A numerical simulation of the geomagnetic sudden commencement: 1. Generation of the field‐aligned current associated with the preliminary impulse

Fujita, Shigeru; Tanaka, Takashi; Kikuchi, Takashi; Fujimoto, Keizo; Hosokawa, K.; Itonaga, M.

doi:10.1029/2002ja009407

Cited by 98 publications

(190 citation statements)

References 40 publications

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“…An MI current pair also formed at about the same location at which the PI currents initiated, propagated antisunward, and then became the post-SC DP-2 currents. The overall current pattern is consistent with the model by Araki (1994), and the coexisting current patterns of the PI and MI as well as their antisunward propagation are quite analogous to results from MHD simulations (e.g., Fujita et al 2003;Samsonov et al 2010). However, the onsets of the PI and MI were not always simultaneous or symmetric in the pre-and post-noon sectors.…”

Section: Resultssupporting

confidence: 73%

“…In these events, we found that the interplanetary shock normals were more tilted from the Sun-Earth line than those in the other events. Because PI currents are considered to arise from compressional waves in the equatorial magnetosphere that are convert into Alfven waves propagating into the ionosphere (Fujita et al 2003), a gradual compression of the magnetosphere would lead to a much weaker PI signal. Since the magnetosphere was compressed from the postnoon side, the post-noon MI started earlier than the pre-noon MI; thus, the PI currents were only seen in the pre-noon sector.…”

Section: Resultsmentioning

confidence: 99%

“…Global MHD simulations predict that an R2-sense FAC pair during the PI forms equatorward of preexisting DP-2 currents near noon and propagates azimuthally away from noon during its lifetime of a few minutes (Slinker et al 1999;Fujita et al 2003;Kim et al 2009;Samsonov et al 2010;Sun et al 2015). An R1-sense FAC pair follows a similar sequence during the MI.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

et al. 2016

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We investigated evolution of ionospheric currents during sudden commencements using a ground magnetometer network in conjunction with an all-sky imager, which has the advantage of locating field-aligned currents much more accurately than ground magnetometers. Preliminary (PI) and main (MI) impulse currents showed two-cell patterns propagating antisunward, particularly during a southward interplanetary magnetic field (IMF). Although this overall pattern is consistent with the Araki (solar wind sources of magnetospheric ultra-low-frequency waves. Geophysical monograph series, vol 81. AGU, Washington, DC, pp [183][184][185][186][187][188][189][190][191][192][193][194][195][196][197][198][199][200] 1994. doi:10.1029/GM081p0183) model, we found several interesting features. The PI and MI currents in some events were highly asymmetric with respect to the noonmidnight meridian; the post-noon sector did not show any notable PI signal, but only had an MI starting earlier than the pre-noon MI. Not only equivalent currents but also aurora and equatorial magnetometer data supported the much weaker PI response. We suggest that interplanetary shocks impacting away from the subsolar point caused the asymmetric current pattern. Additionally, even when PI currents form in both pre-and post-noon sectors, they can initiate and disappear at different timings. The PI currents did not immediately disappear but coexisted with the MI currents for the first few minutes of the MI. During a southward IMF, the MI currents formed equatorward of a preexisting DP-2, indicating that the MI currents are a separate structure from a preexisting DP-2. In contrast, the MI currents under a northward IMF were essentially an intensification of a preexisting DP-2. The magnetometer and imager combination has been shown to be a powerful means for tracing evolution of ionospheric currents, and we showed various types of ionospheric responses under different upstream conditions.

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

et al. 2016

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“…Fujita (2003) presented a quantitative model of the PI, where the PI current is first excited as an enhanced Chapman-Ferraro current in the magnetopause and then turns to the magnetosphere along the wavefront of the compressional signal launched by the impulse. To explain the main feature of PI, namely, its occurrence before the main impulse, such hypotheses as a difference of propagation velocity of SCinitiated waves along and across the magnetic field line, or complex shape of the dayside magnetosphere, or specific shape of the front of disturbance, should be assumed.…”

Section: Polarization Electric Fields Generated By An Elliptic Ionospmentioning

confidence: 99%

Geomagnetic disturbances on ground associated with particle precipitation during SC

Safargaleev

Kozlovsky²,

Honary

et al. 2010

Ann. Geophys.

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Abstract.We have examined several cases of magnetosphere compression by solar wind pressure pulses using a set of instruments located in the noon sector of auroral zone. We have found that the increase in riometric absorption (sudden commencement absorption, SCA) occurred simultaneously with the beginning of negative or positive magnetic variations and broadband enhancement of magnetic activity in the frequency range above 0.1 Hz. Since magnetic variations were observed before the step-like increase of magnetic field at equatorial station (main impulse, MI), the negative declinations resembled the so-called preliminary impulse, PI. In this paper a mechanism for the generation of PI is introduced whereby PI's generation is linked to SCA -associated precipitation and the local enhancement of ionospheric conductivity leading to the reconstruction of the ionospheric current system prior to MI. Calculation showed that PI polarity depends on orientation of the background electric field and location of the observation point relative to ionospheric irregularity. For one case of direct measurements of electric field in the place where the ionospheric irregularity was present, the sign of calculated disturbance corresponded to the observed one. High-resolution measurements on IRIS facility and meridional chain of the induction magnetometers are utilized for the accurate timing of the impact of solar wind irregularity on the magnetopause.

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“…Kataoka et al (2004) studied TCVs caused by a localized density pulse in MHD simulations and concluded that the transient response at the higher latitude is due to the FACs converted from the inertial current associated with the magnetopause deformation via the curvilinear effect, while the lower latitude TCVs result from the FACs that are converted via both curvilinear effect and inhomogeneous effect. Fujita et al (2003a), Fujita et al (2003b) showed simulation results of the response of the geospace environment to a sudden solar wind pressure enhancement under northward IMF conditions. These researchers thoroughly analyzed the generation mechanism by focusing on current systems in the two-phased responses.…”

mentioning

confidence: 99%

The response of the magnetosphere-ionosphere system to a sudden dynamic pressure enhancement under southward IMF conditions

Ridley

2009

Ann. Geophys.

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Abstract.The magnetospheric response to step-like solar wind dynamic pressure increases under southward IMF conditions is studied using the University of Michigan MHD code. A two phased response in the ionosphere is observed, similar to what is observed when the IMF is northward by looking into the residual potential and field-aligned current (FAC) patterns in the ionosphere. The first phase response right after the high pressure enhancement hits the magnetopause is associated with a pair of FACs downward in the postnoon and upward in the prenoon region. These FACs are caused by dusk-to-dawn electric fields inside the dayside magnetopause launched by a fast mode compressional wave. The second phase response shows another pair of potential cells as well as FACs in opposite polarity, which originates from magnetospheric vortices on the equatorial plane. The vortices appear to be formed by the recovery of the system from the fast mode wave.

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A numerical simulation of the geomagnetic sudden commencement: 1. Generation of the field‐aligned current associated with the preliminary impulse

Cited by 98 publications

References 40 publications

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

Geomagnetic disturbances on ground associated with particle precipitation during SC

The response of the magnetosphere-ionosphere system to a sudden dynamic pressure enhancement under southward IMF conditions

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