light-emitting species interacting with the EMP-accelerated electrons. Due to too much overlap of OH and N2 spectrum within the bandwidth of the broadband filter, it was not possible to determine which species are responsible for the observed enhancements. In response to the need to find the causes for such enhancements, ISUAL conducted a 9-day campaign in January 2007, with some observations devoted exclusively to capturing LITEs with the 630 nm filter for such an investigation. We will present the analysis of the observations from the CCD camera, spectrophotometer, and array photometer, and will discuss the implications of the results.

200712 85 A. B. Chen, C. Y. Chiang, C. Su, Y. J. Lee, C. P. Hu, L. Y. Tsai, Y. C. Huang, J. K. Chou, S. M. Huang, R. R. Hsu, H. T. Su, T. Y. Liu, Y. S. Chang, and L.C. Lee( 200712 ).Distribution and seasonal variation of global lightning activities observed by ISUAL experiment, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

Lightnings serve as an important charge transporter between cloud and ground, and emit sferics those propagate in the ground-ionosphere cavity. The question on how global lightning activity might change in the future as a result of the global warming has attracted great attention. During the three-year observation of ISUAL/FORMOSAT-2, besides upper atmospheric transient luminous events more than 60,000 lightnings which exceeded the trigger threshold were recorded. In this presentation, the distribution, occurrence rate, and seasonal variation of these lightnings at local time between 22:30 and 23:00 will be reported, and compared with that of the OTD/LIS experiment (Christian, et al., 2003). Our results may suggest that intensive lightnings are possible more efficient to generate elves, and the production efficient is assessed in this presentation.

200712 86 K. Wang, Y. C. Wang, J. Y. Liu, Y. H. Yang, R. R. Hsu, H. T. Su, Y. I. Chen, and K. Hattori( 200712 ).Polarization Study of ELF-Emissions at Pre-Earthquakes Time, American Geophysical Union, Fall Meeting 2007, San Francisco, USA.

ELF-emissions events below 100Hz from Aug. 24, 2003 to July 9, 2004 were observed at ELF station in Lulin Observatory of Taiwan (120°52' 25" E , 23°28' 07" N, 2862m) [\it Wang \it et \it al., 2005]. Various types of emission patterns are identified. Statistical analysis of these ELF emissions and earthquakes (M ≥ 5.0) occurred in Taiwan at the same observational period have shown that both the occurrence rates and numbers of these emissions significantly enhanced within several days prior to earthquakes. In this presentation, polarizations of these events signals as well as the propagation directions of associated waves will be investigated. The polarization changes prior to occurrences of earthquakes will be the primary focus to study to understand how they are associated with source regions of earthquakes.

200805 87 A. B. Chen, C. L. Kuo, Y. J. Lee, R. R. Hsu, H. T. Su, J. L. Chern, H. U. Frey, S. B. Mende, H. Fukunishi, Y. Takahashi, T. Y. Liu, Y. S. Chang, and L.C. Lee( 200805 ).Ocean-Troposphere-Ionosphere Coupling via Lightning and Transient Luminous Phenomena, Japan Geoscience Union Meeting 2008, Chiba, Japan. E207-003

Thunderstorms are known to be capable of initiating spectacular transient luminous events (TLEs), such as sprites, halos, elves, and jets; however their global distributions and occurrence rates have not been well assessed until recently. ISUAL experiment onboard FORMOSAT-2 satellite recorded thousands of TLEs and lightning flashes in a 3.5-year global survey. Correlations between TLEs, lightning, vertical atmospheric flow and ocean surface temperature indicate there is a strong coupling among ocean, troposphere, stratosphere, and ionosphere, covering an altitudinal range of nearly 100 km. Lightning was known to be an important modulator of the chemical composition in the troposphere and stratosphere. Here we demonstrate that lightning also play an important role in driving the chemistry of the ionosphere D-region by elevating the electron density through the occurrence of elves. In this talk, we present the evidences for the global scale interactions between different layers of Earth atmosphere. Assessments of the impacts of TLEs on the upper atmospheric total electron content and on the electric global circuit will also be discussed.

200805 88 C. L. Kuo, J. K. Chou, L. Y. Tsai, Y. J. Lee, A. B. Chen, R. R. Hsu, H. T. Su, L.C. Lee, S. A. Cummer, H. U. Frey, S. B. Mende, and Y. Takahashi( 200805 ).Upward Electrical Discharges from Thunderstorm Top, Japan Geoscience Union Meeting 2008, Chiba, Japan. E207-004

In our current knowledge, both blue jet [Wescott et al. , 1995; 1998; 2001; Pasko et al. , 2002] and gigantic jet [Su et al. , 2003; Hsu et al. , 2004; van der Velde et al. , 2007] are upward electrical discharge emerging from thunderstorm tops. Unlike sprites or elves, they are believed to be induced by electrostatic field or electromagnetic waves generated in lightning activities, jets make directly contact with their parent clouds. After the discoveries of jets from ground and airplanes campaigns, several models have been proposed to account for their physical characteristics [Pasko et al. , 1996; Sukhorukov et al. , 1996; {i}Razier et al.{i}, 2007]. However, several unanswered questions including their generating mechanism, propagating velocities, and the associated sferics still exist which indicate that further efforts in observations and modeling are still needed in clarifying the jet phenomena. In this paper, we present the most current jet observations from ISUAL (The Imager of Sprites and Upper Atmospheric Lightning) onboard FORMOSAT-2 satellite. Some unresolved issues on the jet phenomena will also be addressed.

200805 89 J. J. Miau, T. Y. Liu, A. B. Chen, C. Z. Cheng, S. Y. Su, H. C. Yeh, R. R. Hsu, H. T. Su, C. Lin, and L.C. Lee( 200805 ).Strategies and aims of Taiwan space program and scientific results derived from FORMOSAT 1~3, Japan Geoscience Union Meeting 2008, Chiba, Japan. J239-011

FORMOSAT 1˜3 is a series of small satellite missions developed under the guide of of first stage plan of a 15 year Space Technology Long Term Developmental Program in Taiwan and these satellites were launched successfully respectively and gained fruitful scientific outcomes. The second phase Space Technology Long Term Developmental Program was approved in December 2002. The entire plan scheduled for15 years; from 2004 to 2018. The second phase space program will continue the performance of the first phase space program. The execution strategy will focus on meeting Taiwan’s national needs, carrying out satellite programs, promoting academic research and industrial development, improving Taiwan’s overall space technology development capacity, and developing added value to the domestic industry. 1˜2 small satellites, 2˜4 micro-satellites missions and several sounding rocket experiments were drew up in this plan. In this talk, the scientific achievement for FORMOSAT 1˜3 will be presented. The strategy and the current plan of Taiwan 2nd phase space program will be covered, too. We hope to seek international collaboration of both science and engineering in the future.

200806 90 H. T. Su, R. R. Hsu, A. B. Chen, H. U. Frey, S. B. Mende, Y. Takahashi and L.C. Lee ( 200806 ).Global Survey of TLEs from ISUAL onboard the FORMOSAT-2 Satellite, Workshop on Coupling of Thunderstorms and Lightning Discharges to Near-Earth Space 23-27 June 2008, Corte, France.
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