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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Time development of field-aligned currents, potential drops, and plasma associated with an auroral poleward boundary intensification
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Time development of field-aligned currents, potential drops, and plasma associated with an auroral poleward boundary intensification

机译：field-aligned电流的时间发展,潜在的下降,和等离子体与一个关联极光边界增强

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We present a detailed case study of the plasma and fields measured by the Cluster spacecraft fleet at the high-altitude auroral zone (-3.5 RE) across the plasma sheet boundary layer and into the polar cap. This event, which occurred during quiet geomagnetic conditions (Kp = AE = 50 nT), is of particular interest in that Cluster provides measurements at key instances during the time development of a new large-scale auroral arc system. Central to the formation of the arc system is the depletion of ionospheric plasma through a region of small-scale, field-aligned currents having the properties of Alfven waves. This depletion occurred prior to the growth of and ultimately bounded a well-defined equatorward moving, upward and downward current sheet pair. In association with the transverse scales approaching the electron inertial scale, the Alfvenic currents have amplitudes that appear to be attenuated subsequent to the formation of the cavity. Potential structures essentially time invariant over particle transit times (quasi-static) associated with the current pair are identified and observed to drive a poleward boundary intensification (PBI) identified in coincident IMAGE satellite far ultraviolet measurements. The PBI formed in association with a local thickening of the plasma sheet via the injection of new magnetospheric plasma, which may be the result of a bursty, patchy reconnection process. Estimates of the ionospheric equatorward velocity and thickness of the PBI are consistent with their ionospheric mapped cavity counterparts, suggesting that the motion and thickness are controlled by the plasma and electrodynamic features at or above the altitude sampled by Cluster. The magnitude of the upward and ' downward current region parallel potentials is correlated with the temperature of the newly injected electrons suggesting that the electron temperature is an important controlling factor. These novel observations indicate that quasi-static systems of field-aligned currents do form out of the highly dynamic Alfvenic region at the plasma sheet boundary layer, and perhaps suggest that the Alfvenic region can be the initial stage in the development of quasi-static systems. The observed time sequence of the currents is qualitatively similar to the expectations of transient response models of magnetospheric-ionospheric coupling, however, such models may need to be modified to account for the attenuation of electron inertial scale currents/Alfven waves.
机译：我们提出一个详细的等离子体和案例研究字段来衡量集群飞船舰队在高空极光区(-3.5再保险)在等离子体片边界层而成极冠。这个事件,发生在安静的地磁条件(Kp = AE = 50元),集群是特别感兴趣的吗提供测量在关键的实例时间发展一个新的大规模的极光弧系统。系统是电离层等离子体的损耗通过小规模的地区,field-aligned电流在阿尔芬波的特性。这个损耗发生之前的增长并最终有界的一个定义明确的阻碍向上或向下移动,电流片。与横向鳞片接近电子惯性规模,Alfvenic电流振幅出现减毒后续的形成腔。不变的粒子在运输时间(静态)与当前的一对识别和观察驱动向极吗边界强化(PBI)中确定同步卫星远紫外线图像测量。通过等离子体的局部增厚表注入新的磁性层的等离子体,这可能重新连接丛发性的结果,不完整的的过程。PBI的速度和厚度是一致的电离层映射腔同行,这表明运动和厚度是由等离子体和控制以上电动功能高度通过集群抽样。和“当前区域并行势向下与最新的温度这表明电子注入电子温度是一个重要的控制因素。观测表明,这些小说准静态系统field-aligned电流形式的高度动态Alfvenic地区等离子体片边界层,也许可以表明Alfvenic区域准静态初始阶段发展系统。电流是定性相似瞬态响应模型的预期然而,magnetospheric-ionospheric耦合这种模式将需要修改电子衰减的惯性电流/阿尔芬波。

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