Estimating the capture and loss of cold plasma from ionospheric outflow
Estimating the capture and loss of cold plasma from ionospheric outflow
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DOI：
10.1029/2012ja017679
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发表时间：
2012-07
影响因子：
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通讯作者：
S. Haaland;A. Eriksson;E. Engwall;B. Lybekk;H. Nilsson;A. Pedersen;K. Svenes;M. André;M. Förster;Kun Li;C. Johnsen;N. Østgaard
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文献类型：
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作者：
S. Haaland;A. Eriksson;E. Engwall;B. Lybekk;H. Nilsson;A. Pedersen;K. Svenes;M. André;M. Förster;Kun Li;C. Johnsen;N. Østgaard
磁层等离子体的一个重要来源是来自地球电离层的冷等离子体。低能量离子沿着磁场线行进并进入磁层叶，在那里它们被对流朝向尾部等离子体片。最近的观测表明，场向离子流出速度有时远高于对流对中心等离子体片。因此，大量的等离子体从尾部逃逸，而从未到达中心等离子体片。在这项工作中，我们使用集群测量的冷等离子体流出和叶对流速度结合模型的磁场，试图确定的命运流出的离子和量化的等离子体损失的量downtail。结果表明，等离子体的环流和离子的直接尾部逃逸都随磁层条件的变化而显著变化。对于具有向南行星际磁场的强太阳风驱动，也通常与高地磁活动相关，大部分流出的等离子体对流到等离子体片并再循环。在行星际磁场向北的时期，对流几乎停滞，而外流虽然有限，但仍然存在。在这种情况下，外流离子的主要部分会向下游逃逸，并直接消失在太阳风中。
An important source of magnetospheric plasma is cold plasma from the terrestrial ionosphere. Low energy ions travel along the magnetic field lines and enter the magnetospheric lobes where they are convected toward the tail plasma sheet. Recent observations indicate that the field aligned ion outflow velocity is sometimes much higher than the convection toward the central plasma sheet. A substantial amount of plasma therefore escapes downtail without ever reaching the central plasma sheet. In this work, we use Cluster measurements of cold plasma outflow and lobe convection velocities combined with models of the magnetic field in an attempt to determine the fate of the outflowing ions and to quantify the amount of plasma lost downtail. The results show that both the circulation of plasma and the direct tailward escape of ions varies significantly with magnetospheric conditions. For strong solar wind driving with a southward interplanetary magnetic field, also typically associated with high geomagnetic activity, most of the outflowing plasma is convected to the plasma sheet and recirculated. For periods with northward interplanetary magnetic field, the convection is nearly stagnant, whereas the outflow, although limited, still persists. The dominant part of the outflowing ions escape downtail and are directly lost into the solar wind under such conditions.