From Solar and Stellar Flares to Coronal Heating: Theory and Observations of How Magnetic Reconnection Regulates Coronal Conditions

  title={From Solar and Stellar Flares to Coronal Heating: Theory and Observations of How Magnetic Reconnection Regulates Coronal Conditions},
  author={Paul A. Cassak and Dermott Mullan and Michael A. Shay},
  journal={The Astrophysical Journal Letters},
  pages={L69 - L72}
There is currently no explanation of why the corona has the temperature and density it has. We present a model that explains how the dynamics of magnetic reconnection regulates the conditions in the corona. A bifurcation in magnetic reconnection at a critical state enforces an upper bound on the coronal temperature for a given density. We present observational evidence from 107 flares in 37 Sun-like stars that stellar coronae are near this critical state. The model may be important to self… 

Figures from this paper

Magnetic Reconnection for Coronal Conditions: Reconnection Rates, Secondary Islands and Onset

Magnetic reconnection may play an important role in heating the corona through a release of magnetic energy. An understanding of how reconnection proceeds can contribute to explaining the observed

Reconnection in Marginally Collisionless Accretion Disk Coronae

We point out that a conventional construction placed on observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse Comptonization in a coronal plasma,


We explore the suggestions by Uzdensky and Cassak et al. that coronal loops heated by magnetic reconnection should self-organize to a state of marginal collisionality. We discuss their model of

Recent Progress in Understanding Solar Magnetic Reconnection

Magnetic reconnection is a fundamental process occurring in a wide range of astrophysical, heliospheric and laboratory plasmas. This process alters magnetic topology and triggers rapid conversion of

Plasmoids in reconnecting current sheets: Solar and terrestrial contexts compared

Magnetic reconnection plays a crucial role in violent energy conversion occurring in the environments of high electrical conductivity, such as the solar atmosphere, magnetosphere, and fusion devices.

Magnetic Reconnection in Astrophysical and Laboratory Plasmas

Magnetic reconnection is a topological rearrangement of magnetic field that converts magnetic energy to plasma energy. Astrophysical flares, from the Earth's magnetosphere to γ-ray bursts and

Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause

Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and

Long-period Intensity Pulsations in Coronal Loops Explained by Thermal Non-equilibrium Cycles

In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon that can occur when the heating is both highly stratified and quasi-constant. Unambiguous observational identification of TNE


It is widely accepted that magnetic reconnection releases a large amount of energy during solar flares. Studies of reconnection usually assume that the length scale over which the global

Scaling of Sweet-Parker reconnection with secondary islands

Sweet–Parker (collisional) magnetic reconnection at high Lundquist number is modified by secondary islands. Daughton et al. [Phys. Rev. Lett. 103, 065004 (2009)] suggested the Sweet–Parker model



Solar flares as cascades of reconnecting magnetic loops.

Numerical simulations show that a power law distribution of flare energies emerges, associated with a scale-free network of loops, indicating self-organized criticality.

A Model for Spontaneous Onset of Fast Magnetic Reconnection

We present a model for the spontaneous onset of fast magnetic reconnection in a weakly collisional plasma, such as the solar corona. When sheared magnetic fields in the corona undergo collisional

Avalanches and the Distribution of Solar Flares

The solar coronal magnetic field is proposed to be in a self-organized critical state, thus explaining the observed power-law dependence of solar-flare-occurrence rate on flare size which extends

Self-organized Criticality from Separator Reconnection in Solar Flares

A new cellular automaton model for solar flares is presented in which a complex coronal magnetic field is stressed by photospheric shear. The minimum current corona model is used to describe the slow

Avalanche models for solar flares (Invited Review)

This paper is a pedagogical introduction to avalanche models of solar flares, including a comprehensive review of recent modeling efforts and directions. This class of flare model is built on a

Laboratory observations of spontaneous magnetic reconnection.

Detailed measurements of spontaneous magnetic reconnection are presented, which document the profile evolution of the plasma density, magnetic flux function, reconnection rate, and the current density during a spontaneous reconnection event in the presence of a strong guide magnetic field.

Petschek-like Reconnection with Current-driven Anomalous Resistivity and Its Application to Solar Flares

Recent simulations of magnetic reconnection with localized resistivity demonstrated the development of a Petschek-like configuration with the width of the inner diffusion region of the order of the

Solar flares, microflares, nanoflares, and coronal heating

Solar flare occurrence follows a power-law distribution against total flare energy W: dN/dW ∼ W−α with an index α ∼ 1.8 as determined by several studies. This implies (a) that microflares must have a

X-Ray Observations of Stellar Flares

The history of stellar X-ray flare observations prior to EINSTEIN is reviewed. X-ray light curves as measured by the IPC are then presented for all time resolved flare events discovered as of July

Impulsive Magnetic Reconnection in the Earth's Magnetotail and the Solar Corona

▪ Abstract Impulsive reconnection dynamics is characterized not only by fast growth but also by a sudden change in the time derivative of the growth rate. I review recent developments in the theory