Large-scale horizontal flows in the solar photosphere

I. Method and tests on synthetic data

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 298, 251 65 Ondřejov, Czech Republic e-mail: [svanda;mklvana;msobotka]@asu.cas.cz
² Astronomical Institute, Charles University in Prague, V Holešovičkách 2, 180 00 Prague 8, Czech Republic

Received: 30 August 2005
Accepted: 5 July 2006

Abstract

We propose a useful method for mapping large-scale velocity fields in the solar photosphere. It is based on the local correlation tracking algorithm when tracing supergranules in full-disc dopplergrams. The method was developed using synthetic data. The data are transformed during the data processing into a suitable coordinate system, the noise is removed, and finally the velocity field is calculated. Resulting velocities are compared with the model velocities and the calibration is done. From our results it becomes clear that this method could be applied to full-disc dopplergrams acquired by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SoHO).