Testing the Alfvén-wave model of the solar wind with interplanetary scintillation

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 Alfvén 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 magneticfield 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.

On the properties of Alfvénic switchbacks in the expanding solar wind: three-dimensional numerical simulations

“…In this section, we show that for R < R A , amplitude scalings are, to the contrary, extremely conducive to the formation of switchbacks, either with or without turbulence. The arguments we make here are based on wellknown and understood scalings [18,29,[41][42][43] that produce reasonable agreement with observations [e.g., 44,45]. Further, global flux-tube simulations, which correctly capture this physics, have already been shown to produce switchbacks starting from low-amplitude initial conditions [20].…”