Evolution of magnetic field twist in an emerging flux region
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 alpha 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 alpha parameter during three days of the observation was rather small. This fact suggests that alpha remains the same throughout the flux emergence, and may further explain the good agreement between Longcope et al.'s (\cite{Longcope1998}) simulation of deep thin flux tubes and observations.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 2000
- Bibcode:
- 2000A&A...357.1056W
- Keywords:
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- SUN: EVOLUTION;
- SUN: MAGNETIC FIELDS;
- SUN: PHOTOSPHERE