A new source of suprathermal O(+) ions near the dayside polar cap boundary
A new source of suprathermal O(+) ions near the dayside polar cap boundary
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DOI：
10.1029/ja090ia05p04099
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发表时间：
1985-05
影响因子：
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通讯作者：
M. Lockwood;J. Waite;T. Moore;J. E. Johnson;C. Chappell
中科院分区：
文献类型：
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作者：
M. Lockwood;J. Waite;T. Moore;J. E. Johnson;C. Chappell
本文描述了极区磁层的一个新的昼侧O ~+离子源，并利用DE-1上的减速离子质谱仪（RIMS）实验在地心距离小于3RE，不变纬度大于40°的条件下，对2年的O ~+离子向上流动进行了统计调查。根据其自旋角分布对流动进行分类。据信，近地点附近的航天器电位通常小于+2 V，在这种情况下，对能量低于约60 eV的整个O+种群进行采样。例子给出了场向流和横向加速的“核心”O+离子;在后者的事件中，总O+离子人口的一大部分已被横向加速，在一些极端情况下，所有观察到的离子（所有离子物种）已被加速，并没有剩余的冷人口观察（“环形”分布）。然而，到目前为止，DE RIMS看到的最常见的O+上升流类型位于向阳面极盖边界附近（特别是在午前部分），并显示出不对称的自旋角分布。在这些事件中，离子携带向上的热通量，并且存在所有物质的强烈向上流动（H+、He+、O+、O++和N+都被观察到具有高达约30 eV的能量，但是大多数离子低于约2 eV）;因此，这些被称为上涌离子事件。上涌离子嵌入在较大的区域的经典轻离子极风，并持续发现在以下条件下：在地心距离大于1.4 RE，在所有的KP在夏季，但只有在高KP在冬季。低能锥形离子（<30 eV）仅在事件的赤道边缘附近发现，其纬度随着Kp的增加而向赤道移动，并且与场向电流的位置高度相关。RIMS的数据与“质谱仪效应”完全一致，即轻离子和更高能量的O+离子流入叶和地幔，因此形成了远尾等离子体片，但较低能量的O+被对流电场扫过极冠，可能成为夜侧极光加速区的来源。上升流离子事件的发生概率相比，低空横向加速的核心离子和场向流，这可能是供应夜侧极光加速区，随后的环电流和近地等离子体片，电离层O+离子的主导机制。结果表明，在上升流离子事件（大于1025 s-1）的总O+流出率是足够的向阳面极冠边界附近的区域是一个重要的电离层重离子源。
A new dayside source of O+ ions for the polar magnetosphere is described, and a statistical survey presented of upward flows of O+ ions using 2 years of data from the retarding ion mass spectrometer (RIMS) experiment on board DE 1, at geocentric distances below 3 RE and invariant latitudes above 40°. The flows are classified according to their spin angle distributions. It is believed that the spacecraft potential near perigee is generally less than +2 V, in which case the entire O+ population at energies below about 60 eV is sampled. Examples are given of field-aligned flow and of transversely accelerated “core” O+ ions; in the latter events a large fraction of the total O+ ion population has been transversely accelerated, and in some extreme cases all the observed ions (of all ion species) have been accelerated, and no residual cold population is observed (“toroidal” distributions). However, by far the most common type of O+ upflow seen by DE RIMS lies near the dayside polar cap boundary (particularly in the prenoon sector) and displays an asymmetric spin angle distribution. In such events the ions carry an upward heat flux, and strong upflow of all species is present (H+, He+, O+, O++, and N+ have all been observed with energies up to about 30 eV, but with the majority of ions below about 2 eV); hence, these have been termed upwelling ion events. The upwelling ions are embedded in larger regions of classical light ion polar wind and are persistently found under the following conditions: at geocentric distances greater than 1.4 RE; at all Kp in summer, but only at high Kp in winter. Low-energy conical ions (<30 eV) are only found near the equatorial edge of the events, the latitude of which moves equatorward with increasing Kp and is highly correlated with the location of field-aligned currents. The RIMS data are fully consistent with a “mass spectrometer effect,” whereby light ions and the more energetic O+ ions flow into the lobes and mantle and hence the far-tail plasma sheet, but lower-energy O+ is swept across the polar cap by the convection electric field, potentially acting as a source for the nightside auroral acceleration regions. The occurrence probability of upwelling ion events, as compared to those of low-altitude transversely accelerated core ions and of field-aligned flow, suggests this could be the dominant mechanism for supplying the nightside auroral acceleration region, and subsequently the ring current and near-earth plasma sheet, with ionospheric O+ ions. It is shown that the total rate of O+ outflow in upwelling ion events (greater than 1025 s−1) is sufficient for the region near the dayside polar cap boundary to be an important ionospheric heavy ion source.