Signatures of the interplanetary helium cone reflected by pick-up ions
Signatures of the interplanetary helium cone reflected by pick-up ions
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DOI：
10.1023/a:1005176229228
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发表时间：
1999-06-01
期刊：
影响因子：
2.8
通讯作者：
Fahr, HJ
中科院分区：
文献类型：
--
作者：
Chalov, SV;Fahr, HJ
长期以来，星际风中性氦原子深深地渗透到内日球层，当穿过太阳重力场时，在顺风方向形成强烈明显的氦密度锥。氦原子被光电离并被太阳风磁场拾取，但作为拾取离子，它们并不像早期出版物中假设的那样简单地随太阳风径向向外对流。相反，他们经历了一个复杂的扩散-对流过程，这里描述了一个适当的动力学传输方程，考虑到绝热冷却和聚焦，俯仰角散射和能量扩散。在本文中，我们解决了这个方程的He+拾取离子注入到太阳风主要是在该地区的氦锥。我们表明，所得到的He+拾取离子密度分布沿着地球轨道在许多方面不同于中性氦锥的密度分布：根据太阳风携带的阿尔芬湍流水平，从地球到太阳看时的密度最大值向锥体的右侧移动，峰密度与翼密度的比率变化，并且He+密度分布的左右不对称是显著的。从这些He+结构中推导星际氦参数，如局部星际介质（LISM）风向，LISM速度和LISM温度，是非常困难的。此外，当从锥结构的左翼到右翼通过时，He+拾取离子的俯仰角谱系统地变得更加各向异性。与低速太阳风相比，高速太阳风中提到的所有效应都更加明显。
As known for a long time, interstellar wind neutral helium atoms deeply penetrate into the inner heliosphere and, when passing through the solar gravity field, form a strongly pronounced helium density cone in the downwind direction. Helium atoms are photoionized and picked-up by the solar wind magnetic field, but as pick-up ions they are not simply convected outwards with the solar wind in radial directions as assumed in earlier publications. Rather they undergo a complicated diffusion-convection process described here by an appropriate kinetic transport equation taking into account adiabatic cooling and focusing, pitch angle scattering and energy diffusion. In this paper, we solve this equation for He+ pick-up ions which are injected into the solar wind mainly in the region of the helium cone. We show the resulting He+ pick-up ion density profile along the orbit of the Earth in many respects differs from the density profile of the neutral helium cone: depending on solar-wind-entrained Alfvenic turbulence levels, the density maximum when looking from the Earth to the Sun is shifted towards the right side of the cone, the ratio of peak-densities to wing-densities varies and a left-to-right asymmetry of the He+-density profile is pronounced. Derivation of interstellar helium parameters from these He+-structures, such as the local interstellar medium (LISM) wind direction, LISM velocity and LISM temperature, are very much impeded. In addition, the pitch-angle spectrum of He+ pick-up ions systematically becomes more anisotropic when passing from the left to the right wing of the cone structure. All effects mentioned are more strongly pronounced in high velocity solar wind compared to the low velocity solar wind.