Abstract
Context. The measurement of the Sun's surface motions with a high spatial and temporal resolution is still a challenge.
Aims. We wish to validate horizontal velocity measurements all over the visible disk of the Sun from Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) data.
Methods. Horizontal velocity fields are measured by following the proper motions of solar granules using a newly developed version of the coherent structure tracking (CST) code.
The comparison of the surface flows measured at high spatial resolution (Hinode, 0.1 arcsec) and low resolution (SDO/HMI, 0.5 arcsec) allows us to determine corrections to be applied to the horizontal velocity measured from HMI white light data. Results.
We derive horizontal velocity maps with spatial and temporal resolutions of respectively 2.5 Mm and 30 min. From the two components of the horizontal velocity v(x) and v(y) measured in the sky plane and the simultaneous line of sight component from SDO/HMI dopplergrams v(D), we derive the spherical velocity components (v(r), v(theta), v(phi)).
The azimuthal component v(phi) gives the solar differential rotation with a high precision (+/- 0.037 km s(-1)) from a temporal sequence of only three hours. Conclusions.
By following the proper motions of the solar granules, we can revisit the dynamics of the solar surface at high spatial and temporal resolutions from hours to months and years with the SDO data.