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Astron. Astrophys. 335, 1077-1084 (1998)

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Determination of the full velocity vector based on vector magnetograph measurements in an asymmetric sunspot

A.M. Krivtsov 1, A. Hofmann 2, J. Staude 2, M. Klvaa 3 and V. Bumba 3

1 St.-Petersburg State Technical University, Department of Theoretical Mechanics, Politechnicheskaya Street 29, 195251 St.-Petersburg, Russia (krivtsov@mail.wplus.net)
2 Astrophysikalisches Institut Potsdam, Sonnenobservatorium Einsteinturm, D-14473 Potsdam, Germany (ahofmann@aip.de, jstaude@aip.de)
3 Astronomical Institute, Czech Academy of Sciences, Ondejov, Czech Republic (mklvana@asu.cas.cz, bumba@asu.cas.cz)

Received 2 March 1998 / Accepted 27 April 1998

Abstract

A new method to determine the distribution of the full velocity vector in an asymmetric sunspot is presented. Measurements of the Doppler velocity and of the vector of the magnetic field are used as initial data for these calculations. The determination is subdivided into two stages: in a first step we obtain the distribution of the velocity projection onto the solar surface, and in the second step the orthogonal component of the velocity field is calculated.

The method has been applied to a sunspot observed from two observatories over 7 days, that is at different positions on the solar disk and in different phases of its development. The resulting vector velocity field is in good agreement with the basic features of the siphon flow model of penumbral flux tubes. The velocities are directed outwards from the sunspot, and they have small values in the umbra and maximum values in the central part of the penumbra, while in the outer penumbra the velocities decrease rapidly. The vertical velocities are mainly localized at the umbral boundary (upflows) and at the outer parts of the penumbra (downflows).

Key words: MHD – Sun: photosphere – Sun: magnetic fields – sunspots

Send offprint requests to: A.M. Krivtsov

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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