“…where the velocity u is recovered from the vorticity ω through u = ∇ ⊥ (−∆) −1 ω or equivalently u(ξ) = iξ ⊥ |ξ| 2 ω(ξ). Other nonlocal and quadratically nonlinear equations, such as the surface quasi-geostrophic equation, the incompressible porous medium equation, Stokes equations, magneto-geostrophic equation in multi-dimensions, have been studied intensively as one can see in [1,2,5,6,7,8,9,12,15,16,18,19,21] and references therein.…”