A generalized method for estimating solar wind speeds and densities using spectral broadening for a Kolmogorov turbulence spectrum

Abstract

We present a unified method to derive both solar wind velocities and coronal electron densities in the near-Sun corona using Doppler spectral broadening of spacecraft radio signals. The method is generalized to be frequency independent under the assumption that electron density fluctuations follow a Kolmogorov spectrum. We validate the approach using S-band data from India’s Mars Orbiter Mission during the October 2021 superior conjunction at 5–8 R⊙, and X-band data from Japan’s Akatsuki during June 2016 and October 2022 conjunctions spanning 1.4–10 R⊙. From S-band we obtained wind speeds of 100–150 km s−1 and electron densities of order (Formula presented) m−3. X-band results show speeds ranging from (Formula presented) 150 km s−1 near the equator to (Formula presented) 400 km s−1 in coronal-hole regions, with consistent radial trends in density. We provide a compact, frequency-scaled relation that maps Doppler spectral width to both v and (Formula presented). The formulation enables consistent application across telecommunication bands and complements in situ probes for coronal plasma studies. © 2026 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.