DOI: 10.1002/2017JA024743
Scopus记录号: 2-s2.0-85040710349
论文题名: Possible Noise Nature of Elsässer Variable z− in Highly Alfvénic Solar Wind Fluctuations
作者: Wang X. ; Tu C.-Y. ; He J.-S. ; Wang L.-H. ; Yao S. ; Zhang L.
刊名: Journal of Geophysical Research: Space Physics
ISSN: 21699380
出版年: 2018
卷: 123, 期: 1 起始页码: 57
结束页码: 67
语种: 英语
英文关键词: magnetic field
; plasma
; solar wind
英文摘要: It has been a long-standing debate on the nature of Elsässer variable z− observed in the solar wind fluctuations. It is widely believed that z− represents inward propagating Alfvén waves and interacts nonlinearly with z+ (outward propagating Alfvén 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 Alfvénic. The large drop observed by Helios 2 spacecraft near 0.3 AU appears at the first nonzero time lag τ = 81 s, where the value of the autocorrelation coefficient drops to 25%–65% of that at τ = 0 s. 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 1 AU. 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 Alfvénic fluctuations, z− may not contribute importantly to the interactions with z+ to produce energy cascade. ©2018. American Geophysical Union. All Rights Reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/114851
Appears in Collections: 气候减缓与适应
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作者单位: School of Space and Environment, Beihang University, Beijing, China; School of Earth and Space Sciences, Peking University, Beijing, China; School of Geophysics and Information Technology, China University of Geosciences (Beijing), Beijing, China; SIGMA Weather Group, State Key Laboratory for Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
Recommended Citation:
Wang X.,Tu C.-Y.,He J.-S.,et al. Possible Noise Nature of Elsässer Variable z− in Highly Alfvénic Solar Wind Fluctuations[J]. Journal of Geophysical Research: Space Physics,2018-01-01,123(1)