Are granules good tracers of solar surface velocity fields?

¹ Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 14 avenue É. Belin, 31400 Toulouse, France
² Institut Universitaire de France
³ Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 57 avenue d'Azereix, BP 826, 65008 Tarbes Cedex, France
⁴ Lund Observatory, Box 43, 22100 Lund, Sweden
⁵ C.R.A.L, École Normale Supérieure, 46 allée d'Italie, 69364 Lyon, France
⁶ Theoretical Astrophysics Center and Astronomical Observatory/NBIfAFG, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁷ Michigan State University, East Lansing, MI 48824, USA

Corresponding author: M. Rieutord, rieutord@obs-mip.fr

Received: 3 July 2001
Accepted: 17 August 2001

Abstract

Using a numerical simulation of compressible convection with radiative transfer mimicking the solar photosphere, we compare the velocity field derived from granule motions to the actual velocity field of the plasma. We thus test the idea that granules may be used to trace large-scale velocity fields at the sun's surface. Our results show that this is indeed the case provided the scale separation is sufficient. We thus estimate that neither velocity fields at scales less than 2500 km nor time evolution at scales shorter than 0.5 hr can be faithfully described by granules. At larger scales the granular motions correlate linearly with the underlying fluid motions with a slope of ≲2 reaching correlation coefficients up to ~0.9.