2015/09/10 by Steven R. Cranmer, Lauren N. Woolsey · 1 citation
Physics and Astronomy · #Amplitude #Astrophysics and Cosmic Phenomena #Chromosphere #Corona (planetary geology) #Coronal hole #Heliosphere #Ionosphere and magnetosphere dynamics #Magnetohydrodynamic drive #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Shock wave #Solar and Space Plasma Dynamics #Sponge spicule #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/812/1/71
Accepted for publication in the Astrophysical Journal. 8 pages (emulateapj style), 5 figures
arxiv created 2015/09/10 · openalex publication_date 2015/10/09 · arxiv updated 2015/10/14 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
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 Alfvén waves. These forces involve the conversion of transverse Alfvén 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 (TR). 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 TR occurring when the amplitudes are large and a lower TR when the amplitudes are small. In this picture, the TR 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.