FOUR-DIMENSIONAL TRANSPORT OF GALACTIC COSMIC RAYS IN THE OUTER HELIOSPHERE AND HELIOSHEATH
FOUR-DIMENSIONAL TRANSPORT OF GALACTIC COSMIC RAYS IN THE OUTER HELIOSPHERE AND HELIOSHEATH
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DOI：
10.1088/0004-637x/701/1/642
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发表时间：
2009-08
期刊：
影响因子：
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通讯作者：
V. Florinski;N. Pogorelov
中科院分区：
文献类型：
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作者：
V. Florinski;N. Pogorelov
2008 年标志着日光层内层太阳黑子周期 24 的开始。航海者号在 2008 年测量到的银河系氢和氦的强度是有记录以来的最高值，据信已经接近星际值。我们通过在稳定等离子体背景条件下跟踪帕克方程的随机相空间轨迹，研究银河宇宙线（GCR）质子在三维不对称日光层（包括内部日鞘区域）中的传输。后者是根据全球日光层的三维 MHD 模型计算得出的，该模型考虑了中性氢原子的影响。该模型适用于适合 2008-2009 年太阳极小值的安静太阳风 (SW) 条件。模型导出的宇宙射线光谱和径向梯度在航海者号日鞘观测的背景下进行了回顾。结果表明，日鞘是低能离子的重要调制势垒。日鞘中的径向宇宙射线梯度预计在航行者号方向上较小（180 MeV 时每 AU 1.5%–1.8%）。在我们的模型中，终止激波并不能非常有效地加速 GCR 离子，并且它们在日鞘中的强度永远不会超过星际值。对日光层不同部分的宇宙射线停留时间的分析表明，在被探测到之前，离子穿过日鞘和日尾的时间比它们在超音速短波中的时间长 3-6 倍。
2008 marked the beginning of sunspot cycle 24 in the inner heliosphere. Intensities of galactic hydrogen and helium measured by the Voyagers in 2008 were the highest ever recorded and believed to be approaching the interstellar values. We investigate transport of galactic cosmic ray (GCR) protons in the three-dimensional, asymmetric heliosphere, including the inner heliosheath region, by tracking stochastic phase-space trajectories of Parker equation under steady plasma background conditions. The latter is calculated from a three-dimensional MHD model of the global heliosphere that takes into account the effect of neutral hydrogen atoms. The model is applied to quiet solar wind (SW) conditions appropriate for the 2008–2009 solar minimum. Model-derived cosmic-ray spectra and radial gradients are reviewed in the context of Voyager observations in the heliosheath. It is shown that the heliosheath is an important modulation barrier for lower energy ions. Radial cosmic-ray gradients in the heliosheath are expected to be small in the directions of the Voyagers (1.5%–1.8% per AU at 180 MeV). In our model the termination shock does not accelerate GCR ions very efficiently, and their intensities in the heliosheath never exceed interstellar values. Analysis of cosmic-ray residence times in different parts in the heliosphere shows that, prior to their detection, ions spend 3–6 times longer transiting the heliosheath and the heliotail than they spend in the supersonic SW.