skip to main content

Title: Walén test and de Hoffmann-Teller frame of interplanetary large-amplitude Alfvén waves

In this study, three methods of analysis are compared to test the Walén relation. Method 1 requires a good de Hoffmann-Teller (HT) frame. Method 2 uses three components separately to find the frame that is slightly modified from Method 1. This method is intended to improve the accuracy of the HT frame and able to demonstrate the anisotropic property of the fluctuations. The better the relation is, the closer the slope of a regression fitting the data of plasma versus Alfvén velocities is to 1. However, this criterion is based on an average HT frame, and the fitted slope does not always work for the Walén test because the HT frame can change so fast in the high-speed streams. We propose Method 3 to check the Walén relation using a sequence of data generated by taking the difference of two consecutive values of plasma and Alfvén velocities, respectively. The difference data are independent of the HT frame. We suggest that the ratio of the variances between plasma and Alfvén velocities is a better parameter to qualify the Walén relation. Four cases in two solar wind streams are studied using these three methods. Our results show that when the solar windmore » HT frame remains stable, all three methods can predict Alfvénic fluctuations well, but Method 3 can better predict the Walén relation when solar wind contains structures with several small streams. A simulated case also demonstrates that Method 3 is better and more robust than Methods 1 and 2. These results are important for a better understanding of Alfvénic fluctuations and turbulence in the solar wind.« less
Authors:
; ;  [1] ;  [2]
  1. Institute of Space Science, National Central University, Jhongli 320, Taiwan (China)
  2. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
Publication Date:
OSTI Identifier:
22356904
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 786; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; ALFVEN WAVES; AMPLITUDES; ANISOTROPY; COMPARATIVE EVALUATIONS; FLUCTUATIONS; MAGNETOHYDRODYNAMICS; PLASMA; SIMULATION; SOLAR WIND; STREAMS; TURBULENCE