A Tale Of Two Spicules: The Impact of Spicules on the Magnetic Chromosphere

TL;DR

This paper identifies and characterizes two distinct types of spicules in the solar chromosphere, revealing their different formation mechanisms, dynamic properties, and their role in wave propagation, based on high-resolution solar observations.

Contribution

It provides the first detailed observational distinction between Type-I and Type-II spicules, linking their properties to different physical processes such as shock waves and magnetic reconnection.

Findings

Type-I spicules are driven by shock waves from global oscillations.

Type-II spicules form rapidly and are heated to transition region temperatures.

Both types carry significant Alfvén wave amplitudes.

Abstract

We use high-resolution observations of the Sun in Ca II H 3968 A from the Solar Optical Telescope on Hinode to show that there are at least two types of spicules that dominate the structure of the magnetic solar chromosphere. Both types are tied to the relentless magnetoconvective driving in the photosphere, but have very different dynamic properties. ``Type-I'' spicules are driven by shock waves that form when global oscillations and convective flows leak into the upper atmosphere along magnetic field lines on 3-7 minute timescales. ``Type-II'' spicules are much more dynamic: they form rapidly (in ~10s), are very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem to be rapidly heated to (at least) transition region temperatures, sending material through the chromosphere at speeds of order 50-150 km/s. The properties of Type II spicules suggest a formation process that is a consequence of magnetic reconnection, typically in the vicinity of magnetic flux concentrations in plage and network. Both types of spicules are observed to carry Alfven waves with significant amplitudes of order 20 km/s.