Quasi-separatrix layers: refined theory and its application to solar flares

V. S. Titov, P. Demoulin, G. Hornig

    Research output: Chapter in Book/Report/Conference proceedingConference contribution


    Although the analysis of observational data indicates that quasi-separatrix layers (QSLs) have to play an important role in magnetic configurations of solar flares, the corresponding theory is only at an initial stage so far. In particular, there is still a need in a proper definition of QSL. This problem is analyzed here on the basis of geometrical properties of the mapping produced by the field lines which connect photospheric areas of positive and negative magnetic polarities of active regions. In general, one can find on the photosphere a unique pair of locally perpendicular line elements at one footpoint of a given field line, so that this pair is mapped into a similar pair of elements at the other footpoint. Along the directions of these elements the field line mapping only stretches and compresses the corresponding displacements of the neighboring field-line footpoints. This fact enables us to get a remarkably clear and concise definition of QSL as a volume filled by coronal field lines for which the ratio of the corresponding stretching and compressing coefficients is anomalously large. The new definition is also compared with the ones previously introduced by other authors. The theory is applied to flare events of the so-called sigmoid-type, using an analytical model of a twisted force-free configuration. It is shown that such a configuration may contain a QSL even if genuine separatrix surfaces are absent. Identifying QSLs is an essential prerequisite for understanding the mechanism of magnetic energy release in this type of flares. It is also demonstrated that the magnetic field under study has a Hamiltonian structure, which makes it possible to reveal a geometrical reason for the appearance of QSL in this case.
    Original languageEnglish
    Title of host publicationMagnetic fields and solar processes: proceedings of the 9th European Meeting on Solar Physics, 12-18 September 1999, Florence, Italy
    EditorsA. Wilson
    PublisherESA Publications Division
    ISBN (Print)9290927925
    Publication statusPublished - 1999
    EventThe 9th European Meeting on Solar Physics: Magnetic Fields and Solar Processes - Florence, Italy
    Duration: 12 Sept 199918 Sept 1999


    ConferenceThe 9th European Meeting on Solar Physics: Magnetic Fields and Solar Processes
    Internet address


    • Quasi-separatrix layers
    • Magnetic topology
    • Solar flares


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