Spatiotemporal inhomogeneous-homogeneous transition of the line-of-sight magnetic field (in G) images superposed by the LIC maps of the horizontal electric current density at a supergranular vertex during a period of vortex expansion of 37.5 min. The white line denotes the objective vortex boundary, the arrows denote the merging plasmoids 1 and 2, and the magenta crosses denote the centers of plasmoid 1 and 2.