Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

Abstract

We report on the occurrence of vortexes in flow fields obtained from the evolution of the line-of-sight component of the photospheric magnetic field in a region around the polarity inversion line (PIL) of a fully emerged active region. Based on a local linear approximation for the flow field, we identify the presence of critical points and classify them according to the eigenvalues of the Jacobian matrix of the linear transformation. Converging vortexes are associated with the presence of a particular kind of critical point, known as the attracting focus. We identified 12 converging vortexes in the analyzed period and detected the occurrence of other types of critical points, which indicate the complexity of the flow field around the PIL. The detected vortexes show a clockwise preferred sense of rotation with approximately 67 % of the cases. A geometrical analysis of the velocity structures produced an average value of D‾=1.63±0.05 for the fractal dimension, which is very close to the one obtained for isotropic homogeneous turbulence (D=5/3). This suggests that the flow around the PIL is turbulent in nature.