Surface links which are coverings over the standard torus

We introduce a new construction of a surface link in the 4-space. We construct a surface link as a branched covering over the standard torus, which we call a torus-covering link. We show that a certain torus-covering $T^2$-link is equivalent to the split union of spun $T^2$-links and turned spun $T^2$-links. We show that a certain torus-covering $T^2$-link has a non-classical link group. We give a certain class of ribbon torus-covering $T^2$-links. We present the quandle cocycle invariant of a certain torus-covering $T^2$-link obtained from a classical braid, by using the quandle cocycle invariants of the closure of the braid.