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题名: Possible Noise Nature of Elsasser Variable z(-) in Highly Alfvenic Solar Wind Fluctuations
作者: Wang, X.; Tu, C. -Y.; He, J. -S.; Wang, L. -H.; Yao, S.; Zhang, L.
作者部门: 空间科学部
通讯作者: Tu, CY (reprint author), Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China.
刊名: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
ISSN号: 2169-9380
出版日期: 2018
卷号: 123, 期号:1, 页码:57-67
收录类别: SCI
项目资助者: National Natural Science Foundation of China [41504130, 41474147, 41674171, 41231069] ; Young Elite Scientists Sponsorship Program by China Association for Science and Technology [2016QNRC001]
英文摘要: It has been a long-standing debate on the nature of Elsasser variable z(-) observed in the solar wind fluctuations. It is widely believed that z(-) represents inward propagating Alfven waves and interacts nonlinearly with z(+) (outward propagating Alfven waves) to generate energy cascade. However, z(-) variations sometimes show a feature of convective structures. Here we present a new data analysis on autocorrelation functions of z(-) in order to get some definite information on its nature. We find that there is usually a large drop on the z(-) autocorrelation function when the solar wind fluctuations are highly Alfvenic. The large drop observed by Helios 2 spacecraft near 0.3AU appears at the first nonzero time lag r = 81s, where the value of the autocorrelation coefficient drops to 25%-65% of that at r = 0s. Beyond the first nonzero time lag, the autocorrelation coefficient decreases gradually to zero. The drop of z(-) correlation function also appears in the Wind observations near 1AU. These features of the z(-) correlation function may suggest that z(-) fluctuations consist of two components: high-frequency white noise and low-frequency pseudo structures, which correspond to flat and steep parts of z(-) power spectrum, respectively. This explanation is confirmed by doing a simple test on an artificial time series, which is obtained from the superposition of a random data series on its smoothed sequence. Our results suggest that in highly Alfvenic fluctuations, z(-) may not contribute importantly to the interactions with z(+) to produce energy cascade.
语种: 英语
内容类型: 期刊论文
URI标识: http://ir.nssc.ac.cn/handle/122/6204
Appears in Collections:空间科学部_期刊论文

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