Abstract
Abstract. A parametric model of the inertial-range energy spectrum is constructed for plasma turbulence in the four-dimensional wave vector and frequency domain. The model is based on that of the Eulerian wavenumber-frequency spectrum developed for describing fluid turbulence, and includes wave vector anisotropies in the three-dimensional wave vector domain by approximating the spectrum to a set of ellipses. The shape of the four-dimensional spectrum is determined by the Doppler shift, the Doppler broadening, and anisotropy coefficients. The model is applied to the magnetic energy spectrum in the near-Earth solar wind measured by four Cluster spacecraft, and the set of the spectral parameters are determined observationally. In this way, space–time structure of plasma turbulence can be condensed into a small number of parameters, which is suitable for evaluating the energy spectra in observational and numerical studies on the quantitative basis.
Highlights
Plasma turbulence appears in various astrophysical systems and plays an important role as an effective transport mechanism of mass, energy, and angular momentum
A parametric model of the inertial-range energy spectrum is constructed for plasma turbulence in the fourdimensional wave vector and frequency domain
The model energy spectrum is constructed in a simple fashion using analytic expression
Summary
Plasma turbulence appears in various astrophysical systems and plays an important role as an effective transport mechanism of mass, energy, and angular momentum. Recent studies using Cluster data support the picture of turbulent fluctuations associated with quasi-perpendicular wave vectors, and suggest axial asymmetry with respect to the directions around the large-scale magnetic field (Turner et al, 2011). In this manuscript, I propose a parametric method to characterize the four-dimensional (4-D) energy spectrum of plasma turbulence using a model spectrum and observational data from Cluster in the solar wind. The energy spectrum model proposed in this manuscript assumes that the hydrodynamic treatment of frequency dependence is valid in that the effect of finite wave propagation speed or dispersion relation is negligible
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