Driving Solar Spicules and Jets with Magnetohydrodynamic Turbulence: Testing a Persistent Idea

TL;DR

This study investigates how magnetohydrodynamic turbulence and Alfven wave mode conversion can generate dynamic, jet-like spicules in the solar chromosphere, aligning with recent observations of Type II spicules.

Contribution

It demonstrates that turbulence-driven Alfven wave mode conversion can produce intermittent, jet-like chromospheric features similar to observed spicules, revisiting a longstanding hypothesis with modern simulations.

Findings

Mode-converted waves cause the transition region to oscillate by several Mm.

Turbulence leads to highly variable, intermittent chromospheric extensions.

Simulated spicule properties match observed Type II spicules.

Abstract

The solar chromosphere contains thin, highly dynamic strands of plasma known as spicules. Recently, it has been suggested that the smallest and fastest (Type II) spicules are identical to intermittent jets observed by the Interface Region Imaging Spectrograph. These jets appear to expand out along open magnetic field lines rooted in unipolar network regions of coronal holes. In this paper we revisit a thirty-year-old idea that spicules may be caused by upward forces associated with Alfven waves. These forces involve the conversion of transverse Alfven waves into compressive acoustic-like waves that steepen into shocks. The repeated buffeting due to upward shock propagation causes nonthermal expansion of the chromosphere and a transient levitation of the transition region. Some older models of wave-driven spicules assumed sinusoidal wave inputs, but the solar atmosphere is highly turbulent and stochastic. Thus, we model this process using the output of a time-dependent simulation of reduced magnetohydrodynamic turbulence. The resulting mode-converted compressive waves are strongly variable in time, with a higher transition region occurring when the amplitudes are large and a lower transition region when the amplitudes are small. In this picture, the transition region bobs up and down by several Mm on timescales less than a minute. These motions produce narrow, intermittent extensions of the chromosphere that have similar properties as the observed jets and Type II spicules.