A flare model based upon photospheric dynamo action

It is noticed, first, that the photospheric dynamo as a generator of solar flares must have the nature of a voltage generator in order to be consistent with the current interruption mechanism applied to the magnetic-energy release process. Then, a consistent dynamo model is given by assuming the existence of ''sub-photospheric'' current and filamentary structure of the field-aligned coronal current. The filamentary structure greatly increases the effective resistance of the coronal circuit. As a result major part of the total current generated by the photospheric dynamo closes through the sub-photospheric layer, and this guarantees that the dynamo behaves as a voltage generator for the coronal circuit. However, it is also shown that the current density in each filament in the corona has a value as large as in the sub-photospheric paths and that it is sufficient to produce a flare. Our model is based on the photospheric dynamo model by Heyvaerts (1974). However, we pay a special attention to the component of a photospheric shear flow parallel to the magnetic polarity-reversal-line and obtain a very sheared magnetic structure well reproducing the active-region filament system. (author)