Flattening of the magnetic field power spectral density profile

The power spectral densities (PSDs) of ion moments and magnetic field turbulence in the solar wind can be fitted by a power law with the power index of -5/3 in the MHD range of frequencies and with the power index ranging from 2 to 4 at frequencies exceeding the proton gyroscale.  However, the density PSD often exhibits a significant flattening at the high-frequency part of the MHD range but a similar effect was not observed for any other quantity. For this reason, the paper analyzes the power spectra of solar wind and magnetic field fluctuations computed in the frequency range around the break between MHD and kinetic scales. We use Spektr-R proton moments and Wind magnetic field at 1 AU and concentrate on the overall PSD profiles of the density, thermal speed, parallel and perpendicular components of magnetic field and velocity fluctuations and investigate statistically the role of parameters like the fluctuation amplitude, collisional age, temperature anisotropy or ion beta. The statistics based on more than 10 thousand of 20-minute intervals shows that the compressive component of magnetic field fluctuations behaves like the density fluctuation in the old, low-beta solar wind. On the other hand, a similar profile was not observed for either bulk or thermal speeds. The dependence on the collisional age initiated the comparison with Solar Orbiter and PSP observations in the inner heliosphere that would shed light on the processes leading to a formation of these spectral features.