太古代地球附近的Cosmic Ray强度
The Cosmic Ray Intensity Near the Archean Earth
摘要：
我们采用三维最先进的磁流体动力学模型的早期太阳风和日光层和宇宙线输运的二维模型来研究太古代地球附近的宇宙线谱和通量。我们评估了宇宙射线谱对太阳黑子位置和磁场强度、大尺度偶极磁场强度、风冲压压力和太阳自转周期的变化有多敏感。总的来说，我们的结果证实了早期的工作，即太古代地球将经历比今天大大减少的宇宙射线通量。早期太阳的宇宙线减少主要是由于太阳自转周期较短，帕克螺线缠绕较紧，以及太阳表面磁场分布较活跃。这些效应导致1AU处的宇宙线通量减少了两个数量级或更多。太阳黑子磁场的变化比偶极场分量的变化对通量的影响更大。风冲压压力通过与周围星际介质的压力平衡影响日光层的大小，从而影响宇宙线通量。太阳系在穿过银河系的轨道上所经历的星际介质压力的变化可能导致地球上宇宙射线通量在几百万年的时间尺度上发生数量级的变化。
英文摘要：
We employ three-dimensional state of the art magnetohydrodynamic models of the early solar wind and heliosphere and a two-dimensional model for cosmic ray transport to investigate the cosmic ray spectrum and flux near the Archean Earth. We assess how sensitive the cosmic ray spectrum is to changes in the sunspot placement and magnetic field strength, the large scale dipole magnetic field strength, the wind ram pressure, and the Sun's rotation period. Overall, our results confirm earlier work that suggested the Archean Earth would have experienced a greatly reduced cosmic ray flux than is the case today. The cosmic ray reduction for the early Sun is mainly due to the shorter solar rotation period and tighter winding of the Parker spiral, and to the different surface distribution of the more active solar magnetic field. These effects lead to a global reduction of the cosmic ray flux at 1AU by up to two orders of magnitude or more. Variations in the sunspot magnetic field have more effect on the flux than variations in the dipole field component. The wind ram pressure affects the cosmic ray flux through its influence on the size of the heliosphere via the pressure balance with the ambient interstellar medium. Variations in the interstellar medium pressure experienced by the solar system in orbit through Galaxy could lead to order of magnitude changes in the cosmic ray flux at Earth on timescales of a few million years.
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