# Reynolds Number and Intermittency in the Expanding Solar Wind: Predictions Based on Voyager Observations

## TL;DR

This paper predicts how turbulence intermittency in the solar wind varies with distance from the Sun, using Voyager data and theoretical scaling, and forecasts increased intermittency near the Sun's critical regions.

## Contribution

It introduces a novel approach linking Reynolds number variations to turbulence intermittency in the expanding solar wind, validated with Voyager data and predicting future Parker Solar Probe observations.

## Key findings

- Reynolds number decreases with heliocentric distance.
- Magnetic field kurtosis decreases with distance, indicating less intermittency.
- Predicted increased intermittency near the Sun's critical regions.

## Abstract

The large scale features of the solar wind are examined in order to predict small scale features of turbulence in unexplored regions of the heliosphere. The strategy is to examine how system size, or effective Reynolds number, varies, and then how this quantity influences observable statistical properties, including intermittency properties of solar wind turbulence. The expectation based on similar hydrodynamics scalings, is that the kurtosis, of the small scale magnetic field increments, will increase with increasing Reynolds number. Simple theoretical arguments as well as Voyager observations indicate that effective interplanetary turbulence Reynolds number decreases with increasing heliocentric distance. The decrease of scale-dependent magnetic increment kurtosis with increasing heliocentric distance, is verified using a newly refined Voyager magnetic field dataset. We argue that these scalings continue to much smaller heliocentric distances approaching the Alfven critical region, motivating a prediction that the Parker Solar Probe spacecraft will observe increased magnetic field intermittency, stronger current sheets, and more localized dissipation, as its perihelion approaches the critical regions. Similar arguments should be applicable to turbulence in other expanding astrophysical plasmas.