The alternative to the MCT is a class of models concerned with the point-to-point photospheric mapping . Each field line can be considered to be topologically unique, since every footpoint is distinct from every other. Some authors prefer instead to think of every field line as topologically equivalent by allowing footpoints to be continuously moved except across PILs. In either case, separatrices in these models are defined by discontinuities in the footpoint mapping. This definition opens the door for the quasi-separatrix layer (QSL, see Section 5.2), where the mapping is “almost” discontinuous.
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