Relationship Between Solar Wind Speed and Coronal Magnetic Field Properties

TL;DR

This study analyzes 24 years of data to reveal a strong linear correlation between solar wind speed and the ratio of photospheric magnetic field strength to flux expansion factor, highlighting key physical parameters for solar wind acceleration.

Contribution

It demonstrates that solar wind speed correlates linearly with B_S/f, providing insights into the physical parameters influencing solar wind acceleration.

Findings

V is inversely proportional to f

V tends to increase with B_S at constant f

V has a strong linear correlation with B_S/f

Abstract

We have studied the relationship between the solar-wind speed $[V]$ and the coronal magnetic-field properties (a flux expansion factor [$f$] and photospheric magnetic-field strength [$B_{\mathrm{S}}$]) at all latitudes using data of interplanetary scintillation and solar magnetic field obtained for 24 years from 1986 to 2009. Using a cross-correlation analyses, we verified that $V$ is inversely proportional to $f$ and found that $V$ tends to increase with $B_{\mathrm{S}}$ if $f$ is the same. As a consequence, we find that $V$ has extremely good linear correlation with $B_{\mathrm{S}}/f$. However, this linear relation of $V$ and $B_{\mathrm{S}}/f$ cannot be used for predicting the solar-wind velocity without information on the solar-wind mass flux. We discuss why the inverse relation between $V$ and $f$ has been successfully used for solar-wind velocity prediction, even though it does not explicitly include the mass flux and magnetic-field strength, which are important physical parameters for solar-wind acceleration.