How to call the scalar "curl" of a vector field in a plane?

Question

I cannot find any standard name or notation for the analog of curl of a vector field in an oriented Euclidean plane.

There is this operator that to a vector field $\mathbf{F}$ given in the standard Cartesian coordinates as $(F_x, F_y)$ associates the scalar field $\partial_xF_y - \partial_yF_x$. How should this operator be called and denoted?