Fine-Scale Features of the Sun's Atmosphere: Spicules and Jets

TL;DR

This paper surveys fine-scale solar atmospheric features, principally spicules and coronal jets, tracing their observational histories and evolving theoretical models. It argues for a continuum of jet-like phenomena spanning spicules to large CMEs, unified by magnetic processes such as flux cancelation and minifilament eruptions, with minifilaments forming via cancelation and erupting to drive jets. Through synthesis of pre-Hinode insights, Hinode/SDO-era observations, and numerical modeling, the work highlights a shift from emerging-flux to minifilament eruption frameworks as the dominant jet mechanism, while acknowledging unresolved questions about AR jets and energy budgets for coronal heating. The discussion emphasizes scale-invariant processes and the potential for small-scale eruptions to contribute meaningfully to coronal heating, plume formation, and CME-like phenomena, with future high-resolution observations expected to clarify these connections.

Abstract

We present an overview of fine-scale features in the Sun's atmosphere, with a focus on spicules and jets. We consider older and newer observations and theories for chromospheric spicules and coronal jets. We also consider the connection between these features and some other solar atmospheric phenomena. We then discuss the possibility that there is a continuum of jet-like features ranging from spicules to large-scale CME-producing eruptions, all driven by similar magnetic processes operating on differing corresponding size scales. Future observational and theoretical studies will help clarify further the nature of these solar events, and elucidate possible connections between them.

Figures (8)

• Figure 1: Examples of chromospheric spicules observed at the solar west limb with the Hinode spacecraft in Ca ii. Dynamic changes can be seen in many of the spicules that reach across the limb over the course of panels (a)---(c). Intensity colors are reversed, so that bright features appear dark and vice versa. Data from this period were analyzed by depontieu.et07a and by zhang.et12.
• Figure 2: Examples of X-ray images of solar coronal jets observed with the Hinode/ X-ray telescope (XRT), with (a) showing the north polar coronal hole limb region (taken with the XRT "Al Poly" filter), and (b) showing a closeup of a jet in an active region on the disk (taken with the "Be thin" filter); white arrows point to the spire. The typical morphology for the jets is a spire shooting away from the Sun, with a bright base at the bottom of the spire. Often one side of the base is particularly bright (e.g., the left side of the base in (b); black arrow), a feature we refer to as a "jet-base bright point" (following sterling.et15). The jets in (a) were studied by cirtain.et07, and that in (b) was studied in sterling.et17.
• Figure 3: Schematic representation of the emerging flux model for coronal jets. shibata.et92 suggested that a jet results when (a) bipolar field emerges from beneath the solar surface, forming a current sheet where the field lines are oppositely directed. (b) Continued emergence results in reconnection at the current sheet (red X), with one reconnection product being a small loop (red semi-circle), which was proposed to represent the jet bright point (JBP); and the other being a new open field line (red line), along which the jet spire flows outward (purple arrow). Dotted lines represent the field that reconnected to give the JBP and the new open field. This schematic appeared in sterling.et15.
• Figure 4: (After sterling.et15.) Observed X-ray jet near at the solar limb in (a) X-rays from XRT, and (b) in 193 Å EUV from AIA on SDO. EUV frequently shows dark (presumably cool) absorbing filament material erupting and traveling out along the spire, and the JBP appearing at the location from which the "minifilament" erupted. Here, the JBP is visible as the bright point-like features in (b), that grows larger and brighter in (c). The arrow in (d) shows the minifilament emanating from the location where the JBP forms; in (e), the erupting minifilament is moving out along the jet spire.
• Figure 5: Minifilament observed erupting in SDO/AIA 171 Å, where the arrows in the panels point to the minifilament, which shows up in absorption. (a) The minifilament is starting to expand upward, while accompanying brightenings are still minimal. (b) Strong brightenings are developing beneath the erupting filament, forming the JBP and auxiliary brightenings. (c) As the minifilament eruption continues, the spire starts to form above the bright base. This event was studied extensively in shen.et12.