| 1. |
- Kullen, A., et al.
(författare)
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Geomagnetic signatures of auroral substorms preceded by pseudobreakups
- 2009
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 114
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of ten growth-phase pseudobreakups and subsequent substorms, identified in Northern Hemisphere Polar UV images during winter 1998-1999, are compared to the AE index, the unified PC indices, and GOES B field data. Comparing substorm onset (auroral breakup) with GOES data and AE and PC indices, it is found that an exact onset determination from these parameters is in most cases not possible. The three weakest substorms leave no clear signatures in the auxiliary parameters. For the other events, the AE increase appears with a time delay of 5-15 min after onset. The PC indices increase, as expected, before the AE index. The time span between PC increase and onset varies widely (-26 to 5 min). A tail dipolarization is seen in GOES data with a time delay of 2-31 min after onset. The dipolarization delay at geosynchronous orbit appears because of the GOES displacement from the tail onset region. Using the mapped GOES distance from the auroral breakup region as an estimate of GOES displacement from the breakup source region, we find that the tail dipolarization region expands in average with an azimuthal speed of 0.22 MLT min(-1) and an equatorward speed of 0.09 degrees min(-1). Pseudobreakups leave hardly any signature in AE or PC index data except in the four strongest substorm cases. In these cases, a bump appears in the PC indices during the pseudobreakup. A bump in geosynchronous B field data is found only in those two cases where GOES is located very close to the pseudobreakup tail source region.
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| 2. |
- Kullen, Anita, et al.
(författare)
-
Geomagnetic signatures of auroral substorms preceded by pseudobreakups
- 2009
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114, s. A04201-
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of ten growth-phase pseudobreakups and subsequent substorms, identified in Northern Hemisphere Polar UV images during winter 1998-1999, are compared to the AE index, the unified PC indices, and GOES B field data. Comparing substorm onset (auroral breakup) with GOES data and AE and PC indices, it is found that an exact onset determination from these parameters is in most cases not possible. The three weakest substorms leave no clear signatures in the auxiliary parameters. For the other events, the AE increase appears with a time delay of 5-15 min after onset. The PC indices increase, as expected, before the AE index. The time span between PC increase and onset varies widely (-26 to 5 min). A tail dipolarization is seen in GOES data with a time delay of 2-31 min after onset. The dipolarization delay at geosynchronous orbit appears because of the GOES displacement from the tail onset region. Using the mapped GOES distance from the auroral breakup region as an estimate of GOES displacement from the breakup source region, we find that the tail dipolarization region expands in average with an azimuthal speed of 0.22 MLT min(-1) and an equatorward speed of 0.09 degrees min(-1). Pseudobreakups leave hardly any signature in AE or PC index data except in the four strongest substorm cases. In these cases, a bump appears in the PC indices during the pseudobreakup. A bump in geosynchronous B field data is found only in those two cases where GOES is located very close to the pseudobreakup tail source region.
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| 3. |
- Ohtani, H., et al.
(författare)
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Equilibrium between fluorite and pyrochlore structures in the ZrO2-Nd2O3 system
- 2005
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Ingår i: Materials transactions. - : Japan Institute of Metals. - 1345-9678 .- 1347-5320. ; 46:6, s. 1167-1174
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Tidskriftsartikel (refereegranskat)abstract
- The phase diagram of the ZrO2-Nd2O3 system has been characterized showing isolated two-phase regions for a cubic fluorite-type ZrO2 solid solution and Nd2Zr2O7 with a pyrochlore-type structure. A thermodynamic analysis was carried out to elucidate the origin of this interesting phase equilibrium. A compound energy model with the formula (Zr4+,Nd3+)(0.5)(Nd3+,Zr4+)(0.5)(O2-,va)(2) was applied to describe the Gibbs energy for these phases in consideration of the ordering of the cation sites in the structure. The ordering arrangement on the anion sites was not taken into account. The Gibbs energy for the liquid was described using an ionic solution model, while the binary compounds, such as tetragonal and monoclinic ZrO2, and cubic and hexagonal Nd2O3, were treated as stoichiometric solid phases. The thermodynamic assessment was based on the experimental phase boundaries as well as the evaluated formation energy for the stoichiometric Nd,2Zr2O7 phase. The phase diagram calculations showed that the peculiar feature of this phase diagram was reproduced well in our work. The results strongly suggest that the two-phase boundaries between the cubic fluorite-type ZrO2 solid solution and the pyrochlore-type structure occur due to the ordering of the Zr4+ and Nd3+ cations.
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| 4. |
- Ohtani, S., et al.
(författare)
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Cluster observations in the inner magnetosphere during the 18 April 2002 sawtooth event : Dipolarization and injection at r=4.6 R-E
- 2007
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 112:A8
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Tidskriftsartikel (refereegranskat)abstract
- The present study examines a sawtooth injection event that took place around 0800 UT on 18 April 2002 when the Cluster spacecraft were located in the inner magnetosphere in the premidnight sector. In association with this injection, Cluster, at a radial distance of 4.6 RE, observed that the local magnetic field became more dipolar and that both ion and electron fluxes increased without notable energy dispersion. These features were accompanied by intensifications of the equatorward component of a double- oval structure and also by an enhancement of the ring- current oxygen ENA flux. The event was also accompanied by large magnetic field ( a few tens of nT) and electric field ( a few tens of mV/ m) fluctuations with characteristic timescales of a few tens of seconds. These observations strongly suggest that this sawtooth injection extended not only widely in local time but also deeply into the inner magnetosphere. Interestingly, Cluster repeatedly observed dipolarization- like signatures afterward, which, however, were not associated with enhancements of local energetic ion flux or with geosynchronous dipolarization or injection signatures. Instead, these magnetic signatures were accompanied by oscillatory plasma motion in the radial direction with a characteristic timescale of about 10 min, which appears to be related to the westward propagation of a spatially periodic auroral structure. The associated azimuthal electric field component was well correlated with the time derivative of the north- south magnetic field component, suggesting that the observed electric field is inductive. These findings suggest that electromagnetic processes far inside geosynchronous orbit play an important role in energization of energetic ions and auroral dynamics during magnetospheric storms.
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