RADIAL EVOLUTION OF THE WAVEVECTOR ANISOTROPY OF SOLAR WIND TURBULENCE BETWEEN 0.3 AND 1 AU
- Department of Geophysics, Peking University, Beijing 100871 (China)
- Institute for Experimental and Applied Physics, Christian Albrechts University at Kiel, D-24118 Kiel (Germany)
- Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States)
We present observations of the power spectral anisotropy in the wavevector space of solar wind turbulence and study how it evolves in interplanetary space with increasing heliocentric distance. We use magnetic field measurements from the Helios 2 spacecraft within 1 AU. To derive the power spectral density (PSD) in the (k{sub Parallel-To }, k ) space based on single-satellite measurements is a challenging task that had not been accomplished previously. Here, we derive the spectrum PSD{sub 2D}(k{sub Parallel-To }, k{sub Up-Tack }) from the spatial correlation function CF{sub 2D}(r{sub Parallel-To }, r ) by a transformation according to the projection-slice theorem. We find the so-constructed PSDs to be distributed in k space mainly along a ridge that is more inclined toward the k{sub Up-Tack} axis than the k{sub Parallel-To} axis. Furthermore, this ridge of the distribution is found to gradually get closer to the k{sub Up-Tack} axis as the outer scale length of the turbulence becomes larger with increasing radial distance. In the vicinity of the k{sub Parallel-To} axis, a minor spectral component appears that probably corresponds to quasi-parallel Alfvenic fluctuations. Their relative contribution to the total spectral density tends to decrease with radial distance. These findings suggest that solar wind turbulence undergoes an anisotropic cascade transporting most of its magnetic energy toward larger k{sub Up-Tack} and that the anisotropy in the inertial range is radially developing further at scales that are relatively far from the ever increasing outer scale. For the ion-scale fluctuations, we speculate, from the radial evolution of the extended oblique major component, a transition tendency from dominance by oblique Alfven/ion-cyclotron waves (<1 AU) to dominance by kinetic Alfven waves (>1 AU)
- OSTI ID:
- 22131047
- Journal Information:
- Astrophysical Journal, Vol. 773, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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