On the Relation Between Jupiter's Aurora and the Dawnside Current Sheet
Y. B. XuZhonghua YaoBinzheng ZhangP. A. DelamereL. C. RayW. R. DunnS. V. BadmanEnhao FengZhiqi ZhengS. J. BoltonDenis GrodentBertrand BonfondYong Wei
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Abstract Jupiter's auroral emission is a spectacular phenomenon that provides insight into energy release processes related to the coupling of its magnetosphere and ionosphere. This energy release is influenced by solar wind conditions. Using joint observations from Juno and the Hubble Space Telescope (HST), we statistically investigate the relationship between auroral power and current sheet variations under different solar wind conditions. In this study, we reveal that during global main auroral brightening events that are closely connected to solar wind compressions, the dawn side current sheet is substantially thinner than during times when a quiet auroral morphology is present. Furthermore, the total current intensity in the current sheet is found to increase under solar wind compression conditions compared to the quiet period. These findings provide important observational evidence for how magnetospheric dynamics driven by solar wind behavior affect auroral activity, deepening our understanding of the coupling between Jupiter's magnetosphere and ionosphere.Keywords:
Current sheet
Jupiter (rocket family)
Plasma sheet
Magnetosphere of Jupiter
We present an analysis, based on the principles of stress balance in a 1‐dimensional current sheet, which considers the problem of closed magnetic flux transport into the deep tail by a “viscous”‐like interaction between the solar wind and the magnetosphere. We illustrate our analysis with an example of ISEE‐3 data showing strong tailward plasma sheet flows on apparently closed field lines in the deep tail. Apart from narrow regions adjacent to the magnetopause, these flows are not driven by the scattering of magnetosheath plasma into the magnetosphere. We estimate the fraction of the magnetosheath momentum flux needed to be anomalously transferred into the plasma sheet to drive the flows. In our example this is ∼6%. No previously suggested mechanism (e.g., the Kelvin‐Helmholtz Instability) has been shown capable of providing anomalous momentum transport of this magnitude. Our current understanding of the “viscous” interaction between the solar wind and magnetosphere is thus insufficient to explain these observations.
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A massive rotating equatorial plasma sheet dominates Jupiter's magnetosphere and the solar wind and the interplanetary magnetic field (IMF) are not thought to be as important as at Earth. However, in a recent simulation study we found that for a purely northward IMF the Jovian magnetosphere reached an unstable state in which a nearly periodic series of magnetic X and O lines were launched tailward. In this study we have carried out three‐dimensional global magnetohydrodynamic simulations to investigate the causes of this dynamic behavior. First, we examined the effects of dynamic pressure on the magnetospheric configuration in the absence of an IMF. We examined a series of northward IMF simulations in which we varied both the IMF magnitude and dynamic pressure. If the outer edge of the rotating plasma sheet is far from the X‐line (for large pressure and small IMF), the reconnected flow reaches the dawn magnetopause and exits down the tail. If the neutral line forms closer to the rotation boundary (small pressure and IMF), then the reconnected flux tubes can convect all of the way around Jupiter. When they reach the nightside, they become stretched tailward and can reconnect again. This leads to the periodic behavior. If the neutral line forms very close to the rotation boundary (large pressure and IMF), the Jupiterward flow compresses the rotating plasma sheet. In this case the flow goes around Jupiter but the flux tubes return along the dusk magnetopause and do not participate in reconnection a second time.
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The Pioneer 11 vector helium magnetometer provided precise, contititious measurements of the magnetic fields in interplanetary space, inside Jupiter's magnetosphere, and in the near vicinity of Jupiter. As with the Pioneer 10 data, evidence was seen of the dynanmic interaction of Jupiter with the solar wind which leads to a variety of phenomena (bow shock, upstream waves, nonlinear magnetosheath impulses) and to changes in the dimension of the dayside magnetosphere by as much as a factor of 2. The magnetosphere clearly appears to be blunt, not disk-shaped, with a well-defined outer boundary. In the outer magnetosphere, the magnetic field is irregular but exhibits a persistent southward component indicative of a closed magnetosphere. The data contain the first clear evidence in the dayside magnetosphere of the current sheet, apparently associated with centrifugal forces, that was a donminatnt feature of the outbound Pionieer 10 data. A modest westward spiraling of the field was again evident inbound but not outbound at higher latitudes and nearer the Sun-Jupiter direction. Measurements near periapsis, which were nearer the planet and provide better latitude and longitude coverage than Pioneer 10, have revealed a 5 percent discrepancy with the Pioneer 10 offset dipole mnodel (D(2)). A revised offset dipole (6-parameter fit) is presented as well as the results of a spherical harmonic analysis (23 parameters) consisting of an interior dipole, quadrupole, and octopole and an external dipole and quadrupole. The dipole moment and the composite field appear moderately larger than inferred from Pioneer 10. Maximum surface fields of 14 and 11 gauss in the northern and southern hemispheres are inferred. Jupiter's planetary field is found to be slightly more irregular than that of Earth.
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The interaction between the solar wind and the earth's magnetosphere has been studied by using a time‐dependent three‐dimensional magnetohydrodynamic model in which the interplanetary magnetic field (IMF) pointed in several directions between dawnward and southward. When the IMF is dawnward, the dayside cusp and the tail lobes shift toward the morningside in the northern magnetosphere. The plasma sheet rotates toward the north on the dawnside of the tail and toward the south on the duskside. For an increasing southward IMF component, the plasma sheet becomes thinner and subsequently wavy because of patchy or localized tail reconnection. At the same time the tail field‐aligned currents have a filamentary layered structure. When projected onto the northern polar cap, the filamentary field‐aligned currents are located in the same area as the region 1 currents with a pattern similar to that associated with auroral surges. Magnetic reconnection also occurs on the dayside magnetopause for southward IMF. The steady dayside reconnection mainly occurs in the antiparallel merging region nearest the subsolar point and drives strong convection near the magnetopause as reconnected field lines flow tailward. This causes an enhancement of the polar cap and region 1 field‐aligned currents. The polar cusp field‐aligned currents evolve from the polar cap ( NB z ) field‐aligned currents as the IMF is rotated from northward to southward.
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Abstract Ultralow frequency (ULF) fluctuations are ubiquitous in the magnetosphere and have significant influence on the energetic particle transport. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) data to give the spatial distribution of the Pi2/Pc4 and Pc5 band magnetic fluctuation amplitude near the magnetic equator in the magnetosphere. Statistical results can be summarized as follows: (1) strong ULF fluctuations are common in the magnetotail plasma sheet; the amplitude of all three components of magnetic fluctuations decreases with decreasing radial distance; (2) during periods of high AE index, fluctuations can propagate toward the Earth as far as the data cutoff in the nightside of the magnetosphere, and the amplitude of magnetic fluctuations is clearly stronger near the dusk sector of the synchronous orbit than that near the dawn sector, suggesting that the substorm particle injection has significant contribution to these fluctuations; (3) intense compressional Pc5 band magnetic fluctuations are a persistent feature near two flanks of the magnetosphere. Clear peaks of the compressional Pi2/Pc4 band magnetic fluctuation power near two flanks can be found during periods of fast solar wind, while the power of compressional Pi2/Pc4 band fluctuations is weak when the solar wind is slow. (4) Solar wind dynamic pressure and its variations can globally affect the ULF fluctuation power in the magnetosphere. Magnetic fluctuations near the noonside can penetrate from the magnetopause to the synchronous orbit or inner when solar wind pressure variations are large.
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