Height correction in the measurement of solar differential rotation determined by coronal bright points

¹ Kiepenheuer-Institut für Sonnenphysik (KIS), Schöneckstr. 6, 79104 Freiburg, Germany e-mail: rbrajsa@kis.uni-freiburg.de; hw@kis.uni-freiburg.de
² Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kačićeva 26, 10000 Zagreb, Croatia e-mail: romanb@geof.hr; bvrsnak@geof.hr; vruzdjak@geof.hr
³ Observatoire Royal de Belgique (ORB), Ave. Circulaire 3, 1180 Bruxelles, Belgium e-mail: Frederic.Clette@oma.be; hochedez@oma.be
⁴ Zagreb Astronomical Observatory, Opatička 22, 10000 Zagreb, Croatia e-mail: drosa@hpd.botanic.hr

Corresponding author: R. Brajša, rbrajsa@kis.uni-freiburg.de

Received: 16 July 2003
Accepted: 3 October 2003

Abstract

Full-disc solar images obtained with the Extreme Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) are used to analyse solar differential rotation by tracing coronal bright points for the period June 4, 1998 to May 22, 1999. A method for the simultaneous determination of the true solar synodic rotation velocity and the height of the tracers is applied to data sets analysed with interactive and automatic methods. The calculated height of coronal bright points is on average 8000–12000 km above the photosphere. Corrected rotation velocities are transformed into sidereal ones and compared with results from the literature, obtained with various methods and tracers. The differential rotation profile determined by coronal bright points with the interactive method corresponds roughly to the profile obtained by correlating photospheric magnetic fields and the profile obtained from the automatic method corresponds roughly to the rotation of sunspot groups. This result is interpreted in terms of the differences obtained in the latitudinal distribution of coronal bright points using the two methods.