Spectroscopy at the solar limb: II. Are spicules heated to coronal temperatures ?

TL;DR

This study uses multi-wavelength observations to investigate whether type II solar spicules are heated to coronal temperatures, finding they generally do not reach such heights or temperatures, thus questioning their role in coronal heating.

Contribution

It provides detailed measurements of spicule heights, temperatures, and velocities, demonstrating that most spicules do not attain coronal temperatures or heights, challenging previous assumptions about their heating role.

Findings

Most spicules reach about 6 Mm height

Line width and temperature decrease with height

Spicules do not reach coronal temperatures or heights

Abstract

Spicules of the so-called type II were suggested to be relevant for coronal heating because of their ubiquity on the solar surface and their eventual extension into the corona. We investigate whether solar spicules are heated to transition-region or coronal temperatures and reach coronal heights (>6 Mm) using multi-wavelength observations of limb spicules in different chromospheric spectral lines (Ca II H, Hepsilon, Halpha, Ca II IR at 854.2 nm, He I at 1083 nm). We determine the line width of individual spicules and throughout the field of view and estimate the maximal height that different types of off-limb features reach. We derive estimates of the kinetic temperature and the non-thermal velocity from the line width of spectral lines from different chemical elements. We find that most regular spicules reach a maximal height of about 6 Mm above the solar limb. The majority of features found at larger heights are irregularly shaped with a significantly larger lateral extension than spicules. Both individual and average line profiles in all spectral lines show a decrease in their line width with height above the limb with very few exceptions. Both the kinetic temperature and the non-thermal velocity decrease with height above the limb. We find no indications that the spicules in our data reach coronal heights or transition-region or coronal temperatures.