Authors: Bennett A. Maruca (University of Delaware), Ramiz A. Qudsi (Boston University), B. L. Alterman (Southwest Research Institute), Brian M. Walsh (Boston University), Vaishali Prabakaran (Boston University), Carson Brown (University of Delaware), Kelly E. Korreck (NASA Headquarters), Daniel Verscharen (University College London), Riddhi Bandyopadhyay (Princeton University), Rohit Chhiber (University of Delaware; NASA Goddard Space Flight Center), Alexandros Chasapis (Laboratory for Atmospheric and Space Physics), Tulasi N. Parashar (Victoria University), William H. Matthaeus (University of Delaware), and Melvyn L. Goldstein (Unviersity of Maryland Baltimore County)

Though the solar wind is characterized by spatial and temporal variability across a wide range of scales, long-term averages of in situ measurements have revealed clear radial trends: changes in average values of basic plasma parameters (e.g., density, temperature, and speed) and a magnetic field with a distance from the Sun. To establish our current understanding of the solar wind’s average expansion through the heliosphere, data from multiple spacecraft needed to be combined and standardized into a single dataset. In this study, data from twelve heliospheric and planetary spacecraft — Parker Solar Probe (PSP), Helios 1 and 2, Mariner 2 and 10, Ulysses, Cassini, Pioneer 10 and 11, New Horizons, and Voyager 1 and 2 — were compiled into a dataset spanning over three orders of magnitude in heliocentric distance. To avoid introducing artifacts into this composite dataset, special attention was given to the solar cycle, spacecraft heliocentric elevation, and instrument calibration. The radial trend in each parameter was found to be generally well described by a power-law fit, though up to two break points were identified in each fit. These radial trends have been publicly released to benefit research groups in the validation of global heliospheric simulations and in the development of new deep-space missions such as Interstellar Probe.