Proper motion of solar filaments

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic
² Kanzelhöhe Solar Observatory of the University of Graz, 9521 Treffen, Austria e-mail: schroll@solobskh.ac.at

Corresponding author: P. Ambrož, pambroz@asu.cas.cz

Received: 31 January 2001
Accepted: 8 August 2001

Abstract

Movement of solar filaments relative to the Carrington reference system is considered to be an appropriate quantity to characterize the horizontal transport of magnetic flux in the solar photosphere and chromosphere. A new method of measurement of both zonal and meridional velocities was developed using an extensive set of Hα observations. The velocity field was derived for many filaments during a few consecutive days and for different Carrington rotations. The proper motion of different parts of the filament relative to the Carrington reference system was determined. A velocity variation with a time-scale of about 10 hours was discovered. The presence of a non-axially symmetric horizontal velocity component in the filamentary motion was confirmed. The latitude- and longitude-dependent distribution of the horizontal velocity field was detected. The relationship between the horizontal velocities of solar filaments and the horizontal velocity field derived from background solar magnetic fields was found. In this paper the sources of errors are also analyzed in detail. Many measurements were disqualified by ill-defined contours of the filaments. The systematic errors, caused by the unknown height and shape of the filaments, are estimated. Only velocity values more accurate than 100 m s^-1 were used in the study. The deviations of the mean horizontal velocities of filaments, magnetic field and sunspots resulting from the selection effect in their position on the Sun were interpreted.