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 Abstract: This paper is devoted to the global (in time) regularity problem for a family of active scalar equations with fractional dissipation. Each component of the velocity field $u$ is determined by the active scalar $\theta$ through $\mathcal{R} \Lambda^{-1} P(\Lambda) \theta$ where $\mathcal{R}$ denotes a Riesz transform, $\Lambda=(-\Delta)^{1/2}$ and $P(\Lambda)$ represents a family of Fourier multiplier operators. The 2D Navier-Stokes vorticity equations correspond to the special case $P(\Lambda)=I$ while the surface quasi-geostrophic (SQG) equation to $P(\Lambda) =\Lambda$. We obtain the global regularity for a class of equations for which $P(\Lambda)$ and the fractional power of the dissipative Laplacian are required to satisfy an explicit condition. In particular, the active scalar equations with any fractional dissipation and with $P(\Lambda)= (\log(I-\Delta))^\gamma$ for any $\gamma>0$ are globally regular. Publication Date: 2012 Electronic Publication Date: 2012 Citation: Chae, D., Constantin, P., & Wu, J. (2012). Dissipative models generalizing the 2D Navier-Stokes and surface quasi-geostrophic equations. Indiana University Mathematics Journal, 1997-2018. DOI: 10.1512/iumj.2012.61.4756 Pages: 1997-2018 Type of Material: Journal Article Journal/Proceeding Title: Indiana University Mathematics Journal Version: Author's manuscript