Solar Coronal Plumes

Abstract

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

Electron acceleration and small‐scale coherent structure formation by an Alfvén wave propagating in coronal interplume region

“…These observations provide strong indications that the propagation of Alfvén waves in interplume regions plays a major role on the acceleration of the fast solar wind. This conclusion is in agreement with several earlier works (see Poletto ). Alfvén waves propagate from the lower solar atmosphere transporting energy to the corona along the regions of open magnetic field, such as polar coronal holes.…”

Solar UV and X-ray spectral diagnostics

“…Within coronal holes, plumes are long-lasting features (see the recent review from Poletto 2015). These were spatially resolved with SOHO CDS, and EM/DEM analyses clearly showed that near their bases, the cross-sections of plumes are almost isothermal (Del Zanna and Bromage 1999a; Del Zanna et al.…”

“…Measurements of electron (and ion) temperatures in coronal holes are very important, especially when defining the lower boundary of models which attempt to explain how the fast solar wind becomes accelerated inside coronal holes (see, e.g., the Living Reviews by Cranmer 2009; Poletto 2015).…”

An Automated Algorithm for Identifying and Tracking Transverse Waves in Solar Images

“…Solar coronal plumes are faint ray-like features that fan outward from coronal holes in white-light and EUV images (see Wilhelm et al 2011;Poletto 2015). Plumes are cooler and denser than the surrounding plasma with typical temperatures in the range of 0.7-1.2 MK and density enhancements of 2-3 (Ahmad & Withbroe 1977;DeForest et al 1997;Del Zanna et al 2003).…”