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Ion velocity distribution functions (VDFs) measured in-situ in the solar wind show often large deviations from a simple Maxwellian distribution. Even a main part of the proton VDF (proton core) situated around the global maximum maintains a bi-Maxwellian character. Moreover, skewness, related to a non-thermal tail or proton beam, is often observed. In addition to these two proton populations, various heavy ion species are present and their VDFs also exhibit the mentioned non-thermal features. In the proton core frame, minor components including ion beams drift along the interplanetary magnetic field and their average differential velocities decrease with an increasing distance from the Sun. We present reprocessing of the VDFs measured by the Helios spacecraft with a motivation to discuss evolutions of relative drifts between three dominant components – the proton core, proton beam, and α -particle core at different distances from the Sun. Our processing is based on assumptions that partial VDFs of all these components can be approximated by a bi-Maxwellian distribution. We compare results of this novel procedure with those from previous computation results and introduce basic characteristics of the VDF components in both slow and fast solar wind streams. Finally, we investigate the correlated variations of the velocity ratios on the ion components and magnetic field orientations occurring independently on the radial distance from the Sun. [ABSTRACT FROM AUTHOR]

Turbulent cascade transferring the free energy contained within the large scale fluctuations of the magnetic field, velocity and density into the smaller ones is probably one of the most important mechanisms responsible for heating of the solar corona and solar wind, thus the turbulent behavior of these quantities is intensively studied. The temperature is also highly fluctuating quantity but its variations are studied only rarely. There are probably two reasons, first the temperature is tensor and, second, an experimental determination of temperature variations requires knowledge of the full velocity distribution with an appropriate time resolution but such measurements are scarce. To overcome this problem, the Bright Monitor of the Solar Wind (BMSW) on board Spektr-R used the Maxwellian approximation and provided the thermal velocity with a 32 ms resolution, investigating factors influencing the temperature power spectral density shape. We discuss the question whether the temperature spectra determined from Faraday cups are real or apparent and analyze mutual relations of power spectral densities of parameters like the density, parallel and perpendicular components of the velocity and magnetic field fluctuations. Finally, we compare their spectral slopes with the slopes of the thermal velocity in both inertial and kinetic ranges and their evolution in course of solar wind expansion. [ABSTRACT FROM AUTHOR]