The lifespan of classical solutions for the inviscid Surface Quasi-geostrophic equation

We consider classical solutions of the inviscid Surface Quasi-geostrophic equation that are a small perturbation $\epsilon$ from radial stationary solution $\theta=|x|$. use modified energy method to prove existence time $\frac{1}{\epsilon}$ scale $\frac{1}{\epsilon^4}$. Moreover, by perturbing in suitable direction we construct global smooth solutions, via bifurcation, rotate uniformly and space.