Substorm convection and current system deduced from the global simulation

Tanaka, Takashi; Nakamizo, Aoi; Yoshikawa, Akimasa; Fujita, Shigeru; Shinagawa, Hiroyuki; Shimazu, H.; Kikuchi, Takashi; Hashimoto, Kumiko

doi:10.1029/2009ja014676

Cited by 69 publications

(233 citation statements)

References 67 publications

(122 reference statements)

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“…Figure 12 illustrates the FC 2 current loop consisting of C1-C2 Birkeland currents (the HCC-LCC currents of Taguchi et al, 1993) with their ionospheric Pedersen current closure and the connection to the cusp dynamo current at high altitudes (on the downstream side of the cusp). The FC 2 current loop is placed in the context of the R1-R2 Birkeland currents with their closure currents in the magnetosphere (ring current and cusp dynamo current) and ionosphere, as described by Tanaka et al (2010) (see their Fig. 20).…”

Section: Discussionmentioning

confidence: 99%

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Polar cap flow channel events: spontaneous and driven responses

2010

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Abstract. We present two case studies of specific flow channel events appearing at the dusk and/or dawn polar cap boundary during passage at Earth of interplanetary (IP) coronal mass ejections (ICMEs) on 10 January and 25 July 2004. The channels of enhanced (>1 km/s) antisunward convection are documented by SuperDARN radars and dawn-dusk crossings of the polar cap by the DMSP F13 satellite. The relationship with Birkeland currents (C1-C2) located poleward of the traditional R1-R2 currents is demonstrated. The convection events are manifest in ground magnetic deflections obtained from the IMAGE (International Monitor for Auroral Geomagnetic Effects) Svalbard chain of ground magnetometer stations located within 71-76 • MLAT. By combining the ionospheric convection data and the ground magnetograms we are able to study the temporal behaviour of the convection events. In the two ICME case studies the convection events belong to two different categories, i.e., directly driven and spontaneous events. In the 10 January case two sharp southward turnings of the ICME magnetic field excited corresponding convection events as detected by IMAGE and SuperDARN. We use this case to determine the ground magnetic signature of enhanced flow channel events (the NHdusk/B y < 0 variant). In the 25 July case a several-hour-long interval of steady southwest ICME field (B z < 0; B y < 0) gave rise to a long series of spontaneous convection events as detected by IMAGE when the ground stations swept through the 12:00-18:00 MLT sector. From the ground-satellite conjunction on 25 July we infer the pulsed nature of the polar cap ionospheric flow channel events in this case. The typical duration of these convection enhancements in the polar cap is 10 min.

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Section: Discussionmentioning

confidence: 99%

“…3 and 7. Schematic illustration of current loops in the magnetosphere-ionosophere system adapted after Tanaka et al (2010). Birkeland current systems (R1-R2 and C1-C2), magnetospheric ring current (RC), cusp dynamo current, and ionospheric closure currents have been marked.…”

Section: Discussionmentioning

confidence: 99%

Polar cap flow channel events: spontaneous and driven responses

2010

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“…1 involves the following basic elements: (i) disruption of the CTC in the near-Earth PS (magnetic field dipolarizations seen at geostationary altitude) leading to the activation of the SCW (Bostrøm type I current system; see McPherron et al, 1973), followed by (ii) plasma intrusion to the partial ring current with activation of the injection dynamo (E · J < 0; see e.g. Tanaka et al, 2010, andYau et al, 2013) with associated Bostrøm type II current systems at dusk and dawn, (iii) M-I coupling at subauroral latitudes giving rise to SYM-H partial recovery, and (iv) the presence of BBFs with ionospheric signatures on both sides of the Harang reversal boundary in the later phase of the substorm expansion (persistent phase-partial recovery).…”

Section: P E Sandholt Et Al: Repetitive Substorm Activity Driven Bmentioning

confidence: 99%

M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

2014

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Abstract. We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δB z /δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross-polar-cap potential due to inductive electric field coupling.

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“…They found that the reconnection during northward IMF predominantly occurs at high latitudes where antiparallel field regions appear in the northern dusk sector and in the southern dawn sector. For substorms under northward IMF conditions, using global MHD simulations, Tanaka et al [2010] showed that the substorm onset is triggered by a sudden collapse of the plasma sheet and a formation of a high-pressure region in the inner magnetosphere.…”

Section: Introductionmentioning

confidence: 99%

MHD simulations using average solar wind conditions for substorms observed under northward IMF conditions

et al. 2015

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Substorms are known to sometimes occur even under northward interplanetary magnetic field (IMF) conditions. In this paper, we perform three‐dimensional global magnetohydrodynamic simulations to examine dayside reconnection, tail, and ionospheric signatures for two cases of substorm observations under prolonged northward and dawnward IMF conditions: (1) a strongly northward/dawnward IMF case with BIMF = (0, −20, 20) nT; (2) a weakly northward/dawnward IMF case with BIMF = (0, −2, 2) nT. Throughout the simulations, we used the constant solar wind conditions to reflect the prolonged solar wind conditions around the substorm times. We found that, in both cases, the tail reconnection occurred after the usual high‐latitude reconnection on the dayside, providing a possible energy source for later triggered substorm observations under northward IMF conditions. The presence of an equal amount of IMF By allows the high‐latitude reconnected magnetic field lines to transport to the tail lobe, eventually leading to the tail reconnection. The simulation results also revealed the following major differences between the two cases: First, the reconnection onset (both on dayside and in the tail) occurs earlier in the strongly northward IMF case than in the weakly northward IMF case. Second, the polar cap size, which is finite in both cases despite the northward IMF conditions and thus supports the lobe energy buildup needed for the substorm occurrences, is larger in the strongly northward IMF case. Accordingly, the polar cap potential is far larger in the strongly northward IMF case (hundreds of kilovolt) than in the weakly northward IMF case (tens of kilovolt). Third, in the strongly northward IMF case, the strong earthward tail plasma flow appears to be caused by the enhanced convection (so enhanced duskward Ey) due to the tail reconnection. In contrast, in the weakly northward IMF case, the earthward tail plasma flow increases gradually in association with a modestly increased duskward electric field. In addition, the inner plasma pressure and the cross tail current near the reconnection site increase significantly in the strongly northward IMF case but less significantly in the weakly northward IMF case after the onset of the tail reconnection. In conclusion, the simulation results support observations of the substorms under northward IMF conditions in the presence of an equal amount of IMF By by demonstrating the energy input via dayside reconnection and the subsequent occurrence of the tail reconnection.

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Substorm convection and current system deduced from the global simulation

Cited by 69 publications

References 67 publications

Polar cap flow channel events: spontaneous and driven responses

Polar cap flow channel events: spontaneous and driven responses

M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

MHD simulations using average solar wind conditions for substorms observed under northward IMF conditions

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