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  • 1
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    Statistical properties of substorm auroral onset beads/rays (2016)
    Wiley
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    Publication Date: 2016-09-04
    Description: Auroral substorms are often associated with optical ray or bead structures during initial brightening (substorm auroral onset waves). Occurrence probabilities and properties of substorm onset waves have been characterized using 112 substorm events identified in THEMIS all-sky imager data, and compared to Rice Convection Model-Equilibrium (RCM-E) and kinetic instability properties. All substorm onsets were found to be associated with optical waves, and thus optical waves are a common feature of substorm onset. Eastward-propagating wave events are more frequent than westward-propagating wave events, and tend to occur during lower-latitude substorms (stronger solar wind driving). The wave propagation directions are organized by orientation of initial brightening arcs. We also identified notable differences in wave propagation speed, wavelength (wavenumber), period and duration between westward and eastward propagating waves. In contrast, the wave growth rate does not depend on the propagation direction or substorm strength but is inversely proportional to the wave duration. This suggests that the waves evolve to poleward expansion at a certain intensity threshold, and that the wave properties do not directly relate to substorm strengths. However, waves are still important for mediating the transition between the substorm growth phase and poleward expansion. The relation to arc orientation can be explained by magnetotail structures in the RCM-E, indicating that substorm onset location relative to the pressure peak determines the wave propagation direction. The measured wave properties agree well with kinetic ballooning interchange instability, while cross-field current instability and electromagnetic ion cyclotron instability give much larger propagation speed and smaller wave period.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Structure and consequences of the kinetic ballooning/interchange instability in the magnetotail (2013)
    Wiley
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    Publication Date: 2013-02-01
    Description: [1]  The structure and dynamical consequences of the kinetic ballooning/interchange instability (BICI) that can be excited in the curved magnetic geometry characteristic of the terrestrial plasma sheet are investigated by means of three-dimensional electromagnetic particle-in-cell simulations. Compared with earlier studies that considered a single B z minimum configuration with an extremely large midtail field, additional simulations are performed in which this maximum is reduced to a more realistic value, the dependence on the values of the plasma beta and of the mass and temperature ratios m i / m e and T i / T e is investigated, and the limiting case of a constant B z profile is examined. The general properties of the BICI modes are found to be unaltered by these changes. Significantly, the BICI excitation is found not to require an explicit tailward magnetic field gradient; it appears to be sufficient for the entropy to decrease with distance down the tail. The BICI wavelength varies inversely with B z , and the eigenmodes are strongly field aligned with parallel electron flows comparable to the ion thermal velocity. In the edge of the plasma sheet, the oscillations in B x and B z have comparable magnitude. Once excited, the growth of the modes is robust and leads to the formation of intense interchange heads that propagate earthward. When the equatorial plasma beta is on the order of 500 or higher, the B z field can be driven southward in the wake of the heads. This results in the onset of localized magnetic reconnection and a violent disruption of the plasma sheet.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 3
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    Observations of kinetic ballooning/interchange instability signatures in the magnetotail (2012)
    Wiley
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    Publication Date: 2012-04-26
    Description: Stimulated by a recent study of a kinetic ballooning/interchange instability by Pritchett and Coroniti (2010), we present THEMIS events that confirm the predictions of this mechanism. In these events the probes were situated in the plasma sheet at 11 Re, near the presumed location of a B minimum. Prior to substorm onset, they observed strong magnetic oscillations with periods 20–100 s and δBX about 10–20 nT. Associated with these were oscillations of the electric field δEY ∼ 1 mV/m and the field-aligned electron velocity of several hundreds of km/s. No comparable perturbations in the ion velocity were observed. For two cases cross-correlation analyses proved duskward propagation of the elongated spatial structures with a cross-tail width of a few ion gyroradii and a propagation velocity of about the ion drift velocity. In one case THEMIS probes confirmed a sausage-like geometry of the structures.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Plasma sheet disruption by interchange-generated flow intrusions (2011)
    Wiley
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    Publication Date: 2011-05-21
    Description: A three-dimensional particle-in-cell simulation is used to examine the interaction of interchange-generated flow intrusions with the near-Earth plasma sheet. The interchange heads narrow in cross-tail extent as they propagate earthward and dawnward, and the maximum Bz in the head increases to be comparable to the lobe field strength. The interaction of the flow heads with the near-Earth plasma sheet leads to a strong disruption involving localized reconnection on east-west scales of a few ion inertia lengths. This mechanism may explain several key signatures of substorm onset associated with pre-breakup auroral streamers and the disruption of the near-Earth plasma sheet.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    The quiet evening auroral arc and the structure of the growth phase near-Earth plasma sheet (2014)
    Wiley
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    Publication Date: 2014-02-25
    Description: [1]  The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient, and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Plasma observations at venus with galileo (1991)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1991-09-27
    Description: Plasma measurements were obtained with the Galileo spacecraft during an approximately 3.5-hour interval in the vicinity of Venus on 10 February 1990. Several crossings of the bow shock in the local dawn sector were recorded before the spacecraft passed into the solar wind upstream from this planet. Although observations of ions of the solar wind and the postshock magnetosheath plasmas were not possible owing to the presence of a sunshade for thermal protection of the instrument, solar wind densities and bulk speeds were determined from the electron velocity distributions. A magnetic field-aligned distribution of hotter electrons or ;;strahl'' was also found in the solar wind. Ions streaming into the solar wind from the bow shock were detected. Electron heating at the bow shock, 〈/=20%, was notably small, with substantial density increases by factors of 2 to 3 at the day side of the shock that decrease for shock crossings further downstream from the planet. A search for pickup ions from the hot hydrogen and oxygen planetary coronas yielded an upper limit for these densities in the range of 10(-3) ion per cubic centimeter, which is consistent with densities expected from current models of neutral gas densities.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Frank, L A -- Paterson, W R -- Ackerson, K L -- Coroniti, F V -- Vasyliunas, V M -- New York, N.Y. -- Science. 1991 Sep 27;253(5027):1528-31.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17784095" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    First plasma wave observations at neptune (1989)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1989-12-15
    Description: The Voyager 2 plasma wave instrument detected many familiar plasma waves during the encounter with Neptune, including electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic turbulence at the bow shock, and chorus, hiss, electron cyclotron waves, and upper hybrid resonance waves in the inner magnetosphere. Low-frequency radio emissions, believed to be generated by mode conversion from the upper hybrid resonance emissions, were also observed propagating outward in a disklike beam along the magnetic equatorial plane. At the two ring plane crossings many small micrometer-sized dust particles were detected striking the spacecraft. The maximum impact rates were about 280 impacts per second at the inbound ring plane crossing, and about 110 impacts per second at the outbound ring plane crossing. Most of the particles are concentrated in a dense disk, about 1000 kilometers thick, centered on the equatorial plane. However, a broader, more tenuous distribution also extends many tens of thousands of kilometers from the equatorial plane, including over the northern polar region.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gurnett, D A -- Kurth, W S -- Poynter, R L -- Granroth, L J -- Cairns, I H -- Macek, W M -- Moses, S L -- Coroniti, F V -- Kennel, C F -- Barbosa, D D -- New York, N.Y. -- Science. 1989 Dec 15;246(4936):1494-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17756006" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    Plasma observations at Io with the Galileo spacecraft (1996)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1996-10-18
    Description: Plasma measurements made during the flyby of Io on 7 December 1995 with the Galileo spacecraft plasma analyzers reveal that the spacecraft unexpectedly passed directly through the ionosphere of Io. The ionosphere is identified by a dense plasma that is at rest with respect to Io. This plasma is cool relative to those encountered outside the ionosphere. The composition of the ionospheric plasmas includes O++, O+ and S++, S+, and SO2+ ions. The plasma conditions at Io appear to account for the decrease in the magnetic field, without the need to assume that Io has a magnetized interior.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Frank, L A -- Paterson, W R -- Ackerson, K L -- Vasyliunas, V M -- Coroniti, F V -- Bolton, S J -- New York, N.Y. -- Science. 1996 Oct 18;274(5286):394-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8832882" target="_blank"〉PubMed〈/a〉
    Keywords: Extraterrestrial Environment ; *Ions ; *Jupiter ; Magnetics ; Oxygen/analysis ; Sulfur/analysis ; Sulfur Dioxide/analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Plasma wave observations at comet giacobini-zinner (1986)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1986-04-18
    Description: The plasma wave instrument on the International Cometary Explorer (ICE) detected bursts of strong ion acoustic waves almost continuously when the spacecraft was within 2 million kilometers of the nucleus of comet Giacobini-Zinner. Electromagnetic whistlers and low-level electron plasma oscillations were also observed in this vast region that appears to be associated with heavy ion pickup. As ICE came closer to the anticipated location of the bow shock, the electromagnetic and electrostatic wave levels increased significantly, but even in the midst of this turbulence the wave instrument detected structures with familiar bow shock characteristics that were well correlated with observations of localized electron heating phenomena. Just beyond the visible coma, broadband waves with amplitudes as high as any ever detected by the ICE plasma wave instrument were recorded. These waves may account for the significant electron heating observed in this region by the ICE plasma probe, and these observations of strong wave-particle interactions may provide answers to longstanding questions concerning ionization processes in the vicinity of the coma. Near closest approach, the plasma wave instrument detected broadband electrostatic noise and a changing pattern of weak electron plasma oscillations that yielded a density profile for the outer layers of the cold plasma tail. Near the tail axis the plasma wave instrument also detected a nonuniform flux of dust impacts, and a preliminary profile of the Giacobini-Zinner dust distribution for micrometer-sized particles is presented.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Scarf, F L -- Coroniti, F V -- Kennel, C F -- Gurnett, D A -- Ip, W H -- Smith, E J -- New York, N.Y. -- Science. 1986 Apr 18;232(4748):377-81.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17792149" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    The kinetic ballooning/interchange instability as a source of dipolarization fronts and auroral streamers (2014)
    Wiley
    Details
    Publication Date: 2014-06-07
    Description: The possibility that the dipolarization fronts (DFs) observed in the plasma sheet could be produced by the Ballooning/InterChange Instability (BICI) is explored using three-dimensional electromagnetic particle-in-cell simulations. The localized interchange heads produced in the nonlinear stage of the instability exhibit the main near-equatorial properties of a DF: the cross-tail extent is on the order of 1 R E , the ramp ups in B z and the magnitude of E y as well as the sharp density decrease all occur on the ion inertial scale, while there is a more gradual increase in the bulk flow. The field-aligned currents associated with the break up of the head should produce a structuring of the corresponding auroral streamer in the ionosphere, a result that is confirmed by THEMIS all-sky imager data. The dissipation associated with the head occurs in electron-scale regions in the center of the plasma sheet. Away from the center, the head is strongly modulated by waves with frequency on the order of the ion gyrofrequency. The strength of the accompanying E y oscillations is in the range of 30–50 mV/m, and the δE/δB ratio is 3–4 times the local Alfvén speed. The waves appear to be produced by the electromagnetic current-driven ion-cyclotron instability.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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