Abstract
Abstract. Recent developments of multi-point measurements in space provide a means to analyze spacecraft data directly in the wave vector domain. For turbulence study this means that we are able to estimate energy, helicity, and higher order moments in the wave vector domain without assuming Taylor's hypothesis or axisymmetry around the mean magnetic field. The methods of the wave vector analysis are presented and applied to four-point data of Cluster in the solar wind.
Highlights
Waves and turbulence observed in the interplanetary space and the Earth’s magnetosphere are one of the most interesting subjects in space physics, as plasmas allow various kinds of linear wave modes as excitation states to exist and various kinds of nonlinear waves and turbulent states (Biskamp, 2003)
Earlier spacecraft observations in 1960s revealed that magnetic field fluctuations in the solar wind are reminiscent of turbulence, as their frequency spectra often exhibited a power-law spectrum characterized by the spectral index −5/3, the index known as Kolmogorov’s inertial-range spectrum for hydrodynamic turbulence
Earlier in-situ observations of space plasma turbulence were primarily limited to analyzing time series data based on single-spacecraft measurements, and the properties of the fluctuating magnetic field and flow velocity were determined in the temporal or frequency domain
Summary
Waves and turbulence observed in the interplanetary space and the Earth’s magnetosphere are one of the most interesting subjects in space physics, as plasmas allow various kinds of linear wave modes as excitation states to exist (that are well documented by, e.g., Stix, 1992 and Gary, 1993) and various kinds of nonlinear waves and turbulent states (Biskamp, 2003). Investigation of spatial properties of the fluctuating fields relied on Taylor’s frozen-in flow hypothesis that neglects wave frequencies in the flow-rest frame when a fluctuating field is sampled in a fast-streaming medium (Taylor, 1938) This hypothesis relates the observed frequency with the wave number in the flow direction using the Doppler shift, ω k · V , where ω is the spacecraft-frame frequency, and k and V are the wave vector and the flow velocity vector, respectively. The wave telescope technique performs a parametric projection of the measured fluctuations into the wave vector domain and does not require any knowledge on dispersion relations nor Taylor’s hypothesis Using this technique and its extended methods, the distributions of energy and helicity can be determined in the frequency-wave vector domain. The eigenvector analysis is another approach in wave analysis and provides methods to determine dispersion relations and highresolution wave number spectra
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call