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Natsuo Sato - One of the best experts on this subject based on the ideXlab platform.
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morphologies of omega band Auroras
Earth Planets and Space, 2017Co-Authors: Natsuo Sato, Akira Sessai Yukimatu, Yoshimasa Tanaka, Tomoaki HoriAbstract:We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east–west-aligned Auroras, rather than via the rotation or shear motion of preexisting east–west-aligned Auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.
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omega band pulsating Auroras observed onboard themis spacecraft and on the ground
Journal of Geophysical Research, 2015Co-Authors: Natsuo Sato, Akira Kadokura, Yoshimasa Tanaka, Tomoaki Hori, Takanori Nishiyama, Akira Sessai YukimatuAbstract:We examined a fortuitous case of an omega band pulsating aurora observed simultaneously on the ground at Sanikiluaq in Canada and onboard the Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft on 1 March 2011. We observed almost the entire process of the generation of the omega band aurora from the initial growth to the declining through expansion period. The omega band aurora grew from a faint seed, not via distortion of a preexisting east-west band aurora. The size scale of the omega band aurora during the maximum period was ~500 km in the north-south direction and ~200 km in the east-west direction. The mesoscale omega band aurora consisted of more than 15 patches of complex-shaped small-scale Auroras. Each patch contained an intense pulsating aurora with a recurrent period of ~9–12 s and a poleward moving form. The footprints of the THEMIS D and THEMIS E spacecraft crossed the poleward part of the omega band aurora. THEMIS D observed significant signatures in the electromagnetic fields and particles associated with the time at which the spacecraft crossed the omega band aurora. In particular, it was found that the Y and Z components of the DC electric field intensity, especially the Z component, modulated with almost the same period as that of the optical pulsating Auroras. The electrostatic low-frequency waves of less than 30 Hz showed quasiperiodic intensity variations similar to those of the DC electric field. These observations suggest that DC electric field variation and low-frequency electrostatic waves may play important roles in the driving mechanism of omega band pulsating Auroras.
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absence of geomagnetic conjugacy in pulsating Auroras
Geophysical Research Letters, 2007Co-Authors: Masakazu Watanabe, Natsuo Sato, Akira Kadokura, Thorsteinn SaemundssonAbstract:[1] We have examined the geomagnetic conjugacy of pulsating Auroras using TV camera data obtained simultaneously at Syowa in Antarctica and at Tjornes in Iceland. In order to exclude the magnetic field mapping problem, we investigated a period during which conjugate points were unambiguously identified from large-scale discrete conjugate Auroras. The conjugacy of pulsating Auroras revealed in this study may be summarized as follows. Some pulsating Auroras appear in both hemispheres, while others appear only in one hemisphere. Even in the former case, the shape of the auroral form is generally different between the two hemispheres, and there is little or no interhemispheric correlation in the intensity variations. We could not find a pulsating aurora that appeared synchronously at the two endpoints of a flux tube. From these observational results and the increasing amount of evidence in recent studies, we conclude that the conjugacy of pulsating Auroras is generally poor.
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synoptic observations of Auroras along the postnoon oval a survey with all sky tv observations at zhongshan antarctica
Journal of Atmospheric and Solar-Terrestrial Physics, 2000Co-Authors: Natsuo Sato, Akira Kadokura, Huigen Yang, Kazuo Makita, Masayuki Kikuchi, Masaru Ayukawa, Ruiyuan Liu, Ingemar HaggstromAbstract:Abstract All-sky TV data obtained at Zhongshan, Antarctica, have been used to survey auroral displays along the postnoon auroral oval. The auroral occurrence peak around 15 MLT, which was previously shown by satellite observations, is confirmed to exist in ground observations as well. The so called ‘midday gap’ of discrete aurora, however, is not confirmed by ground observations. This survey reveals that the noon region appears to involve another auroral occurrence peak. The noon auroral peak observed from the ground is dominated by an aurora termed as dayside corona in the present study. A dayside corona is usually weak and changing rapidly in its appearance, luminosity and locale. The electron precipitation causing the dayside corona might be too soft, have reduced flux and/or have too rapid a motion of its rayed structures which would result in less luminosity, all of which could account for the ‘midday gap’ in satellite observations. We thus argue for a new synoptic picture of auroral displays along the postnoon oval, in which beside the 15 MLT peak, the noon region is filled with the dayside corona rather than a ‘gap’ in discrete aurora.
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conjugacy of isolated auroral arcs and nonconjugate auroral breakups
Journal of Geophysical Research, 1998Co-Authors: Natsuo Sato, Takayuki Nagaoka, Kumiko Hashimoto, Thorsteinn SaemundssonAbstract:Fine examples of both conjugate and nonconjugate isolated auroral arcs were observed at two geomagnetically conjugate stations near L = 6, Syowa Station in Antarctica and Husafell in Iceland on September 12, 1988. These events exhibited some interesting characteristics. An auroral loop structure that appeared in both hemispheres was ∼2.0 times larger in the north-south direction at Syowa than at Husafell. This scale difference is greater than expected from the difference in geographic and geomagnetic (IGRF) coordinates between the two points of observation. However, temporal and spatial variations in the loop structures were almost identical in both hemispheres. After the disappearance of the loop structure, closely conjugate Auroras were formed. Nonconjugate auroral features appeared again at Syowa on the poleward side, while the equatorward Auroras maintained conjugacy. The nonconjugate aurora at Syowa then began to break up, showing fast moving vortex-like structures (auroral spirals). At this time, all auroral features at Husafell seemed to have their conjugate counterparts in equatorward Auroras at Syowa and none exhibited rapid motions. These conjugate Auroras at Husafell were gradually extending poleward, while the corresponding features at Syowa were compressed toward the equator and shrinking in size. The onset of auroral breakup was about one minute earlier at Syowa than at Husafell. The nonconjugate auroral features were reflected in corresponding magnetic field variations on the ground. The events summarized above give interesting clues to the development and decay of auroral conjugacy and the question why the beginning of auroral breakup is not simultaneous at conjugate stations. The time lag and nonconjugacy of auroral breakup in conjugate areas suggests that the triggering source of auroral breakup was not located near the equatorial plane in the magnetosphere but most likely in a localized region near the ionosphere in the southern hemisphere. The nonconjugate auroral spirals also suggest the existence of asymmetrical field-aligned currents.
W.r. Dunn - One of the best experts on this subject based on the ideXlab platform.
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comparisons between jupiter s x ray uv and radio emissions and in situ solar wind measurements during 2007
Journal of Geophysical Research, 2020Co-Authors: W.r. Dunn, R. Gray, A.d. Wibisono, L. Lamy, C. LouisAbstract:We compare Chandra and XMM‐Newton X‐ray observations of Jupiter during 2007 with a rich multi‐instrument dataset including: upstream in‐situ solar wind measurements from the New Horizons spacecraft, radio emissions from the Nancay Decametric Array and Wind/Waves, and UV observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. Non‐Io decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterise 3 types of X‐ray aurorae: hard X‐ray bremsstrahlung main emission, pulsed/flared soft X‐ray emissions and a newly identified dim flickering (varying on short‐timescales, but quasi‐continuously present) aurora. For most observations, the X‐ray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by Iogenic plasma. However, the brightest X‐ray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. X‐ray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power> 1TW) and X‐ray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim and UV main emission power was also lower(<700 GW), suggesting their power scaled together.
C. Louis - One of the best experts on this subject based on the ideXlab platform.
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comparisons between jupiter s x ray uv and radio emissions and in situ solar wind measurements during 2007
Journal of Geophysical Research, 2020Co-Authors: W.r. Dunn, R. Gray, A.d. Wibisono, L. Lamy, C. LouisAbstract:We compare Chandra and XMM‐Newton X‐ray observations of Jupiter during 2007 with a rich multi‐instrument dataset including: upstream in‐situ solar wind measurements from the New Horizons spacecraft, radio emissions from the Nancay Decametric Array and Wind/Waves, and UV observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. Non‐Io decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterise 3 types of X‐ray aurorae: hard X‐ray bremsstrahlung main emission, pulsed/flared soft X‐ray emissions and a newly identified dim flickering (varying on short‐timescales, but quasi‐continuously present) aurora. For most observations, the X‐ray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by Iogenic plasma. However, the brightest X‐ray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. X‐ray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power> 1TW) and X‐ray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim and UV main emission power was also lower(<700 GW), suggesting their power scaled together.
Y Ebihara - One of the best experts on this subject based on the ideXlab platform.
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candidate auroral observations during the major solar terrestrial storm in may 1680 implication for space weather events during the maunder minimum
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Hisashi Hayakawa, Kristian Schlegel, Bruno P Besser, Y EbiharaAbstract:The Maunder Minimum (1645-1715) is currently considered the only grand minimum within telescopic sunspot observations since 1610. During this epoch, the Sun was extremely quiet and unusually free from sunspots. However, despite reduced frequency, candidate aurorae were reported in the mid-European sector during this period and have been associated with occurrences of interplanetary coronal mass ejections (ICMEs), whereas some of them have been identified as misinterpretations. Here, we have analysed reports of candidate aurorae on 1 June 1680 with simultaneous observations in mid-Europe, and compared their descriptions with visual accounts of early modern aurorae. Most contemporary sunspot drawings from 22, 24, and 27 May 1680 have shown that this apparent sunspot may have been a source of ICMEs, which caused the reported candidate aurorae. On the other hand, its intensity estimate shows that the magnetic storm during this candidate aurora was probably within the capability of the storms derived from the corotating interaction region (CIR). Therefore, we accommodate both ICMEs and CIRs as their possible origin. This interpretation is probably applicable to the candidate aurorae in the often-cited Hungarian catalogue, on the basis of the reconstructed margin of their equatorward auroral boundary. Moreover, this catalogue itself has clarified that the considerable candidates during the MM were probably misinterpretations. Therefore, frequency of the auroral visibility in Hungary was probably lower than previously considered and agree more with the generally slow solar wind in the existing reconstructions, whereas sporadic occurrences of sunspots and coronal holes still caused occasional geomagnetic storms.
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long lasting extreme magnetic storm activities in 1770 found in historical documents
The Astrophysical Journal, 2017Co-Authors: Hisashi Hayakawa, Y Ebihara, Delores J Knipp, Kiyomi Iwahashi, Harufumi Tamazawa, Akito Davis Kawamura, Kazunari Shibata, Kentaro Hattori, Kumiko MaseAbstract:Dim red aurora at low magnetic latitudes is a visual and recognized manifestation of magnetic storms. The great low-latitude auroral displays seen throughout East Asia on 1770 September 16–18 are considered to manifest one of the greatest storms. Recently found, 111 historical documents in East Asia attest that these low-latitude auroral displays appeared in succession for almost nine nights during 1770 September 10–19 in low magnetic latitude areas (<30°). This suggests that the duration of the great magnetic storm is much longer than usual. Sunspot drawings from 1770 reveal that the sunspot areas were twice as large as those observed in another great storm of 1859, which substantiates these unusual storm activities in 1770. These spots likely ejected several huge, sequential magnetic structures in short duration into interplanetary space, resulting in spectacular worldwide aurorae in mid-September of 1770. These findings provide new insight into the history, duration, and effects of extreme magnetic storms that may be valuable for those who need to mitigate against extreme events.
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fast moving diffuse auroral patches a new aspect of daytime pc3 auroral pulsations
Journal of Geophysical Research, 2017Co-Authors: Y Ebihara, A T Weatherwax, Akira Kadokura, T Motoba, M J Engebretson, M R Lessard, A J GerrardAbstract:Auroral pulsations are a convenient diagnostic of wave-particle interactions in the magnetosphere. A case study of a daytime Pc3 (22–100 mHz) auroral pulsation event, measured with a ~2 Hz sampling all-sky camera at South Pole Station (74.4°S magnetic latitude) on 17 May 2012, is presented. The daytime Pc3 auroral pulsations were most active in a closed field line region where the aurora was dominated by diffuse green-line emissions and within ±2 hours of magnetic local noon. Usually, but not always, the corresponding periodic variations were recorded with a colocated search coil magnetometer. Of particular interest is the two-dimensional auroral signature, indicating that the temporal luminosity variations at a given point were due to repeated formation and horizontal motion of faint, non-pulsating auroral patches with scale sizes of ~100 km. The individual patches propagated equatorward with speeds of 15 km s–1 up to 20–25 km s–1 one after another along the magnetic meridian through local magnetic zenith. These properties differ considerably from typical pulsating aurorae, being periodic ON–OFF luminosity variations in a particular auroral patch and drifting in accordance with the convection electric field in the magnetosphere. We speculate that such repetitive patterns of the fast-moving auroral patches, being another aspect of the daytime Pc3 auroral pulsations, may be a visible manifestation of compressional Pc3 waves which propagate earthward and cause modulation of precipitating keV electron fluxes in the dayside outer magnetosphere.
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chorus wave scattering responsible for the earth s dayside diffuse auroral precipitation a detailed case study
Journal of Geophysical Research, 2014Co-Authors: J Bortnik, Y Ebihara, Y Nishimura, R M Thorne, V Angelopoulos, A T WeatherwaxAbstract:The diffuse aurora is an almost permanent feature in the Earth's upper polar atmosphere, providing the major source of ionizing energy input into the high-latitude region. Previous theoretical and observational studies have demonstrated that whistler mode chorus scattering primarily accounts for intense nightside diffuse auroral precipitation within ~ 8 RE, but what causes the dayside diffuse aurora remains poorly understood. Using conjugate satellite wave and particle observations on 13 August 2009 from the Time History of Events and Macroscale Interactions during Substorms spacecraft and ground-based all-sky imager measurements at the South Pole on the dayside, we perform a quantitative analysis of wave-driven diffusion and electron precipitation. Our results demonstrate that the dayside chorus scattering was the dominant contributor to the observed dayside diffuse auroral precipitation and that the chorus wave intensity primarily controlled its brightness, indicating that dayside chorus can be the major driver of the Earth's dayside diffuse aurora. While further investigations are required to bring closure to the origin of the dayside diffuse aurora under differing solar wind conditions and geomagnetic situations, our finding is an important complement to recent work on the formation mechanism of the diffuse aurora and provides improved understanding of the roles of resonant wave-particle interactions in diffuse auroral precipitation pattern on a global scale.
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an interhemispheric comparison of gps phase scintillation with auroral emission observed at the south pole and from the dmsp satellite
Annals of Geophysics, 2013Co-Authors: P Prikryl, P. T. Jayachandran, Y Zhang, Y Ebihara, Reza Ghoddousifard, Joe Kinrade, Cathryn N Mitchell, A T Weatherwax, G S Bust, Pierre J CilliersAbstract:The global positioning system (GPS) phase scintillation caused by high-latitude ionospheric irregularities during an intense high-speed stream (HSS) of the solar wind from April 29 to May 5, 2011, was observed using arrays of GPS ionospheric scintillation and total electron content monitors in the Arctic and Antarctica. The one-minute phase-scintillation index derived from the data sampled at 50 Hz was complemented by a proxy index (delta phase rate) obtained from 1-Hz GPS data. The scintillation occurrence coincided with the aurora borealis and aurora australis observed by an all-sky imager at the South Pole, and by special sensor ultraviolet scanning imagers on board satellites of the Defense Meteorological Satellites Program. The South Pole (SP) station is approximately conjugate with two Canadian High Arctic Ionospheric Network stations on Baffin Island, Canada, which provided the opportunity to study magnetic conjugacy of scintillation with support of riometers and magnetometers. The GPS ionospheric pierce points were mapped at their actual or conjugate locations, along with the auroral emission over the South Pole, assuming an altitude of 120 km. As the aurora brightened and/or drifted across the field of view of the all-sky imager, sequences of scintillation events were observed that indicated conjugate Auroras as a locator of simultaneous or delayed bipolar scintillation events. In spite of the greater scintillation intensity in the auroral oval, where phase scintillation sometimes exceeded 1 radian during the auroral break-up and substorms, the percentage occurrence of moderate scintillation was highest in the cusp. Interhemispheric comparisons of bipolar scintillation maps show that the scintillation occurrence is significantly higher in the southern cusp and polar cap.
Akira Kadokura - One of the best experts on this subject based on the ideXlab platform.
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fast moving diffuse auroral patches a new aspect of daytime pc3 auroral pulsations
Journal of Geophysical Research, 2017Co-Authors: Y Ebihara, A T Weatherwax, Akira Kadokura, T Motoba, M J Engebretson, M R Lessard, A J GerrardAbstract:Auroral pulsations are a convenient diagnostic of wave-particle interactions in the magnetosphere. A case study of a daytime Pc3 (22–100 mHz) auroral pulsation event, measured with a ~2 Hz sampling all-sky camera at South Pole Station (74.4°S magnetic latitude) on 17 May 2012, is presented. The daytime Pc3 auroral pulsations were most active in a closed field line region where the aurora was dominated by diffuse green-line emissions and within ±2 hours of magnetic local noon. Usually, but not always, the corresponding periodic variations were recorded with a colocated search coil magnetometer. Of particular interest is the two-dimensional auroral signature, indicating that the temporal luminosity variations at a given point were due to repeated formation and horizontal motion of faint, non-pulsating auroral patches with scale sizes of ~100 km. The individual patches propagated equatorward with speeds of 15 km s–1 up to 20–25 km s–1 one after another along the magnetic meridian through local magnetic zenith. These properties differ considerably from typical pulsating aurorae, being periodic ON–OFF luminosity variations in a particular auroral patch and drifting in accordance with the convection electric field in the magnetosphere. We speculate that such repetitive patterns of the fast-moving auroral patches, being another aspect of the daytime Pc3 auroral pulsations, may be a visible manifestation of compressional Pc3 waves which propagate earthward and cause modulation of precipitating keV electron fluxes in the dayside outer magnetosphere.
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omega band pulsating Auroras observed onboard themis spacecraft and on the ground
Journal of Geophysical Research, 2015Co-Authors: Natsuo Sato, Akira Kadokura, Yoshimasa Tanaka, Tomoaki Hori, Takanori Nishiyama, Akira Sessai YukimatuAbstract:We examined a fortuitous case of an omega band pulsating aurora observed simultaneously on the ground at Sanikiluaq in Canada and onboard the Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft on 1 March 2011. We observed almost the entire process of the generation of the omega band aurora from the initial growth to the declining through expansion period. The omega band aurora grew from a faint seed, not via distortion of a preexisting east-west band aurora. The size scale of the omega band aurora during the maximum period was ~500 km in the north-south direction and ~200 km in the east-west direction. The mesoscale omega band aurora consisted of more than 15 patches of complex-shaped small-scale Auroras. Each patch contained an intense pulsating aurora with a recurrent period of ~9–12 s and a poleward moving form. The footprints of the THEMIS D and THEMIS E spacecraft crossed the poleward part of the omega band aurora. THEMIS D observed significant signatures in the electromagnetic fields and particles associated with the time at which the spacecraft crossed the omega band aurora. In particular, it was found that the Y and Z components of the DC electric field intensity, especially the Z component, modulated with almost the same period as that of the optical pulsating Auroras. The electrostatic low-frequency waves of less than 30 Hz showed quasiperiodic intensity variations similar to those of the DC electric field. These observations suggest that DC electric field variation and low-frequency electrostatic waves may play important roles in the driving mechanism of omega band pulsating Auroras.
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absence of geomagnetic conjugacy in pulsating Auroras
Geophysical Research Letters, 2007Co-Authors: Masakazu Watanabe, Natsuo Sato, Akira Kadokura, Thorsteinn SaemundssonAbstract:[1] We have examined the geomagnetic conjugacy of pulsating Auroras using TV camera data obtained simultaneously at Syowa in Antarctica and at Tjornes in Iceland. In order to exclude the magnetic field mapping problem, we investigated a period during which conjugate points were unambiguously identified from large-scale discrete conjugate Auroras. The conjugacy of pulsating Auroras revealed in this study may be summarized as follows. Some pulsating Auroras appear in both hemispheres, while others appear only in one hemisphere. Even in the former case, the shape of the auroral form is generally different between the two hemispheres, and there is little or no interhemispheric correlation in the intensity variations. We could not find a pulsating aurora that appeared synchronously at the two endpoints of a flux tube. From these observational results and the increasing amount of evidence in recent studies, we conclude that the conjugacy of pulsating Auroras is generally poor.
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synoptic observations of Auroras along the postnoon oval a survey with all sky tv observations at zhongshan antarctica
Journal of Atmospheric and Solar-Terrestrial Physics, 2000Co-Authors: Natsuo Sato, Akira Kadokura, Huigen Yang, Kazuo Makita, Masayuki Kikuchi, Masaru Ayukawa, Ruiyuan Liu, Ingemar HaggstromAbstract:Abstract All-sky TV data obtained at Zhongshan, Antarctica, have been used to survey auroral displays along the postnoon auroral oval. The auroral occurrence peak around 15 MLT, which was previously shown by satellite observations, is confirmed to exist in ground observations as well. The so called ‘midday gap’ of discrete aurora, however, is not confirmed by ground observations. This survey reveals that the noon region appears to involve another auroral occurrence peak. The noon auroral peak observed from the ground is dominated by an aurora termed as dayside corona in the present study. A dayside corona is usually weak and changing rapidly in its appearance, luminosity and locale. The electron precipitation causing the dayside corona might be too soft, have reduced flux and/or have too rapid a motion of its rayed structures which would result in less luminosity, all of which could account for the ‘midday gap’ in satellite observations. We thus argue for a new synoptic picture of auroral displays along the postnoon oval, in which beside the 15 MLT peak, the noon region is filled with the dayside corona rather than a ‘gap’ in discrete aurora.
