Large scale 1/f magnetic field spectrum in the solar wind close to the Sun: comparison between 0.15 and 0.3AU

International audienceWe investigate properties of the spectrum of magnetic field fluctuations observed by PSP in the solar wind inside 0.3 AU. We focus on large scales (low frequencies in the spacecraft frame) above the MHD-inertial range with typical spectral index -5/3, where the spectrum displays a shallower slope, close to -1. The radial evolution of the break scale separating the inertial and 1/f ranges is investigated for different wind regimes and compared with analogous conditions observed by Helios at 0.3 AU and beyond. We analyze data taking into account different physical parameters that can play a role in the evolution of the fluctuations, such as their absolute and relative amplitude, the flow expansion rate, and the estimated non-linear time of turbulent interactions. Observations are discussed in the framework of existing models for the solar wind 1/f spectrum and results are compared with theoretical predictions