Magnetospheric Currents during Substorms

Akasofu, S.‐I.

doi:10.1007/978-94-010-1164-8_8

Cited by 4 publications

(6 citation statements)

References 251 publications

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“…[19] The most remarkable movements occur for K2 (the evening current cell) and K4 (the eastward electrojet), which are associated with equatorward expansion of the auroral oval during substorms [Akasofu, 1977]. When AE increases from 0 nT to 1000 nT, K2 moves toward midnight by 2.9 h and equatorward by 10°, while K4 moves toward midnight by about 1 h and equatorward by 7°.…”

Section: Data and Analysismentioning

confidence: 99%

“…During strong substorms, K4 moves equatorward beyond the observation of AE stations, which are confined in a relatively narrow geomagnetic latitudinal belt from 60.7°to 70.8°. In such cases, the magnitude of AU reaches ''saturation,'' although auroral currents may continue increasing [Akasofu, 1977;Kamide and Akasofu, 1983]. The saturation phenomenon in AE, AU, and AL indices lowers reliability of large values of AE, and also limits extension of the KP model to very intense substorms.…”

Section: A03s11mentioning

confidence: 99%

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Key points model for polar region currents

Chen

et al. 2008

J. Geophys. Res.

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[1] The equivalent ionospheric electric currents in the polar region mainly consist of the DP1 and DP2 systems. The former involves a westward electrojet around midnight, while the later involves a two-cell system with foci on the morningside and eveningside, respectively. In space weather prediction and nowcasting, sophisticated models of the polar currents are needed, but concise and convenient models are also useful to predict or nowcast the principal characteristics of the current systems, such as intensity and position. In this paper, we propose a ''key points model'' for outlining the basic features of the polar region current system for different disturbance levels. The ''key points model'' (or KP model) includes six key points of the current system: the centers of two DP2 cells, the maximum densities of the eastward and westward electrojets, and the maximum densities of the northward and southward currents. Each of six key points is described by three parameters: intensity, local time, and latitude. The AE-dependences of the 18 parameters are deduced from the equivalent current systems for every 5 min during a 2-d period (18-19 March 1978). The KP model reveals systematic variations of the current systems. When AE increases, the currents and the current densities are simultaneously enhanced linearly, and most of the key points concentrate towards midnight. In addition, when AE increases, the key points K2 and K4 for the evening current cell move equatorward, while the key points K1 and K3 for morning cell move poleward.

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Section: Data and Analysismentioning

confidence: 99%

Section: A03s11mentioning

confidence: 99%

Key points model for polar region currents

Chen

et al. 2008

J. Geophys. Res.

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“…It is generally accepted that (Akasofu, 1979;Fairfield et al, 1981) that the onset of a substorm, as determined from ground-based indicators, coincides with the thinning of the plasma sheet followed by a subsequent expansion. The substorm morphology of the magnetic field in the lobe does not seem to show as constant a pattern of increase or decrease ( Akasofu, 1979).…”

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confidence: 99%

“…The substorm morphology of the magnetic field in the lobe does not seem to show as constant a pattern of increase or decrease ( Akasofu, 1979). A southward turning of the field in the magnetotail is sometimes seen, which has been interpreted as a consequence of the formation of an x-type neutral line earthward of the point of observation (Honor, 1979).…”

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Numerical simulation of the interaction of the plasma sheet with the lobes of the Earth's magnetotail

Swift

1982

J. Geophys. Res.

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Codes involving one and two spatial dimensions and three velocity dimensions are used to model the earth's magnetotail. It is shown that the magnetotail can become inflated as a consequence of low‐energy plasma convection toward the neutral plane. The two‐dimensional code shows the development of small‐scale turbulence. However, the growth of the turbulence appears limited and does not lead to substantial dissipation. A one‐dimensional model was used to simulate a particle population consisting of plasma sheet ions and cold lobe plasma. An applied convection electric field causes plasma sheet thinning and later expansion, consistent with observed substorm morphology. During the course of a simulated substorm the cold particles are heated and merge with the plasma sheet population. The magnetic field energy shows a slight increase, followed by a more rapid decrease as all of the cold particles are swept into the magnetotail. The code exhibits a conversion of both magnetic field energy and energy supplied by the convection electric field into particle energy. The simulations suggest that much of the magnetotail substorm morphology may be a simple consequence of an increase, followed by a decrease, in the convection electric field, without the requirement of any magnetospheric size scale plasma instability or other disruptive processes. It is also concluded that the presence of the convection electric field and a continuing replenishment of low‐energy particles in the magnetotail lobes are both necessary for maintenance of the magnetotail.

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Variations of the Auroral Electrojet Belt During Substorms

Xu¹

2009

Chinese J of Geophysics

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Enhancement of auroral activity and intensification of auroral electrojet are the most important manifestations of the magnetosphere-ionosphere coupling. Both aurora and electrojet result from the same mechanism-charged particle precipitation, however, they have rather different behaviors and AE-dependences. In this paper, the dynamic characteristics of the auroral electrojet belt are studied by using equivalent current systems deduced from ground-based magnetic records. The results show that the auroral electrojet belt is divided by the Harang discontinuity into two parts: the afternoon-dusk section with minor eastward electrojet and the midnight-morning section with major westward electrojet, the latter is divided into two subsections: the midnight section and the morning section. Along with AE increasing in substorm expansion phase, the whole auroral oval expanses equatorward, however, the different sections of the auroral electrojet exhibit different dynamic behaviors: the afternoon-dusk and morning sections drifts equatorward, just as the auroral oval does, while the midnight section drifts poleward. A study on electrodynamics responsible for these differences reveals that the principal controlling factor is different for different sections of the electrojet: the afternoon-dusk eastward electrojet and the morning westward electrojet are mainly controlled by the magnetospheric convection electric field, corresponding to DP2 currents of the directly driven process, while the midnight westward electrojet largely depends on the ionospheric conductivities, corresponding to DP1 currents of the unloading process.

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Magnetospheric Currents during Substorms

Cited by 4 publications

References 251 publications

Key points model for polar region currents

Key points model for polar region currents

Numerical simulation of the interaction of the plasma sheet with the lobes of the Earth's magnetotail

Variations of the Auroral Electrojet Belt During Substorms

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