Outflow of energetic ions from the magnetosphere and its contribution to the decay of the storm time ring current
Outflow of energetic ions from the magnetosphere and its contribution to the decay of the storm time ring current
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DOI：
10.1029/2004ja010970
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发表时间：
2005-09
影响因子：
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通讯作者：
K. Keika;M. Nosé;S. Ohtani;Kazue Takahashi;S. Christon;R. Mcentire
中科院分区：
文献类型：
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作者：
K. Keika;M. Nosé;S. Ohtani;Kazue Takahashi;S. Christon;R. Mcentire
[1]我们统计和定量地研究了磁暴期间高能离子从磁层流出的现象。我们还评估了外流对环电流衰减的贡献。我们使用高能粒子和离子组成(EPIC)仪器获得的高能离子(9-210keV)数据和磁场测量(MGF)系统获得的磁场数据，两者都在GeoTail航天器上。流出的能量通量，即流经磁层顶的环流离子损失的能量通量，被定义为垂直于磁层顶的能量通量，并根据在低纬边界层向地面一侧进行的测量计算。我们的统计表明，在主相和恢复相期间，流出的能量通量都在105-108keV/(Cm2)左右。下午的气温比早上的高。与反映对流电场强度的太阳风电场相比，它与太阳风动压的平方根有更好的相关性。根据根据磁场测量确定的低估的泄漏面积，外流对环电流快速衰减的贡献估计至少为23%，可能远远高于2001年9月23日风暴的23%。我们认为控制离子外流的漂移主要是∇B漂移，它的径向分量是由太阳风压缩引起的磁层磁场昼夜梯度引起的。我们的结论是，即使在行星际磁场突然向北转向导致对流电场突然下降的情况下，离子流出也对环电流的快速衰减有显著的贡献。
[1] We statistically and quantitatively examine the outflow of energetic ions from the magnetosphere during magnetic storms. We also evaluate the contribution of the outflow to the decay of the ring current. We use energetic ion (9–210 keV) data obtained by the energetic particle and ion composition (EPIC) instrument and magnetic field data obtained by the magnetic field measurements (MGF) system, both on board the Geotail spacecraft. The outflowing energy flux, that is, the energy flux lost by ring current ions flowing through the magnetopause, is defined as the energy flux normal to the magnetopause and is calculated based on measurements made adjacent to the earthward side of the low-latitude boundary layer. Our statistics show that the outflowing energy flux is about 105–108 keV/(cm2s) during both the main phase and the recovery phase. It is higher on the afternoonside than on the morningside. It is better correlated with the square root of the dynamic pressure of the solar wind than the electric field of the solar wind, which is a proxy for the strength of the convection electric field. The contribution of the outflow to the rapid decay of the ring current is estimated to be at least 23% and could be much higher than 23% for the 23 September 2001 storm, based on an underestimated leakage area which is determined from magnetic field measurements. We suggest that the drift governing the ion outflow mainly is the ∇B drift which has a radial component that arises from a day-night gradient of the magnetic field in the magnetosphere caused by the solar wind compression. We conclude that the ion outflow contributes significantly to the rapid decay of the ring current, even in the case of a sudden northward turning of the interplanetary magnetic field which causes a sudden decrease in the convection electric field.