About the relationship between auroral electrojets and ring currents

Grafe, A.; Feldstein, Y. I.

doi:10.1007/s00585-000-0874-4

Cited by 21 publications

(14 citation statements)

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“…Others showed that auroral electrojets often increased before the ring current increased (Pudovkin et al, 1968), therefore, the ring current formation was claimed to be caused by the substorm events (Rostoker, 1997). However, Siscoe and Petschek (1997) indicated that there was no direct relation between substorm and ring current intensification and they were more like the two independent processes which are caused possibly by the same source (Grafe and Feldstein, 2000). By comparing the dynamics of auroral electrojets with the variations of D st this problem will be examined in this study.…”

Section: Introductionmentioning

confidence: 91%

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

et al. 2008

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Abstract. We investigate variations of the location and intensity of auroral currents during two magnetic storm periods based on magnetic field measurements from CHAMP separately for both hemispheres, as well as for the dayside and nightside. The corresponding auroral electrojet current densities are on average enhanced by about a factor of 7 compared to the quiet time current strengths. The nightside westward current densities are on average 1.8 (2.2) times larger than the dayside eastward current densities in the Northern (Southern) Hemisphere. Both eastward and westward currents are present during the storm periods with the most intense electrojets appearing during the main phase of the storm, before the ring current maximizes in strength. The eastward and westward electrojet centers can expand to 55 • MLat during intense storms, as is observed on 31 March 2001 with D st =−387 nT. The equatorward shift of auroral currents on the dayside is closely controlled by the southward IMF, while the latitudinal variations on the nightside are better described by the variations of the D st index. However, the equatorward and poleward motion of the nightside auroral currents occur earlier than the D st variations. The Space Weather Modeling Framework (SWMF) can capture the general dynamics of the storm time current variations. Both the model and the actual data show that the currents tend to saturate when the merging electric field is larger than 10 mV/m. However, the exact prediction of the temporal development of the currents is still not satisfactory.

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Section: Introductionmentioning

confidence: 91%

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

et al. 2008

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“…The relative contribution of potential and inductive electric field driven convection resulting in the development of the storm‐time ring current has remained an unresolved question in geospace research. Studies have been published supporting each side of this debate, including views that ring current buildup is entirely potential fields [ Iyemori and Rao , ; Grafe and Feldstein , ; Liemohn and Kozyra , ; Keller et al ., ; Zaharia et al ., ] or inductive fields [ Akasofu and Chapman , ; Liu and Rostoker , ; Lemon et al ., ], or some mixture of the two [ Fok et al ., ; Ganushkina et al ., ; Clauer et al ., ; Ganushkina et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Evidence for potential and inductive convection during intense geomagnetic events using normalized superposed epoch analysis

et al. 2013

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[1] The relative contribution of storm-time ring current development by convection driven by either potential or inductive electric fields has remained an unresolved question in geospace research. Studies have been published supporting each side of this debate, including views that ring current buildup is entirely one or the other. This study presents new insights into the relative roles of these storm main phase processes. We perform a superposed epoch study of 97 intense (Dst Min < -100 nT) and 91 moderate (-50 nT > Dst Min > -100 nT) storms using OMNI solar wind and ground-based data. Instead of using a single reference time for the superpositioning of the events, we choose four reference times and expand or contract each phase of every event to the average length of this phase, creating a normalized timeline for the superposed epoch analysis.Using the bootstrap method, we statistically demonstrate that timeline normalization results in better reproduction of average storm dynamics than conventional methods. Examination of the Dst reveals an inflection point in the intense storm group consistent with two-step main phase development, which is supported by results for the southward interplanetary magnetic field and various ground-based magnetic indices. This two-step main-phase process is not seen in the moderate storm timeline and data sets. It is determined that the first step of Dst development is due to potential convective drift, during which an initial ring current is formed. The negative feedback of this hot ion population begins to limit further ring current growth. The second step of the main phase, however, is found to be a more even mix of potential and inductive convection. It is hypothesized that this is necessary to achieve intense storm Dst levels because the substorm dipolarizations are effective at breaking through the negative feedback barrier of the existing inner magnetospheric hot ion pressure peak.Citation: Katus, R. M., M. W. Liemohn, D. L. Gallagher, A. Ridley, and S. Zou (2013), Evidence for potential and inductive convection during intense geomagnetic events using normalized superposed epoch analysis,

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“…The explosive component along with the convection-like one in the EE magnetic field variations were reported based on magnetic, ionospheric, radar and satellite data. Grafe and Feldstein (2000) stressed the differences in the EE and WE development in relation to the magnetic storm phases. Recent investigations indicate that during magnetic storms the ring current is formed due to the joint influence of two factors: the large-scale electromagnetic convection and the repeated electric field pulses related to substorm activation under stormy conditions.…”

Section: The Structure Of the Magnetic Field Variations In The Ee Regionmentioning

confidence: 99%

Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals

et al. 2006

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Abstract. We investigate variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. Special attention was paid to the complex structure of the electrojets and their interrelationship with diffuse and discrete particle precipitation and field-aligned currents in the dusk sector. During magnetospheric substorms the eastward electrojet (EE) location in the evening sector changes with local time from cusp latitudes ( ∼77 • ) during early afternoon to latitudes of diffuse auroral precipitation ( ∼65 • ) equatorward of the auroral oval before midnight. During the main phase of an intense magnetic storm the eastward currents in the noon-early evening sector adjoin to the cusp at ∼65 • and in the pre-midnight sector are located at subauroral latitude ∼57 • . The westward electrojet (WE) is located along the auroral oval from evening through night to the morning sector and adjoins to the polar electrojet (PE) located at cusp latitudes in the dayside sector. The integrated values of the eastward (westward) equivalent ionospheric current during the intense substorm are ∼0.5 MA (∼1.5 MA), whereas they are 0.7 MA (3.0 MA) during the storm main phase maximum. The latitudes of auroral particle precipitation in the dusk sector are identical with those of both electrojets. The EE in the evening sector is accompanied by particle precipitation mainly from the Alfvén layer but also from the near-Earth part of the central plasma sheet. In the lower-latitude part of the EE the field-aligned currents (FACs) flow into the ionosphere (Region 2 FAC), and at its higher-latitude part the FACs flow Correspondence to: A. Prigancova (geofpria@savba.sk) out of the ionosphere (Region 1 FAC). During intense disturbances, in addition to the Region 2 FAC and the Region 1 FAC, a Region 3 FAC with the downward current was identified. This FAC is accompanied by diffuse electron precipitation from the plasma sheet boundary layer. Actually, the triple system of FAC is observed in the evening sector and, as a consequence, the WE and the EE overlap. The WE in the evening sector comprises only the high-latitude periphery of the plasma precipitation region and corresponds to the Hall current between the Region 1 FAC and Region 3 FAC. During the September 1998 magnetic storm, two velocity bursts (∼2-4 km/s) in the magnetospheric convection were observed at the latitudes of particle precipitation from the central plasma sheet and at subauroral latitudes near the ionospheric trough. These kind of bursts are known as subauroral polarization streams (SAPS). In the evening sector the Alfvén layer equatorial boundary for precipitating ions is located more equatorward than that for electrons. This may favour northward electric field generation between these boundaries and may cause high speed westward ions drift visualized as SAPS. Meanwhile, high speed ion drifts cover a wider range...

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About the relationship between auroral electrojets and ring currents

Cited by 21 publications

References 14 publications

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

Evidence for potential and inductive convection during intense geomagnetic events using normalized superposed epoch analysis

Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals

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