Statistical survey of pitch angle distributions in core (0-50 eV) ions from Dynamics Explorer 1: Outflow in the auroral zone, polar cap, and cusp
Statistical survey of pitch angle distributions in core (0-50 eV) ions from Dynamics Explorer 1: Outflow in the auroral zone, polar cap, and cusp
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Dynamics Explorer 1 中核心 (0-50 eV) 离子螺距角分布的统计调查：极光区、极冠和尖点的流出
DOI：
10.1029/94ja00864
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发表时间：
1994
影响因子：
--
通讯作者：
J. Waite
中科院分区：
文献类型：
--
作者：
B. Giles;C. Chappell;T. Moore;R. H. Comfort;J. Waite
针对离子 H+、He+、O+、M/Z=2（D+ 或 He++）和 O++，检查 Dynamics Explorer 1 上的延迟离子质谱仪的核心 (0-50 eV) 离子俯仰角测量值的磁扰动、不变纬度、磁本地时间和高度。包括极光区、极冠和尖峰的流出事件，分为低于和高于 3 RE 的海拔区域。除了通常分为束流分布、圆锥分布和上升流分布之外，高纬度观测还分为与离子体速度相对应的三类，即（1）小于、（2）相当于或（3）高于航天器的速度。这种分离与高度划分一起用于确定电离层源离子受重力束缚的条件以及它们何时更具能量并能够逃逸到外磁层。从单事件研究推断出的裂隙离子喷泉的特征在统计结果中清晰可见。此外，人们发现，无论物种或活动水平如何，白天午前裂隙都是逃逸速度低能离子的一致来源，而白天下午裂隙或极光区则成为增加活动的额外来源。极光椭圆形作为一个整体似乎是逃逸速度 H+ 的稳定源、黄昏区域逃逸速度 He+ 离子的稳定源、以及主要在活动增加期间黄昏局部时间的逃逸速度重离子源。极光带上方的极冠是低能离子的持续来源，尽管平均而言，只有质量较轻的粒子似乎具有足够的速度逃逸到更高的高度。观测结果支持两个流出概念：（1）裂隙离子喷泉由向上流入磁气层的 1-20 eV 能量的电离层等离子体组成，其中高纬度对流电场导致向极的色散。 (2) 极光离子喷泉涉及沿极光纬度场线流出的场对准光束；此外，在当地时间下午晚些时候，它们会经历额外的加速，使得离子能量分布往往超出仪器的检测范围（> 50-60 eV）。
Core (0-50 eV) ion pitch angle measurements from the retarding ion mass spectrometer on Dynamics Explorer 1 are examined with respect to magnetic disturbance, invariant latitude, magnetic local time, and altitude for ions H+, He+, O+, M/Z=2 (D+ or He++), and O++. Included are outflow events in the auroral zone, polar cap, and cusp, separated into altitude regions below and above 3 RE. In addition to the customary division into beam, conic, and upwelling distributions, the high-latitude observations fall into three categories corresponding to ion bulk speeds that are (1) less than, (2) comparable to, or (3) faster than that of the spacecraft. This separation, along with the altitude partition, serves to identify conditions under which ionospheric source ions are gravitationally bound and when they are more energetic and able to escape to the outer magnetosphere. Features of the cleft ion fountain inferred from single event studies are clearly identifiable in the statistical results. In addition, it is found that the dayside pre-noon cleft is a consistent source of escape velocity low-energy ions regardless of species or activity level and the dayside afternoon cleft, or auroral zone, becomes an additional source for increased activity. The auroral oval as a whole appears to be a steady source of escape velocity H+, a steady source of escape velocity He+ ions for the dusk sector, and a source of escape velocity heavy ions for dusk local times primarily during increased activity. The polar cap above the auroral zone is a consistent source of low-energy ions, although only the lighter mass particles appear to have sufficient velocity, on average, to escape to higher altitudes. The observations support two concepts for outflow: (1) The cleft ion fountain consists of ionospheric plasma of 1-20 eV energy streaming upward into the magnetosphere where high-latitude convection electric fields cause poleward dispersion. (2) The auroral ion fountain involves field-aligned beams which flow out along auroral latitude field lines; and, in addition, for late afternoon local times, they experience additional acceleration such that the ion energy distribution tends to exceed the detection range of the instrument (>50-60 eV).