MLT and seasonal dependence of auroral electrojets: IMAGE magnetometer network observations

Guo, Jianpeng; Liu, Huixin; Feng, Xueshang; Pulkkinen, Tuija; Tanskanen, Eija; Liu, Chaoxu; Zhong, Dingkun; Wang, Yuan

doi:10.1002/2014ja019843

Cited by 24 publications

(21 citation statements)

References 39 publications

(60 reference statements)

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“…The westward electrojet (as seen by AL) peaks in the post-midnight region, and the eastward electrojet (as seen by AU) peaks in the post-dusk region. This is consistent with observations (Silsbee and Vestine 1942;Allen and Kroehl 1975;Kamide et al 1994;Guo et al 2014). Figure 2 summarizes the field-aligned current (FAC) in the ionosphere (Ebihara and Tanaka 2018).…”

Section: General Overview Of Simulated Substormsupporting

confidence: 88%

Simulation study of near-Earth space disturbances: 2. Auroral substorms

Ebihara

2019

Prog Earth Planet Sci

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A substorm is a transient phenomenon that lasts for only 1-2 h. One significant manifestation of the substorm is a sudden brightening of the aurora on the nightside. Simultaneously, the auroral electrojets are abruptly intensified in the ionosphere, disturbing the geomagnetic field in the polar region. The near-Earth space environment is highly disturbed, which manifests as an earthward fast flow of plasma, a sudden change in the magnetic field, or a sudden increase in hot plasma. Such disturbances are known to severely affect human society. The ultimate cause of the disturbances is the solar wind, but an explanation of the chain of processes leading from solar wind to the ionosphere is problematic. Here, the evolution of the auroral substorm is reviewed based on the results of a global magnetohydrodynamics (MHD) simulation, called a REProduce Plasma Universe (REPPU) code. The REPPU code is shown to reproduce many aspects of the auroral substorms and to be useful for understanding the primary chain processes from the solar wind to the ionosphere.

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Section: General Overview Of Simulated Substormsupporting

confidence: 88%

Simulation study of near-Earth space disturbances: 2. Auroral substorms

Ebihara

2019

Prog Earth Planet Sci

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“…In fact the westward electrojet on the dawn side is stronger than the eastward electrojet on the dusk side in that season. Such an imbalance was also reported by Guo et al (2014) for the Northern Hemisphere (see their Fig. 2).…”

Section: Electrojetssupporting

confidence: 81%

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Huang¹,

Lühr

Wang³

2017

Ann. Geophys.

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Abstract. On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dualspacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) B y component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF B y orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF B y a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF B y . This is true for both signs of the IMF B z component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF B y signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but it shows only little response to season and IMF B y polarity. An important finding is that all the IMF B y dependences of FACs and Hall currents practically disappear in the dark winter hemisphere.

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“…The westward current had a maximum around 2 MLT, which is where we also observe the equivalent current density maximum as well as the most southward extending equivalent current oval (Figure d). Guo et al [] reported westward electrojet current maxima between 0 MLT and 4 MLT. Viljanen and Tanskanen [] observed the peak of eastward equivalent current around 18 MLT, where we observe the most southward extending equivalent current oval of the eastward equivalent current‐dominated dusk sector.…”

Section: Resultsmentioning

confidence: 99%

“…Viljanen and Tanskanen [2011] also examined the characteristics of the total ionospheric eastward and westward equivalent current in 1994-2010 across the geographic meridian 22.1 ∘ E in the geographic latitude range of 59.0 ∘ -79.4 ∘ N. The westward current had a maximum around 2 MLT, which is where we also observe the equivalent current density maximum as well as the most southward extending equivalent current oval ( Figure 1d). Guo et al [2014a] reported westward electrojet current maxima between 0 MLT and 4 MLT. Viljanen and Tanskanen [2011] observed the peak of eastward equivalent current around 18 MLT, where we observe the most southward extending equivalent current oval of the eastward equivalent current-dominated dusk sector.…”

Section: Equivalent Current Densitymentioning

confidence: 97%

Solar wind control of ionospheric equivalent currents and their time derivatives

et al. 2015

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A solid understanding of the solar wind control of ground magnetic field disturbances is essential for utilizing the existing long time series of ground data to obtain information on solar wind‐magnetosphere‐ionosphere coupling. We have used 20 years of International Monitor for Auroral Geomagnetic Effects magnetometer data (54°–76° magnetic latitude) to study the solar wind control of the ionospheric equivalent current density and its time derivative (<|dJeq/dt|>). We found that <|dJeq/dt|> peaks at the premidnight and prenoon ends of the westward electrojet. The prenoon <|dJeq/dt|> peak was most intense during fast solar wind and radial interplanetary magnetic field (IMF). The location of the peak was not affected by the IMF orientation but persisted at 8–10 magnetic local time and 70°–75° latitude, near the boundary between the westward and eastward electrojets. Sensitivity of this boundary to disturbances was suggested as a possible explanation for the persistent prenoon location of the peak. The premidnight peak was most intense during southward IMF orientation. While faster solar wind mainly resulted in more intense <|dJeq/dt|> in the premidnight sector, stronger IMF caused the region of intense <|dJeq/dt|> to spread to the postmidnight, dawn, and dusk sectors. A good correspondence was found between development of the nightside <|dJeq/dt|> intensification and average substorm bulge and oval aurora as determined by Gjerloev et al. (2007). The bulge aurora covered the western end of the westward electrojet where the equivalent current also had a significant poleward component. The substorm oval aurora, on the other hand, extended eastward along the westward electrojet.

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MLT and seasonal dependence of auroral electrojets: IMAGE magnetometer network observations

Cited by 24 publications

References 39 publications

Simulation study of near-Earth space disturbances: 2. Auroral substorms

Simulation study of near-Earth space disturbances: 2. Auroral substorms

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Solar wind control of ionospheric equivalent currents and their time derivatives

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