Two Types of Solar Confined Flares

Jun Zhang; Lijuan Liu; Ting Li; Yijun Hou

arxiv: 1907.04510 · v1 · pith:LNOWPUM7new · submitted 2019-07-10 · 🌌 astro-ph.SR

Two Types of Solar Confined Flares

Ting Li , Lijuan Liu , Yijun Hou , Jun Zhang This is my paper

Pith reviewed 2026-05-24 23:44 UTC · model grok-4.3

classification 🌌 astro-ph.SR

keywords confined flaressolar flaresmagnetic reconnectionslipping reconnectionfilament eruptionpost-flare loopspolarity inversion lineMHD models

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The pith

Confined solar flares divide into two types distinguished by slipping versus standard reconnection.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper selects 18 confined solar flares observed between 2011 and 2017 and divides them into two categories according to their observed dynamics and magnetic configurations. Type I events feature slipping reconnection, strong magnetic shear, ribbon elongations along the polarity inversion line, and a stable filament, with post-flare loops retaining significant non-potentiality. Type II events show little or no slipping reconnection, post-flare loops closer to a potential state, and an erupting filament that remains confined by a strong overlying strapping field. The split indicates that confined flares arise from at least two different reconnection scenarios, with Type I events requiring three-dimensional MHD models and Type II events consistent with two-dimensional models, and Type I comprising roughly 39 percent of the sample.

Core claim

We classified the confined flares into two types based on their different dynamic properties and magnetic configurations. Type I confined flares are characterized by slipping reconnection, strong shear, and stable filament. Type II flares have nearly no slipping reconnection and reach a configuration in a potential state after the flare, with the filament erupting but confined by a strong strapping field. Type II flares could be explained by 2D MHD models while Type I flares need 3D MHD models. Seven of the 18 events belong to Type I and eleven to Type II. The post-flare loops of Type I flares have stronger non-potentiality while those in Type II are weakly sheared, and all Type I events but

What carries the argument

The two-type classification of confined flares based on presence or absence of slipping reconnection, filament stability versus eruption, and resulting post-flare loop shear.

If this is right

Type I flares require three-dimensional MHD models while Type II flares are consistent with two-dimensional MHD models.
Post-flare loops retain stronger non-potentiality in Type I events than in Type II events.
Ribbon elongations parallel to the polarity inversion line at tens of km/s occur in all Type I flares but only a small fraction of Type II flares.
Slipping reconnections between multiple magnetic systems produce Type I flares while anti-parallel reconnection beneath the filament produces Type II flares.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

If the distinction holds, flare forecasting models must track both 2D and 3D reconnection topologies to distinguish eruptive from confined outcomes.
Higher-resolution vector magnetograms could reveal whether the two types represent discrete states or points along a continuum of magnetic complexity.
The 39 percent fraction of Type I events implies that three-dimensional effects contribute substantially to energy release even in non-eruptive flares and should be included in estimates of total solar magnetic energy dissipation.

Load-bearing premise

The 18 selected events form a representative sample whose observed properties map unambiguously onto two distinct physical reconnection scenarios without significant overlap or additional categories.

What would settle it

Discovery of a large confined flare whose ribbon elongations, filament behavior, post-flare loop shear, and overall topology match neither Type I nor Type II properties would falsify the two-type division.

read the original abstract

With the aim of understanding the physical mechanisms of confined flares, we selected 18 confined flares during 2011-2017, and classified the confined flares into two types based on their different dynamic properties and magnetic configurations. "Type I" of confined flares are characterized by slipping reconnection, strong shear, and stable filament. "Type II" flares have nearly no slipping reconnection, and have a configuration in potential state after the flare. Filament erupts but is confined by strong strapping field. "Type II" flares could be explained by 2D MHD models while "type I" flares need 3D MHD models. 7 flares of 18 ($\sim$39 \%) belong to "type I" and 11 ($\sim$61 \%) are "type II" confined flares. The post-flare loops (PFLs) of "type I" flares have a stronger non-potentiality, however, the PFLs in "type II" flares are weakly sheared. All the "type I" flares exhibit the ribbon elongations parallel to the polarity inversion line (PIL) at speeds of several tens of km s$^{-1}$. For "type II" flares, only a small proportion shows the ribbon elongations along the PIL. We suggest that different magnetic topologies and reconnection scenarios dictate the distinct properties for the two types of flares. Slipping agnetic reconnections between multiple magnetic systems result in "type I" flares. For "type II" flares, magnetic reconnections occur in anti-parallel magnetic fields underlying the erupting filament. Our study shows that "type I" flares account for more than one third of the overall large confined flares, which should not be neglected in further studies.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper sorts 18 confined flares into two types tied to different reconnection pictures, but the split rests on qualitative labels and a small uncharacterized sample.

read the letter

The core claim is that confined flares fall into two groups: type I (7 events) driven by slipping reconnection in sheared, multi-system fields with stable filaments, and type II (11 events) where a filament erupts but stays confined by strapping fields with little slipping and post-flare loops that relax toward potential. The authors argue type I needs 3D MHD while type II fits 2D models, and they note type I makes up more than a third of large confined flares so it should not be ignored. That split and the modeling implication are the new packaged result here. The work does a straightforward job of pulling together ribbon motion, filament behavior, and shear estimates across the events to sketch an organizing scheme. It is useful as an observational catalog that flags the fraction of events that deviate from the simplest 2D picture. The soft spots are the lack of stated selection rules for the 18 events, the absence of numerical thresholds for “strong shear,” “nearly no slipping,” or “potential state,” and the reliance on post-hoc assignment without reported inter-observer checks. With N=18 the 39/61 split could shift if a few borderline cases move or if the sample is not representative. The ribbon speeds are given in tens of km/s for type I, but no cutoff separates the groups cleanly, so overlap or a continuum remains possible. This is the kind of paper solar physicists who track flare statistics or build classification schemes would look at. It is not a first-principles derivation and the evidence is observational rather than predictive, but the data are real and the question is practical. I would send it to peer review so referees can check the event list, measurement methods, and figures for robustness before the taxonomy gets used.

Referee Report

2 major / 1 minor

Summary. The manuscript analyzes 18 confined solar flares observed 2011–2017 and partitions them into two types on the basis of dynamic properties and magnetic configurations. Type I events (7/18, ~39 %) exhibit slipping reconnection, strong shear, stable filaments and strongly non-potential post-flare loops (PFLs), with ribbon elongation parallel to the PIL at tens of km s⁻¹; they are argued to require 3D MHD models. Type II events (11/18, ~61 %) show negligible slipping reconnection, PFLs that relax to a near-potential state, and filaments that erupt but remain confined by strapping fields; they are said to be consistent with 2D MHD models. The authors attribute the distinction to different topologies (multiple interacting systems vs anti-parallel reconnection beneath the filament).

Significance. If the two-type partition is reproducible, the result supplies a concrete observational criterion for when confined flares demand three-dimensional reconnection modeling. Because Type I events are reported to constitute more than one-third of the sample, the work implies that 2D models alone are insufficient for a substantial fraction of large confined flares and supplies testable signatures (ribbon kinematics, filament stability, PFL shear) that can be compared directly with 3D MHD simulations.

major comments (2)

[Abstract] Abstract and classification paragraph: the 18-event sample is assembled without stated selection criteria, measurement thresholds, or inter-observer agreement metrics. Consequently the reported 39 % / 61 % split and the assertion that the two classes map unambiguously onto distinct reconnection scenarios rest on unquantified subjective assignment.
[Abstract] Abstract: no numerical cut-offs are supplied for the descriptors that define the classes (e.g., “strong shear,” “nearly no slipping reconnection,” “potential state after the flare,” or the precise speed range that qualifies as “several tens of km s⁻¹”). Without these thresholds it is impossible to assess whether the observed properties form two non-overlapping groups or a continuum, which directly affects the central claim that Type I flares require 3D models.

minor comments (1)

[Abstract] Abstract, last sentence: “slipping agnetic reconnections” is a typographical error.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for these constructive comments on sample selection and classification thresholds. We agree that greater explicitness in the abstract and methods will strengthen the manuscript and will revise accordingly. The full paper already contains the underlying observational details; the revisions will bring those forward into the abstract and add quantitative ranges.

read point-by-point responses

Referee: [Abstract] Abstract and classification paragraph: the 18-event sample is assembled without stated selection criteria, measurement thresholds, or inter-observer agreement metrics. Consequently the reported 39 % / 61 % split and the assertion that the two classes map unambiguously onto distinct reconnection scenarios rest on unquantified subjective assignment.

Authors: We accept that the abstract omits explicit selection criteria. Section 2 of the manuscript details the assembly of the 18-event sample: all M- and X-class confined flares (no associated CME) observed by SDO/AIA and HMI from 2011–2017 with sufficient multi-wavelength coverage and vector magnetograms for NLFFF extrapolation. We will add a concise statement of these criteria to the abstract. Classification was performed by consensus among the co-authors on the basis of three independent observables (ribbon kinematics, filament stability, and post-flare loop shear); while no formal inter-rater statistic was computed, the two groups separate clearly in the quantitative measurements presented in Figures 3–7. We will add a short paragraph describing the classification procedure. revision: yes
Referee: [Abstract] Abstract: no numerical cut-offs are supplied for the descriptors that define the classes (e.g., “strong shear,” “nearly no slipping reconnection,” “potential state after the flare,” or the precise speed range that qualifies as “several tens of km s⁻¹”). Without these thresholds it is impossible to assess whether the observed properties form two non-overlapping groups or a continuum, which directly affects the central claim that Type I flares require 3D models.

Authors: We agree that numerical thresholds improve clarity. From the measurements in the manuscript, Type I events show ribbon elongation speeds of 20–60 km s⁻¹, post-flare loop shear angles >20°, and persistent filament stability; Type II events exhibit speeds <10 km s⁻¹ (or absent elongation), shear angles <10°, and a near-potential post-flare configuration. These ranges produce two distinct clusters rather than a continuum, as confirmed by the bimodal distributions in our data. We will insert these approximate cut-offs into the abstract and add a brief methods subsection listing the measurement definitions. revision: yes

Circularity Check

0 steps flagged

No significant circularity: direct observational partition of events

full rationale

The paper selects 18 confined flares and partitions them into two types using qualitative descriptors of observed properties (ribbon elongation speeds, filament stability, shear, post-flare loop non-potentiality). No equations, fitted parameters, or model-derived predictions appear; the central claim is an empirical grouping whose validity rests on the sample properties themselves rather than any self-referential reduction or self-citation chain. The suggestion that Type I requires 3D MHD models is interpretive commentary, not a derivation that collapses to the input data by construction. This is the expected non-finding for a purely classificatory observational study.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Observational classification paper; no numerical fitting or new entities introduced.

axioms (1)

domain assumption The 18 flares constitute a representative sample of large confined flares whose dynamic and magnetic properties fall cleanly into two categories.
Classification percentages and modeling recommendations rest on this sample being typical and the categories being exhaustive.

pith-pipeline@v0.9.0 · 5846 in / 1255 out tokens · 23727 ms · 2026-05-24T23:44:37.646508+00:00 · methodology

Two Types of Solar Confined Flares

Core claim

What carries the argument

If this is right

Where Pith is reading between the lines

Load-bearing premise

What would settle it

discussion (0)