Dayside Aurora Poleward of the Main Auroral Distribution: Implications for Convection and Mapping

Elphinstone, R. D.; Hearn, D. J.; Murphree, J. S.

doi:10.1007/978-94-011-1052-5_13

Cited by 10 publications

(5 citation statements)

References 20 publications

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“… Bonnell et al [1999] also observed antisunward flow associated with the arcs with FAST data, investigating cases when the IMF was northward for more than an hour. They discussed three possible source regions: lobe reconnection, the plasma sheet either through bifurcation of the lobe [ Huang et al , 1987, 1989] or through expansion of the plasma sheet into the lobe [ Murphree et al , 1994], and the low‐latitude boundary layer [ Elphinstone et al , 1994]. The LLBL source was ruled out as requiring a bipolar flow.…”

Section: Discussionmentioning

confidence: 99%

Responses of the open–closed field line boundary in the evening sector to IMF changes: A source mechanism for Sun‐aligned arcs

Maynard¹,

Burke

Moen

et al. 2003

J. Geophys. Res.

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[1] Simultaneous measurements from the Polar satellite and by ground-based optical sensors suggest that brief variations of the poleward auroral boundary on the nightside correlate with changes in the interplanetary magnetic field (IMF) about an hour after a structure has propagated in the solar wind past the Earth. Short-lived Sun-aligned arcs may emerge along the open-closed magnetic field line boundary (OCB) and then disappear after $10 min. The arcs are fueled by energetic particles whose spectral characteristics are similar to those of the of boundary plasma sheet (BPS). Polar measurements confirm that these auroral protrusions into the polar cap occur on nearly isolated closed magnetic flux. Optical emissions from these arcs appear strongest at their intersection with the poleward boundary of the auroral oval. Detailed magnetohydrodynamic (MHD) simulations of dayside interactions, when the dominant IMF component B Y changes sign, indicate that near the polarity reversal merging can occur between interplanetary field line segments within the magnetosheath [Maynard et al., 2001b]. Newly formed loops of interplanetary flux sweep past the Earth without interacting with the magnetosphere. Here, we consider some consequences within the distant magnetotail as the loops of disconnected flux propagate to X GSM % À200 R E . The MHD simulations indicate that about an hour after intra-IMF merging events fingers of closed field lines protrude from the OCB into the polar cap. Like the observed Sun-aligned arc, these simulated auroral features grow and decay on scales of $10 min and have ionospheric footprints that are nearly surrounded by open magnetic flux. The simulated auroral fingers are conjugate to high-pressure channels in the distant plasma sheet. We suggest that the short-lived Sun-aligned arcs are created via an interchange process similar to that proposed by Kan and Burke [1985] to explain one class of theta auroral forms. The continuity of magnetotail currents across a highpressure channel requires the development of field-aligned currents carried by obliquely propagating Alfvén waves. Plasma drifts associated with the dusk-to-dawn electric fields of the Alfvén waves are away from the Earth in the magnetotail and poleward in the nightside ionosphere. The correlation of phenomena at the nightside OCB with variations in the IMF indicate that processes other than substorms can influence boundary dynamics. Effects of self-interactions of the IMF within the dayside magnetosheath may be felt along the OCB as much as 1 hour later.

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Section: Discussionmentioning

confidence: 99%

Responses of the open–closed field line boundary in the evening sector to IMF changes: A source mechanism for Sun‐aligned arcs

Maynard¹,

Burke

Moen

et al. 2003

J. Geophys. Res.

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“…So far, the cause of Sun-aligned arc was attributed to local magnetospheric processes such as the instability between the plasma sheet and the lobe, the effect of the bursty bulk flow, the instability between the lowlatitude boundary layer and the plasma sheet, and the cusp reconnection (Bonnell et al, 1999;Elphinstone et al, 1994;Huang et al, 1987;Rodriguez et al, 1997). Tanaka, Obara, et al (2017) were the first who explained the Sun-aligned arc in the context of global magnetospheric structure.…”

Section: Open-closed Boundary and The Facmentioning

confidence: 99%

Cooperatives Roles of Dynamics and Topology in Generating the Magnetosphere‐Ionosphere Disturbances: Case of the Theta Aurora

et al. 2018

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To understand the magnetosphere‐ionosphere (M‐I) disturbances, it is necessary to know the change in the null‐separator structure along with the development of convection. The present paper explains this proposition by taking the case of the theta aurora that occurs after the switch of interplanetary magnetic field By and reveals auroral development inside the polar cap. The interplanetary magnetic field change is followed by the reformation of the null‐separator structure to cause a convection transient and a successive deformation of separatrices inside the magnetosphere, where separatrices separate the space into different volumes that include different types of magnetic field lines, and intersections of separatrices form separators that connect nulls. By the reconnection on the separator, energy inflow occurs from the solar wind to the magnetosphere. Convection driven by this energy transports nulls. In the case of theta aurora, two new nulls on the dayside coexist with two old nulls carried toward the tail by convection. Each set of nulls generates two open‐closed boundaries (separatrices) bounded by separators. Thus, open‐closed boundaries are divide into four parts. Separatrices generated by different sets partially become side by side near the nightside stem limes. The theta aurora is generated at the area corresponding to the low‐latitude side with respect to both of two boundaries. Thus, the occurrence of the theta aurora is a natural consequence of a transition in the null‐separator structure. The present example indicates that the global structure of the magnetosphere is almost decided from the skeleton of nulls.

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“…We see that these deep-tail flank regions project to features resembling polar arcs and fan arcs when B z is large (i.e., the T87 model has this characteristic in its magnetic field configuration). Elphinstone et al [1994b] used this reasoning to suggest that the KHI along the dayside and flanks of the tail is responsible for these fan arc systems. This would suggest that when B z is decreased on the flanks of the magnetotail, polar arcs would tend to disappear and the dayside polar region would become more open.…”

Section: General Mapping Principlesmentioning

confidence: 99%

What is a global auroral substorm?

Elphinstone¹,

Murphree²,

Cogger³

1996

Reviews of Geophysics

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133

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The departure of the aurora from quiet levels in a dynamic manner constitutes some type of auroral “breakup” event. Research into the auroral breakup predates the International Geophysical Year (1957/1958). This feature of the aurora, and the later, more global concept of the auroral substorm, has become a focus for much of the auroral research that occurs today. New instrumentation and global collaborations continue to refine our knowledge of the substorm process and how it proceeds in the ionosphere. In particular, global auroral imaging has advanced our understanding of the dynamics of the process and has given us the ability to put localized observations into a global perspective. Fundamentally new cycles of auroral activity are now understood to exist, and this has provided a means by which auroral activity can answer questions about magnetospheric substorm dynamics. Along with this wealth of observations has come a wide range of theories purporting to explain the mechanism of the onset of this phenomenon. There is, however, no single theory which stands out as clearly explaining the wide range of active auroral phenomena. A synthesis which combines these theories and allows them to each explain individual aspects of the problem appears to be required. This has led to a new way of understanding the active aurora as a set of processes or modules which occur either coupled together or independent of one another to form a particular event. This view represents a fundamental departure from the view of the substorm as a single unchanging entity. Auroral activity can rather be thought of as the earthward end of a diverse set of ionospheric and magnetospheric processes which couple together to form different cyclical patterns. A symbolic representation of this modularization is presented to simplify future schematics of large‐scale auroral dynamics.

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Dayside Aurora Poleward of the Main Auroral Distribution: Implications for Convection and Mapping

Cited by 10 publications

References 20 publications

Responses of the open–closed field line boundary in the evening sector to IMF changes: A source mechanism for Sun‐aligned arcs

Responses of the open–closed field line boundary in the evening sector to IMF changes: A source mechanism for Sun‐aligned arcs

Cooperatives Roles of Dynamics and Topology in Generating the Magnetosphere‐Ionosphere Disturbances: Case of the Theta Aurora

What is a global auroral substorm?

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