Polar cap flow channel events: spontaneous and driven responses

Sandholt, P. E.; Andalsvik, Yngvild Linnea; Farrugia, C. J.

doi:10.5194/angeo-28-2015-2010

Cited by 12 publications

(35 citation statements)

References 26 publications

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“…The unusually strong enhancement of SAPS at an earlier time (1100–1200 UT; see shaded interval in grey in Figure c) was investigated by Makarevich et al [] suggesting the important role of convection bursts in SAPS intensification. Convection bursts occur during FTEs [ Southwood , ; Lee , ] when reconnection rates become enhanced briefly and intensively [ Russell and Elphic , ] and leave their signatures in convection flows appearing as various types of FCs [ Sandholt and Farrugia , ; Sandholt et al ., , ]. Adding to the study of Makarevich et al [], we show that during their earlier and our later SAPS detection, the LANL plots tracked the signatures of substorm injections.…”

Section: Discussionsupporting

confidence: 78%

Investigating the development of double‐peak subauroral ion drift (DSAID)

Horvath

Lovell

2017

JGR Space Physics

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This study focuses on the newly described ionospheric feature, called double‐peak subauroral ion drift (DSAID), which is a subclass of the well‐known single‐peak SAID. Double‐layer Region 2 (R2) field aligned currents (FACs) could be the main driver of DSAID. Our aim is to gain new insights into the development of DSAID during its two‐stage progression. Observational results are provided by five scenarios, each demonstrating a certain progression sequence of DSAID. Results show that SAID/DSAID occurred during flux transfer events and was accompanied by flow channels (FCs) associated with dayside magnetopause (FC‐2) and nightside magnetotail (FC‐3) reconnections, with westward electrojet (eastward FC), and with auroral streamers (FC‐4). In the premidnight magnetic local time (MLT) sector of stage 2, DSAID development was due to the short‐circuiting of the reconnection‐injected plasma jets during substorms or pseudobreakups. Thus, the related ring current pressure buildup enhanced the downward R2 FACs leading to double/multiple circuits forming double‐layer R2 FACs. During the midnight MLT hours of stage 2, DSAID development was closely related to the westward traveling surge (WTS)/substorm current wedge (SCW). WTS/SCW‐related strong upward R1 FACs closed with meriodional currents producing eastward and downward (i.e., downward R2 FAC‐style) return currents enhancing the downward R2 FACs and thus leading to double/multiple circuits forming double‐layer R2 FACs. Auroral streamers/FC‐4 represent a substorm substructure and their occurrence with DSAID after stage 2 demonstrates that this substructure occasionally includes DSAID. Our results demonstrate also that the short‐circuited system underlying SAID/DSAID acted sometimes as a current generator and sometimes as a voltage generator.

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Section: Discussionsupporting

confidence: 78%

Investigating the development of double‐peak subauroral ion drift (DSAID)

Horvath

Lovell

2017

JGR Space Physics

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“…The excitation of FC 1-FC 2 flows (see Fig. 2) during the interval 14:50-15:00 UT on this day can be seen in the IMAGE magnetometer data reported by Sandholt et al (2010) (see their Fig. 3).…”

Section: Pre-substorm Conditionsmentioning

confidence: 52%

“…FC 2 is a result of the persistence of open flux tubes previously opened by bursts of reconnection (flux transfer events; FTEs) along the flanks of the polar cap, as predicted by Southwood (1987). The presence of these flows has been documented by Sandholt et al (2010). The IMF B y dependence and the role of conductivity gradients at the polar cap boundary for the formation of these flow channels have been discussed by Sandholt and Farrugia (2009).…”

Section: Observation Geometry and Global Convection Contextmentioning

confidence: 93%

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Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

2012

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Abstract.The expansion-contraction model of Dungey cell plasma convection has two different convection sources, i.e. reconnections at the magnetopause and in the magnetotail. The spatial-temporal structure of the nightside source is not yet well understood. In this study we shall identify temporal variations in the winter polar cap convection structure during substorm activity under steady interplanetary conditions. Substorm activity (electrojets and particle precipitations) is monitored by excellent ground-satellite DMSP F15 conjunctions in the dusk-premidnight sector. We take advantage of the wide latitudinal coverage of the IMAGE chain of ground magnetometers in Svalbard -Scandinavia -Russia for the purpose of monitoring magnetic deflections associated with polar cap convection and substorm electrojets. These are augmented by direct observations of polar cap convection derived from SuperDARN radars and cross-track ion drift observations during traversals of polar cap along the dusk-dawn meridian by spacecraft DMSP F13. The interval we study is characterized by moderate, stable forcing of the magnetosphere-ionosphere system (E KL = 4.0-4.5 mV m −1 ; cross polar cap potential (CPCP), (Boyle) = 115 kV) during Earth passage of an interplanetary CME (ICME), choosing an 4-h interval where the magnetic field pointed continuously south-west (B z < 0; B y < 0). The combination of continuous monitoring of ground magnetic deflections and the F13 cross-track ion drift observations in the polar cap allows us to infer the temporal CPCP structure on time scales less than the ∼10 min duration of F13 polar cap transits. We arrived at the following estimates of the dayside and nightside contributions to the CPCP (CPCP = CPCP/day + CPCP/night) under two intervals of substorm activity: CPCP/day ∼110 kV; CPCP/night ∼50 kV (45 % CPCP increase during substorms). The temporal CPCP structure during one of the substorm cases resulted in a dawn-dusk convection asymmetry measured by DMSP F13 which is opposite to that expected from the prevailing negative B y polarity of the ICME magnetic field, a clear indication of a nightside source.

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“…The diagrams illustrate the various flow channel (FC) types in magnetic local time and magnetic latitude coordinates. Modified after Figure 1 of Sandholt et al (), these FCs are shown in the context of the Dungey polar convection operating in a (a) forward or (b) reversed manner. Modified after Figure 3 of Sandholt et al (), the diagrams illustrate the various FCs under IMF B Z < 0 conditions for (c) B Y < 0 and (d) B Y > 0 orientations.…”

Section: Introductionmentioning

confidence: 99%

Polar Cap Energy Deposition Events During the 5–6 August 2011 Magnetic Storm

Horvath

Lovell

2018

JGR Space Physics

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We study the 5–6 August 2011 storm for its energy deposition events occurring deep in the polar cap region, where the consequential localized intensifications of earthward directed Poynting flux led to the development of their related localized neutral density increases. For unraveling the underlying physical processes, we investigate the relations among Poynting flux intensifications, flow channels (FCs), and localized neutral density enhancements plus the nature of the underlying reconnection events. Observational results demonstrate Poynting flux increase deep in the polar cap in a FC‐2 type FC during magnetopause reconnections and in a FC‐4 type FC during lobe reconnections. During the latter stages of these different types of reconnection events, energy/momentum transfer occurred along old‐open field lines and commonly led to the development of localized neutral density increases during their respective upwelling events fueled by field‐aligned currents and above/within these polar FCs. The prevailing BY domination and the pulsed nature of this storm created favorable conditions for the development of these FC‐2 and FC‐4 types in the sunlit northern summer hemisphere and caused the observed Poynting flux intensifications deep in the polar cap. The solar wind source of these reconnections taking place along old‐open field lines was situated in the high‐latitude boundary layer. Thus, the high‐latitude boundary layer dynamo provided a vigorous source of energy/momentum transfer during the latter‐stage reconnections unfolding along old‐open field lines.

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Polar cap flow channel events: spontaneous and driven responses

Cited by 12 publications

References 26 publications

Investigating the development of double‐peak subauroral ion drift (DSAID)

Investigating the development of double‐peak subauroral ion drift (DSAID)

Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

Polar Cap Energy Deposition Events During the 5–6 August 2011 Magnetic Storm

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