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  • 1
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    Dual Spacecraft Observations of Lobe Magnetic Field Perturbations Before, During and after Plasmoid Release (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: This study examines a unique data set returned by IMP8 and Geotail on January 29, 1995 during a substorm which resulted in the ejection of a plasmoid. The two spacecraft (s/c) were situated in the north lobe of the tail and both observed a traveling compression region (TCR). From single s/c observations only the length of the plasmoid in X and an estimate of its height in Z can be determined. However, we show that dual s/c measurements of TCRs can be used to model all three dimensions of the underlying plasmoid and to estimate of its rate of expansion or contraction. For this event plasmoid dimensions of Delta(X) approximates 18, Delta(Y) approximates 30, and Delta(Z) approximates 10 R(sub e) are inferred from the IMP8 and Geotail lobe magnetic field measurements. The earthward end of the plasmoid was inferred to be near the mean location of the near-earth neutral line, X approximates -26 R(sub e). Its center was underneath IMP 8 at X approximates -34 R(sub e) and its tailward end appeared to be near X approximates -44 R(sub e). Furthermore, a factor of approximately 2 increase in the amplitude of the TCR occurred in the 1.5 min it took to move from IMP 8 to Geotail. Modeled using conservation of the magnetic flux, this increase in lobe compression implies that the underlying plasmoid was expanding at a rate of approximately 140 km/s. Such an expansion is comparable to recently reported V(sub y) speeds in "young" plasmoids in this region of the tail. Finally, the Geotail measurements indicate that a reconfiguration of the lobe magnetic field closely followed the ejection of the plasmoid which moved magnetic flux tubes into the wake behind the plasmoid where they would convect into the near-earth neutral line and reconnect.
    Keywords: Geophysics
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  • 2
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    Interball substorm observations: Christmas for space scientists (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observational results from the Interball Tail Probe spacecraft are presented. One of the main objectives of the Interball project is to study the dynamic processes in the magnetosphere. Three events observed by the spacecraft's instruments are investigated: a pseudobreakup during which earthward streaming ions were observed in the vicinity of a thin current sheet; a substorm in which the magnetic signatures in the lobe and on the ground were preceeded by northward re-orientation of the interplanetary magnetic field Bz component; and a magnetic storm at the beginning of which extreme deformation of the magnetotail was observed.
    Keywords: Geophysics
    Type: ; 497-506
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  • 3
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    Atmospheric manifestation of tropical instability wave observed by Quikscat and tropical rain measuring mission (2000)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the Pacific equatorial cold tongue.
    Keywords: Geophysics
    Type: Geophysical Research Letters; Volume 27; no. 16; 2545-2548
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  • 4
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    Substorm expansion phases during magnetic storms in April 17-23, 2002: IMAGE FUV observations (2002)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: Fall 2002 American Geophysical Union; San Francisco, CA; United States
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  • 5
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    Recent Simulation Results on Ring Current Dynamics Using the Comprehensive Ring Current Model (2010)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: Plasma sheet conditions and electromagnetic field configurations are both crucial in determining ring current evolution and connection to the ionosphere. In this presentation, we investigate how different conditions of plasma sheet distribution affect ring current properties. Results include comparative studies in 1) varying the radial distance of the plasma sheet boundary; 2) varying local time distribution of the source population; 3) varying the source spectra. Our results show that a source located farther away leads to a stronger ring current than a source that is closer to the Earth. Local time distribution of the source plays an important role in determining both the radial and azimuthal (local time) location of the ring current peak pressure. We found that post-midnight source locations generally lead to a stronger ring current. This finding is in agreement with Lavraud et al.. However, our results do not exhibit any simple dependence of the local time distribution of the peak ring current (within the lower energy range) on the local time distribution of the source, as suggested by Lavraud et al. [2008]. In addition, we will show how different specifications of the magnetic field in the simulation domain affect ring current dynamics in reference to the 20 November 2007 storm, which include initial results on coupling the CRCM with a three-dimensional (3-D) plasma force balance code to achieve self-consistency in the magnetic field.
    Keywords: Geophysics
    Type: Western Pacific Geophysics Meeting (WPGM) Object: 2134; Jun 22, 2010 - Jun 25, 2010; Taipei; Taiwan, Province of China
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  • 6
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    Energetic O+ and H+ Ions in the Plasma Sheet: Implications for the Transport of Ionospheric Ions (2011)
    In:  Other Sources
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    Publication Date: 2019-08-26
    Description: The present study statistically examines the characteristics of energetic ions in the plasma sheet using the Geotail/Energetic Particle and Ion Composition data. An emphasis is placed on the O+ ions, and the characteristics of the H+ ions are used as references. The following is a summary of the results. (1) The average O+ energy is lower during solar maximum and higher during solar minimum. A similar tendency is also found for the average H+ energy, but only for geomagnetically active times; (2) The O+ -to -H+ ratios of number and energy densities are several times higher during solar maximum than during solar minimum; (3) The average H+ and O+ energies and the O+ -to -H+ ratios of number and energy densities all increase with geomagnetic activity. The differences among different solar phases not only persist but also increase with increasing geomagnetic activity; (4) Whereas the average H+ energy increases toward Earth, the average O+ energy decreases toward Earth. The average energy increases toward dusk for both the H+ and O+ ions; (5) The O+ -to -H+ ratios of number and energy densities increase toward Earth during all solar phases, but most clearly during solar maximum. These results suggest that the solar illumination enhances the ionospheric outflow more effectively with increasing geomagnetic activity and that a significant portion of the O+ ions is transported directly from the ionosphere to the near ]Earth region rather than through the distant tail.
    Keywords: Geophysics
    Type: Journal of Geophysical Research; 116
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  • 7
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    Average energetic ion flux variations associated with geomagnetic activity from EPIC/STICS on Geotail (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-16
    Description: The magnetotail ion flux measurements from the Geotail spacecraft are analyzed both with and without the application of selection criteria that identify the plasma regime in which an observation is obtained. The different results are compared with each other. The initial results on the changes of energetic ion flux and composition correlated to average substorm activity in different magnetotail plasma regimes are discussed. The energetic ions are measured using the energetic particles and ion composition (EPIC) experiment and the suprathermal ion composition spectrometer (STICS). The plasma, wave and field instruments of the Geotail satellite were used to identify the principle magnetotail plasma regimes of plasma sheet, lobe, and magnetospheric boundary layer, as well as the magnetosheath and solar wind. Energetic O and H ions were observed in all the plasma regimes.
    Keywords: Geophysics
    Type: ; 527-532
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  • 8
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    Cross-field Current Instability for Substorm Expansions (1997)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: The funding provided by the above-referenced NASA grant has enabled us: (1) to investigate the quasi-linear evolution of the IWI [Lui et al., 1993] and that of the generalized MTSI/IWI [Yoon and Lui, 1993], (2) to carry out the linear analysis of the LHDI to elucidate the difference between it and the MTSI/PM instability [Yoon et al., 1994], (3) to conduct some preliminary nonlocal analyses of the MTSI [Lui et al., 1995] and the IWI [Yoon and Lui, 1996] modes, (4) to study low-frequency shear-driven instability and its nonlinear evolution, which might compete with the CCI [Yoon et al., 1996], and (5) to study the evolution of current sheet during late substorm growth phase by means of 2-D Hall-MHD simulation in order to obtain a better understanding of the current sheet equilibrium crucial for CCI theory [Yoon and Lui, 1997].
    Keywords: Geophysics
    Type: NASA/CR-97-206057 , NAS 1.26:206057
    Format: application/pdf
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  • 9
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    Local and global effects of the cross-field current instability (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: The cross-field current instability (CCI) was proposed elsewhere as a plausible mechanism for the initiation and intensification of substorm expansions. This instability encompasses the modified two stream, the ion-Weibel and the lower hybrid drift modes. The work carried out in relation to this instability and its local and global effects is reviewed. Predicted local effects include current reduction, particle acceleration, the excitation of oblique whistlers and lower hybrid drift waves, and the breakdown of the frozen-in-field condition through anomalous dissipation. The predicted global effects of CCI include the offset of force equilibrium and the generation of field aligned currents at the disruption site, which allow the efficient large scale transportation of mass, momentum and energy within the magnetosphere.
    Keywords: Geophysics
    Type: ; 387-392
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  • 10
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    AMPTE/CCE and SCATHA simultaneous observations of magnetic signatures associated with a substorm onset (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: Magnetic field signatures associated with a substorm onset event are examined by making use of simultaneous observations from the Active Magnetosphere Particle Tracer Explorer (AMPTE)/Charge Composition Explorer (CCE) and Spacecraft Charging AT High Altitude (SCATHA). The observations of the two satellites are discussed in relation to their differences and the relative positions of the satellites. Despite the small separation between the satellites, AMPTE/CCE observed the start of irregular magnetic field fluctuations a few tens of seconds earlier than SCATHA, indicating that the CCE was within, or closer to, the onset region. It was found that the amplitude of the fluctuations was largest in the north-south component. The results indicate that the magnetic field fluctuations were excited locally and the coherence length was less than a multiple of Larmor radius of thermal protons. It is suggested that the tail current disruption is described as a system of chaotic filamentary electric currents which flow in various directions, but preferentially anti-parallel to the cross-tail current, and that ions play an important role in the triggering of the tail current disruption.
    Keywords: Geophysics
    Type: ; 279-283
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