Taylor microscale and effective Reynolds number near the Sun from PSP

TL;DR

This paper uses Parker Solar Probe data to estimate the Taylor microscale and effective Reynolds number near the Sun, revealing less turbulent processing and smaller dissipative scales in the near-Sun solar wind.

Contribution

It introduces a method to estimate the Taylor microscale and Reynolds number in the solar wind using PSP data, providing new insights into near-Sun turbulence.

Findings

Taylor microscale is smaller near the Sun compared to near-Earth values.

Effective Reynolds number is lower close to the Sun.

Solar wind shows less turbulence processing near the Sun.

Abstract

The Taylor microscale is a fundamental length scale in turbulent fluids, representing the end of fluid properties and onset of dissipative processes. The Taylor microscale can also be used to evaluate the Reynolds number in classical turbulence theory. Although the solar wind is weakly collisional, it approximately behaves as a magnetohydrodynamic (MHD) fluid at scales larger than the kinetic scale. As a result, classical fluid turbulence theory and formalisms are often used to study turbulence in the MHD range. Therefore, a Taylor microscale can be used to estimate an effective Reynolds number in the solar wind. NASA's Parker Solar Probe (PSP) has reached progressively closer to the Sun than any other spacecraft before. The collected data have revealed many new findings in the near-Sun solar wind. Here, we use the PSP data to estimate the Taylor microscale and effective Reynolds number near the Sun. We find that the Taylor microscale and Reynolds number are small compared to the corresponding near-Earth values, indicating a solar wind that has been less processed by turbulence, with very small-scale dissipative processes near the Sun.