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Letter to the Editor
Do solar magnetic elements harbor downflows?
C. Frutiger and
Received 22 June 1998 / Accepted 30 June 1998
In a recent paper Bellot Rubio et al. (1997) inverted Zeeman split Stokes profiles to infer the stratification of the temperature, velocity and magnetic field in the photospheric layers of solar magnetic elements (modeled as thin flux tubes). One controversial result of their inversions is the presence of a strong downflow within the flux tubes. In the model underlying their inversion such a downflow is necessary to reproduce the asymmetric shape of the observed V profiles.
We present inversions based on two different flux-tube models, both of which reproduce the Stokes I and V profiles obtained in plages and the network with high accuracy, including the V profile asymmetry. One model is almost identical to that employed by Bellot Rubio et al. (1997), and results in a significant downflow within the flux tube. The other, although similar in most respects, has mass conservation enforced inside the flux tubes, i.e. they contain both an upflow and a downflow which could arise from oscillations or siphon flows. Hence, current data may not be sufficiently sensitive to distinguish between the two velocity structures, so that there is no compelling evidence for a net downflow of matter inside magnetic elements. From a physical point of view the model incorporating mass conservation is to be preferred.
Key words: Sun: magnetic fields Sun: faculae, plages polarization radiative transfer flux tubes
Send offprint requests to: C. Frutiger
Online publication: July 27, 1998