The formation of asymmetric Stokes V profiles in the presence of a magnetopause

A magnetopause that separates two regimes of different flow, additional to the separation of a magnetic field from a field-free plasma, gives rise to the formation of asymmetric Stokes profiles. Using a simple two-layer model atmosphere, where one layer comprises a magnetic field, the other being fi eld-free, it is shown by analytical derivation that a wide variety of Stoke s V profiles can be produced, having amplitude asymmetries deltaa in the ra nge -infinity less than or equal to deltaa less than or equal to infinity. These include two-humped V profiles, which have two lobes of equal sign. Fo r the most simple models, the asymmetry depends on the ratio of continuum i ntensity to the Planck radiation intensity of the magnetic layer at the wav elength of the spectral line under consideration, and on the line depth. Tw o-humped profiles (|deltaa|>1) require the temperature of the magnetic laye r to surpass the temperature of the line-core forming region, implying a te mperature inversion, so that the V profile is partially in emission. The co nfrontation of this formation scenario with properties of observed one-lobe profiles of quiet-Sun network regions is inconclusive due to insufficient spatial resolution and lack of a sufficient sample of simultaneously record ed Stokes spectral lines of varying line depths. It seems, however, to be i n good agreement with the observed frequent occurrence of abnormal V profil es of the very strong Na I D-2 and D-2 spectral line. A possible observatio nal verification for the present formation scenario of abnormal Stokes V pr ofiles and a novel method of Stokes inversion are discussed.