Generation and Propagation of Alfven Waves in Solar Atmosphere

Yu.T. Tsap1,2, A.V. Stepanov2, Yu.G. Kopylova2

1Crimean Astrophysical Observatory, Ukraine
2Pulkovo Observatory, St. Petersburg, Russia

The propagation of Alfven waves from the photosphere into the corona with regard to the fine structure of the magnetic field is considered. Within the framework of the three-layer model the physical aspects of the wave reflection in the stratified atmosphere are discussed. It has been shown that most strong reflection of low frequency waves with period > 10 s takes place in the transition region. The reflection coefficient continuously decreases with an increase of wave period. Influence of the external magnetic field on the values of the Spruit cutoff frequency for transverse (kink) modes excited in the thin magnetic tubes is analyzed. Torsion modes can penetrate into the upper atmosphere most effectively since their amplitudes are not changed with height in the photosphere while kink ones are transformed into shock waves in the lower chromosphere because of an significant increase of amplitudes. In spite of stratification the linearity of torsion modes in the solar atmosphere is conserved due to violation of the WKB approximation. The important role of the magnetic canopy is discussed. Alfven waves generated by convective motions in the photosphere can give essential contribution to the heating of the coronal plasma in quite regions of the Sun.