Global Wellposedness for a Modified Critical Dissipative Quasi-Geostrophic Equation

In this paper we consider the following modified quasi-geostrophic equation \partial_{t}\theta+u\cdot\nabla\theta+\nu |D|^{\alpha}\theta=0, \quad u=|D|^{\alpha-1}$\mathcal{R}$^{\bot}\theta,\quad x\in$\mathbb{R}$^2 with $\nu >0$ and $\alpha \in ]0,1[\cup ]1,2[$. When $\alpha \in ]0,1[$, the equation was firstly introduced by Constantin, Iyer and Wu in \cite{ref ConstanIW}. Here, by using the modulus of continuity method, we prove the global well-posedness of the system with the smooth initial data. As a byproduct, we also show that for every $\alpha \in ]0,2[$, the Lipschitz norm of the solution has a uniform exponential bound.