On excited frequencies for Alfv\'en waves in a coronal arcade

TL;DR

This paper analytically investigates the normal modes of Alfvén waves in a solar coronal arcade, estimating their power spectra and highlighting the potential for future observations to explore high-frequency oscillations.

Contribution

It provides an analytical solution for the wave frequency spectrum generated by reconnection events in coronal arcades, predicting observable high-frequency Alfvén waves.

Findings

Peak power at ~10 mHz frequencies

Substantial power up to ~4 Hz

Current instruments cannot observe these high frequencies

Abstract

The normal modes of oscillation for a magnetic arcade are used to analytically solve an initial value problem and estimate the power spectra of wave frequencies generated by a reconnection event in the solar corona. Over a realistic range of parameters, I find that such a disturbance generates a peak power at $\sim10$s$\mathrm{mHz}$ frequencies, but still substantial power up to $\sim4\mathrm{Hz}$. The cadence and sensitivity of current instrumentation does not allow observations of oscillations at these frequencies, but in the near future, new instrumentation will be able to probe this regime, and observationally determine its energetic importance.