Geotail observations of two-component protons in the midnight plasma sheet

Nishino, Masaki N.; Fujimoto, M.; Ueno, G.; Maezawa, K.; Mukai, T.; Saito, Y.

doi:10.5194/angeo-25-2229-2007

Cited by 17 publications

(19 citation statements)

References 28 publications

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“…While our simulation does compare favorably with the qualitative asymmetry observed in nature, it is not our expectation that this idealized model should quantitatively reproduce any specific event. For instance, Nishino et al (), using a selection of several Geotail events, find the emergence of two‐component protons near midnight typically within 3 after the arrival of strongly northward IMF. As seen in Figure , relatively few flank‐entering particles are within ±10 R E of midnight after 3 hr of test particle integration.…”

Section: Resultsmentioning

confidence: 99%

Solar Wind Ion Entry Into the Magnetosphere During Northward IMF

et al. 2019

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Extended periods of northward interplanetary magnetic field (IMF) lead to the formation of a cold, dense plasma sheet due to the entry of solar wind plasma into the magnetosphere. Identifying the paths that the solar wind takes to enter the magnetosphere, and their relative importance has remained elusive. Any theoretical model of entry must satisfy observational constraints, such as the overall entry rate and the dawn‐dusk asymmetry observed in the cold, dense plasma sheet. We model, using a combination of global magnetohydrodynamic and test particle simulations, solar wind ion entry into the magnetosphere during northward IMF and compare entry facilitated by the Kelvin‐Helmholtz instability to cusp reconnection. For Kelvin‐Helmholtz entry we reproduce transport rates inferred from observation and kinetic modeling and find that intravortex reconnection creates buoyant flux tubes, which provides, through interchange instability, a mechanism of filling the central plasma sheet with cold magnetosheath plasma. For cusp entry we show that an intrinsic dawn‐dusk asymmetry is created during entry that is the result of alignment of the westward ion drift with the dawnward electric field typically observed during northward IMF. We show that both entry mechanisms provide comparable mass but affect entering plasma differently. The flank‐entering plasma is cold and dawn‐dusk symmetric, whereas the cusp‐entering plasma is accelerated and preferentially deflected toward dawn. The combined effect of these entry mechanisms results in a plasma sheet population that exhibits dawn‐dusk asymmetry in the manner that is seen in nature: a two‐component (hot and cold) dusk flank and hotter, broadly peaked dawn population.

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Section: Resultsmentioning

confidence: 99%

Solar Wind Ion Entry Into the Magnetosphere During Northward IMF

et al. 2019

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“…[34] While the cold electrons in the magnetotail plasma sheet have not been well studied, the presence of a cold component of ions in the magnetotail plasma sheet has been well established [e.g., Terasawa et al, 1997;Fujimoto et al, 1998;Øieroset et al, 2005;Wing et al, 2005;Nishino et al, 2007b]. Cold ions are more often observed under northward IMF than southward IMF [Øieroset et al, 2005;Wing et al, 2005], to the extent that a separate cold component is almost exclusively observed under northward IMF [Nishino et al, 2007b[Nishino et al, , 2007c. Transport through the flank magnetopause, perhaps via reconnection in rolled-up Kelvin-Helmholtz vortices [Hasegawa et al, 2004], is thought to be responsible for the presence of cold ions in the magnetotail under northward IMF.…”

Section: Discussionmentioning

confidence: 99%

Sources of electron pitch angle anisotropy in the magnetotail plasma sheet

et al. 2013

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[1] We survey the properties of electron pitch angle distributions in the magnetotail plasma sheet at a distance between 15 and 19 R E from the Earth, using data from the Plasma Electron and Current Experiment (PEACE) instrument. We limit our survey to those pitch angle distributions measured when the interplanetary magnetic field (IMF) had been steadily northward or steadily southward for the previous 3 h. We find that, at sub-keV energies, the plasma sheet electron pitch angle distribution has an anisotropy such that there is a higher differential energy flux of electrons in the (anti-) field-aligned directions. Fitting the measured pitch angle distributions with both a single and two component kappa distribution reveals that this anisotropy is the result of the presence of a second, cold, component of electrons that is observed more often than not, and occurs during both the northward and southward IMF intervals. We present evidence that suggests the cold electron component has an ionospheric, rather than magnetosheath, source and is linked to the large-scale field-aligned current systems that couple the magnetosphere and ionosphere.

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“…Simultaneous observations of Kelvin-Helmholtz vortices on both flanks are rare, and as such it is difficult to address any dawn-dusk asymmetry in their properties. However, Nishino et al (2011) reported one observation of vortices occurring simultaneously on both flanks and showed that while their macroscopic properties were similar, on a microscopic level differences were observed, with more plasma mixing between magnetosheath and magnetospheric populations in the dawnside vortex than the duskside vortex. Gradient drift entry naturally provides a dawn-dusk asymmetry: ions drift into the magnetosphere through the magnetopause on the dawn side, while electrons enter on the duskside (Olson and Pfitzer, 1985).…”

Section: Magnetopause Asymmetriesmentioning

confidence: 99%

Dawn–dusk asymmetries in the coupled solar wind–magnetosphere–ionosphere system: a review

et al. 2014

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Abstract. Dawn-dusk asymmetries are ubiquitous features of the coupled solar-wind-magnetosphere-ionosphere system. During the last decades, increasing availability of satellite and ground-based measurements has made it possible to study these phenomena in more detail. Numerous publications have documented the existence of persistent asymmetries in processes, properties and topology of plasma structures in various regions of geospace. In this paper, we present a review of our present knowledge of some of the most pronounced dawn-dusk asymmetries. We focus on four key aspects: (1) the role of external influences such as the solar wind and its interaction with the Earth's magnetosphere; (2) properties of the magnetosphere itself; (3) the role of the ionosphere and (4) feedback and coupling between regions. We have also identified potential inconsistencies and gaps in our understanding of dawn-dusk asymmetries in the Earth's magnetosphere and ionosphere.

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Geotail observations of two-component protons in the midnight plasma sheet

Cited by 17 publications

References 28 publications

Solar Wind Ion Entry Into the Magnetosphere During Northward IMF

Solar Wind Ion Entry Into the Magnetosphere During Northward IMF

Sources of electron pitch angle anisotropy in the magnetotail plasma sheet

Dawn–dusk asymmetries in the coupled solar wind–magnetosphere–ionosphere system: a review

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