来自电离层的尾向流对近地磁场位形的影响

Effect of Tailward Flows From the Ionosphere on the Near-Earth Magnetic Field

探测一号(TC-1)卫星的观测结果表明,尾向流能够拉伸近地磁尾的磁力线,从而导致磁场位形改变．尾向流具有垂直于磁场的速度分量,这种垂直磁场的速度分量会导致磁力线向尾向拉伸,磁场的结构由偶极型变为非偶极型．而随尾向流的终止,地向流的出现,磁场的结构由非偶极型变为偶极型,磁力线恢复原状．另外在磁场的结构由非偶极型变为偶极型的过程中,伴随磁能的释放热离子温度的迅速升高,温度由各向同性逐渐趋向各向异性．其次,观测结果显示来自电离层的尾向流对磁场By分量有重要的影响,能够引起磁场By分量的显著增强．上述分析结果表明来自电离层的尾向流对近地磁尾动力学过程有着重要的影响．

Tailward flows are often observed in the near-Earth magnetotail by TC-1 satellite during quiet time and substorm active period. The statistical studies show that the perpendicular component of the tailward flow will leads to stretching of magnetic field lines. Due to the tailward flow, the Bx component of the magnetic field distinctly increases or the magnetic field geometry becomes tail-like from dipolar-like. The magnetic field is recovered and back to dipole-like structure when plasma flow is reversed. Along with magnetic field stretch, it is found that both temperature anisotropy and ion temperature decrease at the same time. During the period of the magnetic field recovering dipolar- like, the ion temperature rapidly increases and the temperature becomes anisotropy associated with the release of the magnetic energy. From the observations, it is also shown that the tailward flow causes an enhancement of By component. The results from the TC-1 satellite indicate that the tailward flow from the ionosphere has an important effect on the near-earth magnetotail.