Role of Longitudinal Waves in Alfvén-wave-driven Solar Wind

Abstract

We revisit the role of longitudinal waves in driving the solar wind. We study how the p-mode-like vertical oscillation on the photosphere affects the properties of solar winds in the framework of Alfvén-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 by up to a factor of ∼4, in contrast to the classical understanding that acoustic waves hardly affect the energetics of the solar wind. The addition of the longitudinal fluctuation induces longitudinal-to-transverse wave mode conversion in the chromosphere, which results in enhanced Alfvénic Poynting flux in the corona. Consequently, coronal heating is promoted to give higher coronal density by chromospheric evaporation, leading to the increased mass-loss rate. This study clearly shows the importance of longitudinal oscillation in the photosphere and mode conversion in the chromosphere in determining the basic properties of the wind from solar-like stars.

Role of Longitudinal Waves in Alfvén-wave-driven Solar/Stellar Wind

“…Figure 4 shows that Ṁw obtained from the numerical simulations (blue stars) increases with δv except for the range of δv ≥ 2.7 km s −1 . In addition, these numerical data are roughly reproduced by an analytic relation of Ṁw ≈ L A,cb /v 2 g, (red circles; Cranmer & Saar 2011), where L A,cb is the Alfvénic Poynting flux at the coronal base (see Shimizu et al 2022, for the specific expression) and v g, = 2GM /R is the escape velocity. Since v esc, is constant in our setup, the dependence of L A,cb on δv indicates that the Alfvénic Poynting flux that reaches the corona increases by adding the photospheric longitudinal fluctuation even though the injected Alfvénic Poynting flux at the photosphere is the same.…”

“…In order to take into account cascading Alfvénic turbulence, which plays a role in the dissipation of Alfvén waves (Goldreich & Sridhar 1995;Matthaeus et al 1999), we employ phenomenological dissipation terms in the transverse components of the momentum equation and the induction equation (Shoda et al 2018). See Shimizu et al (2022) for the detailed setup of the numerical simulation.…”

“…Inspired by this observational finding, we studied the effect of vertical oscillations at the photosphere on Alfvén wave-driven solar winds by magnetohydrodynamical (MHD) simulations (Shimizu et al 2022). In this talk, we introduce the results of this paper and explain the importance of the longitudinal fluctuation in driving the wind from the sun and solar-type stars from a theoretical point of view.…”

The Effect of the Chromospheric Temperature on Coronal Heating

“…They dissipate via turbulent cascade and nonlinear mode conversion. The highfrequency longitudinal fluctuations, as well as the transverse ones, also play a role in heating from mode conversion (Shimizu et al 2022). In contrast, low-frequency waves with wavelengths larger than the loop length have different behaviors.…”

Can the Solar p-modes Contribute to the High-frequency Transverse Oscillations of Spicules?

“…The transfer mechanism is still under debate, with several proposed theories. These include the direct excitation process of transverse waves by the interaction between flux tubes and longitudinal waves below the equipartition layer (the so-called mode absorption; Bogdan et al 1996;Hindman & Jain 2008;Riedl et al 2019;, as well as the mode conversion process from longitudinal to transverse waves at the equipartition layer where the local speed of sound and Alfvén speed become equal (Schunker & Cally 2006;Cally 2007;Jess et al 2012;Wang et al 2021;Shimizu et al 2022). Additionally, another mode conversion from fast to Alfvén waves around the refraction height of the fast waves, which is inherently a three-dimensional process unlike the mode conversion at the equipartition layer and the mode absorption (Cally & Goossens 2008;Cally & Hansen 2011;Hansen & Cally 2012;Khomenko & Cally 2012).…”