Magnetic Field Spectral Evolution in the Inner Heliosphere
Fedorov, A.; Horbury, T. S.; Louarn, P.; de Wit, Thierry Dudok; Velli, Marco; Woodham, L. D.; Bale, Stuart D.; Owen, Christopher J.; Stevens, Michael L.; Bonnell, J. W.; Sioulas, Nikos; Huang, Zesen; Shi, Chen; Vlahos, Loukas; Bowen, Trevor A.; Maksimović, Milan; Case, Anthony; Kasper, Justin; Larson, Davin; Pulupa, Marc; Livi, Roberto; Huang, Jia; MacDowall, Robert J.; Tenerani, Anna; Malaspina, David M.; Goetz, Keith; Harvey, Peter R.
United States, Greece, United Kingdom, France
Abstract
Parker Solar Probe and Solar Orbiter data are used to investigate the radial evolution of magnetic turbulence between 0.06 ≲ R ≲ 1 au. The spectrum is studied as a function of scale, normalized to the ion inertial scale d i . In the vicinity of the Sun, the inertial range is limited to a narrow range of scales and exhibits a power-law exponent of, α B = -3/2, independent of plasma parameters. The inertial range grows with distance, progressively extending to larger spatial scales, while steepening toward a α B = -5/3 scaling. It is observed that spectra for intervals with large magnetic energy excesses and low Alfvénic content steepen significantly with distance, in contrast to highly Alfvénic intervals that retain their near-Sun scaling. The occurrence of steeper spectra in slower wind streams may be attributed to the observed positive correlation between solar wind speed and Alfvénicity.