Comparison of solar horizontal velocity fields from SDO/HMI and Hinode data

¹ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, 14 avenue Édouard Belin, 31400 Toulouse, France
e-mail: thierry.roudier@irap.omp.eu
² LESIA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
³ CALMIP, DTSI Université Paul Sabatier, Université de Toulouse, 31062 Toulouse, France
⁴ Lockheed Martin Advance Technology Center, Palo Alto, CA-94304, USA
⁵ Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 18000, Prague 8, Czech Republic
⁶ Astronomical Institute, Academy of Sciences of the CzechRepublic (v. v. i.), Fričova 298, 25165 Ondřejov, Czech Republic
⁷ National Solar Observatory, Sunspot, NM 88349, USA
⁸ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
⁹ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Received: 7 December 2012
Accepted: 6 March 2013

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_θ, v_ϕ). The azimuthal component v_ϕ 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.