Role of Longitudinal Waves in Alfv\'en-wave-driven Solar Wind

TL;DR

This study demonstrates that longitudinal waves originating from the photosphere significantly influence the solar wind's mass-loss rate by facilitating mode conversion and enhancing coronal heating, challenging previous assumptions about acoustic wave effects.

Contribution

It reveals the crucial role of longitudinal oscillations and mode conversion in the chromosphere in shaping solar wind properties, using detailed MHD simulations.

Findings

Mass-loss rate increases up to 4 times with higher longitudinal wave amplitude.

Longitudinal-to-transverse wave mode conversion enhances coronal Alfvénic flux.

Chromospheric evaporation leads to higher coronal density and wind mass-loss.

Abstract

We revisit the role of longitudinal waves in driving the solar wind. We study how the the $p$-mode-like vertical oscillation on the photosphere affects the properties of solar winds under the framework of Alfv\'en-wave-driven winds. We perform a series of one-dimensional magnetohydrodynamical numerical simulations from the photosphere to beyond several tens of solar radii. We find that the mass-loss rate drastically increases with the longitudinal wave amplitude at the photosphere up to $\sim 4$ times, in contrast to the classical understanding that the acoustic wave hardly affects the energetics of the solar wind. The addition of the longitudinal fluctuation induces the longitudinal-to-transverse wave mode conversion in the chromosphere, which results in the enhanced Alfv\'enic Poynting flux in the corona. Consequently, the coronal heating is promoted to give higher coronal density by the chromospheric evaporation, leading to the increased mass-loss rate. This study clearly shows the importance of the longnitudinal oscillation in the photosphere and the mode conversion in the chromosphere in determining the basic properties of the wind from solar-like stars.