Radial evolution of the key solar wind parameters according to the Parker Solar Probe and other missions

Knowing the temporal and spatial behavior of the main plasma parameters in the solar wind is important because of both an academic interest and the necessity to build theoretical models. Meanwhile, the solar wind characteristics are available with good accuracy only from in situspacecraft observations. There are a very limited number of studies that analyzed the radial evolution of the interplanetary magnetic field, the speed, the density, and the temperature of the solar wind. Previously, data from missions carried out in the 1970s were used for these purposes. Meanwhile, none of them approached the Sun closer than ~0.3 AU, and the information available did not allow describing the processes occurring near the solar corona. The launch of the Parker Solar Probe mission has opened up vast opportunities for studying the solar wind, starting from distances of the order of the Alfven radius. At the moment, Parker Solar Probe data are available with approaches to the Sun up to 0.08 AU.

An analysis of data obtained from Parker Solar Probe and Helios 2 (up to 1 AU), and from IMP8 and Voyager 1 (further from the Earth's orbit and up to 7 AU) was performed. The dependencies of the interplanetary magnetic field, the temperature, the speed, and the density of the solar wind on heliocentric distance are revealed and their typical profiles are analyzed. The nature of deviations of observed values from theoretical expectations is discussed. A particular attention is paid to the comparison of the results from the Parker Solar Probe and Helios missions.