Impulsive Phase Flare Energy Transport by Large-Scale Alfvén Waves and the Electron Acceleration Problem

By L. Fletcher, H. Hudson. 2007

342 citations recorded by the source corpus.

The impulsive phase of a solar flare marks the epoch of rapid conversion of energy stored in the preflare coronal magnetic field. Hard X-ray observations imply that a substantial fraction of flare energy released during the impulsive phase is converted to the kinetic energy of mildly relativistic electrons (10-100 keV). The liberation of the magnetic free energy can occur as the coronal magnetic field reconfigures and relaxes following reconnection. We investigate a scenario in which products of the reconfiguration—large-scale Alfvén wave pulses—transport the energy and the magnetic field changes rapidly through the corona to the lower atmosphere. This offers two possibilities for electron acceleration. First, in a coronal plasma with β < me/mp, the waves propagate as inertial Alfvén waves. In the presence of strong spatial gradients, these generate field-aligned electric fields that can accelerate electrons to energies on the order of 10 keV and above, including by repeated interactions between electrons and wave fronts. Second, when they reflect and mode-convert in the chromosphere, a cascade to high wavenumbers may develop. This will also accelerate electrons by turbulence, in a medium with a locally high electron number density. This concept, which bridges MHD-based and particle-based views of a flare, provides an interpretation of the recently observed rapid variations of the line-of-sight component of the photospheric magnetic field across the flare impulsive phase, and offers solutions to some perplexing flare problems, such as the flare “number problem” of finding and resupplying sufficient electrons to explain the impulsive-phase hard X-ray emission.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/0d8b12159e6e425eb7681b287f0f1c99a02e0bbb

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Geophysics

Citations in the corpus

Quasi-periodic Pulsations in Solar and Stellar Flares: An Overview of Recent Results (Invited Review) (2016, background): “Moreover, it has been argued by Fletcher and Hudson (2008); Russell and Fletcher (2013) that MHD waves are responsible for the energy transport from the reconnection site to the main emission sites in the flare foot-points.”
Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares (2018, background): “Some authors suggested that part of the flare energy could rather be transported downward by Alfvén waves (e.g. Fletcher and Hudson 2008) or by thermal conduction (e.g. Antiochos and Sturrock 1978; Cargill et al. 1995; Milligan et al. 2006).”
An Observational Overview of Solar Flares (2011, background): “…undergoing rearrangement – presumably in the low corona – must be strong, and energy transported by magnetic disturbances propagating through the chromosphere to the photosphere may be an important component in the flare chromosphere energization (Emslie & Sturrock 1982; Fletcher & Hudson 2008).”
Magnetic Reconnection in Astrophysical and (2009, background): “This corresponds to 1036–1038 particles and is comparable to the number of particles in a typical flare loop rather than at a single small reconnection site (Aschwanden 2002, Fletcher & Hudson 2008).”
The FIP and Inverse FIP Effects in Solar and Stellar Coronae (2015, background): “The stopping distance of 1 keV electrons is of order 1 km at a density of 1012 cm−3, so downwards heat conduction is unlikely to reach this far, and other authors have recently considered energy transport by Alfvén waves (Fletcher and Hudson, 2008; Haerendel, 2009).”
Alfvén Waves in the Solar Atmosphere (2012, background): “In this regime, magnetic field lines may still be highly distorted from a potential configuration, providing the necessary high-tension force required to induce Alfvén waves (Fig 3; Fletcher & Hudson 2008).”
Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding (2016, background): “Perhaps this mechanism can be considered in conjunction with the role played by Alfvén (or, perhaps, kink) waves in the impulsive phase of a solar flare (Fletcher and Hudson 2008).”
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares (2011, background): “We also discuss some recnt suggestions of acceleration by large-scale Alfvén waves (Fletcher & Hudson 2008) and cceleration involving multiple reconnection regions or in a turbulent environment (Vlahos et al. 2004; Turkmani et al. 2005; Dauphin & Vilmer 2007).”