Solar coronal plumes and the fast solar wind

TL;DR

This paper investigates the peculiar spectral line shapes in coronal holes and plumes, exploring their physical origins, contributions to the solar wind, and the FIP effect, culminating in a model explaining plasma flows and spectral features.

Contribution

It provides a new model of plasma flows in coronal plumes that explains the observed spectral line shapes and their relation to the solar wind and FIP effect.

Findings

Spectral line shapes differ between quiet Sun and coronal holes.

A plume model explains plasma flows and spectral line features.

Plumes contribute to the fast solar wind and exhibit FIP effect signatures.

Abstract

The spectral profiles of the coronal Ne viii line at 77 nm have different shapes in quiet-Sun regions and coronal holes (CHs). A single Gaussian fit of the line profile provides an adequate approximation in quiet-Sun areas, whereas a strong shoulder on the long-wavelength side is a systematic feature in CHs. Although this has been noticed since 1999, no physical reason for the peculiar shape could be given. In an attempt to identify the cause of this peculiarity, we address three problems that could not be conclusively resolved in a review article by a study team of the International Space Science Institute (ISSI; Wilhelm et al. 2011) : (1) The physical processes operating at the base and inside of plumes as well as their interaction with the solar wind (SW). (2) The possible contribution of plume plasma to the fast SW streams. (3) The signature of the first-ionization potential (FIP) effect between plumes and inter-plume regions (IPRs). Before the spectroscopic peculiarities in IPRs and plumes in polar coronal holes (PCHs) can be further investigated with the instrument Solar Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar and Heliospheric Observatory (SOHO), it is mandatory to summarize the results of the review to place the spectroscopic observations into context. Finally, a plume model is proposed that satisfactorily explains the plasma flows up and down the plume field lines and leads to the shape of the neon line in PCHs.