  The Reynolds number, Re, is an important quantity for describing a turbulent
flow. It tells us about the bandwidth over which energy can cascade from large
scales to smaller ones, prior to the onset of dissipation. However, calculating
it for nearly collisionless plasmas like the solar wind is challenging.
Previous studies have used "effective" Reynolds number formulations, expressing
Re as a function of the correlation scale and either the Taylor scale or a
proxy for the dissipation scale. We find that the Taylor scale definition of
the Reynolds number has a sizeable prefactor of approximately 27, which has not
been employed in previous works. Drawing from 18 years of data from the Wind
spacecraft at 1 au, we calculate the magnetic Taylor scale directly and use
both the ion inertial length and the magnetic spectrum break scale as
approximations for the dissipation scale, yielding three distinct Re estimates
for each 12-hour interval. Average values of Re range between 116,000 and
3,406,000, within the general distribution of past work. We also find
considerable disagreement between the methods, with linear associations of
between 0.38 and 0.72. Although the Taylor scale method is arguably more
physically motivated, due to its dependence on the energy cascade rate, more
theoretical work is needed in order to identify the most appropriate way of
calculating effective Reynolds numbers for kinetic plasmas. As a summary of our
observational analysis, we make available a data product of 28 years of 1 au
solar wind and magnetospheric plasma measurements from Wind.
