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Yukihiro Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Multivariate analysis of dim Elves from ISUAL observations
Journal of Geophysical Research: Atmospheres, 2015Co-Authors: Marc Offroy, Cheng-ling Kuo, A. Chen, Rue-ron Hsu, Thomas Farges, Pierre Gaillard, Yukihiro TakahashiAbstract:The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite, launched in 2004, records Transient Luminous Events (TLEs). ISUAL has an imager and a spectrophotometer that observe TLEs all over the globe. Among these phenomena, Elves are particularly difficult to detect. ISUAL often records events that correspond to significant far ultraviolet (FUV) emissions in the spectrophotometer but have no discernible TLEs in the imager. These FUV events are called “dim” Elves. Therefore, it is important to develop mathematical tools to analyze the data to obtain a better evaluation of the number of Elves and their occurrence. Multivariate approaches are applied to characterize the unlabeled events. The first approach is the principal component analysis which distinguishes two different groups, one including Elves and dim Elves. The second approach is the PARallel FACtor analysis which provides a waveform model for each group. These methodologies confirm that FUV signal is the evidence of TLE presence. A crude classification method was then suggested taking into account these results. The proportion of Elves, relatively to the considered ISUAL data set, is found to be about 40%. It is similar to previous results and confirms that relatively weak lightning peak current is sufficient to produce Elves. This new strategy demonstrates the potential for discriminating between lightning and TLEs without prior knowledge within the selectivity of the FUV spectral band.
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occurrence of Elves and lightning during el nino and la nina
Geophysical Research Letters, 2012Co-Authors: Yenjung Wu, J. K. Chou, A. Chen, Shu-chun Chang, H. U. Frey, S. B. Mende, Hantzong Su, Yukihiro TakahashiAbstract:[1] We analyzed the ISUAL-FORMOSAT2 Elves, the LIS-TRMM lightning, the sea surface temperature (SST), and the El Nino southern oscillation (ENSO) indices (the Nino 3.4 Index and the Southern Oscillation Index - SOI) in the period between June 2005 and May 2010 to explore the impacts of ENSO on the occurrences of the mesospheric Elves and the troposphere lightning. The standardized anomalies of the elve and the lightning occurrence densities are used to quantify the deviation of the elve and lightning occurrences during an ENSO event. The areas in the ENSO-sensitive western Pacific, central Pacific and Tahiti regions with a significant event anomaly are taken to be the impact indicators of ENSO. Also the SOI is used to examine the correlation of the temporal intensity variation between ENSO, elve and lightning. The results indicate that elve shows clear responses to ENSO with a correlation over 0.6 in the coastal and the oceanic regions. The lightning occurrence is responsive to ENSO in the oceanic regions, but shows a low correlation in the coastal regions, due the overwhelming influence of the landmass. Therefore, between elve and lightning as proximity indices of ENSO, elve has a broader applicable geographic range. However, elve is known to be the mesospheric luminous manifestations of the high-peak-current lightning, and the response of the intense lightning to ENSO would be similar to that of the elve. Hence, alternatively, the intense lightning can also be used as an indicator of ENSO.
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ISUAL far‐ultraviolet events, Elves, and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, Lou-chuang LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
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isual far ultraviolet events Elves and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, L C LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
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On the Global Occurrence and Impacts of Transient Luminous Events (TLEs)
AIP Conference Proceedings, 2009Co-Authors: Rue-ron Hsu, Cheng-ling Kuo, A. Chen, Harald U. Frey, Stephen B. Mende, Yukihiro Takahashi, Lou Chung LeeAbstract:Based on the first four years of the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) experiment onboard the FORMOSAT‐2 satellite, Elves are found to be the most abundant type (∼80%) of TLEs (transient luminous events), whereas sprites and halos only combine to account for ∼20%. The distribution of sprites and halos closely resemble that of the cloud‐to‐ground lightning. However, nearly 60% of Elves occurred over the ocean, a feature indicating that the high peak current lightning is more abundant over the ocean. The global TLE occurrence rates are inferred to be 72, 3.7, and ∼1 events/minute, respectively, for Elves, halos, and sprites. Comparing with the results from the first three years of the ISUAL experiment reported by Chen et al. [1], the global occurrence rates for Elves and halos are higher due to the adoption of different correction factors. Using these updated TLE rates, the free electron content over an ELVE hot zone is estimated to be elevated by more than 10%. From analyzing ISUAL ...
Hiroshi Fukunishi - One of the best experts on this subject based on the ideXlab platform.
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Ground‐based detection of TLE‐producing intense lightning during the MEIDEX mission on board the space shuttle Columbia
Geophysical Research Letters, 2004Co-Authors: Colin Price, Eran Greenberg, Yoav Yair, Gabriella Sátori, József Bór, Hiroshi Fukunishi, Mitsuteru Sato, Peter Israelevich, M. Moalem, Adam DevirAbstract:[1] In January 2003 Transient Luminous Events (TLEs) also known as sprites and Elves were observed by the astronauts on board of the Columbia space shuttle, during the Mediterranean Israeli Dust Experiment (MEIDEX). Throughout the 16-day mission, electromagnetic data at four ground-based Extremely Low Frequency (ELF) stations (Israel, Hungary, Japan and Antarctica) were collected to geo-locate and determine the parameters of the parent lightning that triggered the TLEs. From our analysis 7 Elves and 7 sprites have been detected so far in our data. ELF transients were detected for 5 of 7 Elves at all ground stations with accurate geo-location of these events. However, none of the sprites were associated with ELF transients. This is contrary to the present theories of TLE formation, and may require some new thinking into the mechanisms that produce sprites and Elves.
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Ground‐based observations of ULF transients excited by strong lightning discharges producing Elves and sprites
Geophysical Research Letters, 1997Co-Authors: Hiroshi Fukunishi, Y Takahashi, M. Sato, A. Shono, M. Fujito, Y. WatanabeAbstract:Optical and search coil magnetometer data obtained from the SPRITES'96 campaign carried out at Yucca Ridge Field Station, Colorado in July 1996 have presented clear evidence for the excitation of ULF transients with their dominant power at 1–2 Hz by strong lightning discharges producing Elves and sprites. The most striking feature is that the ULF transients exhibit different wave forms in the case of sprites without preceding Elves and the case of sprites with preceding Elves. In the former case damped, quasi-sinusoidal oscillations commence impulsively at the onset of sprites, while in the latter case quasi-sinusoidal wavelets with a duration of ∼3 s are excited, and Elves and sprites occur within each wavelet. It is likely that these ULF transients are due to the nonlinear excitation of the ionospheric Alfven resonator by strong lightning discharge, as proposed by Sukhorukov and Stubbe [1997].
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ground based observations of ulf transients excited by strong lightning discharges producing Elves and sprites
Geophysical Research Letters, 1997Co-Authors: Hiroshi Fukunishi, Y Takahashi, M. Sato, A. Shono, M. Fujito, Y. WatanabeAbstract:Optical and search coil magnetometer data obtained from the SPRITES'96 campaign carried out at Yucca Ridge Field Station, Colorado in July 1996 have presented clear evidence for the excitation of ULF transients with their dominant power at 1–2 Hz by strong lightning discharges producing Elves and sprites. The most striking feature is that the ULF transients exhibit different wave forms in the case of sprites without preceding Elves and the case of sprites with preceding Elves. In the former case damped, quasi-sinusoidal oscillations commence impulsively at the onset of sprites, while in the latter case quasi-sinusoidal wavelets with a duration of ∼3 s are excited, and Elves and sprites occur within each wavelet. It is likely that these ULF transients are due to the nonlinear excitation of the ionospheric Alfven resonator by strong lightning discharge, as proposed by Sukhorukov and Stubbe [1997].
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Elves lightning induced transient luminous events in the lower ionosphere
Geophysical Research Letters, 1996Co-Authors: Hiroshi Fukunishi, Y Takahashi, Minoru Kubota, Kazuyo Sakanoi, U S Inan, Walter A LyonsAbstract:Observations of optical phenomena at. high alti- tude a, bove thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040 ' N, 104o.56 ' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These newneasurements indicate that diffuse optical flashes with a duration of < I ms and a hori- zontal scale of-.- 100-300 km occur at 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as 'alves" to distinguish them from 'i'ed sprites" . This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.
Cheng-ling Kuo - One of the best experts on this subject based on the ideXlab platform.
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Multivariate analysis of dim Elves from ISUAL observations
Journal of Geophysical Research: Atmospheres, 2015Co-Authors: Marc Offroy, Cheng-ling Kuo, A. Chen, Rue-ron Hsu, Thomas Farges, Pierre Gaillard, Yukihiro TakahashiAbstract:The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite, launched in 2004, records Transient Luminous Events (TLEs). ISUAL has an imager and a spectrophotometer that observe TLEs all over the globe. Among these phenomena, Elves are particularly difficult to detect. ISUAL often records events that correspond to significant far ultraviolet (FUV) emissions in the spectrophotometer but have no discernible TLEs in the imager. These FUV events are called “dim” Elves. Therefore, it is important to develop mathematical tools to analyze the data to obtain a better evaluation of the number of Elves and their occurrence. Multivariate approaches are applied to characterize the unlabeled events. The first approach is the principal component analysis which distinguishes two different groups, one including Elves and dim Elves. The second approach is the PARallel FACtor analysis which provides a waveform model for each group. These methodologies confirm that FUV signal is the evidence of TLE presence. A crude classification method was then suggested taking into account these results. The proportion of Elves, relatively to the considered ISUAL data set, is found to be about 40%. It is similar to previous results and confirms that relatively weak lightning peak current is sufficient to produce Elves. This new strategy demonstrates the potential for discriminating between lightning and TLEs without prior knowledge within the selectivity of the FUV spectral band.
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ISUAL multi-band observations of Elves
2011 XXXth URSI General Assembly and Scientific Symposium, 2011Co-Authors: Cheng-ling Kuo, Ta-yin Huang, Shu-chu Chang, Li-jou Lee, J. K. Chou, A. Chen, Rue-ron Hsu, Harald U. Frey, Stephen B. MendeAbstract:The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) experiment on the FORMOSAT-2 satellite inferred the global occurrence rates of sprites, halos and Elves to be ∼1, ∼1 and 35 events/min, respectively [1, 2]. Hence, elve is the most abundant type of transient luminous events (TLEs). From analyzing brightness observed by ISUAL Imager through different filters (1PN 2 , 762, 630, 557.7, 427.8 nm), the relative intensity of the OH (9,3), O1D, O1S, 1NN 2 + and O 2 Atmosphere band (0,0) emissions in Elves will be discussed.
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ISUAL far‐ultraviolet events, Elves, and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, Lou-chuang LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
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isual far ultraviolet events Elves and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, L C LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
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On the Global Occurrence and Impacts of Transient Luminous Events (TLEs)
AIP Conference Proceedings, 2009Co-Authors: Rue-ron Hsu, Cheng-ling Kuo, A. Chen, Harald U. Frey, Stephen B. Mende, Yukihiro Takahashi, Lou Chung LeeAbstract:Based on the first four years of the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) experiment onboard the FORMOSAT‐2 satellite, Elves are found to be the most abundant type (∼80%) of TLEs (transient luminous events), whereas sprites and halos only combine to account for ∼20%. The distribution of sprites and halos closely resemble that of the cloud‐to‐ground lightning. However, nearly 60% of Elves occurred over the ocean, a feature indicating that the high peak current lightning is more abundant over the ocean. The global TLE occurrence rates are inferred to be 72, 3.7, and ∼1 events/minute, respectively, for Elves, halos, and sprites. Comparing with the results from the first three years of the ISUAL experiment reported by Chen et al. [1], the global occurrence rates for Elves and halos are higher due to the adoption of different correction factors. Using these updated TLE rates, the free electron content over an ELVE hot zone is estimated to be elevated by more than 10%. From analyzing ISUAL ...
Y Takahashi - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal structures of sprites and Elves observed by array photometers
Cospar Colloquia Series, 2002Co-Authors: Hiroaki Fukunishi, A. Uchida, Y. Watanabe, Y TakahashiAbstract:Abstract To observe rapid spatial and temporal structures of sprites and Elves, we developed high-speed array photometers using multianode photomultipliers and operated these photometers and image intensified CCD cameras at Yucca Ridge Field Station (40.7°N, 104.9°W), Colorado during the SPRITES campaigns in the summer seasons from 1996 to 1999. We also operated these instruments at Dodaira Observatory (36.0°N, 139.2°E) and Sendai (38.3°N, 140.9°E) in Japan in December 1998 and January 1999, and succeeded for the first time in observing sprites and Elves above the coast of the Sea of Japan near the Hokuriku region in the winter season. The obtained space-time structures of sprites and Elves are consistent with those predicted from the quasi-electrostatic (QE) model and the electromagnetic pulse (EMP) model, respectively.
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Ground‐based observations of ULF transients excited by strong lightning discharges producing Elves and sprites
Geophysical Research Letters, 1997Co-Authors: Hiroshi Fukunishi, Y Takahashi, M. Sato, A. Shono, M. Fujito, Y. WatanabeAbstract:Optical and search coil magnetometer data obtained from the SPRITES'96 campaign carried out at Yucca Ridge Field Station, Colorado in July 1996 have presented clear evidence for the excitation of ULF transients with their dominant power at 1–2 Hz by strong lightning discharges producing Elves and sprites. The most striking feature is that the ULF transients exhibit different wave forms in the case of sprites without preceding Elves and the case of sprites with preceding Elves. In the former case damped, quasi-sinusoidal oscillations commence impulsively at the onset of sprites, while in the latter case quasi-sinusoidal wavelets with a duration of ∼3 s are excited, and Elves and sprites occur within each wavelet. It is likely that these ULF transients are due to the nonlinear excitation of the ionospheric Alfven resonator by strong lightning discharge, as proposed by Sukhorukov and Stubbe [1997].
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ground based observations of ulf transients excited by strong lightning discharges producing Elves and sprites
Geophysical Research Letters, 1997Co-Authors: Hiroshi Fukunishi, Y Takahashi, M. Sato, A. Shono, M. Fujito, Y. WatanabeAbstract:Optical and search coil magnetometer data obtained from the SPRITES'96 campaign carried out at Yucca Ridge Field Station, Colorado in July 1996 have presented clear evidence for the excitation of ULF transients with their dominant power at 1–2 Hz by strong lightning discharges producing Elves and sprites. The most striking feature is that the ULF transients exhibit different wave forms in the case of sprites without preceding Elves and the case of sprites with preceding Elves. In the former case damped, quasi-sinusoidal oscillations commence impulsively at the onset of sprites, while in the latter case quasi-sinusoidal wavelets with a duration of ∼3 s are excited, and Elves and sprites occur within each wavelet. It is likely that these ULF transients are due to the nonlinear excitation of the ionospheric Alfven resonator by strong lightning discharge, as proposed by Sukhorukov and Stubbe [1997].
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Elves lightning induced transient luminous events in the lower ionosphere
Geophysical Research Letters, 1996Co-Authors: Hiroshi Fukunishi, Y Takahashi, Minoru Kubota, Kazuyo Sakanoi, U S Inan, Walter A LyonsAbstract:Observations of optical phenomena at. high alti- tude a, bove thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040 ' N, 104o.56 ' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These newneasurements indicate that diffuse optical flashes with a duration of < I ms and a hori- zontal scale of-.- 100-300 km occur at 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as 'alves" to distinguish them from 'i'ed sprites" . This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.
Shu-chun Chang - One of the best experts on this subject based on the ideXlab platform.
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occurrence of Elves and lightning during el nino and la nina
Geophysical Research Letters, 2012Co-Authors: Yenjung Wu, J. K. Chou, A. Chen, Shu-chun Chang, H. U. Frey, S. B. Mende, Hantzong Su, Yukihiro TakahashiAbstract:[1] We analyzed the ISUAL-FORMOSAT2 Elves, the LIS-TRMM lightning, the sea surface temperature (SST), and the El Nino southern oscillation (ENSO) indices (the Nino 3.4 Index and the Southern Oscillation Index - SOI) in the period between June 2005 and May 2010 to explore the impacts of ENSO on the occurrences of the mesospheric Elves and the troposphere lightning. The standardized anomalies of the elve and the lightning occurrence densities are used to quantify the deviation of the elve and lightning occurrences during an ENSO event. The areas in the ENSO-sensitive western Pacific, central Pacific and Tahiti regions with a significant event anomaly are taken to be the impact indicators of ENSO. Also the SOI is used to examine the correlation of the temporal intensity variation between ENSO, elve and lightning. The results indicate that elve shows clear responses to ENSO with a correlation over 0.6 in the coastal and the oceanic regions. The lightning occurrence is responsive to ENSO in the oceanic regions, but shows a low correlation in the coastal regions, due the overwhelming influence of the landmass. Therefore, between elve and lightning as proximity indices of ENSO, elve has a broader applicable geographic range. However, elve is known to be the mesospheric luminous manifestations of the high-peak-current lightning, and the response of the intense lightning to ENSO would be similar to that of the elve. Hence, alternatively, the intense lightning can also be used as an indicator of ENSO.
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ISUAL far‐ultraviolet events, Elves, and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, Lou-chuang LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
-
isual far ultraviolet events Elves and lightning current
Journal of Geophysical Research, 2010Co-Authors: Shu-chun Chang, Cheng-ling Kuo, Li-jou Lee, Stephen B. Mende, Yukihiro Takahashi, Alfredb. Chen, Rue-rou Hsu, H. U. Frey, L C LeeAbstract:[1] The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of Elves. After analyzing the imager-N21P brightness of the Elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest Elves and is less than 1 × 104 photons/cm2. Combining all the information, the FUV events are identified as dim Elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb Elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multiElves, which are FUV events from the M-components or the multiple strokes in lightning flashes.