Authors: Daniel Wrench (Victoria University of Wellington), Tulasi N. Parashar (VUW), Kevin de Lange (VUW), Sean Oughton (University of Waikato), Marcus Frean (VUW)

The Reynolds number, Re, is an important quantity for describing a turbulent flow, but is not easily calculated for a collisionless fluid like the solar wind. Previous studies have employed various formulations to define an “effective Reynolds number”. These include using either the break scale or the ion inertial length as proxies for Kolmogorov scale, and the magnetic Taylor scale. In this study, we use the Taylor scale approximation after first applying a correction factor to reduce bias in estimating the Taylor scale. These three methods are compared and found to show significant disagreement, with linear associations of between 0.43 and 0.75. Average values of Re from the various methods range between 58,000 and 174,000, considerably lower than some previous estimates. We therefore suggest that more theoretical work needs to be done in order to identify the most valid way of calculating the Reynolds number of a collisionless fluid such as the solar wind. We also compare three different methods of estimating the correlation scale, finding good agreement, and make available a data product of 28 years of 1 AU solar wind and magnetospheric plasma measurements from both Wind and OMNI.