Dispersion relation analysis of turbulent magnetic field fluctuations in fast solar wind
- 1Institut für Theoretische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
- 2Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
- 3Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
- 4Space Science Institute, Boulder, Colorado 80301, USA
- 5Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, Rutherfordstr. 2, 12489 Berlin, Germany
- 6Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
Abstract. Physical processes of the energy transport in solar wind turbulence are a subject of intense studies, and different ideas exist to explain them. This manuscript describes the investigation of dispersion properties in short-wavelength magnetic turbulence during a rare high-speed solar wind event with a flow velocity of about 700 km s−1 using magnetic field and ion data from the Cluster spacecraft. Using the multi-point resonator technique, the dispersion relations (i.e., frequency versus wave-number values in the solar wind frame) of turbulent magnetic fluctuations with wave numbers near the inverse ion inertial length are determined. Three major results are shown: (1) the wave vectors are uniformly quasi-perpendicular to the mean magnetic field; (2) the fluctuations show a broad range of frequencies at wavelengths around the ion inertial length; and (3) the direction of propagation at the observed wavelengths is predominantly in the sunward direction. These results suggest the existence of high-frequency dispersion relations partly associated with normal modes on small scales. Therefore nonlinear energy cascade processes seem to be acting that are not described by wave–wave interactions.