Solar Flare Model Research Articles

A New Model of Solar Flares

view Abstract Citations (50) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Model of Solar Flares Sturrock, P. A. ; Coppi, B. Abstract Observational data concerning solar flares are reviewed briefly in order to list the salient requirements of a model of solar flares. The requirements of a theory of the flash phase are discussed in more detail, and previous flare theories are reviewed to determine the extent to which they meet these requirements. It is submitted that no theory meets enough of the requirements to be acceptable. A new model is proposed in which the preflare state consists of a mass of gas supported by a sheared magnetic field. This field configuration is likely to be met in the neighborhood of a fault line, across which there has been a shear displacement of the photosphere, since such a fault line tends to coincide with the dividing line between regions of opposite magnetic polarity. Such a configuration of gas and magnetic field is believed to be responsible for quiescent prominences, but the energy released in a flare is believed to come from lower parts of such a system, involving stronger fields and greater mass. This model there- fore explains the close relationship between flares and quiescent filaments. The flash phase of a solar flare is identified with a gravitational resistive instability of the above plasma-field configuration. It is shown that the rise time of this instability is sufficiently rapid to explain the very rapid development of the flash phase. The instability tends to break up the plasma into filaments with dimensions of a kilometer or less, in agreement with certain inferences which have been drawn from flare spectra. The development of fine-scale structure provides conditions for subsequent slower release of stored energy; this subsequent release is identified with the main or decay phase of flares. The flash-phase instability develops high current parallel to the magnetic field, which must be driven by an electric field parallel to the magnetic field. This permits one to identify the acceleration process in solar flares as runaway acceleration, and it is shown that this interpretation enables one to explain the observed energies of protons produced by solar flares. There is a brief discussion of the possibility of interpreting certain secondary flare phenomena, such as surges and loop prominences, by means of the proposed model. Publication: The Astrophysical Journal Pub Date: January 1966 DOI: 10.1086/148472 Bibcode: 1966ApJ...143....3S full text sources ADS |

A New Model for Solar Filaments.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Model for Solar Filaments. Sturrock, P. A. ; Woodbury, E. Abstract Filaments are known to run along the "neutral line" which divides regions of the photo sphere of opposite magnetic polarity. However, this characteristic alone does not account for the properties of filaments. It is suggested that filaments (quiescent prominences) result from slippage of the photo sphere, and that such slippage occurs preferentially along a neutral line. The resulting magnetic field will not be current-free but if the amount of gas supported is not too large, it will be nearly force-free. A relaxation method has been devised for computing force- free magnetic field configurations and used to calculate the structure of a model filament. It is found that, for heights smaller than the slip distance, the magnetic field lines' rise almost vertically, run nearly parallel to the slip line almost horizontally, and then descend almost vertically. Such a field configuration is well suited for supporting a mass of gas. The shape of the suspended gas would then simulate the "sheet" or "veil"-like structure of a filament. It is also clear that such a structure permits flow of gas parallel to the neutral line. This interpretation of a filament provided a mechanism for supplying the dense gas supported by the magnetic field, since slippage tends to raise magnetic- field lines and so to raise the gas in which the field lines are embedded. The relationship between filaments and flares may be understood by identifying the pre-flare state of a recent flare model (Sturrock, P. A., and Coppi, B., "A New Model of Solar Flares," Stanford University Rept. SUPR 6, April 1965) with a massive filament (or part of a filament) in the low chromosphere. Work supported by the U. S. Air Force Office of Scientific Research. Publication: The Astronomical Journal Pub Date: November 1965 DOI: 10.1086/109801 Bibcode: 1965AJ.....70..694S full text sources ADS |

A New Model of Solar Flares.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Model of Solar Flares. Sturrock, P. A. ; Coppi, B. Abstract A review of observational data concerning solar flares, including in particular data concerning homologous flares, leads to a statement of the principal requirements to be met by a flare model. It is submitted that earlier theories do not meet these requirements. A new model of solar flares is proposed in which the pre-flare state consists of a heavy mass of gas partially supported by a compressed magnetic field. Such a configuration is likely to form in those parts of the low chromosphere of a center of activity for which the magnetic field is nearly horizontal and for which the radius of curvature is directed upwards. The pre-flare state may have its origin in gas circulation due either to photo spheric temperature differences at a center of activity or to the nonthermal (acoustic) energy flux, or to a small vertical (upward) displacement of the magnetic field configuration. The instability appropriate to this configuration, to be identified with the flash phase of solar flares, is a gravitational resistive instability. This instability is sufficiently rapid, and it develops electric fields of sufficient magnitude to explain observed particle acceleration in solar flares. The instability also causes the plasma-field configuration to break up into fine filaments, in agreement with observations. This finescale structure effects a decoupling of the plasma and magnetic fields, permitting the overlying mass of gas to sink to the photosphere and the compressed magnetic field to relax to a force-free state; energy released in this phase corresponds to the main part of the light curve of a flare. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109651 Bibcode: 1965AJ.....70S.331S full text sources ADS |

A New Model of Solar Flares

THE extensive observational results and theoretical investigations of solar flares have recently been compiled in refs. 1 and 2. Most models of solar flares have assumed that the only reasonable mechanism for energy storage is that of magnetic field. Parker3 has recently criticized these theories and shown, in particular, that they do not explain the rapidity (102 sec) of the flash phase.