Ring current and the magnetosphere‐ionosphere coupling during the superstorm of 20 November 2003
Ring current and the magnetosphere‐ionosphere coupling during the superstorm of 20 November 2003
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DOI：
10.1029/2004ja010924
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发表时间：
2005-09
影响因子：
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通讯作者：
Y. Ebihara;M. Fok;S. Sazykin;M. Thomsen;M. Hairston;D. Evans;F. Rich;M. Ejiri
中科院分区：
文献类型：
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作者：
Y. Ebihara;M. Fok;S. Sazykin;M. Thomsen;M. Hairston;D. Evans;F. Rich;M. Ejiri
我们研究了2003年11月20日一次日冕物质抛射（CME）及其相关磁云对地球环电流的影响，该磁云严重干扰了地球磁层。这次日冕物质抛射使Dst指数降至- 472 nT，使其成为1957年至2004年间观测到的第二大Dst指数。来自DMSP、NOAA和LANL卫星的数据显示了这场风暴的独特特征；极帽电位至少增加到200 kV，极帽边界移动低至约60°MLAT，当Dst指数接近最小值时，等离子体片密度在L = 6.6时增加到5 cm−3，等离子体片离子种群的内缘渗透到L≤1.5的区域。为了研究环电流的动力学和相关的磁层-电离层耦合，我们进行了环电流模拟，计算了环电流离子的相空间密度的演变以及磁层和电离层之间电流的闭合。主要结果如下：(1)考虑到模型中使用的极帽电位，从Dst指数和等离子体片内缘来看，对流电场的增强可以产生环电流；(2)太阳风粒子可能以80 min左右的滞后时间迅速渗透到夜侧地球同步高度，导致环电流进一步增强；(3)稠密的日冕中性氢或较大的俯角扩散系数（>10−4 s−1）可能需要解释等离子体片（或环电流）种群的内缘快速运动到更高的L值；(4)模拟和观测的场向电流（FAC）分布都显示出多个电流片，而不是通常预期的两个电流片。极帽电位和等离子体片密度的波动被认为是造成多片场向电流的原因；(5)区域2型场向流的赤道边缘扩展至40°MLAT，与模拟结果一致；(6)由于2区FAC较强，对流模式比平均模式复杂得多。一个值得注意的特征是在黎明面出现的纬向电离层等离子体流的反转。特别地，在黎明向东的等离子体流的赤道区域观测到一个向西的流。其速度局部最大值在流向反转方向约5°。流动逆转被认为是由于相对较强的屏蔽电场。
[1] We investigated the impact on the terrestrial ring current of a coronal mass ejection (CME) and the associated magnetic cloud that severely disturbed the Earth's magnetosphere on 20 November 2003. This CME decreased the Dst index to −472 nT, which makes it the second largest storm, based on the minimum Dst index values, observed between 1957 and 2004. Data from the DMSP, NOAA, and LANL satellites showed the unique characteristics of this storm; a polar cap potential that increased to at least 200 kV, a polar cap boundary that moved as low as about 60° MLAT, a plasma sheet density that increased to 5 cm−3 at L = 6.6 when the Dst index was near its minimum, and the inner edge of the plasma sheet ion population that penetrated into a region for which L ≤ 1.5. In order to study the dynamics of the ring current and the associated magnetosphere-ionosphere coupling, we performed a ring current simulation that computed the evolution of the phase space density of the ring current ions and the closure of the electric current between the magnetosphere and the ionosphere. Major results were as follows: (1) The ring current, in terms of the Dst index and the inner edge of the plasma sheet, can result from the enhancement of the convection electric field, given the polar cap potentials used in the model; (2) The solar wind particles probably penetrated quickly into the geosynchronous altitude on the nightside with a lag of about 80 min, resulting in further enhancement of the ring current; (3) Dense geocoronal neutral hydrogen or a large coefficient of pitch angle diffusion (>10−4 s−1) is probably needed to account for the rapid motion of the inner edge of the plasma sheet (or the ring current) population to a higher L value; (4) Both the simulated and observed field-aligned current (FAC) distributions show multiple current sheets, rather than the normally expected two current sheets. Fluctuations in the polar cap potential and the plasma sheet density are believed to cause the multiple sheets of field-aligned currents; (5) The equatorward edge of the Region 2 type field-aligned currents was observed to expand as low as 40° MLAT, which is consistent with the simulation; and (6) The convection pattern can be much more complicated than an average one due to a strong Region 2 FAC. A noticeable feature was the reversal of the zonal ionospheric plasma flow that emerged on the dawnside. In particular, a westward flow was observed in the equatorial region of the eastward plasma flow at dawn. Its speed had a local maximum of about 5° equatorward of the flow reversal. The flow reversal is thought to have resulted from the relatively strong shielding electric field.