Omega band pulsating auroras observed onboard THEMIS spacecraft and on the ground

Sato, Natsuo; Kadokura, Akira; Tanaka, Yoshimasa; Nishiyama, Takanori; Hori, Tomoaki; Yukimatu, A. S.

doi:10.1002/2015ja021382

Cited by 11 publications

(15 citation statements)

References 65 publications

(127 reference statements)

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“…Observations of these two major types of aurora have been made for a long time by using high‐resolution all‐sky imagers (ASIs) [e.g., Mendillo et al , ; Nishitani et al , ] or magnetospheric satellites [e.g., Zhang et al , ; Ebihara et al , ]. In recent years, simultaneous observations on the ground and in the magnetosphere have been reported [e.g., Sato et al , ; Donovan et al , ] and the “Conjunction Event Finder,” a useful tool for finding conjugate observation events, was developed by Miyashita et al [].…”

Section: Introductionmentioning

confidence: 99%

“…Observations of these two major types of aurora have been made for a long time by using high-resolution all-sky imagers (ASIs) [e.g., Mendillo et al, 1989;Nishitani et al, 1994] or magnetospheric satellites [e.g., Zhang et al, 2005;Ebihara et al, 2010]. In recent years, simultaneous observations on the ground and in the magnetosphere have been reported [e.g., Sato et al, 2015;Donovan et al, 2008] and the "Conjunction Event Finder," a useful tool for finding conjugate observation events, was developed by Miyashita et al [2011]. 10.1002/2016JA023774 the pressure-driven instability can be either interchange or ballooning instabilities. The interchange instability has zero wave number along the magnetic field line, and the whole magnetic flux tube moves together.…”

Section: Introductionmentioning

confidence: 99%

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Conjugate observation of auroral finger‐like structures by ground‐based all‐sky cameras and THEMIS satellites

2017

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In this study, we analyze the first conjugate observation of auroral finger‐like structures using ground‐based all‐sky cameras and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites and investigated associated physical processes that are a cause of auroral fragmentation into patches. Two events are reported: one is a conjugate event, and the other is a nearly conjugate event. The conjugate event was observed at Narsarsuaq (magnetic latitude: 65.3°N), Greenland, at 0720–0820 UT (0506–0606 LT) on 17 February 2012. Analysis of the event revealed the following observational facts: (1) variation of parallel electron energy fluxes observed by THEMIS‐E shows a correspondence to the auroral intensity variation, (2) plasma pressure and magnetic pressure fluctuate in antiphase with time scales of 5–20 min, and (3) perpendicular ion velocity is very small (less than 50 km/s). In the latter event, observed at Gakona, Alaska, on 2 February 2008, the THEMIS‐D satellite passed across higher latitudes of finger‐like structures. The data from THEMIS‐D also showed the antiphase fluctuation between plasma pressure and magnetic pressure and the small perpendicular ion velocity. From these observations, we suggest that the finger‐like structures are caused by a pressure‐driven instability in the balance of plasma and magnetic pressures in the magnetosphere.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conjugate observation of auroral finger‐like structures by ground‐based all‐sky cameras and THEMIS satellites

2017

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“…The growth signatures and the movements of pulsating aurora elements of this event are very similar to the omega event shown in Figs. 3 and 7 of Sato et al (2015). The dynamics of this event are shown in Additional file 10: Movie S10.…”

Section: Dynamic Signatures During the Initial Phase Of The Growth Ofmentioning

confidence: 99%

“…As the band structure with its temporally stationary current system moves above ground-based magnetometers, Ps6-type magnetic pulsations (with periods of 5-40 min) are observed (Saito 1978;Rostoker and Barichello 1980). Omega bands generally consist of intense pulsating auroras (Oguti et al 1981;Sato et al 2015). However, the mechanism responsible for omega band formation remains unclear.…”

Section: Introductionmentioning

confidence: 99%

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Morphologies of omega band auroras

Sato

Yukimatu

Tanaka

et al. 2017

Earth Planets Space

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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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Temporal characteristics and energy deposition of pulsating auroral patches

et al. 2016

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We present a careful statistical analysis of pulsating aurora (PA) using all‐sky green line (557.7 nm) images obtained at 3.3 Hz. Six well‐defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on‐time and off‐time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term “pulsating” is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

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Omega band pulsating auroras observed onboard THEMIS spacecraft and on the ground

Cited by 11 publications

References 65 publications

Conjugate observation of auroral finger‐like structures by ground‐based all‐sky cameras and THEMIS satellites

Conjugate observation of auroral finger‐like structures by ground‐based all‐sky cameras and THEMIS satellites

Morphologies of omega band auroras

Temporal characteristics and energy deposition of pulsating auroral patches

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