Field‐aligned currents generated in magnetotail reconnection: 3D Hall‐MHD simulations

Yamade, Yoshinobu; Fujimoto, M.; Yokokawa, Narutoshi; Nakamura, Masahiko

doi:10.1029/1999gl003688

Cited by 28 publications

(34 citation statements)

References 11 publications

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“…Hence, the FACs of the Hall current circuit form a thin double-sheet structure near the separatrix layer. Hall-MHD simulations showed that such smallscale currents can be seen even away from the reconnection site (Yamade et al, 2000).…”

Section: Phenomena Occurring In the Vicinity Of The Nightside Polar Cmentioning

confidence: 97%

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EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

Aikio

Pitkänen

Fontaine³

et al. 2008

Ann. Geophys.

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Abstract. The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6 • cgmLat) and Longyearbyen (75.2 • cgmLat) on 27 February 2004 by using the coordinated EIS-CAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5 • cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm.During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H + and O + ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be furtherCorrespondence to: A. T. Aikio (anita.aikio@oulu.fi) energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations.The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2 • during ∼5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.

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Section: Phenomena Occurring In the Vicinity Of The Nightside Polar Cmentioning

confidence: 97%

“…At the boundary, Alfvén waves carried a FAC pair with upward FAC on the equatorward and downward FAC on the poleward side. Yamade et al (2000) estimated from their simulation that the current densities at the ionospheric level would be 5 µA/m 2 .…”

Section: Phenomena Occurring In the Vicinity Of The Nightside Polar Cmentioning

confidence: 99%

EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

Aikio

Pitkänen

Fontaine³

et al. 2008

Ann. Geophys.

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“…According to Lockwood (1997) the open-closed boundary can be identified from the diffuse electron precipitation from the plasma sheet boundary layer or from the equatorward drifting arcs which form just equatorward of the open-closed boundary Hoffman et al, 1994) and are embedded in this diffuse precipitation. These arcs are also associated with intense electric fields (Pedersen et al, 1985) and thought to be Alfvén wave signatures of processes near or at the reconnection line (Hesse et al, 1999;Yamade et al, 2000). The accuracy by which one can determine the open-closed boundary is therefore highly dependent on the sensitivity and spatial resolution of the instruments that are used.…”

Section: Introductionmentioning

confidence: 99%

Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements

et al. 2005

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Abstract.Dayside merging between the interplanetary and terrestrial magnetic fields couples the solar wind electric field to the Earth's magnetosphere, increases the magnetospheric convection and results in efficient transport of solar wind energy into the magnetosphere. Subsequent reconnection of the lobe magnetic field in the magnetotail transports energy into the closed magnetic field region. Combining global imaging and ground-based radar measurements, we estimate the reconnection rate in the magnetotail during two days of an EISCAT campaign in November-December 2000. Global images from the IMAGE FUV system guide us to identify ionospheric signatures of the open-closed field line boundary observed by the two EISCAT radars in Tromsø (VHF) and on Svalbard (ESR). Continuous radar and optical monitoring of the open-closed field line boundary is used to determine the location, orientation and velocity of the openclosed boundary and the ion flow velocity perpendicular to this boundary. The magnetotail reconnection electric field is found to be a bursty process that oscillates between 0 mV/m and 1 mV/m with ∼10-15 min periods. These ULF oscillations are mainly due to the motion of the open-closed boundary. In situ measurements earthward of the reconnection site in the magnetotail by Geotail show similar oscillations in the duskward electric field. We also find that bursts of increased magnetotail reconnection do not necessarily have any associated auroral signatures. Finally, we find that the reconnection rate correlates poorly with the solar wind electric field. This indicates that the magnetotail reconnection is not directly driven, but is an internal magnetospheric process. Estimates of a coupling efficiency between the solar wind electric field and magnetotail reconnection only seem to be relevant as averages over long time intervals. The oscillation mode at 1 mHz corresponds to the internal cavity mode withCorrespondence to: N. Østgaard (nikost@ssl.berkeley.edu) additional lower frequencies, 0.5 and 0.8 mHz, that might be modulated by solar wind pressure variations.

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“…The effect of the Hall term to produce an additional current system in the proximity of the reconnection site has been known for a long time from a theoretical point of view (e.g., Sonnerup, 1979;Terasawa, 1983;Mandt et al, 1994;Hesse and Winske, 1994;Lottermoser et al, 1998;, and has been recently reported to be observed in the magnetotail (Oieroset et al, in preparation;Nagai et al, 1998). In order to see if this effect will modify the global FAC pattern, we have run a series of 2D Hall-MHD simulations to find that this additional current system can indeed be significant globally (Yamade et al, 2000). 2D simulations are started from the same initial condition as described above except that R y = ∞.…”

Section: Study On the Earth's Casementioning

confidence: 98%

Hall effects on field-aligned current generation in three-dimensional magnetic reconnection

et al. 2014

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Understanding the generation mechanisms of intense field-aligned currents (FACs) during auroral substorms is one of the central themes of magnetospheric physics. Three-dimensional (3D) magnetohydrodynamic (MHD) simulations of the Earth's magnetotail reconnection has been performed extensively to understand the global aspects of the generation mechanisms. In this study, however, by noting that the ion inertia length is not negligibly small compared to the current sheet thickness in the magnetotail, we investigate the FAC generation mechanism in the Hall-MHD system. With an idealized one-dimensional current sheet as the initial condition, we find that the FAC pattern obtained to be totally different from the MHD results. From a series of simulations, we also find that the predominance of this new FAC pattern is not necessarily due to the small thickness of the current sheet but is controlled more by the three-dimensionality of the system. The Hall-driven FAC dominates as long as the system is more two-dimensional-like than a critical value even for a relatively thick current sheet. Since this critical value turns out to be moderate, we conclude that reconnection in the Earth's magnetotail belongs to a general class of reconnection involving strong FACs generated by the Hall term.

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Field‐aligned currents generated in magnetotail reconnection: 3D Hall‐MHD simulations

Cited by 28 publications

References 11 publications

EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements

Hall effects on field-aligned current generation in three-dimensional magnetic reconnection

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