Testing the Alfv\'en-wave model of the solar wind with interplanetary scintillation

TL;DR

This study tests the wave/turbulence-driven (WTD) model of solar wind acceleration using interplanetary scintillation data, finding better agreement at high latitudes and supporting wave-driven mechanisms in solar wind physics.

Contribution

The paper provides a self-consistent MHD simulation comparison with IPS observations, validating the WTD model's effectiveness at high latitudes and highlighting areas for model improvement.

Findings

High-latitude wind velocities match observations better than empirical models.

Mid-latitude agreement is less accurate, indicating model limitations.

Waves and turbulence likely drive high-latitude solar wind.

Abstract

Understanding the mechanism(s) of the solar wind acceleration is important in astrophysics and geophysics. A promising model of the solar wind acceleration is known as the wave/turbulence-driven (WTD) model, in which Alfv\'en waves feed energy to the solar wind. In this study, we tested the WTD model with global measurement of wind speed from interplanetary scintillation (IPS) observations. For Carrington rotations in minimal and maximal activity phases, we selected field lines calculated by the potential-field source-surface method in high- and mid-latitudes and compared the simulated and observed wind velocities. The simulation was performed in a self-consistent manner by solving the magnetohydrodynamic equations from the photosphere to the solar wind. In high-latitude regions, the simulated solar wind velocity agrees better with the IPS observation than with the classical Wang--Sheeley empirical estimation, both in maximal and minimal activity phases. In mid-latitude regions, the agreement worsens, possibly because of the inaccuracy of the WTD model and/or the magnetic-field extrapolation. Our results indicate that the high-latitude solar wind is likely to be driven by waves and turbulence, and that the physics-based prediction of the solar wind velocity is highly feasible with an improved magnetic-field extrapolation.