We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
Possible Noise Nature of Elsässer Variable <bold>z</bold><sup>−</sup> in Highly Alfvénic Solar Wind Fluctuations.
- Authors
Wang, X.; Tu, C.‐Y.; He, J.‐S.; Wang, L.‐H.; Yao, S.; Zhang, L.
- Abstract
Abstract: It has been a long‐standing debate on the nature of Elsässer variable <bold>z</bold>− observed in the solar wind fluctuations. It is widely believed that <bold>z</bold>− represents inward propagating Alfvén waves and interacts nonlinearly with <bold>z</bold>+ (outward propagating Alfvén waves) to generate energy cascade. However, <bold>z</bold>− variations sometimes show a feature of convective structures. Here we present a new data analysis on autocorrelation functions of <bold>z</bold>− in order to get some definite information on its nature. We find that there is usually a large drop on the <bold>z</bold>− 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 <italic>τ</italic> = 81 s, where the value of the autocorrelation coefficient drops to 25%–65% of that at <italic>τ</italic> = 0 s. Beyond the first nonzero time lag, the autocorrelation coefficient decreases gradually to zero. The drop of <bold>z</bold>− correlation function also appears in the Wind observations near 1 AU. These features of the <bold>z</bold>− correlation function may suggest that <bold>z</bold>− fluctuations consist of two components: high‐frequency white noise and low‐frequency pseudo structures, which correspond to flat and steep parts of <bold>z</bold>− 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, <bold>z</bold>− may not contribute importantly to the interactions with <bold>z</bold>+ to produce energy cascade.
- Publication
Journal of Geophysical Research. Space Physics, 2018, Vol 123, Issue 1, p57
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1002/2017JA024743