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Astron. Astrophys. 357, 1056-1062 (2000)

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Evolution of magnetic field twist in an emerging flux region

Tongjiang Wang 1,2 and V.I. Abramenko 1,2,3

1 Beijing Astronomical Observatory, Datun Rd. #20A, Chaoyang District, Beijing, 100012, P.R. China (wtj@sun10.bao.ac.cn)
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012, P.R. China
3 Crimean Astrophysical Observatory, 334413, Nauchny, Crimea, Ukraine

Received 5 November 1999 / Accepted 28 March 2000

Abstract

The observations of vector magnetic field for the emerging active region NOAA 7321 are analyzed. The measurements were performed with SMFT of Huairou Solar Observing Station. The aim is to study the variations of the total flux, total electric current and [FORMULA] parameter (as a measure of the field twist) throughout the flux emergence. We show that: (1) the total positive (negative) electric current grew simultaneously and linearly with the increase of the total positive (negative) flux; (2) the linear extrapolation to the zero flux gives non-vanishing total current which can be regarded as an indirect support for the idea of pre-existing twist of the emerging flux tube; (3) the change in [FORMULA] parameter during three days of the observation was rather small. This fact suggests that [FORMULA] remains the same throughout the flux emergence, and may further explain the good agreement between Longcope et al.'s (1998) simulation of deep thin flux tubes and observations.

Key words: Sun: evolution – Sun: magnetic fields – Sun: photosphere

Send offprint requests to: T. Wang

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000
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