High-frequency torsional Alfvén waves as an energy source for coronal heating

Abstract

The existence of the Sun’s hot atmosphere and the solar wind acceleration continues to be an outstanding problem in solar-astrophysics. Although magnetohydrodynamic (MHD) modes and dissipation of magnetic energy contribute to heating and the mass cycle of the solar atmosphere, yet direct evidence of such processes often generates debate. Ground-based 1-m Swedish Solar Telescope (SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time, the ubiquitous presence of high frequency (~12–42 mHz) torsional motions in thin spicular-type structures in the chromosphere. We detect numerous oscillating flux tubes on 10 June 2014 between 07:17 UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60” (1” = 725 km). Stringent numerical model shows that these observations resemble torsional Alfvén waves associated with high frequency drivers which contain a huge amount of energy (~105 W m−2) in the chromosphere. Even after partial reflection from the transition region, a significant amount of energy (~103 W m−2) is transferred onto the overlying corona. We find that oscillating tubes serve as substantial sources of Alfvén wave generation that provide sufficient Poynting flux not only to heat the corona but also to originate the supersonic solar wind.

Two-fluid Numerical Simulations of the Origin of the Fast Solar Wind

“…See also Ofman et al (1995) and Shestov et al (2017) for a similar analysis. However, Alfvén waves are difficult for detection, particularly when high-frequency waves are concerned (Srivastava et al 2017); in an inhomogeneous and structured medium, these waves can experience reflection, mode coupling, phase-mixing and resonant absorption (Ofman et al 1995;Nakariakov et al 1997;Zaqarashvili & Roberts 2006;Goossens et al 2012).…”

Observations of the solar corona during the total solar eclipse on 21 August 2017

“…Currently there are mainly two competing proposals: heating through small‐scale reconnection (Parker, 1988) and dissipation of waves. The ubiquitous presence of low‐frequency coronal waves has been recently revealed through advanced ground‐based and space observations (e.g., Tomczyk et al, 2007; McIntosh et al, 2011; Tian H et al, 2012; Hahn et al, 2012; Morton et al, 2015; Jiao FR et al, 2015; Srivastava et al, 2017). While high‐frequency waves with a period shorter than a few seconds are rarely reported in the quiet corona, due obviously to the fact that most coronal observations use a cadence lower than 10 seconds.…”

Nonlinear Evolution of Short-wavelength Torsional Alfvén Waves

“…In solar physics, Alfvén waves are mainly considered to be candidates for coronal heating due to their ability to freely propagate from lower layers of the solar atmosphere to the corona (e.g., Ruderman 1999;Srivastava et al 2017). For example, Copil et al (2008) suggested that propagating Alfvén waves could locally heat coronal plasma threads.…”