On the simultaneity of substorm onset between two hemispheres

Morioka, A.; Miyoshi, Yoshizumi; Tsuchiya, F.; Misawa, Hiroaki; Kasaba, Yasumasa; Asozu, Takuhiro; Okano, Shinji; Kadokura, Akira; Sato, Natsuo; Miyaoka, Hiroshi; Yumoto, K.; Parks, G. K.; Honary, F.; Trotignon, Jean-Gabriel; Décréau, Pierrette; Reinisch, B. W.

doi:10.1029/2010ja016174

Cited by 14 publications

(23 citation statements)

References 71 publications

(79 reference statements)

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“…The latter effect was interpreted as being driven by the solar extreme ultraviolet (EUV) fluxes with maxima around the solstices because of Earth's axial tilt of 23.4°. A north‐south asymmetry was also reported in the time difference between northern and southern AKR breakup during the substorm onset [ Morioka et al , ]. The primary breakup of the AKR during substorms occurred as a “one‐sided” breakup in the Northern (summer) Hemisphere without the southern (winter) breakup, followed by a secondary simultaneous breakup in the Northern and Southern hemispheres ∼ 10 min later.…”

Section: Introductionmentioning

confidence: 70%

“…The height distribution of the SKR source location was deduced from the SKR spectra with reference to the terrestrial studies by Morioka et al [, , , , ]. Referring to the validations by previous studies based on remote and in situ measurements in the SKR sources [ Cecconi et al , ; Lamy et al , ; Lamy et al , , ; Mutel et al , ; Menietti et al , ], we assumed the SKR emissions are predominately right‐handed extraordinary (R‐X) mode waves excited via the CMI process [ Wu and Lee , ].…”

Section: Assumptionsmentioning

confidence: 99%

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Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

et al. 2013

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[1] Saturn's auroral activities have been suggested to be controlled by the seasonal variations of the polar ionospheric conductivities and atmospheric conditions associated with the solar extreme ultraviolet (EUV) flux. However, they have not yet been explained self-consistently by only the seasonal solar EUV effects. This study investigates the long-term variations of Saturnian Kilometric Radiation (SKR) as a proxy of the auroral activities, which were observed by Cassini's Radio and Plasma Wave Science experiment mostly during the southern summer (DOY (day of year) 001 2004001 to DOY 193 2010. We deduced the height distribution of the SKR source region in the Northern (winter) and Southern (summer) Hemispheres from the remote sensing of SKR spectra. The peak spectral density of the southern (summer) SKR was found to be up to 100 times greater than that of the northern (winter) SKR, and the altitude of the peak flux was similar ( 0.8 R s ) in the Northern and Southern Hemispheres. The spectral densities in both hemispheres became comparable with each other around equinox in August 2009. These results suggest a stronger SKR source region during the summer than the winter related to the seasonal EUV effect, which is opposite to the trend observed in the Earth's kilometric radiation. A long-term correlation analysis was performed for the SKR, solar EUV flux, and solar wind parameters extrapolated from Earth's orbit by an magnetohydrodynamical simulation focusing on variations on timescales longer than several weeks. We confirmed clear positive correlations between the solar wind dynamic pressure and peak flux density in both the Southern and Northern Hemispheres during the declining phase of the solar cycle. We conclude that the solar wind variations on the timescale of the solar cycle control the SKR source region. In addition, it was also confirmed that the south-to-north ratios of SKR power flux and source altitudes are positively correlated with the solar EUV flux. This result strongly supports a seasonal EUV effect on the SKR source region. The variations of SKR activity over both seasonal and solar cycles are discussed in comparison to the terrestrial case.Citation: Kimura, T., et al. (2013), Long-term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux,

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Section: Introductionmentioning

confidence: 70%

Section: Assumptionsmentioning

confidence: 99%

Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

et al. 2013

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“…Another often overlooked point of complexity concerns the role of the ionosphere. Recent and past conjugate observations reveal breakup timing differences on the order of a few minutes at opposite hemispheres [e.g., Morioka et al , 2011]. These differences suggest that the auroral ionosphere may partly control auroral breakup timing.…”

Section: Substorm Onset Timing and Locationmentioning

confidence: 99%

Recent advances in understanding substorm dynamics

Сергеев¹,

Angelopoulos²,

Nakamura³

2012

Geophysical Research Letters

134

151

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[1] Magnetospheric substorms are elemental processes of solar wind energy storage and explosive release in Earth's magnetosphere. They encompass fundamental plasma physics questions, are ubiquitous during all types of geomagnetic conditions, contribute significantly to magnetic storms, and are a key element of Space Weather applications. This paper reviews recent major advances enabled by modern multi-point space-based and groundbased platforms. These datasets have also empowered a system-wide perspective and advanced modeling. We particularly highlight progress in two areas: (1) substorm onset timing and evidence for current sheet preconditioning and destabilization and (2) fast flows and dipolarizations, including the role of entropy in magnetotail plasma propagation. Citation: Sergeev, V. A., V. Angelopoulos, and R. Nakamura (2012), Recent advances in understanding substorm dynamics, Geophys. Res. Lett., 39, L05101,

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“…A similar time difference between both stations was seen in the transition into the larger-scale spiral forms (not shown), as well as the onsets of Pi1-Pi2 power. Such a hemispheric difference might be a reflection of differences in the acceleration of precipitating auroral particles [e.g., Morioka et al, 2011], as well as the background conditions mentioned above, although it is inconclusive without further study.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…Although spatial and temporal evolution of aurora is generally perceived to be similar in the Northern and Southern Hemispheres, the optical signatures often represent interhemispheric asymmetries in terms of the timing, location, and intensity. A few simultaneous optical observations of auroral substorms in both hemispheres [ Frank and Sigwarth , ; Morioka et al ., ], which have been very rare, indicated that the onset brightening of auroral substorm in one hemisphere precedes that in another hemisphere by ~1–2 min. Such a nonsimultaneous nature of interhemispheric auroral substorm onsets potentially suggested that the processes creating aurora operate independently in each hemisphere, presumably in/around the auroral acceleration region.…”

Section: Introductionmentioning

confidence: 99%

Interrelationship between preonset auroral and magnetic signatures at a geomagnetically conjugate Iceland‐Syowa pair

et al. 2014

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We present the initiation and development of Pi1-Pi2 band pulsations in concert with spatiotemporal evolution of preonset auroral arc during an isolated auroral substorm reported by Motoba et al. (2012), and their interhemispheric similarities/dissimilarities, based on the colocated optical and magnetic field measurements at a geomagnetically conjugate Iceland-Syowa pair. At least~7 min prior to the auroral expansion onset, the first identifiable signature of preonset arc began with a small-scale (~30-50 km) azimuthal beading. Interestingly, the early development of the visible arc beading for~3-4 min was not accompanied by any ground magnetic perturbation. Then the bead-like forms in the arc evolved into brighter, larger undulations, eventually developing into the poleward expansion. Such a preonset optical sequence was almost identical at both stations. In the transition from the beads into undulations, Pi2 pulsations were first identified clearly, followed by Pi1 pulsations a few minutes later. Whereas the Pi2 onset was coincident with the initiation of progressive increase of the preonset arc luminosity, the Pi1 onset was associated with a subsequent steep increase. The Pi2 wave cycles superimposed on the magnetic negative bay were well correlated with the preonset arc luminosity time series. These results imply the potential linkage between the ground Pi1-Pi2 signatures in the onset region and the preonset auroral arc processes. Although the Pi1-Pi2 features were generally similar between the two hemispheres, there was also some dissimilarity in their temporal behaviors, which could reflect a small but noteworthy interhemispheric asymmetry in the overhead conjugate preonset aurora.

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On the simultaneity of substorm onset between two hemispheres

Cited by 14 publications

References 71 publications

Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

Recent advances in understanding substorm dynamics

Interrelationship between preonset auroral and magnetic signatures at a geomagnetically conjugate Iceland‐Syowa pair

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