On the validity of the Taylor Hypothesis in the inner heliosphere as observed by the Parker solar probe

We examined the plasma velocity and magnetic field data in order to asses the validity of the Taylor hypothesis throughout the first two orbits of Parker Solar Probe. The Taylor hypothesis is of crucial importance for single-point observations, since it allows for the conversion of a measured time series into a spatial profile of a turbulent flow. In the case of the solar wind at 1AU, the validity of the Taylor hypothesis has generally been well established. However, this is not always the case for the Parker Solar Probe, since the velocity of the solar wind near the perihelion becomes comparable to the local Alfven speed of the plasma. Additionally, the spacecraft's orbital velocity is also of similar order for a part of the approach. Finally, turbulent velocity fluctuations can also become significant enough to undermine the frozen flow assumptions. We demonstrate that the validity of the Taylor hypothesis is less robust for the parts of the orbit below 40 solar radii. Additionally, local plasma conditions or increased turbulent fluctuations can impact the validity throughout the approach at larger distances.