Phase mixing of propagating Alfven waves in a stratified atmosphere: Solar spicules

TL;DR

This study investigates how phase mixing causes damping of propagating Alfvén waves in solar spicules, considering stratification and steady flows, revealing that damping occurs over longer timescales than observed lifetimes.

Contribution

It introduces a numerical model that accounts for stratification and steady flows to analyze Alfvén wave damping in solar spicules, highlighting differences between theoretical damping times and observations.

Findings

Damping occurs in space rather than time due to stratification.

Exponential damping follows exp(-At^3) law under spicule conditions.

Calculated damping times are longer than observed spicule lifetimes.

Abstract

Alfvenic waves are thought to play an important role in coronal heating and solar wind acceleration. Recent observations by Hinode/SOT showed that the spicules mostly exhibit upward propagating high frequency waves. Here we investigate the dissipation of such waves due to phase mixing in stratified environment of solar spicules. Since they are highly dynamic structures with speeds at about significant fractions of the Alfven phase speed, we take into account the effects of steady flows. Our numerical simulations show that in the presence of stratification due to gravity, damping takes place in space than in time. The exponential damping low, exp(-At^3), is valid under spicule conditions, however the calculated damping time is much longer than the reported spicule lifetimes from observations.