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题名: Influence of the Solar Cycle on Turbulence Properties and Cosmic-Ray Diffusion
作者: Zhao, L. -L.; Adhikari, L.; Zank, G. P.; Hu, Q.; Feng, X. S.
作者部门: 空间科学部
通讯作者: Zhao, L. -L. ; Adhikari, L. ; Zank, G. P. ; Hu, Q. ; Feng, X. S.
关键词: cosmic rays ; solar wind ; Sun: activity ; turbulence
刊名: ASTROPHYSICAL JOURNAL
ISSN号: 0004-637X
出版日期: 2018
卷号: 856, 期号:2, 页码:94
收录类别: SCI
项目资助者: National Science Foundation of China [41504133, 41531073, 41304137] ; China Scholarship Council ; NASA [NNX08AJ33G, 37102-2, NNX14AC08G, NNX14AJ53G, A99132BT, RR185-447/4944336, NNX12AB30G, NNX17AB85G] ; International Space Science Institute (ISSI) ; Johannes Geiss Fellowship ; framework of an International Team Project 504 entitled "Current Sheets, Turbulence, Structures and Particle Acceleration in the Heliosphere" ; SAO subcontract [SV4-84017] ; NSF EPSCOR RII-Track-1 Cooperative Agreement [OIA-1655280]
英文摘要: The solar cycle dependence of various turbulence quantities and cosmic-ray (CR) diffusion coefficients is investigated by using OMNI 1 minute resolution data over 22 years. We employ Elsasser variables z(+/-) to calculate the magnetic field turbulence energy and correlation lengths for both the inwardly and outwardly directed interplanetary magnetic field (IMF). We present the temporal evolution of both large-scale solar wind (SW) plasma variables and small-scale magnetic fluctuations. Based on these observed quantities, we study the influence of solar activity on CR parallel and perpendicular diffusion using quasi-linear theory and nonlinear guiding center theory, respectively. We also evaluate the radial evolution of the CR diffusion coefficients by using the boundary conditions for different solar activity levels. We find that in the ecliptic plane at 1 au (1), the large-scale SW temperature T, velocity V-sw, Alfven speed V-A, and IMF magnitude B-0 are positively related to solar activity; (2) the fluctuating magnetic energy density < z(+/- 2)>, residual energy E-D, and corresponding correlation functions all have an obvious solar cycle dependence. The residual energy E-D is always negative, which indicates that the energy in magnetic fluctuations is larger than the energy in kinetic fluctuations, especially at solar maximum; (3) the correlation length lambda for magnetic fluctuations does not show significant solar cycle variation; (4) the temporally varying shear source of turbulence, which is most important in the inner heliosphere, depends on the solar cycle; (5) small-scale fluctuations may not depend on the direction of the background magnetic field; and (6) high levels of SW fluctuations will increase CR perpendicular diffusion and decrease CR parallel diffusion, but this trend can be masked if the background IMF changes in concert with turbulence in response to solar activity. These results provide quantitative inputs for both turbulence transport models and CR diffusion models, and also provide valuable insight into the long-term modulation of CRs in the heliosphere.
语种: 英语
内容类型: 期刊论文
URI标识: http://ir.nssc.ac.cn/handle/122/6241
Appears in Collections:空间科学部_期刊论文

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