A Numerical Study of the Solar Modulation of Galactic Protons and Helium from 2006 to 2017
A Numerical Study of the Solar Modulation of Galactic Protons and Helium from 2006 to 2017
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2006年至2017年银河质子和氦太阳调制的数值研究
DOI：
10.3847/1538-4365/ac281c
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发表时间：
2021-12-01
影响因子：
8.7
通讯作者：
Geng, Zekun
中科院分区：
文献类型：
--
作者：
Song, Xiaojian;Luo, Xi;Geng, Zekun
通过AMS-02和PAMELA等星载宇宙射线探测器的连续测量，已经可以获得11年太阳周期内银河宇宙射线的精确光谱。在这项研究中，我们利用2006年至2017年这些任务中低于10 GV的质子和氦光谱构建了一个宇宙射线传输模型，用于定量研究太阳调制过程。这个数值模式是基于帕克的传输方程，其中包括四个主要的传输过程。利用马尔可夫链蒙特卡罗方法，通过再现和拟合所述观测光谱来搜索与漂移和扩散系数相关的相关参数空间。得到的最佳拟合归一化χ 2主要小于1。结果表明：（1）在再现这些观测时，漂移系数和扩散系数所需的参数具有明显的时间依赖性，扩散系数的大小与太阳活动密切相关;（2）所得平均自由程的刚度依赖性随时间变化，在低刚度时，它们的刚度依赖性甚至比在高刚度时有更大的斜率;（3）对每对观测的质子和氦能谱使用一组调制参数，大部分能谱在观测不确定度范围内重现;（4）模拟的质子-氦通量比与观测值在长期时间依赖性方面一致，但也存在一些差异，这种差异主要来自于对质子通量的低估。
With continuous measurements from space-borne cosmic-ray detectors such as AMS-02 and PAMELA, precise spectra of galactic cosmic rays over the 11 yr solar cycle have become available. For this study, we utilize proton and helium spectra below 10 GV from these missions from 2006 to 2017 to construct a cosmic-ray transport model for a quantitative study of the processes of solar modulation. This numerical model is based on Parker’s transport equation, which includes four major transport processes. The Markov Chain Monte Carlo method is utilized to search the relevant parameter space related to the drift and the diffusion coefficients by reproducing and fitting the mentioned observed spectra. The resulting best-fit normalized χ 2 is mainly less than 1. It is found that (1) when reproducing these observations the parameters required for the drift and diffusion coefficients exhibit a clear time dependence, with the magnitude of the diffusion coefficients anticorrelated with solar activity; (2) the rigidity dependence of the resulting mean free paths varies with time, and their rigidity dependence at lower rigidity can even have a larger slope than at higher rigidity; (3) using a single set of modulation parameters for each pair of observed proton and helium spectra, most spectra are reproduced within observational uncertainty; and (4) the simulated proton-to-helium flux ratio agrees with the observed values in terms of its long-term time dependence, although some discrepancy exists, and the difference is mostly coming from the underestimation of proton flux.