  We investigate coarsening dynamics in the two-dimensional, incompressible
Toner-Tu equation. We show that coarsening proceeds via vortex merger events,
and the dynamics crucially depend on the Reynolds number Re. For low Re, the
coarsening process has similarities to Ginzburg-Landau dynamics. On the other
hand, for high Re, coarsening shows signatures of turbulence. In particular, we
show the presence of an enstrophy cascade from the intervortex separation scale
to the dissipation scale.
