Radial Evolution of the Solar Wind and Associating Turbulence Based on the Synergetic Measurement from Parker Solar Probe and 1 au Observations

The 4th encounter (~30 Rs away from the sun) of the Parker Solar Probe (PSP) is a great opportunity to observe the radial evolution of the solar wind from the inner heliosphere to the near-earth environment when the sun, PSP, and the earth are quasi-radial aligned. Similar features of the solar wind are observed from both PSP and Wind (at 1 au) measurements. The accelerating-solar-wind model could be more suitable than the constant speed model for the observation, which means the solar wind is still accelerating from 30 Rs to 1 au. Both PSP and Wind measure the co-existence of the Alfvenic and compressive fluctuations in the solar wind. The correlated radial velocity (dVR), proton density (dn) and temperature (dT) fluctuations indicate the nature of the compressive fluctuations are outward-propagating slow waves. However, dn and dB is not correlated from PSP, but correlated from Wind, which indicates the propagating direction of the slow waves is changed. Comparing the radial evolution of the energies of both Alfvenic and compressive fluctuations with the WKB model, we find the observed energy decays slower than the theoretical prediction, which indicates an extra energy injection during the solar wind propagation.