Vorticity and helicity of the solar supergranulation flow-field^*

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: pegorov@aip.de

Received: 26 March 2004
Accepted: 9 June 2004

Abstract

Box simulations of rotating convection are presented with the aim to study the divergence-vorticity correlation computed from the horizontal velocity components of the turbulent flow field. Our investigation is motivated by new observations of the solar velocity field in the upper convection zone using the techniques of so-called time-distance helioseismology (Duvall et al. [CITE]). From such observations can be derived directly and because of the close relation to the helicity it is an important quantity for solar dynamo theory. The divergence-vorticity correlation obtained from the simulations with Taylor number 10³ is found to be in agreement with the observations of supergranulation. In particular, vanishes at the equator and is negative (positive) in the northern (southern) hemisphere. For larger Taylor numbers the amplitude of increases, which is consistent with the increase in strength of the Coriolis force acting on the turbulent flow. We also demonstrate that the correlation  and the kinetic helicity of the flow field have very similar spatial profiles. The observed values of , therefore, yield a clear indication of the existence of negative (positive) kinetic helicity in the surface layers of the northern (southern) hemisphere.