Multipoint analysis of compressive fluctuations in the fast and slow solar wind. Issue 7 (12th July 2017)

• Record Type: Journal Article
• Authors: Roberts, O. W.; Narita, Y.; Li, X.; Escoubet, C. P.; Laakso, H.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 7(2017)
• Page Start: 6940
• Page End: 6963
• Publication Date: 2017-07-12
• Subjects: turbulence -- waves -- solar wind; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023552
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Compressible turbulence in the solar wind is a topic of much recent debate. To understand the various compressive fluctuations at scales comparable to proton characteristic lengths, we use multipoint magnetic field and density data (derived from spacecraft potential which allows higher time resolution than is typically possible than with particle instruments) from the Cluster spacecraft when they were in undisturbed intervals of slow and fast solar wind. The application of the multipoint signal resonator technique is performed for the first time, to the analysis of scalar time series. Fluctuations in the measurements of electron density and in magnitude of the magnetic field (used as a proxy for compressible magnetic fluctuations) are used as inputs in addition to the traditional vector components of the magnetic field. This analysis is performed on two streams of solar wind, one which can be classed as a slow stream and one which can be classed as a fast stream to investigate the difference in the compressible components in the two types of wind. The recovered plasma frame frequencies for the incompressible component show low propagation speed in the plasma frame consistent with previous applications of the method, while the compressible components are more scattered, some with very high phase speeds. Based on these results, we propose a picture of compressive solar wind turbulence as a mixed state of (1) linear modes such as kinetic Alfvén, kinetic slow, and ion Bernstein modes; (2) coherent structures with very small intrinsic frequencies; and (3) nonlinear or sideband modes. Key Points: Turbulence in the solar wind is analyzed with multipoint measurements Incompressible turbulence is found to be dominated by kinetic Alfvén waves/advected structures Compressible turbulence appears to be a complex mix of different fluctuation types